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Hello all,

I am having some issues that have become more perplexing than my knowledge has the answers for so hopefully someone can steer me in the right direction. 
 

I started off by trying to improve the rough idle my Jeep has had for years. I rebuilt the TBI, new O2 sensor, new ISA, TPS, coolant temp sensor, MAP sensor, spark plugs, distributor, plug wires, battery, fuel and air filter and installed new vacuum lines wherever I could (minus the hard lines which are difficult to find replacements for). 
 

After this, the Jeep was running great for a week or so, idling smooth and better throttle response. However, few days ago it started stalling and dying after I would put it into gear and apply any gas to it. I started digging through old forums here on this site and working through the EGR system and cleaning up grounds. Now it actually won’t fire up at all, or will for a second and then die. Before this it would idle fine for a while then choke out and die. 
 

I have an inkling that the progressive nature of this may help figure out what’s going on... I’m thinking fuel pump, EGR, something electrical; but I honestly am lost at this point. My mechanical knowledge is pretty novice and I just work on my Jeep in my garage as a hobby so I have no electrical testing tools. Any help or thoughts would be much appreciated! Thanks in advance!

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jcbbgator...Does sound like a fuel supply issue from the sequence and progression of the trouble.  Before doing anything else, check the fuel flow on the engine side of the fuel filter.  Observe the fuel flow volume when the pump runs;  fuel should flow forcefully and steadily.  If not, try another fuel filter and test again.

If this hasn't solved the problem, check the TBI regulator pressure, simple enough at the TBI check port.  The best way to perform this test is with a pressure gauge at the check port.  You want pressure within range (14-15 psi at an engine idle).  You also want a steady flow of fuel here, and that can be checked at the port or the fuel return line near the tank.  Fuel return flow should be steady—with normal fuel pump pressure and volume, there should always be a steady flow of fuel returning to the tank. 

Note:  Do not stop the flow of fuel to the tank or pinch the return line for more than a few seconds!  Fuel pressure will spike up dramatically under full fuel pressure from the pump.  You're looking for return flow volume.  Do not restrict this return line with a gauge.

If flow volume or pressure is off, consider a clogged fuel pump pickup or a defective fuel pump.  The fuel pump motor can actually be analyzed with the pump still in the tank.  However, this requires a wave form oscilloscope that can calculate the amperage draw of the pump motor, the running voltage wave form, the condition of each commutator segment plus the pump's running rpm.  I'm guessing you do not have an oscilloscope (Pico, Autel Maxiscope, Hantek, etc.).  The mechanical tests I suggested are useful and practical alternatives.  They will work.

Should you need to replace the fuel pump, make sure the new pump is for the TBI 2.5L four.  Operating pressure is much lower than the inline 4.0L six or the 1991-up MPI engines.  There is a difference between TBI/EFI and MPI/EFI fuel pumps.

Other possibilities for the trouble you describe would be the MAP sensor or the Crankshaft Position Sensor (CPS) at the flywheel end of the engine.  Check the MAP sensor against the factory specs and verify the vacuum to the sensor before replacing the sensor.  (You've purchased plenty of parts already.)  The CPS can get oil on it from rear main seal oil seepage.  That can lead to trouble and intermittent misfire or no-start.  Also check the wires to the CPS, make sure they're not cooking against the manifold.

Places to start...Let us know what you find.

Moses

 

 

Moses 

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  • Moses Ludel changed the title to 1989 Jeep Wrangler YJ 2.5L TBI Stalling and No Start

Moses, thank you so much for the detailed reply. I cleaned up the CPS which didn't seem to help but was an easy starting point. I tried disconnecting the engine side of the fuel filter and there was nothing except some initial dribbling of what was in the fuel filter... so I am going to start by replacing that again (even though it was barely used - maybe it sucked up some crap from the tank) and I think i'm going to drop the tank just to make sure the sock is on and the pump isn't clogged so I don't do the same thing to the next filter. I have a feeling the pump/sending unit may be clogged defective because my fuel gauge is also not giving a reading at all either. 

 

Thanks again for the advice - it is very much appreciated. I am going to work through this in the next day or so and see if I can figure out the cause and I will post here what I find in case it helps someone else with a similar issue in the future. Thanks for all you do

 

Have a great day everyone

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  • 2 weeks later...

