2002 SSEi rough idle / fuel pressure loss

[Paragongx]

Good morning all. Well the wife's Bonnie is having a bit of issue I was hoping you all might have some input on. A couple weeks back I got in it to move it across the street and when I started it up it was running real rough, seemed to be missing and the SES light was on. Asked the wife how long it's been like that and she said it was fine earlier (her version of fine in the car world a lot of times is different than my version though). So I took it for a drive and at speed it seemed OK and as the car warmed up, it smoothed out a bit but something still didn't seem right. So I got my dads scanner hooked it up and the codes came back with a misfire on cylinder 6 and a lean condition. I neglected to actually write the codes down, yeah I know shame on me. But the code reader said the most likely fix was to replace the fuel pump. Knowing the fuel pump has been an issue with these cars I figured I'd order one with my next Rock Auto order of other stuff to fix on her car. So it sat for a couple weeks till I got all the parts sorted out. I was planning on renting the fuel pressure tester from our O'Reilleys auto before ripping into the fuel pump but it was already loaned out the day I checked. So I went ahead and tore into the fuel pump anyways. I bought just the pump module from Rock Auto not the whole assembly so after getting the assembly out, taken apart, cleaned, pump replaced, put back together, popped it back in, primed it up a couple times it started up and was just as rough as it was before. Bummer. Oh well, the pump was only $45 bucks. Done for the day

So last night, I rented the fuel pressure tester. Hooked it up per the manual (and the GM service manual), turned the key to ON a couple times to get the maximum fuel pressure reading and it was at 52psi. Which seemed to be on the low end according to the service manual. So following the flowchart in the service manual it said (my interpretation) to let it sit for a minute with the key in the on condition and see if it drops more than 5psi. Well it pretty much drops to 0 in 30 seconds. So I guess first question is did I test this the correct way? I know the GM service manual assumes I have a Tech 2 that I can command the pump on and off with. Obviously I don't and was doing this with just turning the ignition to ON. So the next thing it told me to do was remove the vac line from the fuel pressure regulator, turn the ignition to ON and see if any fuel leaked out the fuel pressure regulator. No fuel leaked out, and I tried a couple of times just to make sure. So now not having the appropriate fuel shutoff hoses the service manual is calling for to generalize the location of the pressure loss I jumped around a bit and figured I'd see if I had a leaky injector. Fast forward 30 minutes of unhooking stuff to get the fuel rail popped off I've got the wife in the car turning the ignition to ON to see if any injectors are leaking. Did not see a drop of fuel leak from any of them. Bummer, running out of easy stuff. So done for last night.

So that's where I'm at right now. Going out of town for the holiday weekend so the cars gonna sit for a bit, but any ideas? I'm not yet sure if I can rent the fuel shutoff hoses but if I can I'll do that when I get back. Is it possible that I've puked a fuel pressure regulator? I just replaced it last year with a new ACDelco one and as expensive as those little buggers are I'd like to feel a little more confident that's what it is before I shell that coin out. Or am I off base from the beginning with not checking the fuel pressure correctly? I did a quick cursory search last night and didn't see much that matched my situation but if there is a thread on a similar topic I would love to get the link to it. Sorry for the long-winded post. Just trying to provide as much info as possible. Thanks all.

[redzmonte]

IIRC the fuel pressure normally is about 45psi so you should be fine there. If your getting a misfire code i would look closer at the plugs and wires, have you replaced them recently? also if you have not replaced the fuel filter i would also look at doing so. I would say your FPR is fine. our cars have a return fuel system so when the key goes off the pressure bleeds back into the tank.. I would be inclined to say thats normal... i dont remember if it holds pressure or not. If you can test the fuel pressure when driving it should stay solid.. if it drops when the car runs poorly then i would say you have to look closer at it but i bet it stays solid and you have some other issue.

You said the issue was better as the car warms up? any visable vac leaks under the hood? Intake gasket leaks? did you spray some carb cleaner around the intake gasket to see if it caused a stumble? if it gets better as the engine warms up it makes me think there is a vac leak (as the metal heats up it expands and closes the leak... making it run smoother). That would explain the lean code..

[Paragongx]

Plugs and wires were new as of last year. I think I went with the NGK's, I know I went with the Belden wires. Did the lower intake manifold gaskets last year plus all the gaskets above that. Fuel filter was replaced last year as well. Hadn't gotten to looking real seriously for vac leaks yet. Looked at some of the hoses last night as I pulled them off to get fuel rail access. They looked OK, but they are 10-11 years old so I may end up changing them out in this go around as well. With the fuel pressure bleeding back down to 0 that quick, I wasn't sure if that was normal for these cars. I might check my Mystique tonight (it is a return type fuel system as well) and see what the pressure does on that in a similar test.

The couple times I've driven the car recently before the rough running, it's seemed to lack "zip" as well with it really taking a heavy foot to get it up on boost. Since it's her daily driver now and I drive it very infrequently I'm not sure if it's really lacking zip or I'm just jaded by my daily driver and its overzealous zip.

[Archon]

The fuel system should hold pressure, and not drop that quickly. The usual cause is a bad check valve in the pump. You may want to look for any other fuel leaks. It could leak down through the FPR, also.

[Paragongx]

I'm assuming the check valve is in the pump body itself? Since the pump was just replaced and it didn't fix the problem, I'm going to think that the pump is probably not the issue. There is a chance it could be I guess, I have bought new products that were defective before. Since I don't see any visible leaks in the engine compartment or on the ground under the car I'm thinking it is a defective component. I guess at this rate the next likely component to replace is the FPR. If that doesn't do it a diggin deeper I shall go. Thanks

[redzmonte]

I would still do a pressure test while the car is running/driving to make sure you are after the right problem. the FPR should not have any effect on the fuel when the engine is shut off. if your loosing pressure and not supposed to then i would look closer at the sending unit for a check valve or something like mentioned above. if the car is i guess choking when your throttling into it watch the Fuel pressure and see if it holds or drops.. if it holds then i think you have something much different going on.... Bad MAF, Miss fire, bad wire, bad coil, cracked plug.. could be alot of things.. they will all give you a miss and poor performance. my buddies vette did the same thing were it would not hold pressure with the key off. the only thing that will be annoying is you have to prime it before you start it so you have pressure in the line.

My new plug wire rested against the manifold and the wire grounded out and car ran like poop.... then it would be fine then like poop... repalced wire and all good. so i would again check everythign before throwing parts at it.

S