Fuel pressure is bleeding off past the outlet check valve in pump

The pressure in my fuel lines is going to 0 after shutting the jeep down -- within 35 minutes. According to the leak down test that indicates the loss of pressure is through the check valve.

I know that means replacing the pump in the tank -- question I have is what effects/impacts/hassles/symptoms can be attributed to a this issue?

When the system depressurizes as you described; the main problem will be a longer starter crank time until the system and fuel rail repressurizes to start the engine.
My own experience with the system depressurizing is slightly different than yours.
The fuel injectors on my '98 XJ had a leakby problem that caused depressurizing of the sytem after the fuel pump stopped. The leakby would cause a longer crank time and rough idle once the engine was restarted. Four weeks ago I replaced the fuel injectors and now the engine starts quicker, idles better, throttle response is better although I haven't noticed much of a change in gas mileage.

How does one check for leak-by on the injectors?

I have a 90, so Renix; 4L engine

Several minutes after shutting off the engine pull a few sparkplugs and check for damp or wet plugs.

Install an inline check valve I have done this on mine its a 92 . I think the valve is from a BMW but will have to check do a search and it will come up on installing those type of valves to fix this prolbem with out having to replace the pump

box_goblin, what year is your XJ?

In the later models (97 on)you don't have to replace the fuel pump...

Here is what you need:

http://www.jeep4x4center.com/product-information.asp?number=4798301

. . . or you can pull the fuel rail off and cycle the ignition on/off a couple times to build up the pressure and see if any are leaking. It takes 5 minutes to remove and $10 for some new o-rings(I'm gonna do it w/in the next week or so--gotta find out why mine's acting up).

You are experiencing pressure drop. But you don't know where.

You need a fuel pressure gauge and an adapter that allows you to clamp pressure so you can isolate whether the drop is taking place "AFTER" that adapter towards the gas tank, or "BEFORE" the adaptor which means an injector or two is leaking.

Pressure drop can occur anywhere between the gas tank and the injectors, so don't assume anything until you know where the pressure drop is taking place and the only way you can efficiently do that is by TESTING.

There is a procedure for this in the factory service manual; the el-cheapo manuals like Haynes and Chiltons probably don't cover this.

birchlakeXJ said:

You are experiencing pressure drop. But you don't know where.

You need a fuel pressure gauge and an adapter that allows you to clamp pressure so you can isolate whether the drop is taking place "AFTER" that adapter towards the gas tank, or "BEFORE" the adaptor which means an injector or two is leaking.

Pressure drop can occur anywhere between the gas tank and the injectors, so don't assume anything until you know where the pressure drop is taking place and the only way you can efficiently do that is by TESTING.

There is a procedure for this in the factory service manual; the el-cheapo manuals like Haynes and Chiltons probably don't cover this.

Click to expand...

Thank you for that, birchlakeXJ -- I'm all about testing; unfortunately I do not have a FSM so I hadn't come across this information yet. Definitely makes sense to test by clamping off pressure.
My understanding of the system is that some pressure is meant to bleed past the fuel pressure regulator (Renix manual says a drop of up to 20 PSI over 30 minutes is in spec?) so I didn't want to keep that pinched off in case that would stress the system by cutting off the designed bleed down path. I hadn't thought about clamping off the supply line, however. I suppose if I clamp that, and don't have the drop it would tell me the drop is in that line (and likely the pump check valve).

Thanks!

A word to the wise. If you have the original style injectors on your Renix Jeep, you may want to replace them as a matter of course. They are notorious for leaking fuel externally from a seam and spraying gas on your intake and exhaust manifolds. Check out www.precisionautoinjectors.com where you can get a set of 4 disc, flow matched injectors, with o-rings for about $100. I've installed 2 sets and I'm very happy with the results.

JP Magazine article on fires from leaking Jeep injectors: http://www.jpmagazine.com/techarticles/engine/154_0811_preventing_jeep_engine_fires/index.html

There is a seller on eBay, jbass195 has check valves $16 + $2 s/h, put one between the tank and fuel filter.