94 suburban rough idle/stalling

[Flatspin]

Anyone help please?

Sorry for the long description, but I am trying to include all relevant information.

I have a 94 5.7L k-1500 with 170K miles on it. It started hesitating on acceleration, and I tracked the problem to low fuel pressure. Rather than just replace the pump I opted for an Edelbrock Multi-point conversion with new pump, filter and the chip for the ECM. Since then I am getting a rough idle and stalling on deceleration. I have replaced the O2 sensor and back-probed the TPS, MAP and EGR, getting results within the parameters from Haynes. Compression test is happy at +/- 150 PSI. Pulling a vacuum directly on the EGR causes the motor to stumble, so I assume that the EGR valve is working? Ditto the MAP sensor. My local auto-parts guy lent me an ICM which did not solve the issue. I have tried new rotor, cap, wires and plugs. I am getting no codes except a sporadic 33 (High MAP at idle) caused by the stumble/stall (I think) The timing is set at zero per the manual, if I advance the timing to 4 degrees BTDC static the problem is better, but not fixed. I have not been able to find any vacuum leaks, although I did remove the throttle body and install another gasket just for grins. At highway speed the truck goes like stink and I am highly impressed but the sudden loss of power steering and brakes when it stalls is getting old really fast. Edelbrock says that the Multi-point conversion is not as tolerant of faults as the TBI system, and the problem was probably there all along.

Any ideas where to look? Thank you in advance.



***** Turns out the EGR Solenoid, which held a vacuum and back-probed OK when tested was actually at fault. Don't know exactly what was wrong but I suspect that the solenoid was sporadically opening at idle (vibration maybe?) and causing all kinds of vacuum problems for the computer when the EGR valve unexpectedly dumped exhaust gas into the intake. I changed the solenoid 2 days ago and have not had any of the symptoms since.

[Flatspin]

Today, with the help of a (very) helpful auto-parts store manager I "borrowed" a distributor with ICM (excellent reason to go to your small auto parts store and not the "supermarkets" like Pep-Boys and AutoZone), and got no improvement. I now have installed a "test" MAP sensor, even though the original tested good, and have not yet had a stall - altough I have only done about 10 miles which is not enough to be sure.

I also plugged the EGR line before I installed the MAP, which seemed to stabilize things. If the MAP is not the issue I will go for the EGR next.

Does anyone know, if you pull a vacuum on the EGR valve, should it hold or bleed shut quickly. Mine will open when I use a hand vacuum pump, but will not hold the vacuum.

[Flatspin]

Wasn't the MAP sensor, It quit on me again today. I had re-connected the EGR, now it is disconnected and plugged again and it hasn't quit since (normally on the drive home it dies 3 to 5 times). I am told the EGR will not "hold" a vacuum on GM vehicles, but I am beginning to think it must be the problem anyway.

[CaptainZoom]

I saw the date on this thread, but thought I 'd give it a shot.
I seem to have the same problem as You, did it turn out to be the EGR in Your case?

[fatmacsumo]

please tell me your symptoms i can help you i have 24 years exp in the auto ind i need year make & model with engine size this message is for zoom

[CaptainZoom]

Originally Posted by fatmacsumo

please tell me your symptoms i can help you i have 24 years exp in the auto ind i need year make & model with engine size this message is for zoom

Hi Fatmacsumo, that´s excellent of You!
Specs:
-89 Silverado k1500
5,7L Engine
4x4 Stepside

Symptoms:
Runs great on all 8 by the sound of it. -When cold!!!
But as soon as it has reached operating temperature it starts:
When I try to accelerate it loses power dramatically and lose revv. But it doesn´t die completely. It sounds like it is beeing smothered/choked.
Brrrrrrrrr(accel.)...oouuuuhrfhrfrrfhhh...(let go)..r.r.rrrrrrrrrrrrrrrr

If I ease up on the pedal it returns to normal idle. It always starts, and idles ok. even when warm.

And it comes very abruptly. The first 5-7 minutes of driving is totally OK, and then it starts acting up. Seems like there´s something that occurs when the engine goes into "ordinary working loop"?
After it closes off the choke, so to speak... (I´m Swede so my english is probably not 100%...)
Someone suggested disconnecting the EGR-valve.
(The former owner said it might be faulty on my car, but I have not experienced any problem at all until now, so I never got around to check it...)
The "Check engine" light comes on every now and then, only to go out again 5 min later...
BTW It came overnight. One day it was ok, next day it was not.
Thanks again for Your input!

[CaptainZoom]

I got another thought, what about the choke?
Could it be stuck in "on" position, always mixing air/fuel ratio for a cold engine? And could it be causing this problem?

[fatmacsumo]

first you need to change fuel filter, usually when the choke sticks during cold starts it will run rich. to check the choke when cold take off the breather have some one start the engine the choke should open about a quarter of an inch on start up. when it warms up about 15 minutes it should open completely. if it don't check power to the automatic choke on the side of the carburator should be a grey connecter with the switch on test light hooked to ground stick the other end in the grey connector. if it lights up its ok. only check this if the choke doesn't open completely in 15 minutes.
the next thing that might cause this is a stopped up catalytic converter on your exhaust.

[CaptainZoom]

Ok Mac, Thanks for all help. I'll check these things out.

[94burban]

I have a 1994 suburban with a 5.7 today it started to idel a little rough and on acceleration it wants to cut out and die sometimes. When i pump the brakes repeditivly it jumps the idel and sometimes will kill the motor. Also when i put it into grear if i dont catch the throughtal occasionally it will die.
And last of all when i push the gas it has a chuggy acceleration. I am leaning towards the egr but would greatly appreiciate any input.

Thanks

Originally Posted by fatmacsumo

please tell me your symptoms i can help you i have 24 years exp in the auto ind i need year make & model with engine size this message is for zoom

[J-Ri]

Welcome to AF

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