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Discussion Starter #1
Hi Everyone,
I have been having a starting issue with my 89 YJ for about a year now. I have stumped 2 shops and my wife wants the jeep gone. The jeep is an 89 4.2 with a fuel injected system. The PO upgraded the 4.2 header to a 4.0L fuel injection system.

Issue:
The jeep takes about 3 cranks to finally start. once it starts it runs for ~3 seconds and dies. During those 3 seconds if i touch the gas pedal, it dies immediately. I hear the fuel pump come on when i turn the key on and if i disconnect the fuel supply at the rail with the key on, i get a ton of fuel gushing out.

I have tested the MAP sensor, the Fuel Injectors, and the TPS. all good. Battery is charged. I am going to buy a fuel pressure test kit today and check the pressure at the rail today.

Anyone with some other suggestions? i am leaning towards the ECU, but who knows.
 

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Find a post by Got it at last. In his signature there's a free link to several Factory Service manuals and a couple Factory Parts Manuals.
Open that link and click on the manual that you need. It won't have any information about the aftermarket fuel injection, but it should give you enough information in the electrical troubleshooting section to make the proper connections.

In your earlier post, you stated that your engine was a 4.0 Jasper engine that the PO had installed with fuel injection. If you have a 4.2, it's probably the original engine. I suggest doing a compression test and letting us know what you find.

In order for us to help you, I suggest that you back out one page and find a sticky titled "A better way to get help in the YJ tech forum".
With more information, someone here should be able to help you get your Jeep running.

Good Luck, L.M.
 

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Go back to the basics. Fuel, air, spark. Which one is cutting out. Fuel pressure gauge would be a good thing to start. Hook it up and see if the pressure cuts out. Also you could put a spark tester on one plug to see if spark cuts out.

I wonder if in the conversion if the upgraded the fuel pump. The fuel injection should require more PSI than a carb'd motor.
 

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Discussion Starter #4
I will take a look through the service manuals in got it at last’s signature, but those manuals haven’t helped me thus far, especially the electrical diagrams.

I rented a fuel pressure gauge from autozone and tested pressure at the fuel rail. When I turned the key to the on position, the fuel pump came on and the gauge was at 0psi. After a few cranks the Jeep started and the fuel gauge raised to about 10 psi before the engine died (after about 3 seconds). I had a new spare pump and I swapped the pumps. The psi was lower than the old fuel pump (fuel gauge rose to about 6 psi before the engine shut off). No visible leaks or anything like that.

The chiton manual I have is for a carbonated yj, so maybe the fuel injected manual will have some better troubleshooting suggestions.
I’ll try a compression test next.

I appreciate your help.
 

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If that is a mopar fuel injection set up which sounds like it is requires over 30 psi. What you have is too low. Confirm for us that the fuel rail has a return line. I would think the fuel system needs to be corrected before anything else is troubleshot. Has the Jeep ever run with the fuel injected setup? Did you buy someone’s unfinished swap?
 

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You might be better off buying a complete in-tank stock fuel pump assembly with fuel gauge sending unit.
That means dropping the tank and examining all the related plumbing, but then you can check to see if you have a true 20 gallon fuel tank.

Do you have a Jeep fuel injection system or an aftermarket FI system? I think the stock FI needs 30 PSI to run. Other more knowledgeable posters can confirm this.

Good Luck, L.M.
 

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Discussion Starter #7
Luckymac, i was thinking the exact same thing. I would assume the only reason why the fuel pump was relocated to the rail was for convenience sake. Before i drop $200 on the fuel pump /sending unit, i was going to work from the fuel rail back tank and look for issues. Maybe something will be obvious (although unlikely). The tank is 20-gal, plastic. I dropped the tank a few weeks back to verify what i had to and fix the float since my fuel gauge always read Full.

The FI system appears to be Jeep.

The concern i have is that the pump only turns on (i can hear it) for a second or 2 when the keep is on the "On" position. I do not hear the pump when the jeep is running for those 3 or 4 seconds. I would think if the jeep was starving for fuel, that the computer would be telling the fuel pump to turn on and stay on. But i could be wrong. I hate the idea of spending $200 on a fuel pump/sending unit only to find out there is something else going on.
 

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I hate to say you may have more than $200 worth of work left in this cause it sounds like someone partially did the FI swap, got stuck and sold the jeep. Did this ever run for you longer than a few seconds?

There are a couple of things I'd check:
- are there 2 lines coming from the fuel rail back to the gas tank. Send and return
- Is there a fuel pressure regulator.
- Jump the fuel pump relay and see what is the max psi that pump can produce. Maybe look at the pump model number and see what the stats are and see that pump can even work in this application.
- Sounds like you have questions about pump control. Need to validate that the pump is running when the jeep is running. I'd validate that the pump relay is really controlled by the PCM output. Start by having someone feel the pump and make sure it's on when the jeep is running. But I'd possibly even validate wiring.

Anyways some thoughts. Sounds like you can get this project to run.
 

