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I've got a 86 Cherokee Pioneer 4X4 with the 2.5L TBI engine and 904 auto trans that I'm working to get back on the road.It has only 70k miles and is in good shape but hasn't been driven for the past 5 yrs. due to minor issues.I bought the Jeep to fix the issues and repaint it and this forum has been very helpful.I've gone trough all sensor checks in the 2.5L tune up section and adjusted or replaced anything that was out of spec.I now have a good running and idling 4 banger with one exception.When the engine is cold(60 degrees)it will crank over several times before starting as it should.When it starts it will usually stall or try to before the idle speed control can kick the throttle open to increase the rpm's.If it can stay running long enough the ISC brings the rpm's up after a few seconds and it idles like a dream.As it warms up the rpm's drop as they should to about 700-750 and all is well until I shut it off again.Then it will start right up and stall once due to low idle even warmed up and start and stay running the second time after the ISC has increased the idle some.I can get it to start and idle the first time hot or cold if I push the throttle a bit on start up.If I just bump the starter once without starting it and then start it the ISC has time to kick the throttle open some and it starts and idles as it should.

In a nut shell the ISC is a little slow in doing it's job before the engine starts.I have adjusted the ISC  and TPS as described in the tune up section and I believe they are correct.The Jeep starts and runs much better after the tuning but still has this start and stall issue.Somehow the idle speed controls needs to respond quicker as the engine is cranking in order to do it's job better but I don't know how can I get that to happen.

Is there any chance the ECU will need time to right itself now that I have fixed all that was wrong with this little bugger(broken vac lines, bad EGR valve,TPS adjustment + more)I haven't been able to give it a workout yet as I'm not done with the body work.

Has anyone else had this problem or got suggestions on hoe to fix it?

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Hi, Tenny, welcome to the forums...We could go into the ISA motor issues, though it sounds like you have ruled that out for the moment.  Before walking through the troubleshooting steps, have you changed the fuel filter?  This could be an issue, and so could the fuel pump check valve.  

Try bumping the key through a few fuel pump cycles before cranking the engine over.  See whether that changes the start-and-stall situation.  See whether it helps the idle speed stabilization.  If so, you may have a fuel flow volume issue or a check valve issue at the pump.

Having set up for a lengthy time, there could be water in the bottom of the fuel tank.  Picked up by the pump, this will swell and clog the filter.  If you run a fuel alcohol-based cleaner through the system, the filter (new or used) will likely clog from water passing through.  Try a fuel system cleaner before changing the fuel filter.

Moses

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Thanks for the reply Moses.I'll give a little(lot) more info on what I've done to my Jeep.Since it was running when I bought it 5 years ago,I drove it only a little but enough to know it was so gutless that something wasn't right.I kept good non-ethanol gas with stabilizer in it and would start it a few times a year.It always did this start stall thing but I figured a tune up and tinkering would cure the problem of low power and the stall.I also have done the key on and off a few times to cycle the pump but it made no difference. 

I suspected a bad pump and filter was at fault for lack of power so I removed the gas tank and put in a new pump and inline filter.I also had to run a new vapor line as the original one was rusted.At this point it still would stall once on start up then run fine.

Next I did plugs,wires,cap and rotor.I also had to reposition the dist. as described in your tune up section so the hold down bolt would line up with bolt notch in dist housing when rotor is at about 6: O clock TDC.Who ever messed with it before me didn't have your guidance on how to set the base timing and the entire dist. was clocked about 90 degrees off but it still ran OK since the drive tang was also off the same amount.They must have adjusted the dist. old school with a light until they got the proper base timing even though the it wasn't in the right place.

I've checked the base timing with a light now and it's at about 16 BTDC at warm idle and advances as it should with RPM's.

I had to replace rotted vac hoses to the MAP and a few other key places.I poured Seafoam into the throttle body while keeping it running @ high idle to clean intake and also replaced a dead EGR valve that now functions as it should.I've checked all the sensors except the 02 which I'll do today.I was hoping the coolant sensor would prove to be bad but it tested good as did all the rest.I did have to adjust the TPS however but it has a smooth and steady sweep as the throttle is opened.

The lack of power turned out to be a seized kickdown lever where it goes into the transmission.It wouldn't allow the throttle linkage to travel more then 1/3 it's way to wide open.I changed the trans fluid and filter,adjusted the bands and freed up the kickdown lever.It operates the valve plunger as it should but still isn't as free as I think it should be.You can tell when the throttle is pushing it by the pressure it takes but at least it will allow full travel of the throttle linkage now and lets the valve plunger work as it should.I think if I work it a little more with penetrating oil it will improve

The way I set the ISA motor without the special tool is after the engine was fully warm,I shut it off and measured how far open the throttle was.Then I bumped the starter a few times and each time the ISA would open the throttle a little more.When I could hear the ISA ratchet mechanism click twice each time I bumped the starter, I measured how far the throttle was open and bumped the starter a couple more times to be sure the throttle measurement didn't increase any more.I figured this meant the ISA was fully extended and then I unplugged it leaving it fully extended even if I started the engine.

