Rapid Fuel Pressure Loss after Shutdown

I have been having starting issues for quite some time now on my '97 XJ. It will turn over several times then partially detonate and die. When I go to start it the second time it fires right up but usually idles rough for a few seconds. It will do this when the engine is cold or hot.


I checked the fuel pressure at the rail test port. 47psi running...but as soon as I shut the engine off it drops like a rock down to 0psi.

After doing some searching on the forums it looks like this is either my fuel pump, pressure regulator, or injector o-rings. I know this doesn't mean much but thought I would add that I do hear the pump 'charging' up when I turn the key to on. Which makes me lean towards leaking injectors.


I don't just want to start throwing parts and $$$ at it though. Has anybody had symptoms like these or any ideas on where to start checking next to isolate the pressure leak?

97xjcrawler said:

I have been having starting issues for quite some time now on my '97 XJ. It will turn over several times then partially detonate and die. When I go to start it the second time it fires right up but usually idles rough for a few seconds. It will do this when the engine is cold or hot.


I checked the fuel pressure at the rail test port. 47psi running...but as soon as I shut the engine off it drops like a rock down to 0psi.

After doing some searching on the forums it looks like this is either my fuel pump, pressure regulator, or injector o-rings. I know this doesn't mean much but thought I would add that I do hear the pump 'charging' up when I turn the key to on. Which makes me lean towards leaking injectors.


I don't just want to start throwing parts and $$$ at it though. Has anybody had symptoms like these or any ideas on where to start checking next to isolate the pressure leak?

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If it drops to 0 that fast, i would say its gotta be the fuel pump or the pressure regulator, however i could be wrong.
Our pumps have a check valve in them that goes bad sometimes... if it did, your pump would still "whirr" when you turn the key and seem normal, but you would have leak down.

Id replace the regulator first though since its cheaper.

How do your plugs look? Do they have gas on them? That i think would be an easy way to tell if you have gas leaking from the injectors into the cylinders. I doubt o-rings would cause leak down that fast...

Maud'Dib said:

How do your plugs look? Do they have gas on them? That i think would be an easy way to tell if you have gas leaking from the injectors into the cylinders. I doubt o-rings would cause leak down that fast...

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The plugs look normal. No gas on them...so I guess that would mean it's not leaking at the injectors.

As for the pressure regulator, I heard on the 97+ XJ's the FPR/filter has to be replaced as a whole fuel pump unit. I also heard that the FPR/filter can be bought seperately. So I am a little confused.

Am I better off just buying the whole pump assembly(O' Reilly's quoted $190) or trying to get the pressure regulator/filter assembly?

97xjcrawler said:

The plugs look normal. No gas on them...so I guess that would mean it's not leaking at the injectors.

As for the pressure regulator, I heard on the 97+ XJ's the FPR/filter has to be replaced as a whole fuel pump unit. I also heard that the FPR/filter can be bought seperately. So I am a little confused.

Am I better off just buying the whole pump assembly(O' Reilly's quoted $190) or trying to get the pressure regulator/filter assembly?

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You apparently have a newer Jeep?

I dont know much about the FPR and pumps on those except that you HAVE to drop the tank to pull or replace the pump. You may be right. Ill let someone else chime in ... but yeah if you already have to pull the damn thing down, might as well replace everything.

Yeah I do have the newer model, the '97.

Anybody who knows how the FPR/pump assembly goes together please chime in.

I have heard the whole unit has to be replaced and I have heard that that the FPR can be replaced seperately.

It is a failed check valve on the fuel pump. The check valve holds the pressure in the fuel system while the motor is off. It should hold pressure for days or weeks.

Check with the dealership or get a copy of the Factory Service Manual about the pressure regulator.

DO NOT get your fuel pump from Checker/AutoZone/O'Reilly etc. More than one member has had one of those cheap ones fail totally within 12-18 months. Even if they are warrantied, your have to repeat all the labor to drop the tank and get the pump out.

You can just live with it. Turn the key to on, let the fuel pump prime. Turn the key off, back to on, let the pump prime again, turn to start. I have been doing the key on/off trick for almost 3 years.

Install a inline check valve. Put it in the fuel line as close to the fuel tank as you can.

Tim_MN said:

DO NOT get your fuel pump from Checker/AutoZone/O'Reilly etc. More than one :: member has had one of those cheap ones fail totally within 12-18 months. Even if they are warrantied, your have to repeat all the labor to drop the tank and get the pump out

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Where should I go to get a new pump? Is the stealership my best bet on a quality pump or does anyone know of somewhere to get a quality pump with warranty?

I have almost the same thing happening to me. I just turn the key on and wait a few seconds, then it starts right up, no problem. I guess it never bothered me enough to find the "problem". I just wonder of it is effecting performance or anything???

As far as having to replace the whole fuel pump assembly...you don't have to. I learned this after disassembling the fuel pump assembly on the trail to fix things. I have a 98, so it should be the same as your 97. It is inside the gas tank, so it's a PITA to get out. The assembly is basically a tall cylinder with the float attached on the outside and the fuel pump in the inside. The filter is below the pump on the very bottom of the cylinder. The fuel pump is also a PITA to get out out, but it's just stuck in there with a rubber plug and then the filter is an even bigger PITA to get out, lol! Anyway, you can get a new pump for around $120 and the filter for $8. The whole assembly will cost you that $190. It depends if you want to save the PITA and pay the extra money how you want to do it.

My Jeep does the same thing though with having to crank a lot on cold starts. Hot starts it fires right up though.

I've gone through 2 aftermarket pumps since I bought my jeep, the most recent was for the same problem the OP had. Went back to an OEM pump since the aftermarkets pumps crapped out so soon. Lesson learned.

Could be the checkvalve but you mentioned that it runs rough for a bit after starting.......that leads me more to a leaky injector or a fuel delivery problem. Normally if its the checkvalve, it doesn't run rough when it starts, it runs cleanly.

If an injector leaks fuel into the cylinder, the engine runs rough for a few seconds after starting while burning off the excees fuel that has dripped into the cylinder. Are you pulling the plugs immediately after you see the 0 pressure on the gauge after shutdown? If it is dropping that fast and it was an injector, I would definitely think that the plug with the bad injector would be wet....

As for the fuel pump "assembly", yea you can piece it out but why? If dropping the tank, I highly recommend replacing the entire assembly (pump/regulator/filter) so you're not back in there again in a few months replacing something else. And as mentioned, get a high quality OEM style pump; there is a TON of junk fuel pump assemblies floating around and they just do not hold up over time.

The FSM has some extensive fuel system troubleshooting diagnostics in it. May be worth the time to perform them to isolate this definitively.

I had a similar problem with my 90 comanche. Slow to start, quick to loose pressure on key off. I ordered an aftermarket pump. Pulled the unit out of the tank. There is a short piece of fuel hose on the pressure side of the pump to the fuel line. This fuel hose was split, the pump was fine.
You may find the same thing. MikeB

got the same issue with my 99 sport. i find if i cycle the ignition to "run" 4 or 5 times for a second at a time, she'll fire up quickly. My FSM states the fuel pressure reading "0 PSI" is a normal condition on a cold engine. Seems to me the lack of a return line from the fuel rail requires the bleed back at the fuel pressure regulator at the fuel tank. FSM shows check valve in the FPR and fuel pump. Just figuring this is a "Jeep thing"!