Hello from the different part of the world. I just signed up and this forum/tech help seems to be the best forum for old 4WD cars, specially for jeeps. Lots of topics about problem finding and other cool stuff. I like this kind of helpful forums and reading multiple topics, seems that you Moses have a full time job to answer for everybody 😄

All your answers are pretty long and go trough very specific information, I like this way of doing this. But anyway let's get into the business! I live here in Finland (no, we DON'T have polar bears roaming around our streets) and we have very few these jeeps around here. My case is about this 1990 Wrangler Laredo model. It is equipped with 2.5L TBI and currently has 241000km (~ 150000 miles). It is actually in good condition (only surface rust, never had been welded) and mostly original with Best top brand hard top.

Only problem is that it won't start (surprise). Last time it was on the road it became stalling and not responding to throttle. Just managed to get it to the garage and now it just cranks but no start. I have been reading many topics and there is many possible things that may cause this. What I have done so far:

- changed plugs, plug wires, distributor cap and rotor also new coil

- checked that it will provide gas to the tbi

- checked that it will give spark

- cleaned CPS

What could be so major problem that when these kind of "simple" engines get spark and fuel => it won't even start? Usually getting both will give you start, but engine is running rough etc? I was thinking (and I have been reading) that perhaps ECM can be faulty? Perhaps spark is not coming even and missing? Worst case scenario is timing off?

I haven't measured how much there is pressure in fuel system, but when I unplugged fuel incoming line there is a lot of fuel coming out of the unplugged line. When fuel is coming to injector there is mist coming from it. I don't know how even the mist should be (because it won't idle). One possible cause is injector o-ring leaking? I read one topic that had same symptoms I do and that guy had leaking o-ring. After changing it, all trouble went away.

I don't like to throw a parts cannon buying everything. Most of the parts I have to buy from US and they cost a bit of money 😐

What should I check next? ECM? Grounds? Anything else? Ideas?

I didn't want to start a new topic, I think here is enough "2.5L TBI WONT START"-topics 😄

And sorry for my bad english if there is writing errors or wrong words used. Hope you understand everything 😁

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And one notification: should check engine light come on when I turn the key? Only light that is on is seat belt. What I have been reading CEL should come on when turning key? That is why I'm thinking that there might be something wrong with ECM, perhaps loose connection or corrosion?

And it won't even fire up with starter spray. Usually if everything is okay it should fire up with this method?

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Greetings, WranglerFIN...Interesting scenario with the 2.5L.  The stalling condition sounds like lack of fuel or a low fuel supply pressure.  Before doing anything else, I would change the fuel filter.  The filter is inline along the frame rail. It is not uncommon for the fuel filter to clog or restrict fuel after adding a single tank of fuel with water content.  This would be the simplest fix if that is the problem.  Also, try a new fuel pump relay or try swapping same-amperage relays to see whether the fuel pump relay is defective.

If that does not work, check the fuel supply and pressure.  I would use a pressure gauge and check the fuel pressure at the TBI fuel test port.  You should see 14-15 psi if the TBI regulator works properly.   Also check the fuel volume, which should be steady and produce 1 liter per minute or so with the pump running steadily.  If that is okay and there is still no restart, I would check the MAP sensor voltages. 

I fully agree that you should not just buy and replace sensors.   Your thought about the ECU is worthwhile.  The connections can corrode.  If you still have a no start, consider carefully disconnecting the ECU plug.  Inspect the contacts for black oxidation.  Clean the connections with a spray electrical cleaner and soft (nylon) probe.  Do not scrape the contacts with anything metal.  

There is a timer used in these models for emissions inspection at a given mileage.  Rather than reset the timer and light as dealerships did, some disconnect or tamper with this device when the service light comes on.  This could be a related problem to your CEL issue.  The current mileage could be a check point for the timer.

Start with the small and basic concerns like the fuel filter.  If you did not get strong, consistent spark, the ignition module would be a possibility.  If you have a low fuel supply, the filter, pump or a restricted pickup sock would be possibilities.  The O-ring issue you mention is a possibility though not likely to occur suddenly.  The symptom you describe sounds more like fuel supply.

