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Hi,

 

I have a 1988 Jeep Yj 2.5 with the renix computer.

My last stop before I drive this thing off a cliff is here.  I should have come here first.  I hope one of you can help me.  I love my Jeep but am so frustrated with it right now.

Problem: Jeep is running super rich.  I do not think it is ever coming out of closed loop.  

Points to know:

- O2 sensor is recognizing that the jeep is rich.  Volts sit between .94V and .99V

JEEP RUNS AWESOME.  No loss of power.  No hesitation.  Idles between 900 and 750

- Fuel smell coming from the tailpipe

Emissions high on HC and CO

 

Things I have tried:

-Replaced o2 sensor

-replaced fuel pressure regulator

-replaced CTS

replaced ISA

replaced ECU

replaced MAP

Replaced MAT

checked return fuel line for blockage.

Had Head rebuilt.  Vacuum was fluctuating and needed new valve guides.  Was hoping this was impacting the MAP sensor.  Nope

I have gone through entire FSM diagnostic tree.  The only thing that failed was the MAT sensor resistance never got down to 150ohms.  Always stayed above 300.  

I even paid a mechanic $600 to try and uncover the problem.  He confirmed it was not coming out of closed loop.  Recommended changing the ECU.  Which I did.

 

I hope someone can help.

 

Thank you all in advance.

 

Carlos

 

 

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Carlos, you've been very thorough and methodical!  Did replacing the MAT sensor drop ohms to normal?  Is the exhaust system clear of excess back-pressure?

I'm intrigued by your troubleshooting effort, parts replacement strategy and the negative results...Let's pursue this...

Moses

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Hi Moses.  Thank you for responding.  I replaced the MAT sensor with one I got from a junk yard.  The ohms stayed about the same.  The temp in the intake manifold is still around 160 degrees based on the registered ohms.  It is hot enough to let the ECU know that the vehicle is warm.  I think it is lower than the CTS because the added fuel is lowering the temp?  Not sure there.  

 

As for back pressure.  I am sure my cat is shot by now will all the fuel being dumped down the exhaust.  I have never checked the back pressure on the exhaust and dont think the mechanic did either.  He did say I was getting a 60 degree delta on the cat but I dont remember the significance of that.  He said it wasn't good but want really bad either.  

 

How do I go about testing the back pressure?  Would disconnecting at the down pipe allow for the pressure to be relieved?  It has an aftermarket CAT that is welded in place.

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Carlos...See my red highlighted comments below:

3 hours ago, Carlos said:

Hi Moses.  Thank you for responding.  I replaced the MAT sensor with one I got from a junk yard.  The ohms stayed about the same.  The temp in the intake manifold is still around 160 degrees based on the registered ohms.  It is hot enough to let the ECU know that the vehicle is warm.  I think it is lower than the CTS because the added fuel is lowering the temp?  Not sure there.

Manifold air temp sounds normal, you have an ambient air flow streaming through the manifold, it would be hotter near the cylinder head due to transferred heat.  Coolant temp is thermostatically controlled.  The signals need to keep the engine off its richer warm-up cycle.  As long as the coolant temp sensor is reading high enough to register as a warmed up engine, you should be okay.  The engine needs at least a 195-degree F thermostat to stay off the warm-up cycle.  On MPI systems, 180 degrees F is too cold...What is the coolant temp and signal to the ECU?

As for back pressure.  I am sure my cat is shot by now will all the fuel being dumped down the exhaust.  I have never checked the back pressure on the exhaust and dont think the mechanic did either.  He did say I was getting a 60 degree delta on the cat but I dont remember the significance of that.  He said it wasn't good but want really bad either.

Here is interesting information in simple terms from AutoZone:   http://www.autozone.com/repairinfo/common/repairInfoMain.jsp?targetPage=productsHowToInspect&leftNavPage=productsHowTo&pageId=0996b43f80a0125f&subtitle=test.  Note the comments on a manifold vacuum gauge test.  This is a very old and reliable test method.  Attach a vacuum gauge to the intake manifold below the TBI unit.  Raise engine speed and watch the gauge.  There is a normal drop in manifold vacuum as speed and load increase, but an abrupt drop in vacuum without any vehicle load applied (just increasing the engine speed) is a hint that the exhaust has too much back-pressure.

As for heat degree drop front to rear of the converter (delta test), you can skip the expensive tools and simply use an inexpensive surface temp infrared testing device.  This should be close enough to indicate an issue.  