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Discussion Starter #9
Sequel,
There is a supply and return and it is hooked up correctly.
There is a fuel pressure regulator at the fuel rail.
I will check to see if the fuel pump is running when the jeep is running, but i do not believe it is. I don't hear it running when the jeep is running, only when the key is "On", but i can confirm tonight. If the pump isn't running when the jeep is running, i would assume wiring or pcm?

I don't know how to jump the fuel pump relay, but will google it today. I am a "work in progress" mechanic (little to no experience, but getting better).

The jeep drove when i purchased it back in July 2018. I drove it approximately 100 miles with no issues then it had a series of issues (clutch went out, backfires, lost spark, etc.). its been from shop to shop, tow truck to tow truck, in my garage broken. no luck.
 

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Discussion Starter #10
Update.
so last night i checked the fuel pressure at the fuel pump and still had nothing. Just to recap, no pressure at the fuel rail and no pressure on the external pump. So i dropped the gas tank and disconnected the supply and return lines from the top of the tank. i used a bike pump and pressurized the supply line from the rear of the jeep. Due to my stupidity, the gas came gushing out of the return line... duh. so after the lines basically purged themselves empty, i plugged the return line and reapplied pressure to the supply so i could check for leaks. The supply line held pressure and i noticed the pressure gauge connected to my fuel rail increased and held as well. Just for $hits and giggles, i turned the jeep over and it fired up on first crank (immediately) - it usually takes 4 or more cranks for it to fire up. it ran for about 7 or 8 seconds which is longer than it was running. it died since it had no fuel in the lines.

It appears to be dying due to lack of fuel (which makes sense). let me know if i am off track here before i start buying replacement parts.

couple of questions:
1. what holds the pressure at the fuel rail? i had to plug the return line to get the supply to hold pressure. obviously, i am not going to be able to keep it plugged when i reinstall the fuel system.

2. Should i go back to an internal pump system (with new sending unit) or leave it external? my existing sending unit has been altered (pertinently) by the PO.

i sincerely appreciate everyone's help with this
 

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Looks like you got the problem identified. Now just a matter of fixing it and that's a little harder cause it's not just swapping factory parts it's figuring out a fix given you have a swapped fuel system.

I would check a few things on the fuel system. We don't know if the issue is the pump itself or control of the pump (by ECM, wiring, relays). Here is what I'd check:
1) Go to the fuel pump relay. Pull it and bridge pins 30 and 87. Doublecheck and triple check this so you don't send unloaded power to the PCM (on pin 85/85). Let it run for a 10-15-30 seconds. What is the max pressure you can build at the rail.
2) Need to check control of the pump. I am curious if the pump gets power for a) 3 second prime and b) when the engine is starting. You can do this by connecting to the power in the external pump with a VOM and see when you have power and when you don't. Trying to understand if you need to condemn the pump or if control of the pump is the problem. You can also do this test with a test light and by probing the relay socket. You can put the test light where across pin 85/86 of the relay socket and see if it lights up during start. If it doesn't, you won't have the pump commanded to run.


couple of questions:
1. what holds the pressure at the fuel rail? i had to plug the return line to get the supply to hold pressure. obviously, i am not going to be able to keep it plugged when i reinstall the fuel system.


There is a check valve most fuel pumps to hold pressure on the rail. I believe the regulator should keep it from returning on the return line but I am not 100% certain.

2. Should i go back to an internal pump system (with new sending unit) or leave it external? my existing sending unit has been altered (pertinently) by the PO.

This isn't necessary but it gets you closer to stock which is easier for troubleshooting and there are advantages to why the factory did this. Mainly the pump stays cool. The pump is closest to the source. Usually you want pumps to push and not pull.
 

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Many times people will use the oil pressure sender to control a high psi fuel pump for safety reasons. Check there.
 

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Discussion Starter #13
So.... i am an idiot.... lets just leave it at that for now.
Last night i continued to troubleshoot the fuel pump issue and got the fuel pump to work, correctly. I connected the fuel pump up directly to the battery and it fired up and ran at 30 psi. So the pump is good. So i reinstalled the fuel pump and jumped the 30/87 pins on the fuel pump relay and boom. Fuel was gushing from the tank to the fuel rail. Pressure at the fuel rail was constant 8 psi. What i noticed is that the fuel is gushing to the fuel rail and then right out of the return line back to the tank. The fuel rail cant build up pressure and it looks to be coming into the fuel rail at the same rate it leaves it. With the 30-87 pins jumped, i turned the key and it fired up, ran for a few seconds and then shut off. What would prevent fuel pressure to build up at the rail? bad fuel pressure regulator or something else?

After the jeep shut off, I smelled a burning smell from the engine, which concerned me, and so i stopped. Could i be doing any damage to the engine with these efforts?
 

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Discussion Starter #14
One last thing, i still think there is a control issue going on here (something with the ecu or relay or something). but at least i can rule out that the pump is bad.
 