Spark timing should not be "adjusted".  The ECU adjusts timing from the CPS (#1 cylinder TDC) signal.  I would make sure the distributor housing clamp is snug and not loose.  The distributor should position in one location, there is a locating ear.  It should not be moved.  If you want to see whether the ignition will fire the engine, try carefully priming the engine by pouring a small amount of fuel down the TBI throat then crank the engine.  If the engine starts and runs momentarily then stalls, the ignition is likely firing okay.  If no start, I would suspect the ignition.

Caution:  Be careful when priming an engine with fuel.  Watch for backfire.  Use a small amount of fuel or a spray starter fluid and avoid starting a fire!  If there is a backfire, continue cranking to draw ignited fuel downward into the engine.  A fire extinguisher nearby is a good practice.

Finally, if you still cannot get a start, make sure there is normal compression and not an issue with the valve timing or timing chain.  Cranking should sound normal if compression is good and valve timing is okay.

Let us know what you discover.  We can go from there...

Moses

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Thanks Moses for answers! Next things I will do:

1. Check ECU plug for corrosion and if the connector is loose. Not done this yet.

2. I just bought a fuel pressure gauge set, and I will check how much pump is giving pressure to TBI unit. I saw that there is port for adapter and gauge to hook up. How much pressure should be when you just turn key (no cranking)? I saw that MPI pressure should be 31psi, but TBI should not be that "high"? When car runs (in my case not) pressure should be 14-15psi.

3. Just checked out that distributor is very snug and not moving at all.

4. After all this I will check compression. Should there be how much in each cylinder? 110-130?

5. I will take out the dash and gauges. I will change every light bulb for new ones. What kind of unit is this "timer" for emissions? Is it under dash somewhere? What kind of thing I have to look for?

I will report after checked all above.

Where is the location of fuel pump relay? In the engine bay or in the cabin?

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WranglerFIN...See answers below...Moses

15 hours ago, WranglerFIN said:

Thanks Moses for answers! Next things I will do:

1. Check ECU plug for corrosion and if the connector is loose. Not done this yet.

Good idea after 30 years...

2. I just bought a fuel pressure gauge set, and I will check how much pump is giving pressure to TBI unit. I saw that there is port for adapter and gauge to hook up. How much pressure should be when you just turn key (no cranking)? I saw that MPI pressure should be 31psi, but TBI should not be that "high"? When car runs (in my case not) pressure should be 14-15psi.

Pressure at the test port should be 14-15 psi with the engine running or not.  The fuel pump pressure is much higher, and the regulator at the TBI unit will drop that pressure to 14-15 psi and send the rest of the fuel back to the tank via the return line.  If pressure is high at the port, the cause is either the regulator/setting or a restriction in the return line to the fuel tank.  If there is low pressure or fuel volume at the test port, that could be pump supply pressure or a clogged fuel filter.  Check or replace the fuel filter at the frame rail.

3. Just checked out that distributor is very snug and not moving at all.

As it should be...

4. After all this I will check compression. Should there be how much in each cylinder? 110-130?

I want to see 130 or higher psi.  Crank the engine with the throttle held wide open during the  compression test.  If there is a low cylinder(s), I do a leak down test.  The key words "leak down" or "leakdown" have been discussed many times at the forums.  For details, use the forums search box with these key words.  

5. I will take out the dash and gauges. I will change every light bulb for new ones. What kind of unit is this "timer" for emissions? Is it under dash somewhere? What kind of thing I have to look for?

The emissions timer and other modules are described in the factory workshop manual.  I buy a new/used print, reprint or CD version of the FSM for any vehicle we own or work on.  I strongly suggest that you find an FSM for your YJ Wrangler.  Here is a manual at eBay that may be of service:

https://www.ebay.com/itm/1989-Jeep-Cherokee-Comanche-Wrangler-Shop-Service-Repair-Manual-CD/132408471190  [A CD or download copy in English.  This is a copy of the 1989 official edition that I have on my shelf in original print form.  This CD or possible download includes both the chassis/powertrain and electrical volumes.  This CD or download will work for the 1987-90 YJ Wrangler models.]

https://www.ebay.com/itm/Workshop-Manual-Supplement-Jeep-Cherokee-Type-XJ-Wrangler-Yj-Stand-1990/353148569665  [Rare German Edition of a genuine Mopar original print FSM.  Before buying this book, make certain that it contains powertrain (engine, fuel system, etc.) and all other service areas.  I am concerned about the reference "Supplement".  A supplement is usually only partial coverage and requires more books for full vehicle coverage.  Ask the seller to provide a copy of the table of contents page.]