How do I go about testing the back pressure?  Would disconnecting at the down pipe allow for the pressure to be relieved?  It has an aftermarket CAT that is welded in place.

See comments above...Have you considered the EGR system?  The EGR valve supply vacuum should be "ported" to eliminate EGR gases when the engine is at an idle and as speed increases.  If the EGR is either stuck open, leaking by or attached to a manifold vacuum source instead of a ported vacuum source, you could have a problem here.

Also, is there a possibility that your fuel pump is for an EFI/MPI system and not the lower pressure output required for TBI?  Are you checking regulator pressure at the TBI test port?  If the pump puts out too much volume, you could have overall fuel enrichment due to the fuel tank return flow backing up.  I have shared pump pressure output details at the forum's 2.5L TBI topics.  The pumps can look alike yet have entirely different pressure/volume output.

Moses

 

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Answers back in green. :)

i Moses.  Thank you for responding.  I replaced the MAT sensor with one I got from a junk yard.  The ohms stayed about the same.  The temp in the intake manifold is still around 160 degrees based on the registered ohms.  It is hot enough to let the ECU know that the vehicle is warm.  I think it is lower than the CTS because the added fuel is lowering the temp?  Not sure there.

Manifold air temp sounds normal, you have an ambient air flow streaming through the manifold, it would be hotter near the cylinder head due to transferred heat.  Coolant temp is thermostatically controlled.  The signals need to keep the engine off its richer warm-up cycle.  As long as the coolant temp sensor is reading high enough to register as a warmed up engine, you should be okay.  The engine needs at least a 195-degree F thermostat to stay off the warm-up cycle.  On MPI systems, 180 degrees F is too cold...What is the coolant temp and signal to the ECU?

My thermostat is a 195.  It is brand new.  The resistance on the CTS registers around 200MV.  According to the register that is around 190-200 degrees.  

 

As for back pressure.  I am sure my cat is shot by now will all the fuel being dumped down the exhaust.  I have never checked the back pressure on the exhaust and dont think the mechanic did either.  He did say I was getting a 60 degree delta on the cat but I dont remember the significance of that.  He said it wasn't good but want really bad either.

Here is interesting information in simple terms from AutoZone:   http://www.autozone.com/repairinfo/common/repairInfoMain.jsp?targetPage=productsHowToInspect&leftNavPage=productsHowTo&pageId=0996b43f80a0125f&subtitle=test.  Note the comments on a manifold vacuum gauge test.  This is a very old and reliable test method.  Attach a vacuum gauge to the intake manifold below the TBI unit.  Raise engine speed and watch the gauge.  There is a normal drop in manifold vacuum as speed and load increase, but an abrupt drop in vacuum without any vehicle load applied (just increasing the engine speed) is a hint that the exhaust has too much back-pressure.

I will check this tonight and send you a video.  

As for heat degree drop front to rear of the converter (delta test), you can skip the expensive tools and simply use an inexpensive surface temp infrared testing device.  This should be close enough to indicate an issue.  

Would it work to pull the exhaust at the down pipe and see if it impacts the fuel mixture?  Will I get a false reading because it will be open right below the O2?

How do I go about testing the back pressure?  Would disconnecting at the down pipe allow for the pressure to be relieved?  It has an aftermarket CAT that is welded in place.

See comments above...Have you considered the EGR system?  The EGR valve supply vacuum should be "ported" to eliminate EGR gases when the engine is at an idle and as speed increases.  If the EGR is either stuck open, leaking by or attached to a manifold vacuum source instead of a ported vacuum source, you could have a problem here.

EGR solinoid tests good.  no vacuum going to EGR at idle.  If I unplug the plug I get vacuum at the EGR and it opens.  BUT, it will not work automatically when i increase the RPM's.  It is suppose to engage between idle and WOT I believe.  I think this is happening because the ECU is still in closed loop and does not initiate the EGR in closed loop.  I have checked and double checked the vacumn lines.  They are going to the right place and hold vacumn.

Also, is there a possibility that your fuel pump is for an EFI/MPI system and not the lower pressure output required for TBI?  Are you checking regulator pressure at the TBI test port?  If the pump puts out too much volume, you could have overall fuel enrichment due to the fuel tank return flow backing up.  I have shared pump pressure output details at the forum's 2.5L TBI topics.  The pumps can look alike yet have entirely different pressure/volume output.

Pressure was tested and adjusted by the mechanic that worked on it.  I do not have the right plug to connect to the TB.  This is the same fuel pump that has been in it since I got it.  So I doubt it is the wrong one.  The mechanic did say he was able to adjust the fuel pressure to 14.5 lbs.  Thinking along these same lines I did change the fuel presuure regulator and no change in fuel mixture.  