I hitched up a digital tach meter and positioned it where it could be seen when I started the engine.I then turned the ISA adjusting bolt in some to be sure I'd stay under 3500 RPM's on my first start up.It fired right up and stayed running of course due to the high idle situation and ran up to 2800 RPM's. I shut her down and adjusted the ISA bolt out a few turns at a time, starting and shutting it down until the last tweak brought it right to 3500 RPM's after it settled in for a couple seconds to be sure.This seemed to work good as I never had to run the engine for more the a couple seconds to check the speed.When I plugged the ISA in and started the engine,it fired right up at high idle and stayed running,quickly returning to a good warm engine idle when the ISA retracted as it should.

Anyways after all the tweaks and adjustments it runs and idles great but just has the stall once issue due to the ISA not opening the throttle as it turns over.It's seems that the ISA doesn't get the open signal until after the engine starts.If I bump the starter once or twice then start it,it will stay running and idle fine.I've also tried holding the key on for a second after it starts and that also gives the ISA time enough to crack the throttle open.

Do you think my method of fully extending the ISA is an accurate way to get the desired 3500 RPM ? It idles great warm or cold and I can punch the gas from a idle to spin the tires(on dirt) and let right off and it won't stall.I can always hold the gas pedal down a bit when I start it like an older rig with a carburetor but I'd like it to be right.

Any ideas?             

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Tenny...See my reply below...Moses

23 hours ago, Tenny said:

Thanks for the reply Moses.I'll give a little(lot) more info on what I've done to my Jeep.Since it was running when I bought it 5 years ago,I drove it only a little but enough to know it was so gutless that something wasn't right.I kept good non-ethanol gas with stabilizer in it and would start it a few times a year.It always did this start stall thing but I figured a tune up and tinkering would cure the problem of low power and the stall.I also have done the key on and off a few times to cycle the pump but it made no difference. 

I suspected a bad pump and filter was at fault for lack of power so I removed the gas tank and put in a new pump and inline filter.I also had to run a new vapor line as the original one was rusted.At this point it still would stall once on start up then run fine.

Have you checked the fuel regulator pressure before, during and after start-up?  A pressure gauge test at the TBI test port?  Fuel volume?  With a pressure gauge attached, you can momentarily pinch the fuel return line and should expect to see the fuel pressure spike quite high.  (Do not pinch for more than two or so seconds to prevent damage to the gauge and any parts.)  Otherwise, pressure should be stable before, during and after cranking if the pressure regulator is okay and adjusted properly.  If high pressure, rule out a return restriction.  Rule out low or erratic pressures.  Consider the TBI regulator O-ring, which has been a source of idle and stalling issues.

Next I did plugs,wires,cap and rotor.I also had to reposition the dist. as described in your tune up section so the hold down bolt would line up with bolt notch in dist housing when rotor is at about 6: O clock TDC.Who ever messed with it before me didn't have your guidance on how to set the base timing and the entire dist. was clocked about 90 degrees off but it still ran OK since the drive tang was also off the same amount.They must have adjusted the dist. old school with a light until they got the proper base timing even though the it wasn't in the right place.

That PO's timing approach usually winds up with the rotor and cap's spark contacts misaligned.  This concern is lost on many.  The aim is not just accurate base timing.  There must also be close alignment between the rotor contact and the distributor cap contacts.  Otherwise, spark resistance will increase and draw heavily on the coil.  Sounds like you resolved that issue.

I've checked the base timing with a light now and it's at about 16 BTDC at warm idle and advances as it should with RPM's.

Sounds close, certainly not "off a tooth"!  10-12 degrees BTDC is typical, no hard rules here, as several sensors and the ECU are at play.  Spark advance is an ECU and sensor function entirely.  Base timing is the only concern.

I had to replace rotted vac hoses to the MAP and a few other key places.I poured Seafoam into the throttle body while keeping it running @ high idle to clean intake and also replaced a dead EGR valve that now functions as it should.I've checked all the sensors except the 02 which I'll do today.I was hoping the coolant sensor would prove to be bad but it tested good as did all the rest.I did have to adjust the TPS however but it has a smooth and steady sweep as the throttle is opened.

You've been thorough and systematic, Tenny.  The EGR was a good move, as is checking out the O2 sensor.  Presumably the crankshaft position sensor (CPS) is clean and reads well, too?

