[THRSSTY]

Did a search, nothing quite like my situation.

New Walbro fuel pump in summer 09.
New Delphi FPR yesterday
CAI; 93 tune from PCMPERFORMANCE; 52 MM throttle body - also yesterday.
Tri-Y headers; hi-flow cats last week (had to pull head on one side due to broken bolt). No codes after driving a few days after this upgrade.

PROBLEM - running rich, and won't start after warm.

Details:
36 psi fuel pressure while running. 30 - 32 psi after shutdown. 38 pis after pump prime. 3 psi loss after shutdown 2 min, reading about 22 psi after 45 minutes. 45 psi while running with vacuum line removed.

No codes, but hasn't run for more than 10 minutes at a time.

She's flooding. She'll restart if I floor the accelerator. Once running, at slight throttle, or slight movement of the throttle body makes her want to stall, but she catches up and keeps running. At "lots" of throttle (my hand moving throttle body 30% - 50%) she runs like a dream. Loud and NASTY!

Thinking leaky fuel injector, but reading the lower than ideal pressures makes me nervous. Read that at excess throttle, the thing is sucking in enough air to handle the extra fuel (from the leaking injector).

Any ideas?

PS - tomorrow I'll put back in the old regulator. I theorized it wasn't working, and allowed fuel to flow back into gas tank rather than hold pressure on the injectors, thus, no flooding before. My buddy doesn't like that theory. ALSO, will swap in the old PCM to see if its the tune that has it running rich.

I know, lots of variables, but any ideas would still be appreciated.

Oh yea.....I've run out of gas twice. Think I got some bad Marathon gasoline, that caused my fuel light to stop working. Light used to come on at 5 gallons, now it comes on at 1 or 2 gallons.

PPS - I work for Marathon Oil Company - imagine the irony. cwm3

 

[chile]

i wouldn't put the old pcm back in. I would check the simple things first. Make sure the fuel filter is not clogged. you could take the injectors off with the fuel rail and the lines atttached. Prime the fuel pump and see if anything happens and when you pirme the pump at any time unless the system was empty it should go right up to about 43 psi.

 

[THRSSTY]

fuel filter was replaced at the same time as the fuel pump in 09. I've since put 5,000 miles on the car. I was considering replacing it, especially since I think I got some bad gas....Also, the PCM will be a lot easier to remove than the fuel rail. I just tried removing the fuel rail when installing the new FPR, and it sucked....I was unsuccessful. But thanks for the comment. I see a fuel rail removal in my near future.

 

[sherlock9c1]

Make sure there are no exhaust leaks. Replace the Oxygen sensors if you haven't already. Have the injectors sent out to someone like WitchHunter Performance to be serviced. I had at least two injectors that were way out of spec.

Pulling the fuel rail really isn't that hard. Clean the top of the intake manifold first so you don't drop any dirt down into the engine, then spray some penetrating oil like PB Blaster or WD40 around the injector o-rings to allow them to come loose from the intake manifold. Remove the four bolts and then gently wiggle the whole fuel rail and injectors up and it'll come out. Record each injector's location on each individual bag before you send them out to be serviced.

 

[Gregg-O]

I would think that the addition of a lager TB & headers wouold require a re-tune.

 

[THRSSTY]

The car was tuned for a larger TB. I told PCMPERFORMANCE that I was also getting headers on my order form. I'm not sure if there's a tune for this, but they were informed. I don't think not having a tune is the issue (however to take the fact that the car has been tuned out of the equation, I was going to swap in my old PCM. She should be fine to run, just not fine to drive. That would eliminate the tune as a variable).

Also, I just had it checked for exhaust leaks. Nothing before the O2 sensors. Secondly, my understanding is when you start a vehicle up, it doesn't take readings from O2 sensors or MAF until normal operating temperature is reached. Whatever the case, the 02 sensors before the hi-flow cats are new (ac delco, 09). The difficulty with the injectors came from me not wanting to undo all the wire connections. I had it all loosened up. Probably will be doing this in the near term. Will let you know.

 

[THRSSTY]

Oddest thing - original regulator is at 42 psi after pump prime, and about 40 while at idle. Its performing better than the new Delphi regulator.

light throttle stumble's still there. Still running rich.

Damn injectors are holding pressure now. Been 30 min, and haven't dropped from 42 psi. But she's acting like she's flooded.

Got her started normal, she ran, I saw the stumble at light throttle again. Shut her down, and she would not restart. Fuel readings were great. Floored accelerator, and now she just catches, then shuts right off. So, I guess its still flooding.