One thing to add.  About a year ago my injector stopped working.  I rebuilt and cleaned the throttle body and replaced the injector.  There is not much to them but since we are dealing with a fuel issue that may be important.  I did change the fuel pressure relief valve yesterday and took the throttle body back apart to see if there was something obvious.  I could not find anything.

 

Carlos

Moses

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so I went ahead and bought a Mt-2500 scanner.  I wish I had done that a long time ago.  Would have saved me a bunch of volt meter work.  

 

The scanner confirms that the jeep is not going out of open loop.  It also shows that exhaust is rich

 

Couple of intersting points:  Maybe

1.  RPMs show between 500 and 600.

2.  TPS measures fine 4.73 at WOT but only .09 at idle.  Scanner says it should be .45 at idle.

3. Scanner says EGR on.  This is regardless of if the connector is connected.  With it connected to the EGR solenoid no vacumn at EGR.  Disconnected yes vacuum at EGR.  Do you know where this reading is coming from?

4.  MANIFOLD vacumn reads zero.  MAP vacumn reads fine.  When I disconnect the vacumn hose to MAP and reconnect it, MAnifold vacumn jumps up to 60 (not the foot lbs measurement)

5.  Injector pulse reads 2.5ms  the scanner says it should read 4.5 -20ms

 

Thoughts?

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Your video is very helpful and shows no extremes around back-pressure, Carlos....

Temp is normal and in a workable range to step beyond the cold-start enrichment.  CTS works accordingly.  The delta temp test is at the front and rear of the converterin place with the engine running.  What you're searching for is an increase in temperature, which reflects proper catalytic burn.  The surface temp can be read all along the exhaust system, from the exhaust manifold, down the head pipe, at both ends and the body of the converter, at the muffler, and at the tailpipe.  Could be revealing.

You did a thorough assessment of the EGR function.  Can you see an rpm difference when the EGR valve opens (unplugged)?  ISA will try to compensate idle speed, so you'll need to make this observation immediately upon disconnecting the solenoid plug.  Need to research whether EGR is off-line in closed loop like you suggest...Yes, an EGR valve opens just off-idle and stays open until ported vacuum drops off with increased throttle valve opening.  We're thinking "carburetor", and the TBI behaves in many ways like a carburetor, and so does the EGR on this system.

Thought you might be onto something with the injector.  Does regulator pressure stay constant at 14.5 PSI regardless of engine throttle opening?  Is there a circuit leak or increase in fuel pressure from either the pump or regulator?  I'm still curious about the actual pump output pressure.  Checking maximum output is tricky, as pinching a line or test hose will cause a high spike in pressure for either the MPI or the TBI pump.  I listed pump pressures and part numbers at the TBI 2.5L troubleshooting exchanges.  In the Search box, change the search to "All Content" and enter "fuel pump pressure".  You'll get a roster of 2.5L TBI exchanges.

High pump pressure is like boosting the pressure regulator.  If the volume is too high, it might overload the return flow to the tank, and this would be much like pinching the return hose and jacking up the pressure.  You checked for restriction in the fuel return line—but will it flow enough fuel back to the tank without creating back-pressure?

I have a suggestion...A technique that works only on TBI systems is to hook a timing light to #1 cylinder spark wire lead; hold the beam over the throat of the TBI unit.  You can watch the spray pattern and should see a very uniform "conical" shape to the spray.  This is also a way to see bleed-off or dripping of excess fuel.  You can pinpoint where it is leaking, the timing light beam is quite bright.  Try this with the engine idling and see whether you turn up a spray pattern and/or fuel flow issue at the injector itself.

Moses

 

 

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Just caught your latest post...You do want/need normal TPS voltage at an idle.  This has an impact on fuel flow, and the ISA motor/system must compensate.  This could create an issue.

The EGR reading should be a signal from the solenoid circuit to ECU.  Is there a wiring issue with the ECU and engine harness?  Do you need to perform a "pin out" check of the circuits going to the ECU?  If you have the factory wiring diagram, this is not as daunting a task as it sounds.  There could be a poor ground (epidemic on the engine harness for your model) or a short between wires within a harness.  Does the wiring on your Jeep look "original" and intact?

I would also check out the vacuum circuits.  See whether they match up with the FSM schematic.  I've posted PDFs of the vacuum circuit for the 2.5L TBI, available at the forums with a simple search.