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The fuel rail cant build up pressure and it looks to be coming into the fuel rail at the same rate it leaves it.
but at least i can rule out that the pump is bad.
I'm no 4.2l expert lol, but I would say that 8psi at the fuel rail is insufficient. On the 2.5 it's supposed to be 25-35psi, so if you're measuring 8psi, that could be why it's leaving as fast as it's going, instead of getting enough pressure to get sprayed through the injectors properly. So just because the pump is working when electrically activated, it's a possibility it could not be working to spec in regards to pressure output.

Did you try changing relays? Does the 4.2 have a Auto-Shutdown-Relay? I would say the ECU is ok because you can get the fuel pump to turn while jumped. A long time ago I had a loose pin come out from the -bottom- of the fuse-block on the ASD relay, which was not allowing my Jeep to start but it would run if I jerry-started it. Check the wiring on the bottom of the FP and ASD relay, be tender with the fuse-box when you slide it off the rail and bend it around lol.

But so far it sounds like you are having a pressure problem, don't eliminate the FP from the equation just yet lol.
 

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Couple of different areas to troubleshoot here but glad you know the pump works. Let me attempt to break them down on what I would check:


Command and power of pump - I think there may be a couple things to check here. First is command. Is the relay turning on when its supposed to. The second, is enough power getting to the pump to run it. If it's only running at 8psi, it indicates the pump is turning on but maybe there is too much voltage drop that the pump is only running at a fraction of it's capacity. I'd start with enough power to the pump before fuel regulation because you proved with direct battery power, you get the desired 30+ psi.

a) for command of pump. I'd pull the relay and run a test light from pins 85/86 of the relay. This is to check the control side of the relay. I will trust you can hook up the test light without jamming it into the pins and spreading them. That will create more headaches you don't need. If you don't, just ask. Once the test light is in place. Turn the key to "run". Does light come on? You should get the 3 second prime, then light shuts off. Turn key to "start", light should come on. Once you let the key go to "run" the light may stay on but will probably go off cause the PCM stops the run process without a signal from the crank and cam sensor.

b) for power of the pump check, I'd do a voltage drop test. Look it up if you don't know what that means. This will allow you to determine if enough power is getting to the pump to create the necessary PSI. I really think this is the problem given when you connect the pump straight to the battery you get 30 psi. Do a voltage drop test from battery positive to positive on the fuel pump. Attempt to start or jump relay pins 30/87 (jumping pins may be easier). Your VOM should be close to zero or at least less than half a volt. If it's more than that you are loosing power because of a bad connection. Next connect your VOM to the battery negative and negative of the fuel pump. Again, you should have less than half a volt. Preferably less. If you have more, you have a bad ground somewhere. This would not surprise me. Heck, It may be worth just running a jumper from battery negative to the negative terminal on the fuel pump just as a wild guess and attempt to start.


Fuel pressure regulator - It is strange that your rail cannot get to 30+ Psi. This may be a regulator but it may also be not enough power is getting to the pump. I'd troubleshoot the lack of power or command of pump first. You did hit 30 psi with power going straight to the pump. But here are a few ways to check the regulator. First is you can pull the vacuum line off the regulator. See if there is fuel in that line. There should be none. If there is, then the diagram is torn and you need a new one. You can also pull the vac line off the fuel pressure reg, and you should see fuel pressure change on the rail. This is with the engine running. There are specs out there for this but don't have them in front of me. One thing you can also do is pinch off some of the rubber line on the return line. That should restrict the return and cause fuel pressure to rise. Be careful dead heading the pump as it can damage it. This means you stop all flow and pressure builds and builds.


Not sure what the burning smell is. Is it a rubber smell? Fuel smell? Need to look for what is causing it. Maybe have a fire extinguisher on hand in case.
 

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Pinch off the fuel return line. if it starts and runs get a new pressure regulator
 
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Discussion Starter #18
First off, thank you all for your help.
Ok. Following sequels suggestions I performed letter a.
I was able to test light pins 85 and 86. When I turned the key to “run” it light up for 1 second and shut off. I turned the key off and tried it again and it lit then turned off after 1 second. When I tried it a third time, it didn’t light at all. The fourth attempt it light for 1 sec then shut off.

When I turned the key to start, it remained lit (during crank) and went off when I put the key back to run.

I am going to google enter b.

Also, when I pinched the return line, and with the fuel pump pins 30/87 jumped, the fuel rail pressurized to 30 psi. It started right up and ran until I let off the pinched return line-
 

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It also stayed running when my son pressed the gas
Give the jeep to you son and buy a running YJ. (JK).

It sounds like you're getting it narrowed down.
What happens if you don't jump pins 85 & 86, just try to start the Jeep with everything hooked up as you think it belongs, but pinch off the return line?
Will it start?
If so, will it continue to run with the return line pinched.

If it won't start and continue to run with the line pinched and wired normally, I'd look at what might be going on with the relay and the connections to it.

You might be dealing with two issues.
1- fuel pressure regulator.
2- a faulty relay or connections to it.

Keep plugging away and keep posting. I think you're narrowing the issue down. You're close!

Good Luck, L.M.
 
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