 

 

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The lack of power turned out to be a seized kickdown lever where it goes into the transmission.It wouldn't allow the throttle linkage to travel more then 1/3 it's way to wide open.I changed the trans fluid and filter,adjusted the bands and freed up the kickdown lever.It operates the valve plunger as it should but still isn't as free as I think it should be.You can tell when the throttle is pushing it by the pressure it takes but at least it will allow full travel of the throttle linkage now and lets the valve plunger work as it should.I think if I work it a little more with penetrating oil it will improve.

You can confirm the pressures with a check of the transmission line pressure.  Using a gauge and the FSM procedure, make sure the throttle valve pressures line up with the kickdown linkage adjustment and position of the lever.  A simpler, cursory clue is whether the transmission downshifts when the throttle hits the floor level.

The way I set the ISA motor without the special tool is after the engine was fully warm,I shut it off and measured how far open the throttle was.Then I bumped the starter a few times and each time the ISA would open the throttle a little more.When I could hear the ISA ratchet mechanism click twice each time I bumped the starter, I measured how far the throttle was open and bumped the starter a couple more times to be sure the throttle measurement didn't increase any more.I figured this meant the ISA was fully extended and then I unplugged it leaving it fully extended even if I started the engine.

I hitched up a digital tach meter and positioned it where it could be seen when I started the engine.I then turned the ISA adjusting bolt in some to be sure I'd stay under 3500 RPM's on my first start up.It fired right up and stayed running of course due to the high idle situation and ran up to 2800 RPM's. I shut her down and adjusted the ISA bolt out a few turns at a time, starting and shutting it down until the last tweak brought it right to 3500 RPM's after it settled in for a couple seconds to be sure.This seemed to work good as I never had to run the engine for more the a couple seconds to check the speed.When I plugged the ISA in and started the engine,it fired right up at high idle and stayed running,quickly returning to a good warm engine idle when the ISA retracted as it should.

If the ISA cold/high idle speed is within specification, you should be good.  The other concern is freedom of movement and lubrication within the mechanism.

Anyways after all the tweaks and adjustments it runs and idles great but just has the stall once issue due to the ISA not opening the throttle as it turns over.It's seems that the ISA doesn't get the open signal until after the engine starts.If I bump the starter once or twice then start it,it will stay running and idle fine.I've also tried holding the key on for a second after it starts and that also gives the ISA time enough to crack the throttle open.

Check the crankshaft position sensor for oil or debris, including around the flywheel.  Did you check the CPS signal?...Have you disconnected the ECU connector and carefully cleaned the contacts with contact cleaner and a nylon probe?  There may be resistance on this circuit, check connections and grounds for resistance, too.  Make certain your ground resistance is not too high between the engine and body. 

Ground points, terminals and fasteners lose connectivity from oxidation.  I like to start ohms resistance testing with the long run resistant—like between the battery cable terminal and the major body ground points.  If there is a resistance issue, you can narrow testing down to shorter length ground runs.  Body ground points are often oxidized between the fastener, terminal and body threads.  Also, an alternator issue or voltage interruption can cause stalling.  A lab scope would pick this up.

Do you think my method of fully extending the ISA is an accurate way to get the desired 3500 RPM ? It idles great warm or cold and I can punch the gas from a idle to spin the tires(on dirt) and let right off and it won't stall.I can always hold the gas pedal down a bit when I start it like an older rig with a carburetor but I'd like it to be right.

I think you're good on the ISA despite the unorthodox method.  Your aim was sound.  The result works.  Have you watched the MAP reading while the fault occurs? This could be a clue.  Another vacuum related issue is the vacuum bulb reservoir (below the battery on my later XJ).  A vacuum hose leak or defective bulb, a defective one-way vacuum check valve or any other vacuum drop or loss can create the symptom you describe.  It is very common on an XJ for battery electrolyte to eat through the vacuum line and allow vacuum to bleed off.  The engine could stall from loss of a stable initial vacuum signal or from a momentary vacuum fluctuation. 

Your XJ has a vacuum disconnect front axle.  That system is notorious for vacuum leaks at the shift motor, lines, the transfer case vacuum switch or anywhere in that circuit.  I would use a vacuum hand pump with gauge and apply the same troubleshooting strategy as with a ground circuit check:  Make sure there is not a loss of vacuum that could momentarily impact the MAP or other readings.  You noted vacuum hose changes, but vacuum leaks of any kind are problematic, including the vacuum controls for the front axle.

Any ideas?             

 

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Thanks for pointing out more trouble spots to look for.I'd planed to check the CPS signal as well as the O2 sensor but forgot.I didn't check fuel pressure before replacing the fuel pump because I had it out repairing the sending unit that lost ground due to loose a connection.I also replaced the tank straps and hoses and didn't want to drop the tank again if the old pump failed even though I think it was OK.Turning the key on and off, cycling the pump before starting hasn't had any effect on my stalling issue before or after repairs but will do the pressure checks to be sure it's correct.