Injector pulse is an issue.  If this is an accurate scanner reading, you need to remedy the 'ms' deviation.  Otherwise, the O2 sensor will constantly be calling for additional fuel.  See my last reply, I suggest the use of a timing light to study the spray pattern...

Moses

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Just caught your latest post...You do want/need normal TPS voltage at an idle.  This has an impact on fuel flow, and the ISA motor/system must compensate.  This could create an issue.

I will try and adjust the tps so it is at .45 at idle.  

The EGR reading should be a signal from the solenoid circuit to ECU.  Is there a wiring issue with the ECU and engine harness?  Do you need to perform a "pin out" check of the circuits going to the ECU?  If you have the factory wiring diagram, this is not as daunting a task as it sounds.  There could be a poor ground (epidemic on the engine harness for your model) or a short between wires within a harness.  Does the wiring on your Jeep look "original" and intact?

I was reading the scanner wrong I think.  I think it was saying EGR soliniod is energized/close.  I can get it to read open briefly when accelerating.  One thing with the EGR, the idle does not change when I disconnect the wiring harness even though I can see vacumn of 15 lbs at the hose at the egr valve.  When I manually press the egr, the engine sputters and dies.  

I would also check out the vacuum circuits.  See whether they match up with the FSM schematic.  I've posted PDFs of the vacuum circuit for the 2.5L TBI, available at the forums with a simple search.

All have been checked and triple checked.

Injector pulse is an issue.  If this is an accurate scanner reading, you need to remedy the 'ms' deviation.  Otherwise, the O2 sensor will constantly be calling for additional fuel.  See my last reply, I suggest the use of a timing light to study the spray pattern...

The problem is the 02 sensor is recognizing that the exhaust is rich.  so wouldn't it call for less fuel?  In closed loop.  I tried the timing light test.  I cannot see any clear cone.  I just looks like the entire throttle body throat is full of fuel.  It is bouncing back up off the throttle fly plate.

Moses

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Your video is very helpful and shows no extremes around back-pressure, Carlos....

No YOU are very helpful.  I really do appreciate you trying to work through this with me and everyone else.

Temp is normal and in a workable range to step beyond the cold-start enrichment.  CTS works accordingly.  The delta temp test is at the front and rear of the converterin place with the engine running.  What you're searching for is an increase in temperature, which reflects proper catalytic burn.  The surface temp can be read all along the exhaust system, from the exhaust manifold, down the head pipe, at both ends and the body of the converter, at the muffler, and at the tailpipe.  Could be revealing.

I need to get a temp gun and will try this.

You did a thorough assessment of the EGR function.  Can you see an rpm difference when the EGR valve opens (unplugged)?  ISA will try to compensate idle speed, so you'll need to make this observation immediately upon disconnecting the solenoid plug.  Need to research whether EGR is off-line in closed loop like you suggest...Yes, an EGR valve opens just off-idle and stays open until ported vacuum drops off with increased throttle valve opening.  We're thinking "carburetor", and the TBI behaves in many ways like a carburetor, and so does the EGR on this system.

see other post.

Thought you might be onto something with the injector.  Does regulator pressure stay constant at 14.5 PSI regardless of engine throttle opening?  Is there a circuit leak or increase in fuel pressure from either the pump or regulator?  I'm still curious about the actual pump output pressure.  Checking maximum output is tricky, as pinching a line or test hose will cause a high spike in pressure for either the MPI or the TBI pump.  I listed pump pressures and part numbers at the TBI 2.5L troubleshooting exchanges.  In the Search box, change the search to "All Content" and enter "fuel pump pressure".  You'll get a roster of 2.5L TBI exchanges.

I don't have the ability to check the fuel pressure.  That was done at the mechanics.  I do not have the needed plug that goes into the throttle body. any work around for that?   As far as the return line.  I did some stuff on that yesterday thinking the same thing.  With some force, I can blow(manually with my mouth) air back through the return line.  I can hear it bubbling back in the tank.  I took the gas cap off.  So I tried to run comressed air through it.  It actually shot gas our of the filler.  As far as the pump, this is the same pump that has passed smog the last three times.  If it possible for a fuel pump to go bad and send more pressure?

High pump pressure is like boosting the pressure regulator.  If the volume is too high, it might overload the return flow to the tank, and this would be much like pinching the return hose and jacking up the pressure.  You checked for restriction in the fuel return line—but will it flow enough fuel back to the tank without creating back-pressure?