I will report after checked all above.

Where is the location of fuel pump relay? In the engine bay or in the cabin?

On 1987-90 2.5L models, the fuel pump relay should be next to the battery box/tray.  Clean and inspect the fuel pump relay and socket.  Swap or install a new relay to test whether the engine will pump fuel and start up.

Your fuses should be under the dash:

https://fuse-box.info/jeep/jeep-wrangler-yj-1987-1995-fuses-and-relays#Passenger_Compartment_Fuse_Box  [Underdash fuse panel.  The fuel pump relay is not here on your model.]

 

 

 

 

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Something has been done. First of all, I didn't remember that this earlymodel YJ doesn't have CEL light. Well, I checked ecu connector/pins and they were like they were build yesterday. Brand new condition. Then I checked fuel pump relay. Just little a bit dirty, nothing major.

I tried to crank it and for my surprise, engine started! But it run VERY rough and immediatly died when I pushed gas pedal.

I took multimeter and measured TPS. It gave very weird readings. If I remember right, input voltage was something like 5,085V and output 0,845V. That can't be right? What is the right way to measure it? Ignition on, without pressing any gas? I did it that way.

I haven't read the fuel pressure yet because I'm still waiting for gauge to arrive.

Next I think I will order new CPS and TPS. They are kind of cheap parts and CPS is very important for spark and ignition to work properly.

What do you think Moses?

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WranglerFIN...The CPS usually works or does not work.  You can check ohms-resistance and connections.  If okay, I would leave that one for now.  The TPS is a wear item.  I replaced the TPS on our 1999 XJ Cherokee engine around 150,000 miles.  Voltage readings were erratic and off.

Normal 2.5L TPS voltage:  Approximately 1 volt with throttle closed (idle position);  5 volts at wide open throttle.  Your range is close.

Have you changed the fuel filter yet?  Your description of start and die still sounds like no fuel supply or low fuel volume and pressure to the TBI unit.  The filter is located at the inside of the frame rail on the left hand side (U.S. driver's side), forward of the fuel tank.  There is a metal shield beneath the filter.  Follow the line from the tank toward the engine, you will find the filter.  Easy item to replace and test.

Moses

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Yeah. I think I will start checking fuel system after I got the fuel pressure gauge. Then I can check the pressure and also filter. I would like to drop the tank, but unfortunately before Jeep had this problem I filled the tank so I have to drain all fuel.

Well, I'll be back soon and tell what I will discover..

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  • 3 weeks later...

Ok, just worked yesterday with Jeep. Checked these things:

TPS. I took it out from throttle body and measured again. It shows 4,999V when throttle is wide open and I gradually moved that position and voltage changed from 0-5V very well without having problems. So, TPS is fine.

I checked fuel pressure and when cranking it gave 12-14PSI. No start. Should cranking pressure be more than that? I measured pressure from fuel incoming line but not from the throttle body pressure port (I didn't have correct fitment for fuel pressure port) but under Jeep (where is the quicklocking system at hardline).

Next time I will check CPS and fuel filter (actually I have ordered new CPS, it was only 10€ and easy to replace also fuel filter). I also wonder if ignition module is okay. There was a way to check that?

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Hi, WranglerFIN...You do need to check pressure at the test port.  When you check fuel pressure at the incoming line, there is no return to the tank unless you put a "T" in the connection and had fuel running from the "T" to 1) the TBI unit, 2) the incoming line and 3) your gauge.  If you measured at the fuel incoming line only (from the filter to the engine) without fuel returning to the tank, then you would be measuring fuel pump pressure only.  Correct?

If your fuel pressure from the tank pump is only 12-14 PSI, that would be very low.  Pressure at the regulator should be 14 PSI constantly with the fuel pump running because the pressure regulator is mechanical and will hold that 14 PSI pressure while excess fuel returns to the fuel tank.