Before replacing the EGR valve I checked to be sure the EGR control solenoid was functioning correctly and it was.I have 20-21 in. of vac @ the switch input line and can hear and feel the EGR working when reving the engine from under the hood.In fact when I let off the throttle I can feel the diaphragm vibrate as it closes making a slight snorting noise.I hope this isn't a sign of a crappy valve.

The PO had a garage replace the ECU and do a few other repairs shortly before the Jeep was parked due to it failing our state inspection.It needed brakes, exhaust and suspension work which I have done.The distributor install not being correct among a few other quick repairs makes me question the shops knowledge of this Jeep so the grounds and ECU connections will be a good place to look.

I'm not 100% sure what is the correct operation of the ISA.It works well to keep a good idle once the engine is running but when should it correct the throttle position for the conditions, while the engine is cranking or after it starts? Mine doesn't adjust until after the engine starts but not quick enough to keep it running.After it stalls once the ISA extends, opening the throttle before I crank the engine again to start and it idles good.If I bump the starter once before starting,the ISA will open the throttle and then when I start it, it will stay running.If I shut the engine off even warm and immediately restart, it will sputter along trying to stall for a second or two until the ISA has time to increase the idle and stay running. Hopefully the problem lies in one of the above checks.

I'm use to working on older vehicles with mechanical linkage and adjustments but enjoy the new challenge of trouble shooting the newer sensor and electrical systems. knowing what is out of spec and causing the problem when I test it is the key.Boy there are a lot of sensors to check ! The info on this site has gone a long way in giving me the knowledge in what to look for.

There is one last thing that I question.I assume once the stationary idle set screw stop in the TBI throttle bracket is set it never should never need to be adjusted again.When the engine is running the ISA adjustment bolt should maintain contact with the throttle, keeping it off the set screw stop and the correct the idle as needed.When the engine is shut off should the throttle be held off the stationary stop screw by the ISA ? If the PO adjusted the set screw stop in an attempt to correct another issue, it could through off the closed TPS adjustment.Would the correct adjustment of this stop screw be to just contact the throttle stop tang when the throttle blade is fully closed just to prevent damage to the blade? I'm going to check on this as well.

Once I go through the list of checks hopefully one or more will cure my problem.I'll post again(shorter) what I find.

       

 

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Hi, Tenny...See comments below.

33 minutes ago, Tenny said:

Thanks for pointing out more trouble spots to look for.I'd planed to check the CPS signal as well as the O2 sensor but forgot.I didn't check fuel pressure before replacing the fuel pump because I had it out repairing the sending unit that lost ground due to loose a connection.I also replaced the tank straps and hoses and didn't want to drop the tank again if the old pump failed even though I think it was OK.Turning the key on and off, cycling the pump before starting hasn't had any effect on my stalling issue before or after repairs but will do the pressure checks to be sure it's correct.

Gotcha...The grounds check could be helpful in any case...

Before replacing the EGR valve I checked to be sure the EGR control solenoid was functioning correctly and it was.I have 20-21 in. of vac @ the switch input line and can hear and feel the EGR working when reving the engine from under the hood.In fact when I let off the throttle I can feel the diaphragm vibrate as it closes making a slight snorting noise.I hope this isn't a sign of a crappy valve.

Try putting a vacuum gauge inline on the EGR vacuum hose when you decelerate the throttle.  See if you catch the flutter.  Then vacuum check the EGR source hose with the EGR disconnected (hose directly to the gauge).  See what that looks like.  If stable when testing without the EGR and fluttering with the EGR online, the EGR is a bit sticky.  EGRs do flutter, there is mass here, and engine "vacuum signals" reflect rapid cylinder pressure differential changes.

The PO had a garage replace the ECU and do a few other repairs shortly before the Jeep was parked due to it failing our state inspection.It needed brakes, exhaust and suspension work which I have done.The distributor install not being correct among a few other quick repairs makes me question the shops knowledge of this Jeep so the grounds and ECU connections will be a good place to look.

Grounds are always important on D.C. voltage systems. Amperage is equal over grounds, just the negative or reverse reading.  Ohms-volt testing is valuable on wiring circuits that carry constant voltage, like battery current and engine/chassis grounds. For real time sensor behavior, alternator voltage, motors and anything involving a time interval versus voltage changes, an automotive lab scope is the optimal test tool.  I am moving to this kind of equipment and will be sharing automotive scope functions and troubleshooting advantages throughout this year.

I'm not 100% sure what is the correct operation of the ISA.It works well to keep a good idle once the engine is running but when should it correct the throttle position for the conditions, while the engine is cranking or after it starts? Mine doesn't adjust until after the engine starts but not quick enough to keep it running.After it stalls once the ISA extends, opening the throttle before I crank the engine again to start and it idles good.If I bump the starter once before starting,the ISA will open the throttle and then when I start it, it will stay running.If I shut the engine off even warm and immediately restart, it will sputter along trying to stall for a second or two until the ISA has time to increase the idle and stay running. Hopefully the problem lies in one of the above checks.