I have a suggestion...A technique that works only on TBI systems is to hook a timing light to #1 cylinder spark wire lead; hold the beam over the throat of the TBI unit.  You can watch the spray pattern and should see a very uniform "conical" shape to the spray.  This is also a way to see bleed-off or dripping of excess fuel.  You can pinpoint where it is leaking, the timing light beam is quite bright.  Try this with the engine idling and see whether you turn up a spray pattern and/or fuel flow issue at the injector itself.

One more thing on the injector.  I did replace it about a year ago.  Is it possible I got the wrong one?  I ordered another one about a month ago and had the same issues.  with how finiky these jeeps are should I try a third injector?  if the injector is flowing too much per opening, that would explain why it is only opening for 2.5ms and still being rich?

 

Can you see yet why I am ready to run this thing off a cliff. :)  I know there is something simple.  I just need to find it.

 

Carlos

Moses

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Try my spray pattern and injector leak/drip test with an induction timing light, Carlos...

Harbor Freight has an inexpensive fuel injection pressure tester.  Others have used this successfully.  You will likely find yourself at a NAPA store looking through the Weatherhead fittings to plumb from the pressure regulator plug point to the fuel pressure tester.  

I do discuss pressure tests at a number of the 2.5L TBI topics and replies.  I know this is frustrating and time consuming, but the issue is mechanical with a clear underlying cause.  Consider my comments about wiring, opens, grounds and shorts.  Vacuum issues or vacuum test points can cause MAP and manifold pressure signal quirks.  Take time to compare schematics for the wiring and vacuum circuits.

Moses

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Some of your earlier comments, see reply below:

37 minutes ago, Carlos said:

Just caught your latest post...You do want/need normal TPS voltage at an idle.  This has an impact on fuel flow, and the ISA motor/system must compensate.  This could create an issue.

I will try and adjust the tps so it is at .45 at idle.

Concern here is that raising the base TPS setting will also raise the WOT setting.  This is like a linear rheostat or potentiometer.  Raise the bottom, the top goes up, too.  You may have a worn or defective TPS.  You'll see what I mean if you attempt to change the idle voltage...

The EGR reading should be a signal from the solenoid circuit to ECU.  Is there a wiring issue with the ECU and engine harness?  Do you need to perform a "pin out" check of the circuits going to the ECU?  If you have the factory wiring diagram, this is not as daunting a task as it sounds.  There could be a poor ground (epidemic on the engine harness for your model) or a short between wires within a harness.  Does the wiring on your Jeep look "original" and intact?

I was reading the scanner wrong I think.  I think it was saying EGR soliniod is energized/close.  I can get it to read open briefly when accelerating.  One thing with the EGR, the idle does not change when I disconnect the wiring harness even though I can see vacumn of 15 lbs at the hose at the egr valve.  When I manually press the egr, the engine sputters and dies.

Sounds like the EGR valve itself is working.  Unseating it should roughen the idle.  Closed should stabilize.  That's the test... 

I would also check out the vacuum circuits.  See whether they match up with the FSM schematic.  I've posted PDFs of the vacuum circuit for the 2.5L TBI, available at the forums with a simple search.

All have been checked and triple checked.

Injector pulse is an issue.  If this is an accurate scanner reading, you need to remedy the 'ms' deviation.  Otherwise, the O2 sensor will constantly be calling for additional fuel.  See my last reply, I suggest the use of a timing light to study the spray pattern...

The problem is the 02 sensor is recognizing that the exhaust is rich.  so wouldn't it call for less fuel?  In closed loop.  I tried the timing light test.  I cannot see any clear cone.  I just looks like the entire throttle body throat is full of fuel.  It is bouncing back up off the throttle fly plate.

Perhaps the leak or over-fueling is within the boundaries of the O2 sensor's feedback.  The trim works but stays on the fat or rich side due to the constant excess of fuel flow...Are you going into open loop or staying in closed?  Let's go down that path next.  Sounds like a lot of fuel in the TBI throat.

Moses

 

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I was thinking the same thing on the TPS.  I will try another one.

 

12 minutes ago, Moses Ludel said:

Perhaps the leak or over-fueling is within the boundaries of the O2 sensor's feedback.  The trim works but stays on the fat or rich side due to the constant excess of fuel flow...Are you going into open loop or staying in closed?  Let's go down that path next.  Sounds like a lot of fuel in the TBI throat.

Moses

it never goes into closed loop.  Always open.  I am able to momentarily go into decel mode when rev the engine and quickly release the throttle.

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ok Moses.  I am loveing this scanner.  Greatest thing since sliced bread.  