You do need to measure pressure at the fuel test port on the TBI.  Find the correct fitting and run the test at the test port with all fuel lines hooked up normally.  This will show the regulated fuel pressure with the excess fuel volume returning normally to the tank.

Moses

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Thanks Moses. I perhaps explained it wrong. I had T-piece when I checked the fuel pressure. T-piece was under car (end of hard line and start from hose line) fuel flow trough throttle body normally to return line to gas tank. I know that optimal would be checking pressure from test port but I have hard time finding correct fitment (is there any link to ebay or some other place where I can find correct fitment?).

But, yeah, you are correct; that way we measured was incoming line from fuel pump, not from test port. How much it should be? 30-40psi when cranking? If so, then we have clogged filter or pump itself is "kaput".

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Hi, WranglerFIN...Even though you were not measuring at the TBI unit, the pressure at the "T" should be reasonably accurate.  The way you measured, the pressure regulator was releasing at 12-14 PSI.  You would want a steady 14-15 PSI pressure if the fuel pump flow is good.  Again, the test would be more accurate at the TBI test port.  

The fitting in the shop manual looks like a plug.  (Did you buy a shop manual or CD yet?)  However, in the Mopar parts catalog, there was (discontinued now) a fitting kit available that looks like a common EFI fuel rail Schrader valve fitting.  The thread into the throttle body looks like straight threads in the illustration.  (See #15 below.)  The Mopar part number for the original test port connector kit (fitting with Schrader as shown in #15) was P/N 83501572.   From the illustration, this would not be a pipe (tapered) thread.

You need to carefully measure the port thread size and also determine whether the thread is straight or tapered.  There may be an EFI Schrader valve fitting available.  A test port with a quick connect Schrader fitting would be valuable if you can make that conversion.

Otherwise, you could make/find a connector fitting that goes from the port thread to the thread size for your pressure gauge.  Weatherhead or Eaton catalogs (see the online websites for Weatherhead and Eaton) would be a source for fittings.  Find an adapter fitting that will connect from the TBI port thread to your gauge hose. 

This is the fitting assembly that Mopar offered (P/N 83501572, now discontinued).  The hose adapter to the gauge would attach to the fitting:

image.png

If you can find a fitting with Schrader valve that will fit your TBI port, does your gauge have the connection adapter?  There are inexpensive fuel injection pressure test kits available in the U.S. at outlets like Harbor Freight or eBay.  They have the hose coupler adapters.  I am not sure what is available at Finland or Europe.  Start by measuring the test port thread.  Determine whether it is a straight thread and what size.  See if you can find a Schrader valve test fitting like #15.

When you checked fuel pressure, did you test the fuel volume or flow amount?  The pump should put out approximately 1 liter of fuel per minute.  If not, the problem could still be as simple as a clogged fuel filter.  

With the fuel filter removed, you could test the pump pressure and fuel flow volume at the tank side line to the fuel filter.  Fuel pressure from the pump should be in the 15-30 PSI (1-2 BAR) range.  I had a difficult time finding the actual pressure rating for the OEM part number fuel pump.  I eventually found it.  There is a parts source at the UK that lists the BAR rating for the replacement fuel pumps.  Using the pump's original part number , this is a good reference for 1987-90 Jeep 2.5L TBI replacement pump pressures:

https://www.bestpartstore.co.uk/83502995-oen

I would use the Airtex pump as a guide at 1.2 BAR.  (This is much lower pressure than MPI pumps.)  If you need a pump, stay with the original Mopar Part Number 83502995 cross reference.  Do not use an MPI (high pressure) fuel pump for your 2.5L TBI fuel supply.

Moses

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Thanks Moses, you are wonderful!

Main issue finding correct fitment is that we have everything sized by centimeters. And that plug in test port is sized by inches. I have now unplugged it and my friend will ask around in stores if they have that kind of right size fitment for it. If we find right fitment size I have many different adapters to fit my fuel pressure gauge for it.

I have now bought fuel filter and before trying to start engine, we will change it first.

Yesterday when turning key in ignition we heard fuel pump every time buzzing, so I think it might be filter or pump sock. First filter and if it doesn't help, then the sock inside gas tank.