The slow ISA response is a distinct clue.  Sounds like the adjustment is correct but response time is not.  Again, a scope would be handy here for watching the wave function of the ISA voltage 1) before cranking, 2) as you crank and 3) immediately after the engine fires and you experience the delay. The ISA trigger signal is ECU based, typically a square wave ground like .5 volts or whatever.  You can't pick this up with a voltmeter because the voltmeter's capture time interval is too slow.  If lucky, an "average" voltage will appear on a meter, or more likely, an erratic volt reading will occur.  The signal is in milliseconds, the domain of a wave form automotive scope.  I am optimistic that these mystery behaviors can be narrowed to specific issues.  More on that when I demonstrate scope use. 

I'm use to working on older vehicles with mechanical linkage and adjustments but enjoy the new challenge of trouble shooting the newer sensor and electrical systems. knowing what is out of spec and causing the problem when I test it is the key.Boy there are a lot of sensors to check ! The info on this site has gone a long way in giving me the knowledge in what to look for.

We've been using a mechanical approach in most of our 2.5L TBI troubleshooting.  I look forward to seeing the difference when diagnosing with a scope.  The electronic or ECU side of the system, as I noted, is square wave and doesn't respond to traditional test equipment for voltage on or off.  I'll try to illustrate that with the automotive scope.  (Unfortunately, I will have to simulate tests that can apply to a Jeep 2.5L TBI engine, I do not have immediate access to one.)  Your ISA situation is a classic example of how continuity and voltmeter tests fall short.  Any signal involved with the ECU can be better served with a lab scope.  As an example:  What if this narrows down to a square wave signal error?  Is the ECU defective?  Neither of us are fans of "parts replacer" approaches.  It would be optimal to watch the interaction between the ECU and ISA in live, real time to see whether the rebuilt ECU is working properly and providing the right signal at the right time.  Experimental parts replacing is costly and often misses the mark.  You want to pinpoint real causes.

There is one last thing that I question.I assume once the stationary idle set screw stop in the TBI throttle bracket is set it never should never need to be adjusted again.When the engine is running the ISA adjustment bolt should maintain contact with the throttle, keeping it off the set screw stop and the correct the idle as needed.When the engine is shut off should the throttle be held off the stationary stop screw by the ISA ? If the PO adjusted the set screw stop in an attempt to correct another issue, it could through off the closed TPS adjustment.Would the correct adjustment of this stop screw be to just contact the throttle stop tang when the throttle blade is fully closed just to prevent damage to the blade? I'm going to check on this as well.

I happen to have an as-new copy of the 1984-85 original FSM  (AMC/Jeep® Workshop Manual M.R.244) for the XJ Cherokee/Wagoneer.  It's the revised July 1985 edition.  The section devoted to the ISA is interesting.  There is no discussion on adjusting the ISA, just how to replace it.  The original intent with the ISA was to replace the factory preset unit with another factory set unit.  The discussion talks about the motor being integral.  Period, no adjusting for the early XJ techs, just order a new ISA assembly.

Fast forward to my 1989 FSM edition that covers all Jeep® models for that year (1987-90 for all purposes) and is a two book set (Electrical as a separate volume).  All of the 2.5L TBI PDFs that I have shared at the forums have been from the '89 edition.  If you have not done so already, you will find in-depth discussion of the 2.5L TBI and ISA motor with supportive PDF info, using the search word "ISA" here at the forums.  

Despite your concern, it does seem like the range of ISA function and speeds are correct.  Your only remaining concern is the response time of the plunger.  Correct? 

I do have one more suggestion here.  The 2.5L engines require a signal from the power steering gear to adjust for engine rpm changes due to power gear load.  This is not needed with a six-cylinder engine, as the power steering will not impact the idle speed much...Does your 1984 system have that power steering pressure sensor, and if so, have you checked the connections and ohms reading of that sensor?  Is there a possibility that your sluggish ISA response is the ECU hunting for a power steering pressure signal?  There should be a relay (see below) if you have the sensor; the relay could be ratcheting, defective or sticky.

This is a Mopar Parts Catalog listing for an XJ Cherokee/Wagoneer "Power Steering Relay".  It does not show for 1984, rather "1986" four-cylinder.  If you find a relay, there should be a sender on the P/S system (at the pressure hose, pump, gear, wherever).  It may not have been used in 1984 models, the stalling issue may have been remedied later:

RELAY (22), Power Steering
53003069  1986: Four Cylinder

         image.png

Once I go through the list of checks hopefully one or more will cure my problem.I'll post again(shorter) what I find.