 

So when I start the car:

Exhaust reads rich jeep in open loop for 5 10 seconds.

jeeps goes into CLOSED loop and the ST trim decreases from 128 to zero.  Sits at zero for one second and goes back to open loop.  Waits 5 seconds and does it again.  It only does it twice then stays in open loop.  I have heard of a Limp home mode?  so the jeep is trying to lean itself out and cant.  when i cant it stops trying.  

 

I have never actually seen this before because it is for such a short period of time.  I changed the TPS and was watching the voltage.  That is the only reason I saw this.

 

NOW WE ARE COOKING WITH GAS.  TOO MUCH GAS BUT GAS NONE THE LESS

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This is an insightful development, Carlos!...Kudos to the Snap-On scan tool, these tools are valuable...

Yes, "limp home mode" is actually open loop.  The mode is a default program that will allow the engine to run, regardless of emissions and whether or not the A/F ratio is correct.  As a rule, limp home will run to the rich side, which is exactly what you're experiencing...As you know, this mode will not pass a smog test!

I'm excited, too.  The question is why does the system go into open loop or limp mode?  That's in effect what is happening.  Focus on reasons why the system will trip into limp mode or open loop.

Before delving deeper, check the grounds underhood.  The most common trouble spot is the ground near the oil dipstick on the 2.5L engine.  I check grounds in a quick, simple manner:  Using a digital volt-ohmmeter set for ohms resistance readings, I clip one lead to the battery's negative/ground post and touch the other lead to each grounding point at the engine, body/firewall and ECU.  This will take the ground continuity and resistance into account over the entire span between these points.

Note:  High resistance indicates poor connections, frayed or corroded wires or corroded body attachment points and/or hardware.  Simple. Correct the cause of the higher resistance.  Unstable or high resistance grounds will cause a voltage drop on a given circuit; low voltage will cause the ECU to fault into limp mode.  If you have poor grounds with too much resistance, that is a voltage drop.  If the ECU supply voltage is too low, the ECU will go to limp/open mode.  This may not have anything to do with voltage from the alternator, so you cannot rely on the dash voltmeter to determine whether there is sufficient voltage at the ECU.  A defective alternator or rectifier bridge, however, can cause the ECU to fault and go into limp mode.  Make sure the alternator grounding is sufficient, including the attachment hardware!

Paint, corrosion and oxidation are the most common poor ground issues on these models.  Make certain that each of the engine, ECU and chassis grounds have normal resistance.  High resistance is a sure sign of either poor connections, corroded wires within the ground wire/cable terminals, or too much load on the circuit.

If the problem is not a ground, voltage drop or alternator issue, we can look to other causes for an open loop default.  Does the scanner show any stored trouble codes?  Retrieving codes is another valuable function of the scanner.

Moses

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Hi Moses.

 

Yea the scanner is awesome.

 

Grounds:  I have gone through every ground I can find and checked the resistance.  There is no resistance over 1 ohm WITH THE KEY OFF.  As soon as I turn on the ignition the OHMS jump to 2.5-3.  I do not know if this is normal.  I also sanded all connectors and added a second ground from the negative terminal to the radiator.  I will check them again tonight.

 

Limp home mode:  Does the fact that we can see the ST trim try and go to zero in open loop mean anything?  I feel like it is trying to lean it out and cannot.  W

how go I check the imput voltage to the ECU?

Fuel Pressure:  So i did the napa thing and built an adaptor to test the fuel pressure.  It sits at 14.5 regardless of the RPMs.  Doesnt even wiggle.

 

retriving codes:  I dont believe this is possible?

Other:  I went to the autoparts store today where I got my injector.  They are going to swap it out.  New one arrives Tuesday.  Just a shot in the dark.

Would the EGR not working cause these symptoms?  I cannot get it to engage with vacumn.  Even with a vacumn pump I cannot get it to change the idle.

 

Carlos

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See comments below...

1 hour ago, Carlos said:

Hi Moses.

 

Yea the scanner is awesome.

Glad you made that investment!  You're way ahead on insight and saving a good deal of time now...

Grounds:  I have gone through every ground I can find and checked the resistance.  There is no resistance over 1 ohm WITH THE KEY OFF.  As soon as I turn on the ignition the OHMS jump to 2.5-3.  I do not know if this is normal.  I also sanded all connectors and added a second ground from the negative terminal to the radiator.  I will check them again tonight.

Looking forward to your new ohms measurements...

Limp home mode:  Does the fact that we can see the ST trim try and go to zero in open loop mean anything?  I feel like it is trying to lean it out and cannot.

