Slow loss in fuel pressure

Alwaysdutch · Mar 14, 2017

I have been having some fuel pressure issues lately. I noticed that when I start my '01 XJ, it takes several turns before it fires up. I went to Autozone to hang a fuel pressure gauge on the rail, and noticed that the fuel pressure drops slowly from 46 psi to 38 psi in about 15 minutes. So if you let it sit for a few hours, the pressure is just getting lower.

I do have 4-sprayer injectors that I put in a while back, and the engine seems to run just fine with an average of 18-19 mpg.

I am thinking a leaking injector or the valve that keeps the fuel from going back. The weird thing is that there are times it starts right up, while other times it takes several turns/seconds.

Ideas?

waxer · Mar 14, 2017

There are a lot of failure points between the fuel tank and the fuel rail that can cause this..

Double check your rubber hose coming off the fuel sending unit that goes to the frame mounted fuel filter. Make sure it's not dry and cracked and that the hose clamps are nice and tight.

Then check the rubber hose from the output of the fuel filter that goes to the steel line running on the drivers side frame. That one should not be dry or cracked and the hose clamps also need to be tight.

Then check the connection at the other end of that steel line to make sure the quick disconnect isn't leaking or showing signs of damage. That line then runs up to the fuel rail and make sure the quick disconnect is also in good condition.

Then you have the return line circuit to check everything on as well. Rule out these 2 circuits as the source first.. They are the number one causes of this issue.

old_man · Mar 14, 2017

Actually your numbers are pretty good. If the wait bothers you, just cycle the key a couple of times before actually cranking and it will start up faster.

Alwaysdutch · Mar 14, 2017

waxer said:
There are a lot of failure points between the fuel tank and the fuel rail that can cause this..

Double check your rubber hose coming off the fuel sending unit that goes to the frame mounted fuel filter. Make sure it's not dry and cracked and that the hose clamps are nice and tight.

Then check the rubber hose from the output of the fuel filter that goes to the steel line running on the drivers side frame. That one should not be dry or cracked and the hose clamps also need to be tight.

Then check the connection at the other end of that steel line to make sure the quick disconnect isn't leaking or showing signs of damage. That line then runs up to the fuel rail and make sure the quick disconnect is also in good condition.

Then you have the return line circuit to check everything on as well. Rule out these 2 circuits as the source first.. They are the number one causes of this issue.

I was wondering if the '01s actually have an outside mounted fuel filter, or if it part of the fuel pump assembly.

md21722 · Mar 14, 2017

97-01 have no separate fuel filter, it is part of the fuel pump assembly.

Treleaven · Mar 14, 2017

I had this same issue. Mine would never start on the first start regardless if it was just running 5 minutes before or if it sat all night. I did the 4 hole injectors and thought that maybe there was a leak in one. I had just put in a new fuel pump so I ruled out the built in check valve(97+). Turns out the Spectre fuel pumps REALLY ARE BAD which is exactly what I was warned about when I bought it.

I ordered a Bosch fuel pump and installed last night. The only time the Jeep did not fire right up was after it sat for 45 min after a hot run and I barely turned the key over for a second before turning it back.

Ralph77 · Mar 15, 2017

I have a similar issue with my '00. Before and after a 4 hole injector upgrade. My thinking is that it is the check valve on top of the fuel pump. Thing is you still have to drop the tank to fix it. Or cut a hole in the floor. And for the price of the part and labor required you might as well replace the fuel pump. So I just live with it. Turn the key, let it sit till all the lights go off, and she usually starts right up.

http://www.morris4x4center.com/fuel-filter-fits-all-engines-4798301.html

waxer · Mar 15, 2017

The other thing I realized, which may or may not play a part into this described problem, are the fuel pumps for the 97-01 are a single port style. Meaning, there is only a feed line coming from the pump to the fuel rail. I don't see any return line, so it pressurizes when powered and there may be air in the line pushed up and causing the slow start.

The pumps prior to this have 2 ports, one for feed and one for return. So when you turn that key on, the pump starts and it's pumping fuel up to the rail and returning it to the tank, purging any air...

It makes sense this isn't an issue with pre-97 XJ's and how my 92 never had this issue.

nathanems · Mar 20, 2017

Check valve in fuel pump assembly is known to bleed off when defective. Do you have heat shielding installed around the fuel rail and injectors? Excess heat can cause a similar starting issue.

Slow loss in fuel pressure

Alwaysdutch

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waxer

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old_man

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Alwaysdutch

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md21722

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Treleaven

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Ralph77

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waxer

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nathanems

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