94 Vortec fuel pressure... what when? (engine sputtering & stumbling)
 

Pardon me if this is a FAQ type thing, I've been searching off and on for a couple days, but the answers I get aren't answering my question 100%

94 Vortec with running problems. With a fuel pressure gauge on it, when I turn the key on (and hear the pump run) it's right at 60psi. When the pump cycles off it drops to 30psi or so, and seems to stay there steady. Is that right?


When it starts and runs (which it does just fine) the pressure is in the 50-60 range (needle isn't still). What's happening is it will idle just fine for a while, but at higher RPMs it sputters and stalls. After a while it will do that at idle as well. I need to leave the pressure gauge on it and see if it tells me anything when it starts to stall, don't know that it will, since the needle is just a blur. Darkness and cold temps kept me from trying that tonight, but I still need to know about the 60 to 30 thing.

Key on - 58-62...
Running - 55-60 seems what most poeple get, should not fluctuate more than one point even when revving the engine.
Turned off - better hold that 55-60 for a few minutes or you have a LEAK

Since you have fluctuating fuel pressure, I am guessing you have a malfuctioning or leaking FPR or fuel pressure regulator. That is what it does it maintain a steady pressure - or regulate fuel pressure. The reason it will run fine is cause its not leaking into the combustion chambers, its leaking into the crankcase and diluting the oil.

So yeah, if you are dropping off to 30 when you shut off, you my friend, have a leak. Now its time to check that regulator and injector unit for the leak. Do youself a forums search on "CPI injector" and there is many photos of what you are looking for and how to take this stuff apart and where to order the cheapest parts for it.

A whole injector assembly is typically about 300 bucks and comes with new everything thats inside the plenum. If its just the regulator thats leaking, those are about 90 bucks at the parts shops. A new injector unit comes with a new FPR attached to it.

When I said the needle wasn't still I mean it seems to vibrate back and forth across and arc of say 10psi or more. I just assumed it was vibration and the way the gauge works. ???

I would check the fuel pressure regulator.

i'd say FPR as well. The gauge is supposed to hold a steady pressure and MAYBE drop after like 5 mins or more.

A couple interesting things....

The previous owner suggested I pull/clean the EGR valve because he had similar trouble twice from it. I did, but it was pretty clean. I cleaned it up and reinstalled it with no change.

Tonight I put the pressure gauge back on. Tonight while running the gauge is steady, maybe a 1psi +/- tremble in the needle. Not the 10psi earthquake shake it was doing yesterday.

The engine is still stumbling.... watching the gauge when this happens I expected the pressure to be dropping out. But at the moment it seems like the pressure goes up a bit when it happens. It's out there idling now, warming up. It seems to happen more when it's warm so I'll go double check what it's doing.

So much fun in the freezing rain.


Edit to add:

Ah crapola.

Okay I'm starting to think I had a loose fitting or something yesterday when the pressure was dropping on it.

Key on, pump making noise, the pressure goes to 60. When the pump stops running the needle drops to 58 and stays there. (not 30 like yesterday. Between the violently shaking needle and the pressure drop, something must have been wrong with how the gauge was on.)

When the engine stumbles, the pressure does drop, ever so slightly, only a couple pounds. The spike I was seeing was in the recovery afterwards.

ETA: Almost an hour later and it's only dropped to 45psi.

I was really hoping it was the FPR. Now I'm at a loss.

could be the fuel spider.

Not much to see, but this is what it's doing.... have the gas peddle depressed some, held in one spot.

http://www.youtube.com/watch?v=7iKr03mXewI

Did you clean the manifold port when you cleaned the EGR valve? BUT.....
I'm kinda thinking spider too.

There was really nothing to clean. This EGR is pretty new. I "cleaned" it since I had it off, but I didn't gain much because there wasn't really anything to clean.