Here's a good explanation of fuel trim:  https://www.obd-codes.com/faq/fuel-trims.php  You're right, the system is trying to self-regulate the A/F and cannot. After a few tries, it apparently goes into limp/open mode.  This could be that the injector is simply unable to control the fuel flow, there could be a significant and constant fuel dribble or flow (unregulated) down the throttle body.  The O2 sensor sends a rich signal to the ECU, the ECU tries to lean mixture, but the TBI unit still flows too much fuel.  This goes back to your out of range "ms" readings for the injector.  There's a problem here!

how go I check the imput voltage to the ECU?

This is more a function of the ignition circuit and grounds.  You can read ignition circuit voltage with a voltmeter at a convenient point, don't disassemble the column or switch!  There's a range of voltage that the ECU can tolerate.

Fuel Pressure:  So i did the napa thing and built an adaptor to test the fuel pressure.  It sits at 14.5 regardless of the RPMs.  Doesnt even wiggle.

Great, that's the fuel pressure constant that you want, and you know it's right now...Time and tools but worth it!

retriving codes:  I dont believe this is possible?

Yes it is!  There is a diagnostics plug for the engine.  It is under the hood and usually near the battery.  Your Snap-On kit should have adapter connectors, this one is Jeep/Chrysler type.  The tool and its software should be able to read "OBD" codes from this diagnostic plug.  Don't disconnect the battery.  You want stored codes!

Other:  I went to the autoparts store today where I got my injector.  They are going to swap it out.  New one arrives Tuesday.  Just a shot in the dark.

Good shot in the dark!  Look for any issue with the TBI throttle body itself that could create an independent leak and a constant dribble of fuel.  It doesn't take a lot to create rich mixtures!

Would the EGR not working cause these symptoms?  I cannot get it to engage with vacumn.  Even with a vacumn pump I cannot get it to change the idle.

That's an issue for EGR function, which affects the NOX readings.  You may also need EGR to get normal A/F readings past an idle; EGR engines are set slightly rich.  i would remove the EGR and clean its metal parts.  You can dip the base and plunger in carburetor cleaner but do not expose the diaphragm to carburetor cleaner, it will swell or weaken!  See if the EGR valve is sticky or carbon fouled.  You operated it by hand with success, but the resistance might be too great for vacuum actuation. 

 

Carlos

 

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Hi Moses.

 

Yea the scanner is awesome.

Glad you made that investment!  You're way ahead on insight and saving a good deal of time now...

Grounds:  I have gone through every ground I can find and checked the resistance.  There is no resistance over 1 ohm WITH THE KEY OFF.  As soon as I turn on the ignition the OHMS jump to 2.5-3.  I do not know if this is normal.  I also sanded all connectors and added a second ground from the negative terminal to the radiator.  I will check them again tonight.

Looking forward to your new ohms measurements...

What about the increase in resistance when I turn the ignition on.  Is that normal?

 

Limp home mode:  Does the fact that we can see the ST trim try and go to zero in open loop mean anything?  I feel like it is trying to lean it out and cannot.

Here's a good explanation of fuel trim:  https://www.obd-codes.com/faq/fuel-trims.php  You're right, the system is trying to self-regulate the A/F and cannot. After a few tries, it apparently goes into limp/open mode.  This could be that the injector is simply unable to control the fuel flow, there could be a significant and constant fuel dribble or flow (unregulated) down the throttle body.  The O2 sensor sends a rich signal to the ECU, the ECU tries to lean mixture, but the TBI unit still flows too much fuel.  This goes back to your out of range "ms" readings for the injector.  There's a problem here!

Lets see if the new injector fixes it.  If not I may have done something to mess up the TB when I rebuilt it.  I  will look for a used one.

how go I check the imput voltage to the ECU?

This is more a function of the ignition circuit and grounds.  You can read ignition circuit voltage with a voltmeter at a convenient point, don't disassemble the column or switch!  There's a range of voltage that the ECU can tolerate.

Fuel Pressure:  So i did the napa thing and built an adaptor to test the fuel pressure.  It sits at 14.5 regardless of the RPMs.  Doesnt even wiggle.

Great, that's the fuel pressure constant that you want, and you know it's right now...Time and tools but worth it!

Cross that off the list.

retriving codes:  I dont believe this is possible?

Yes it is!  There is a diagnostics plug for the engine.  It is under the hood and usually near the battery.  Your Snap-On kit should have adapter connectors, this one is Jeep/Chrysler type.  The tool and its software should be able to read "OBD" codes from this diagnostic plug.  Don't disconnect the battery.  You want stored codes!

