Stumble stall upon accelerator depress after warm

[needragr]

well nobody replied so I pressed on. Checking fuel pressure per the manual. all checked out in spec. Regulator appears to be operating as detailed as well. One more thing I found was duing a test drive after a few mins of driving it would start failing - any throttle input GAG, got it home still bucking & gagging & it still be exhibited behavior sitting idling in the driveway. Depress the throttle.. stumble. gag . I had hoped to test pressure while in fail mode BUT found if you turn off the eng. symptoms go away !!!

[1990new]

You might want to consider that the problem could be something other that a fuel supply problem.
The problems that you describe could also be cause by a failing ICM. If I were you I would maybe do a little research on that.

That would be a simple thing to test if you have a spare ICM. I would also change the Supression Capacitor at the same.
If you don't have extras of these parts and want to change them out, PM me your name and and address and I will send them to you free of charge.

Be sure to disconnect the battery ground before you change them out.

[needragr]

Thanks but Ive already replaced the ICM. Suppression capacitor? While I do appreciate the help & obviously want to get it resolved & running I do also want to understand ..why

[WmWatt]

Since I'm not familliar with EFI engines let's see what the Haynes manual troubleshooting section says under "engine stumbles on accelleration"
- spark plugs fouled (chpt 1)
- problem with fuel injection system (chpt 4)
- fuel filtre clogged (chpt 1, 4)
- fault in engine control system (chpt 6)
- intake manifold air leak (chpt 2, 4)
- EGR system malfunction (chpt 6)
That's certainly not very specific is it? Two or three could be checked easily but the rest look complicated.
Could that "intake manifold air leak" include loose and caracked vacuum hoses? They have been mentioned in this forum a lot.

1990new suggests the ignition control module might be going bad.They are heat sensitive but my experience was when the aging ICM heated up the car would quit (stall). I would stand around until the engine cooled and it would start up again and be fine for a few days.

[ricko1966]

I don't believe an egr valve will throw a code on a festiva.I would make sure it's closed and disable it and go for another drive.EGR is inactive on cold start until engine reaches operating temperature.

[needragr]

? EGR valve is new (part of the tuneup performed as soon as I got it) so I know its working correctly. What would plugging it tell me?

[WmWatt]

According to Mr Haynes the EGR valve position sensor sets trouble code 16 on the EFI engine '90-'95, same as the carburetted engines. The check engine light on my vehicle didn't come on. I got a warning during emissions testing that the nitrogen in the exhaust was creeping up. I cleaned the EGR valve and next year the test was fine. When I cleaned the valve I started then engine with the car up on one stand and the check engine light came on and set trouble code 16 but when I put the car back down on the ground the light didn't come on any more.

[Rick the Quick]

At this point I would try another distributor. One that is known to be good. I know a guy that runs a small salvage yard here and he tells me back in the day many a Festiva was junked due to a bad distributor. This is what he told me when I was having trouble with my newly aquired '91. On his advice I plunked down $25 for a used distributor and never looked back....Keep us posted. Good luck.

[needragr]

While scatter shot replacement of parts isnt out off the question at this point. Im continuing down the path of following the symptoms. Most notable is a verified loss of fuel pressure AFTER the car warms. Ive now replaced the pump twice.(once with a used one from another running car I own & the 2nd a new Denso unit) & didnt solve the problem. How exactly would the distributor cause a loss of fuel pressure? I went through the EVAP system Sat. to eliminate any clogging or plugged lines, one ? i did have is what is the Purge valve supposed to do? I see its electrically connected (Red +Yellow w/blk) + a line off the plenum vacuum that then routes to the EVAP can, then to atmosphere.

[WmWatt]

Logic rules!

[Rick the Quick]

Sorry I missed the part about the lost fuel pressure.

[needragr]

So Im pressing on. Problem persists. I pulled the IAC cleaned & bench tested it while it was open, It wasent opening much. I soaked it with some penetrating oil then triggered the thermo switch with hot water. it now seems to work ..better. Then tested & adjusted the TPS. Unplugged the O2 sensor to find it didnt seem to have ANY effect? No CEL no change in running, no perceptibal richening (or leaning) of exhust. put a meter on it & it seemed to be oerating in the opposite I expected.
Still I dont it understand how any of that can negitivly affect the fuel pressure

[WmWatt]

Is the fuel pressure computer controlled? The odd O2 sensor behaviour may mean the car computer is compromised. Did you say you have a spare vehicile from which you can borrow? Assume the engine was warm when you checked the O2 sensor as they don't work and are ignored until warm.

[needragr]

Is FP controlled by the ECU? Not to my understanding, It gets operating voltage so that consistent pressure can be fed to the rail, manifold vacuum is used to control the regulator to bleed off or hold back fuel in the rail. Yes the O2 was hot as I had been doing test (driving) loops after each change or update. I dont understand how the Oxygen sensor being unplugged doesn't throw an CEL or error code!

[needragr]

So its been some time & behind the scean I been going over ..every...last ..system on the car. Only to come back to the pump.
So I pulled it again, to find a MASSIVE amount of rust had been released from the bowels of the tank on my many diagnostic drives.
Enough silt had broken free that it had settled in the baffle & on every drive it would take a few min of driving to suck a sufficent qty of trash to completly clog the sock at which point it would still run but could not pull enough fuel to maintain speed under load.
I spent easter swapping tanks out my 91 ...whats that principle.... Occam;s razor...DOH!