[cullen_merchen]

Howdy all,


I've recently been having some fuel pressure problems with my 95 4.0L YJ. After fixing some other problems with it (including spark and ecu issues) I noticed that my jeep wasn't getting any fuel pressure, I checked the schrader valve and there was no fuel coming out. I couldn't hear my fuel pump priming and decided to buy and install a new fuel pump and that didn't work, or so I thought. I checked my valve again and there was fuel coming out, so I decided to try and start her up. Once I turned the key I noticed that the engine wanted to start, and actually managed to start only for it to die a second or two later. What could my problem be? I was considering that the fuel pump might not be getting enough power and as a result isn't building up enough pressure to supply the engine... I actually have a video of one of my start attempts; however, I'm not allowed to place it on here since I am a new user.

Thanks!


EDIT:
After cleaning the fuel lines, changing the fuel filter, fuel pump and cleaning the injectors I still don't have adequate fuel pressure/any. The fuel pump won't send any fuel through the lines. I am starting to think that it may be a bad sensor somewhere/ wire. I am still open to any second thoughts though and they would be greatly appreciated!

 

[mikewiz38]

If you have an autozone by you, I would get the loaner fuel pressure test kit to make sure you're pulling the right PSI and also not having any bleed off after having it sit for awhile.

Did you also change the fuel filter when you changed the pump? Something may had clogged the lines as well.

 

[cullen_merchen]

Howdy,



Just checked the fuel filter and some bad gas is coming out of the clean side along with metal chunks and filings. Starting to consider that there might be some clogged injectors. Thanks for the tip!

 

[mikewiz38]

Howdy,
Just checked the fuel filter and some bad gas is coming out of the clean side along with metal chunks and filings. Starting to consider that there might be some clogged injectors. Thanks for the tip!

Wow, glad I could help. I've been on a roll for the past couple of days; maybe I should try the lotto!

 

[Flyer58]

Bad gas will do it but there's also a fuel pressure regulator on the fuel rail. If it fails I believe the engine will run very rich and poorly.

 

[Chrisnvegas]

Do you clearly hear your fuel pump?
Does your check engine light come on when the key is turned to on?

 

[cullen_merchen]

Does your check engine light come on when the key is turned to on?

Yes, I actually replaced the ECM not that long ago. It died one day, but miraculously came back after a week.

Do you clearly hear your fuel pump?

No actually, I did yesterday. Something is going wrong with that, I replaced the fuel pump yesterday and it seemed to get some fuel pressure going. It doesn't seem to want to run fuel after cleaning the injectors. There may be a bad sensor or wire somewhere, any ideas on what sensors might be at play, if any?

 

[mikewiz38]

Yes, I actually replaced the ECM not that long ago. It died one day, but miraculously came back after a week.

No actually, I did yesterday. Something is going wrong with that, I replaced the fuel pump yesterday and it seemed to get some fuel pressure going. It doesn't seem to want to run fuel after cleaning the injectors. There may be a bad sensor or wire somewhere, any ideas on what sensors might be at play, if any?

One of the sensors you may want to check is the MAP sensor. It's mounted on the middle of the firewall towards the top and has a vacuum tube going to it and a plug. Here's a page on how to test...

https://www.fixjeeps.com/map-sensor.html

I forgot to plug this back in and the jeep would crank but not run because, I believe, it was being starved for fuel.

 

[jbolty]

why are you looking at sensors when there are metal chunk in the fuel filter, or did I misread that earlier? sounds like the previous fuel pump came apart.

 

[Siva283]

There are no sensors on hte fuel system. If you have no pressure you have a very limited number of things to look at. First rent the fuel pressure tester. Second get a brand new fuel filter. Third Drop the tank and clean it. You have metal in there man that will destroy injectors but isnt from them. So clean the tank test the feul pump and replace the filter. Still no pressure check hte fuel pressure regulator. By that point you should have fuel. When the pressure reg fails it doesnt run rich it runs lean if your pump can pump enough fuel.

 

[cullen_merchen]

why are you looking at sensors when there are metal chunk in the fuel filter.

After switching that out along with cleaning the injectors, my jeep wasn't getting fuel pressure. It has been intermittently working. I'm now trying to figure out why my fuel pump won't prime.

 

[cullen_merchen]

One of the sensors you may want to check is the MAP sensor. It's mounted on the middle of the firewall towards the top and has a vacuum tube going to it and a plug. Here's a page on how to test...

https://www.fixjeeps.com/map-sensor.html

I forgot to plug this back in and the jeep would crank but not run because, I believe, it was being starved for fuel.

I checked my MAP sensor today using the guide that you gave me. It and its connectors appear to be working fine. I don't know why else my fuel pump wont prime.

 

[cullen_merchen]

There are no sensors on hte fuel system. If you have no pressure you have a very limited number of things to look at. First rent the fuel pressure tester. Second get a brand new fuel filter. Third Drop the tank and clean it. You have metal in there man that will destroy injectors but isnt from them. So clean the tank test the feul pump and replace the filter. Still no pressure check hte fuel pressure regulator. By that point you should have fuel. When the pressure reg fails it doesnt run rich it runs lean if your pump can pump enough fuel.

So far I've rented the fuel pressure tester, bought and installed a new fuel filter, dropped the tank and cleaned it, bought and installed a new fuel pump and checked the MAP sensor. I'm off to replace the regulator just cause it had bad gas in it, would that be a possible cause of my fuel pump not priming?

 

[jbolty]

is power getting to the pump? you are throwing a lot of parts at this without a diagnosis.

have you done anything with the parking brake? the ground for the fuel pump is attached there.

 

[TSEJEEPERS]

You said you got a fuel pressure tester. What did it say?

 

[xpage]

Howdy fellow Ag,
I would check for proper voltage to the fuel pump, if you aren't getting enough volts a new pump or old pump will behave the same. Checking grounds on the YJ are important as it might be corroded where they ground. If it isn't shiny, get some sandpaper or a wire brush and make it shiny. Then add a tiny dab of dieletric grease and make a light coating so it won't corrode.

The others were correct to recommend to change the filter and clean the tank. How did you clean the fuel injector? I had mine professionally done $15/per injector, and found mine were off by 8-13% or so. Though my major issue was corroded relays, so be sure to check yours. That can stop a Jeep from starting or drop your volts too.

 

[sequel]

You said you got a fuel pressure tester. What did it say?

Agree. Hook up a fuel pressure tester and turn key. You can even jump the fuel pump relay (pins 30 and 87) to get the pump running without the key. Just make sure you do those pins. If you get them wrong you can damage the pcm.

 

[letitloose06]

FUEL SYSTEM Testing Steps from the factory service manual.

https://jeep-manual.ru/index.php?page=320