Is this a different port than the one I am connecting to with the scanner to get real time data?  D1 with 6 pins and D2 with 15?  attached.  

Other:  I went to the autoparts store today where I got my injector.  They are going to swap it out.  New one arrives Tuesday.  Just a shot in the dark.

Good shot in the dark!  Look for any issue with the TBI throttle body itself that could create an independent leak and a constant dribble of fuel.  It doesn't take a lot to create rich mixtures!

Would the EGR not working cause these symptoms?  I cannot get it to engage with vacumn.  Even with a vacumn pump I cannot get it to change the idle.

That's an issue for EGR function, which affects the NOX readings.  You may also need EGR to get normal A/F readings past an idle; EGR engines are set slightly rich.  i would remove the EGR and clean its metal parts.  You can dip the base and plunger in carburetor cleaner but do not expose the diaphragm to carburetor cleaner, it will swell or weaken!  See if the EGR valve is sticky or carbon fouled.  You operated it by hand with success, but the resistance might be too great for vacuum actuation. 

I pulled it off and it was pretty black.  I could move the pin but it was difficult.  I will try and clean it and see if it works better.  

I also pulled off the vacuum canister.  Should that hold vacuum?  It does not.

 

Carlos

diagnostic connector.PNG

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Carlos...Key On will load the circuits.  Negative side resistance should occur if there are "driver" draws taking place on the positive side.  This is a D.C. system.  If grounds were good with no signs of corrosion or wire and terminal weaknesses that could lower the amperage capacity on a given ground circuit, you should be okay.  

Continuity tests only show that some strands of the wires are intact.  Ohms-resistance indicates weakening load capacity.  On D.C., however, the grounds reveal loads on the positive side, and any device or load will show up, including the coil, lamps, the wiper motor and other resistance items.  A visual inspection of terminal ends and their connectivity is usually enough.  I watch for corrosive "wicking" from the terminals upward into the wires, especially on battery cables exposed to acids.

Looks like you're hooking to the diagnostic ports.  D1 provides direct check points for Ignition and Ground, very useful.  D2 #4 would be a good comparison between battery voltage and downstream voltage.)  The ECU does store OBD trouble codes on these early systems.  Not as sophisticated as OBD-II, but you should be able to retrieve whatever codes are available.  The scanner should have a read mode for trouble codes.  These are diagnostics ports.  You can see they are limited.  Great that your scanner came with OBD Chrysler adapters.  For comparison, AutoZone and others have less sophisticated scanners that come with early OBD adapters.  Take a look at these diagnostic hook-up connectors.  This should be a clue.

If the EGR diaphragm won't hold vacuum, you have a defective EGR valve.  I'm surprised these valves last as long as they do, the diaphragm moves continuously over time...

Waiting to see what comes of the TB changeout or a repair of your current unit plus the new injector.  There's likely an internal fuel circuit leak or seepage at the TBI unit that's adding unchecked fuel to the engine.  Will be great to turn up an "Aha!" moment.

I'm not sure how your time management is working, but the investment in these tools is very valuable for future work and automotive self-sufficiency.  Of course there's a learning curve, but that's a lot cheaper than subletting work at the current shop labor rates.  This should be gratifying, ending the cycle of dependency upon dealerships and third party technicians.  

Moses

 

 

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Well I guess I have to try a new Throttle Body now.  The casing around the fuel pressure test port cracked while I was reinstalling the plug.  Fuel spitting out.  I am going to see if my machine shop can fix it.  But with not knowing ifthe TB is bad, I am not going to spend too much time on it.

 

#$%!#$%#$%!$#^%#$^$#%@

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Well, Carlos, you were headed down the replacement path anyway...Sorry about the mishap, but you will eliminate some guesswork with a new/used/rebuilt TB.

Moses

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Moses,

 

I am happy to report that my jeep passed smog with flying colors today.  Finally got my hands on a new throttle body and it went right into closed loop.  UGG.  That was a lot of work and money to find out I screwed something up when I rebuild the TB last year.  Thanks again for your help and everything you do for the jeep community.

 

 

Carlos

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You're very welcome, Carlos!  Congratulations...This has been a valuable lesson for other owners.

Enjoy the YJ 2.5L, it's smog legal and reliable once more!  The good news:  You're way up the learning curve on understanding the 2.5L TBI system and troubleshooting it.  This is useful insight!

Moses

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