Good...If you perform the pinch test on the fuel return line, limit the pinch to just enough time to watch the gauge spike.  FSM recommendation is no more than two or so seconds.  Holding the pressure spike too long can damage a fuel gauge and other parts;  avoid putting excess pressure on the lines and TBI unit.  Keep in mind when running the pressure test that pressure is only part of the equation.  Steady fuel flow and volume are equally important.

Final tip/reminder:  Some have replaced the TBI fuel regulator O-rings (fuel grade, OEM style) to relieve idle roughness and other symptoms.  The same shop that timed the engine wrong may have replaced the TBI O-rings, possibly with non-fuel grade rings that are deteriorating.    

 

 

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It's been a week of testing and tinkering on my 86 XJ when ever I could find some time so I thought I'd give an update on what I've found.

Although it seems to run well, maybe even perfect, I was annoyed that it would have to stall once after starting warm or cold and be restarted before the ISA would open the throttle to maintain a good idle.After cleaning all grounds, testing all sensors, including the power steering pressure switch that my 2.5L does have, I was convinced my issued lied elsewhere.I rechecked all vacuum lines changing any that were questionable.I removed the ECU and cleaned the terminals as you suggested and was sure this was the problem since a couple did have grey corrosion on them.I was hoping for a good startup but it stalled as it had always done, needing to be restarted.I haven't checked my fuel pressure yet because I can't get the test port plug out.Although I want to check the fuel pressure at some point, I will have to remove the throttle body to do it but not right now since it runs well except for the start up problem.I really didn't think this was the reason why the ISA wasn't opening the throttle when the engine was started but more likely an electrical issue so I didn't want to open up a throttle body can of worms.

After a lot of looking around under the hood for wiring problems and fixing anything that looked dicey, I noticed an empty connector for a relay next to the fuel pump relay.I figured this was for an AC relay that wasn't needed since I don't have AC.After more fishing around about this empty relay block I found it's called a "Power System Relay" and it delays the power being turned off to the ISA when the engine is shut off for a few seconds.This few seconds of power is enough time for the ECU to extend the ISA, opening the throttle for the next start up.Now I know when the ISA is supposed to extend and mine wasn't. I was hopeful but couldn't believe the fix could be so easy.I got the relay which turns out to be the same as the fuel pump relay and bingo-it made the ISA work as it should.I can't imagine why the PO removed this relay unless it was needed for the fuel pump some time years ago.I was so relieved I really didn't care.

Now when I fire the engine up hot or cold, it idles perfect on the first start up.I'm glad I went through all the systems as you suggested on the way to finding this relay fix. Many things were in need of cleaning, tightening and adjustment giving me a better running, more dependable Jeep in the future. New problems that arise down the road will be easier to fix now,I hope .Plus when the ECU was replaced in 2012, the PO only put the 1 easy bolt back in leaving out the other 2 hard ones. This was causing a under dash rattle that I couldn't find until now.

I do plan to remove and clean the throttle body and injector in the future.I'll also get the frozen test port plug out but want to get it on the road and drive it first to find any other issues.

As for my new EGR valve, although it seems to function OK at idle and when opening the throttle quickly, it does make a fluttering and quacking noise, mainly when I let off the throttle.If I hold the throttle around 1500 rpm the EGR diaphragm will vibrate and cause a vac flutter and the engine to run a little uneven as well but when I throttle up past 1500 it will smooth out and run good.The engine doesn't do this if I disconnect the line at the EGR.The vac flickers up and down quickly a couple of inches at idle with or with out the EGR but not when I throttle up with out the EGR, only with it.Do you think I might have a bad EGR valve even though it's new? I got a standard brand which came with 3 washers and a chart instructing me which one to put in according to my old EGR part number.It called for the #10 washer which is consistent with what I've read about others doing. I also rechecked the base timing with a test light and it does show 12 degrees BTDC now.Ether all my tweakings have corrected this from the 18ish I saw earlier or I just misread it before but I like the proper 12 now.

So now that my little Pioneer runs and yard drives well it's time to switch my efforts to making it look good.

Thanks for the education and help. TJ         

 

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Tenny, I couldn't be more pleased than to know how your thoroughness and determination paid off!  On later models, the ASD system is somewhat equivalent to your Power System Relay, though the TBI 2.5L ISA motor is more basic and mechanical.  Your fix makes perfect sense!  Congrats...This should be gratifying and may help others.

The EGR sounds like the load from the EGR valve and plunger is causing the flutter.  The intake vacuum may not be uniform for all four cylinders.  Though a vacuum gauge shows vacuum as a uniform and constant in/hg measure, what we're really dealing with is differential pressure between the intake stream and each cylinder's individual change in differential pressure.  If the gauge needle actually flutters at 1500 rpm, that's from pulsing pressure, which we relate to as vacuum.