We will continue investigating and I will inform how it progress!

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  • 4 weeks later...

Well well well. Time has passed since we have worked with Jeep, but I think we might have found the problem today.

What we have done now:

1) Changed fuel filter.

2) Changed CPS (it was cheap, so why not?).

3) Changed O-rings to injector. Cleaned throttlebody.

4) Measured fuel pressure and here what we figured: Fuel pressure gets only to maximum 10psi when cranking, no more. And after not cranking pressure drops to zero after 10 seconds. Pump can't hold pressure so I think it leaks back to tank (no leaks under car or anywhere else)? It might be fuel pressure regulator also? But I don't think so..

But pump is original and driven 241tkm so..

I think now we order new pump, drop the tank and change it. Moses, what do you think? And yes, pressure was measured from TB-port as I mentioned in my last post.

Now we need to buy right pump for TBI engine. Any good place to link?

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WranglerFIN...You never reset or adjusted the pressure regulator, right?  You did test the fuel pump pressure at the filter, it was 12-14 PSI, not good.  The fuel pump pressure should exceed 15 PSI.  The pressure regulator adjusts the pump pressure down to 14-15 PSI from a higher pressure.

10 PSI while cranking is not enough pressure or volume to start and run.  At 241tkm, this is a good time to replace the fuel pump.  The pump you found is for a 15-gallon (U.S.) fuel tank.  If that is your fuel tank size, you found the correct pump module.  This is a combination fuel pump and fuel gauge sender with float arm.  Crown is a reliable Jeep parts supplier.

There are two 1987-90 Jeep YJ Wrangler 2.5L TBI fuel tanks:  15-gallon and 20-gallon.  That determines the pump to order.

Let us know whether this fixes the problem.  The pressure regulator is the only other possibility for the 10 PSI.  The 12-14 PSI at the fuel filter would indicate a bad fuel pump.

Moses

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That is true, I never touched or reset pressure regulator. Yeah, this 1990 wrangler is with a 15 gallon tank. In Europe (Finland) we talk about litres and 15 gallon is approximately 57 litres. I will order that pump with combination of fuel sender and assembly. It will take some time to arrive here in Finland from US. I will inform if this fixed the problem and I'm able to drive Jeep again!

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Wow, I was surprised, it was actually 20 gallon tank! And a plastic tank. I always tought it was metal. Well well. Pump looks original, there text stanced on it:

8933 002 251

5550

30389-3

PAT NO 4500270

I think it is original 1990 factory pump?

Otherwise the whole assembly looks pretty good and there was only a little bit grud in a tank, nothing major. Good time to clean with soapy water and order new pump..

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IMG_20210425_155901.thumb.jpg.7e20515e26fa4d4f172e375479313019.jpg

IMG_20210425_170850.thumb.jpg.da2205eb0c3ac39592195c7d4f66edb2.jpg

IMG_20210425_170829.thumb.jpg.139499f4dcad951a97df2f45fe291d8a.jpg

IMG_20210425_170837.thumb.jpg.5f59df53e2544565e4aa85be20d6482e.jpg

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Nice work, WranglerFIN...Good that you dropped the tank before ordering the pump:  20-gallon style pump and fuel gauge sender.

You will be happy that you changed the pump.  It looks original, and that's a lot of wear.

I have begun using an automotive lab oscilloscope for diagnostics.  There is a wonderful method for testing the condition of the fuel pump while it is still in the tank and the tank is still in the chassis:  You measure the current flow through the pump's fuse or relay.  On the screen this reads as a wave form in milliseconds and micro voltage.  You can determine the rpm of the pump motor and its amperage draw.  It is possible to observe a single bad sector in the fuel pump motor's commutator.  This is all done in real time without removing anything except the pump fuse or relay.  The pump motor's amperage draw and rpm determine the pump's capacity to flow fuel.

In your case, without an expensive lab scope, you did all the diagnostics possible.  It is reasonable that this 241tkm pump is defective and needs replacement.

BE SURE TO ORDER THE CORRECT PUMP AND SENDER FOR A 20-GALLON TANK.

Moses

 

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  • 2 weeks later...

