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Fuel Pressure All Over

StylerG

StylerG

NAXJA Forum User
Location
Oklahoma City
help with a 97 jeep

searched and found threads about fuel pressure being too high and fuel pressure being too low but couldnt find anything about being all over the place

at idle pressure bounces all over the place from 30psi to 55psi, with a small bit a throttle it will settle in to 45-47 range

Jeep is hesitating or running like its bogged down at stop signs when accelerating sometimes this sounds like a backfire when taking off for the first block or two driven. Settles down and starts all over if you stop the jeep let it sit for 30 mins or so and begin to drive it again.

New 02 sensors front and rear and new exhaust including cat installed recently.
 
StylerG said:
help with a 97 jeep

searched and found threads about fuel pressure being too high and fuel pressure being too low but couldnt find anything about being all over the place

at idle pressure bounces all over the place from 30psi to 55psi, with a small bit a throttle it will settle in to 45-47 range

Jeep is hesitating or running like its bogged down at stop signs when accelerating sometimes this sounds like a backfire when taking off for the first block or two driven. Settles down and starts all over if you stop the jeep let it sit for 30 mins or so and begin to drive it again.

New 02 sensors front and rear and new exhaust including cat installed recently.
Click to expand...

Not that familiar with your year, I believe the fuel pressure regulator is in the tank on top of the fuel pump assembly. There is a fuel pressure dampner listed for the 97 on rockauto.com, and that would be on the fuel rail if rockauto's listing is correct.

NORMAL failure for a pressure regulator is pressure too HIGH.

With a 30 psi reading I would suspect a failing pump, or crud sloshing around in the tank possibly. Is the fuel filter on yours internal or external?

Anyway, I think you have to pull the tank to get at things, so it doesn't look like a fun weekend for you.
 
its my brothers-but everything is in the tank. Was hoping that the fuel pressure could have some variance and we could begin troubleshooting other things...i think id rather pull the whole engine than drop the tank i absolutely hate doing it
 
StylerG said:
its my brothers-but everything is in the tank. Was hoping that the fuel pressure could have some variance and we could begin troubleshooting other things...i think id rather pull the whole engine than drop the tank i absolutely hate doing it
Click to expand...

No problemo--make your brother do it while you sip beer! And make him buy the beer!
 
I'm not that familiar with the newer XJs but the early ones had a fuel pressure regulator that was controlled by the vacuum. The pressure varied with manifold pressure, which changes with load, throttle plate position, etc.

If the newer units still use this technique a vacuum leak can cause fluctuations.
 
old_man said:
I'm not that familiar with the newer XJs but the early ones had a fuel pressure regulator that was controlled by the vacuum. The pressure varied with manifold pressure, which changes with load, throttle plate position, etc.

If the newer units still use this technique a vacuum leak can cause fluctuations.
Click to expand...

Yes, that is what I have on my renix. His is a 97, and I wasn't sure, so I looked up the pressure regulator at rockauto.com, then looked up the fuel pump assembly and it appears to sit at the top of the assembly. I think the change was 95/96, when the fuel pressure changed from 30/39 w/o vacuum to a flat 49 psi.
 
The fuel pressure regulator would lead to the gauge being all over the place but would it also be the cause of the stutter/backfire?
 
The Weez said:
The fuel pressure regulator would lead to the gauge being all over the place but would it also be the cause of the stutter/backfire?
Click to expand...

Could be maybe? To check, OP should duct tape the pressure gauge to the windshield and go for a ride.
 
I'm leaning towards the pump.....regulators of that year are pretty problem free.
 
joe_peters said:
Yes, that is what I have on my renix. His is a 97, and I wasn't sure, so I looked up the pressure regulator at rockauto.com, then looked up the fuel pump assembly and it appears to sit at the top of the assembly. I think the change was 95/96, when the fuel pressure changed from 30/39 w/o vacuum to a flat 49 psi.
Click to expand...
Thanks for clueing me in. I knew things changed but I didn't know how much.
 
old_man said:
Thanks for clueing me in. I knew things changed but I didn't know how much.
Click to expand...

I get tunnel-vision on Renix all the time! I try and double check before inserting foot-in-mouth because I have 13 EEEE tootsies. :cheers:
 
I had the same prob on a renix but it was the line in the tank from the pump to the metal line coming out of the sender. the clamp came loose and it was pumping the fuel back into the tank.

low fuel rail pressure
the gf jeep started running bad and I checked the TPS changed the filter . I thought it was the pump so I got ready to replace it, pulled the sender out of the tank and found the line was almost all the way off the sender.
 
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