Sent a note to PCMPERFORMANCE to see if they dial up the fuel delivery with their tune. I guess the next step for me is to swap in the old PCM to take the tune out of the equation. I'm no longer gonna pursue a leaking injector. After PCM swap, I guess I'm looking at plugs and wires...

 

[THRSSTY]

Swapped in the old PCM, tuned for a stock throttle body, and the stumble goes away. Still runs rich, though.

Regardless of PCM, after a few hours, the fuel pressure bleeds down to zero when sitting. Earlier, I said it seemed to hold with the old regulator, well, now its back doing what the new regulator was doing. Duplicating all the same pressures in all aspects.

According to PCMPERFORMANCE, they don't step up fuel delivery with their tunes. Rather, they will increase spark and decrease fuel delivery. They are checking their program to make sure they didn't mess something up.

Would love any ideas out there. I guess next step is to actually pull the fuel rail, and visually confirm leaking injectors. I wonder how the idle air control valve would play a part in this...

Also noteworthy, with the old PCM, after running 3 - 5 minutes, she starts wanting to cut out.

 

[Rocko350]

Hey bud, unplug the 02 sensors and repeat drive. Please post results.

chris

 

[cletus284]

Check the engine coolant temperature sensor.

 

[THRSSTY]

Check the engine coolant temperature sensor.

Good call on the temp probe. I never stated, but when I jiggle the connection, the engine does respond a bit. I'll make sure during my next test, its fully engaged (its loose because I tried to fix it with epoxy, now I'm not getting a good connection).

Still haven't pulled the O2 sensors.....but will see.

 

[cletus284]

Good call on the temp probe. I never stated, but when I jiggle the connection, the engine does respond a bit. I'll make sure during my next test, its fully engaged (its loose because I tried to fix it with epoxy, now I'm not getting a good connection).

Bingo! A bad ECT reading will cause all sorts of problems with idle speed and the engine running rich. Fix this first!

 

[THRSSTY]

i wouldn't put the old pcm back in. I would check the simple things first. Make sure the fuel filter is not clogged. you could take the injectors off with the fuel rail and the lines atttached. Prime the fuel pump and see if anything happens and when you pirme the pump at any time unless the system was empty it should go right up to about 43 psi.

Pulled the fuel rail, not a single leak for 10 minutes, and multiple primings.

42 psi while priming, then 37 once done priming. Slowly bleeds down (about 32 psi after 5 minutes; 24 psi after 20 min).

So, apparently, the FPR is working because it maintains 42 psi when it has to. Fuel must be leaking back into the gas tank. That sux. I don't wanna drop it again. Is there a check valve in there?

Low fuel pressure can not cause this thing to run rich, can it?

I found a **** ton of gasoline in my crankcase (can't say I "found it" more like I confirmed it was there). Oil pressure may be why it isn't starting. I shall change the oil on the car before proceeding any further.

Checked resistance across injectors, 12.3, everyone of them (one was 12.4).

I had to make the IAC coolant housing -to - throttle body gasket out of RTV, and reuse the original fresh air gasket on top of the throttle body when I switched from the original 48 mm to the new 52 mm. I just bought gaskets, so I'll change those out.

So oil change, change out TB gaskets, try to reset IAC valve (per the Haynes Manual) and see if the flooding problem remains.

I'll check back in, probably late Friday night (parts arrive on Friday).

 

[Interceptor9C1]

ever get around to checking your coolant temp sender? Should be hooked up to a scan tool to read what it says. GM's usually read -40* when they fail for some reason, which on a cold start up can seem fine, a hot restart the engine still thinks its ice cold and dumps a ton of fuel in which will make a hard start-no start condition.

 

[cletus284]

Sounds like your fuel system is fine, the anti-drainback valve in your fuel pump is just leaking a little. All that will do is cause a little more cranking at startup. It will not effect how the engine runs once it starts.

If I were you, I would be starting with that suspect ECT sensor.

 

[THRSSTY]

Resolution (kinda)

Sorry it took so long to get back, but I've been having too much fun driving the damn thing.

1 - Replaced all TBI gaskets (total of 4)
2 - Installed new ECT
3 - Changed oil & filter
4 - Re-installed new Delphi fuel regulator

Starts right up.

Had a rough idle, almost like it was too low. I took the steps to reset the IAC, and it might have improved slightly.

After 30 mi of driving, the idle seems to have worked itself out, and only code is dead rear O2 sensor on passenger side, which shouldn't affect how she runs.

Stumble at light throttle is non-existent.
No longer running rich.

Thanks fellas for the advice on this.

 

[llorelei]

ditch the walbro pump. i had one, i got just over 1 year out of it. i have been told by a few folks thats just not the best pump for a chevy. I put a cheap airtex or delphi from o'reilly's on there 3 years ago, all is well.