Oh man.. today I installed new pump and test it. This Jeep must be cursed.. still not enough pressure. Nothing changed, same as my previous post. It must be the fuel pressure regulator? It has this kind of regulator: https://www.ebay.com/itm/Fuel-Injection-Pressure-Regulator-Standard-PR150-/274786462710?_trksid=p2349624.m46890.l49286

BUT. It is impossible to remove regulator without taking whole throttle body assemble out of the Jeep. There is three screws. Two is accessible but last one is not. Why it was engineered this way 😞

Oh man, what a job.. haven't start it yet and I need to dig up some motivation.

If I understand correct there is spring inside regulator? If there is, I think it has broken and might explain this sudden dying of Jeep. Well, who knows..

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WranglerFIN...Look at the bright side of this:  The fuel pump was very old and in questionable condition.  Replacing it was not a waste.  You also cleaned the tank thoroughly and eliminated any risks inside the fuel tank.

The pressure regulator would be the only item left.  If fuel returns normally to the tank, and if the rollover valves at the tank are okay, the issue must be the regulator.  These regulators do fail.  Sometimes an adjustment helps, but sudden loss of pressure like you experienced indicates a defective regulator.  Again, given the age and mileage, a new regulator is a good idea, anyway.

Please keep us posted on this development.  When you install the new regulator, check the port pressure at the TBI unit to be sure the regulator pressure is adjusted properly.  If the new regulator's pressure needs adjusting to 14-15 PSI, adjust it.

Moses

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Yes Moses, it is a good thing that is has now new pump. Also the fuel gauge shows now right amount gas in the tank (it was previously showing too much) and also it is good thing that tank is cleaned :)

I need to buy that regulator and install it. Only downside is that taking off the whole throttlebody is a big job. But it needs to be done.

I will inform how it goes and tell if it fixes the problem!

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Today I was charged with motivation and took whole throttle body assembly out of the Jeep. I opened three torx holding the cup and that rubber "thingy" is the fuel pressure regulator. That seems to be okay but I dont know? I dont know what broken one looks like? Well anyways I'm going to buy new one. Seems that throttle body repair kits are available at ebay for reasonable price. Meanwhile I will clean whole assembly and split it twice and some more cleaning. What do you think Moses?

 

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Well, WranglerFIN, the silicone diaphragm looks stretched.  This is what you would expect after many years and miles. 

You can see the relationship of the adjuster at the bottom of the cup.  The adjustment applies more or less tension to the spring.  Pump fuel pressure is the counter-force to the balance spring.  (The spring still looks okay, and it will provide good service.)  If the spring has minor wear, an adjustment of the regulator will bring the pressure into the 14-15 PSI range.  You already know how to test the pressure at the TBI test port when you have installed the TBI unit and primed the fuel system.

I am looking forward to the results when you install the new regulator/diaphragm.  It was smart to change all of the parts that you did.

Moses

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  • 4 weeks later...

Back in business! Last week repair kit arrived here in Finland. Long journey from States. I assembled all together and started the car. BUT, same symptoms. Nothing changed. Then I screwed fuel pressure regulator and now it gets 15 psi pressure at cranking engine. But still no start and when it tries to start it shuts down immediately and fuel pressure drops to zero.

BUT now I think I might found the real reason for this problem. INJECTOR leaking badly. I don't know how I missed this with my friend. Injector totally floods the system and spraying isn't fine mist, instead it splashes gas everywhere. It is not the o-rings, they are new (there was new o-rings with repair kit) so it must be injector itself.

Next thing was that I ordered new injector TJ39 from this link yesterday: https://www.ebay.com/itm/293891762548?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 (again from States) and it takes some time to arrive here in Finland (again). But hopefully this solves "mystery problem". It explains a lot of symptoms about stalling from driving the car and after starting it won't start because plugs are wet from overdose of gasoline. And I think somehow injector leaks pressure out of systems (is it possible if injector is stuck in open mode for some reason?).

But anyway, after injector arrives and I get to install it, I will tell you how it went :)

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WranglerFIN...Well, the silver lining to all of this is that each of these components wear over time.  Their duty cycle will now be renewed uniformly.  You've given the entire fuel system a renewal.

Let us know how the new injector performs.  You likely will need to fine adjust the pressure to 14-15 PSI on the new injector.

Moses

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