If you could measure each of the four cylinders for individual manifold vacuum or pressure differential, you might see a variation in vacuum per cylinder.  At 1500 rpm, the EGR valve should be near full opening if your vacuum hoses are routed correctly.  In your engine, the EGR Solenoid controls when vacuum is available to the EGR valve.  The EGR valve is controlled by "ported vacuum" (above the throttle valve) and fully closed at idle, opening fully as you tip-in the throttle.  You can read ported vacuum on this line from the TBI unit to the EGR with the solenoid open or directly at the TBI hose pipe.

There may be a simple cause for the fluctuation.  On the hose from ported vacuum to the EGR  solenoid, some applications use a check valve or "delay valve". The vacuum hose attaches to each side of this plastic check valve.  These valves either stabilize vacuum or only allow pressure one way.  Explore whether or not you need that valve.  It's a common, inexpensive item, though you would need the correct function/type valve.

Beyond that possibility, the EGR fully opens to the exhaust stream, which also creates a differential pressure change.  If the exhaust flow through the EGR is pulsing, that could cause a manifold vacuum fluctuation, too.  Could there be a back-pressure issue at the catalytic converter or muffler?  Set the throttle at 1500 rpm and feel the tailpipe pressure for uniform, unrestricted exhaust flow.  Above 1500 rpm, the EGR gradually closes, that rate is dependent on the balance spring pressure at the EGR. The issue could simply be an EGR valve with a balance spring that is unstable.  You could fiddle with the washers and spring pressure to see whether that helps stabilize the diaphram and plunger. 

This could also be uneven vacuum per cylinder or the natural effect of a TBI manifold with uneven air flow to the outer cylinders (1-4).  Or you might have a vacuum leak at the intake manifold to cylinder head junction.  With the engine idling, a light mist of non-volatile penetrant like WD-40 around each of the intake flange ports would create a change in engine speed if there is a leak.  If a leak exists, you can try re-torquing the intake/exhaust flange fasteners.  If the leak persists, change the gasket...

Moses

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  • 2 weeks later...

Another quick update on my quacking EGR valve.Now that we've had some spring weather I've been sidetracked with other projects but think I've found the problem.

I found I have a constant 12-14" of vac in the line going to the EGR valve.I  ran a line directly from the EGR solenoid to the EGR valve, bypassing the charcoal canister and  it(EGR) works as it should with out noise.I'm assuming there is a diaphragm inside that has a leak?

I bought another used canister off Ebay since I couldn't find a new replacement although I feared it wouldn't be any better then the one I had.It did come with a guarantee that it was tested and worked but I had to return it when I could shake charcoal bits out of the vac ports.

The seller is living up to his word and sending me another so I'm now waiting for it to arrive but don't dare to get my hopes up that it will be OK.

Do you know of a new replacement that will work if I need to go that route.I did find one at Summit for a mid 80's Nissan that looks about right but not sure of the inner workings.

I'll post back with my progress when there is some.

Thanks for all your help. 

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Hi, Tenny...Insightful, thanks for sharing!  The EVAP canister causing the EGR vacuum loss and flutter will be helpful troubleshooting for others.

I did some research for your canister.  1986 four-cylinder is different than the six-cylinder, which would be the GM 2.8L V-6.   Here are the part numbers for both, your canister should be #1 in the parts illustration below and also under the part numbers.  See whether you can cross over the 33000056 Mopar part number to any other application or replacement.  Try a Google search under the keyword/phrase "Mopar 33000056".  There may be other, more common AMC or Mopar car or van applications.  Or at least this expands your interchange options.  If there are aftermarket manufacturers of canisters, the Mopar 33000056 number could be crossed over.

ITEM PART
NUMBER QTY BODY MODEL DESCRIPTION
VAPOR CANISTER XJ CHEROKEE, XJ WAGONEER, COMANCHE
1 CANISTER
Four Cylinder
J3239479 1 1984-85
33000056 1 1986
2 CANISTER
Six Cylinder
53001850 1 1984-86

image.png

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  • 2 weeks later...

OK,the new(used)charcoal canister is in and it works great.Now I only have vacuum to the EGR valve when the engine is warmed up and I open the throttle as it should.Also the EGR no longer makes a flutter noise when I let off the throttle.

I cut my old one open to see what was wrong with it and at least the foam filters were still intact keeping the charcoal from being sucked out.Then I popped the cap off that has the EGR line port and the little diaphragm did have a cut in it which would cause the vacuum issue I had .If I could have found that diaphragm I could have fixed my old canister easy.Also if leaking charcoal was the only problem, a person could replace the foam filters and glue the canister back together since it is hard to find a good one.Just thinking it could be an option for someone.

On to the painting part of this Pioneer project.When it's done and I can drive it more I'm sure I'll be back with more issues, hopefully little ones.

Thanks for your help, it's been a learning experience working my way through these problems.  

TJ   

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Tenny...Glad this all worked out...Where did you source the canister—new or used?  Good point about rebuilding the original.  Not sure if component parts are available, two used units might provide enough parts to get through a rebuild.

I am curious how the 2.5L TBI four performs with a 904 automatic and 4x4.  The '86 XJ Cherokee should be light, around 2,900 pounds curb weight or so.  This is an interesting powertrain.  In 1986, this buyer took the right route and avoided the small-journal 2.8L GM V-6.  The 904 automatic should be quite robust at this weight package and engine output.  I recall these transmissions in full-size (3,600-plus pound) sixties Chrysler cars with 318 V-8s.   

Your transmission does lack overdrive, but if the axle ratios are reasonably tall, that should be okay.  Do you have 3.55 or 3.73 axle ratios?  The overdrive manual transmission CJs and Wranglers with four-bangers were mostly 4.10 axles.

Moses

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I'm curious to drive this Cherokee and see how it handles the hilly roads we have around here.I'm hoping the light weight is enough to allow the little engine to not feel totally gutless but to be honest I'm not expecting much so I won't be to disappointed.It's just going to be a summer toy anyways.I did find a tag on the rear axle with 3.54 on it.Does this make sense? I thought it was strange because until now I didn't realize only the manuals came with 4.10.

The PO did put a nice 2" spring lift and 30" tires on so not having overdrive is a good thing.I wished I did have the 4.10 axles and if it's too much of a dog I'll take out the lift springs and put smaller tires on.I hate to go to that expense and it does look nice lifted a little.

I've driven the older CJ 5's and YJ's with the 4 banger and thought they were OK but they had the low gears and manual trans.I like putting turbo's on rigs that were built to early to have one and have toyed with the idea of doing it to the Cherokee but only as a last resort.Someone drove it 70k miles the way it is so it must not be un-driveable.We'll see and I'll keep you posted.

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Tenny...Nice package...I think you'll be okay with the 30" tires and 3.54:1 gears.  (Yes, that should be the axle ratios, front and rear.)  The 2.5L TBI four has okay torque;  however, that torque comes a bit up the power curve.  I tested the first 1997 TJ Wranglers with 2.5L MPI engines, 5-speed AX5 overdrive manual transmissions and 4.10 gearing.  On a six-percent grade, overdrive was out of the question.  The 904 automatic's 1:1 third gear equates to approximately 2443 rpm at 60 mph and 2646 at 65 mph.  (These rpm figures allow for converter slippage and are slightly higher than a true 1:1.) 

This is well below the torque peak for an AMC 2.5L four!  From one source reference, your '86 engine specs look like:

117 hp (87 kW) @ 5000 rpm, 135 lb·ft (183 N·m) @ 3500 rpm

That's not a lot of horsepower for openers, and the torque isn't a world beater, either.  Surprisingly, however, the horsepower was in the range of a carbureted 4.2L inline six during the eighties.  Many consumers just saw the horsepower figure and selected the four over the six...The 2.5L's 5000 rpm horsepower peak is a hint about the torque.  3500 rpm is a fairly high rpm for torque peak when compared to an inline six.  The 4.2L at one point peaked torque at 1600 rpm, a torque rise similar to a diesel.  The 4.0L torque peak was above 2000 rpm.  Four cylinder engines typically develop peak torque between 3000 and 4000 rpm.

This explains the chronic downshifting of 2.5L Wranglers, even with 4.10 gears.  I recall shifting the 5-speed models down to fourth (direct) gear on a six-percent interstate grade.  At certain points, I would slow slightly and downshift to 3rd gear, especially when altitude entered the equation.  These vehicles had stock tires and, surprisingly, weighed more than your XJ Cherokee.

So, you'll see how the XJ performs.  Let us know...30-inch tires and a mild 2-inch lift is pleasant to look at and not radical by any means.  It would be great to keep this setup.  Frankly, gearing is the only workaround if you want more performance from this engine's power curve.  I did get some relief on the 4.0L six in our XJ Cherokee by loading MaxEnergy software from Hypertech.  The noticeable gain came from the torque peak rpm that dropped to 2,000.  The bore/stroke on the 4.0L lost the legendary bottom end "stump pulling" torque of the 4.2L sixes.   Unfortunately, the 2.5L four is patterned after the 4.0L's bore/stroke and not the 4.2L. 

On Wranglers with 33" tires and a 2.5L four with a manual overdrive transmission, the popular axle ratios are 4.56 and 4.88.  Your 3-speed automatic and 30-inch tires would call for 3.73 or 4.10 axle gears.  4.10 would be peppy but possibly higher fuel consumption without an overdrive gear.

Moses

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