mikie1

working on my friends 1991 rag top corvette automatic 350 (none zr-1)
has 22,000 miles never been tuned the only thing that was changed when it was new is the computer because it failed to start.
THIS IS MY PROBLEM first the car starts cold runs alittle rich SECOND idles like crap THIRD get on the car and at 3000 rpm just boggs and at times will stall from the bogg (LIKE NO FUEL)
so i decided to do a complete tune up wires,plugs,cap,rotor,pcv valve,gas filter,air filter checked timing and still runs and boggs.
NEXT i put a fuel pressure gauge on the fuel injection rail idle pressure is about 34 pounds get on the car goes to 40 pounds so fuel is not the problem i changed the coil and computer sending switch still a problem
I REALLY NEED HELP!!!! ANY TAKERS?
ALSO no check engine on light on and its works i ordered a scanner for the car wont be here till next week just to see if there is a code and no light on.
thanks mike

bogus

gee... this is a stumper.

you didn't touch the O2s... but they are not the problem.

I would wonder if the injectors are over fueling, and/or the cats are toast.

mikie1

no did not touch the o-2s

mikie1

and i dont think its a cat problem the car reves right up no problem just seems like it shut right down from no fuel or no spark but like i said i had a gauge on the fuel rail
man i need a G-M COMPUTER GUY

MikeC4

you may want to pop your O2's out and see if they are covered with black carbon. This could foul them up and they could be reporting constant lean condition to computer, hence your injector pulse width may be too long creating rich condition.

Also pop out a plug or two and see if they are carbon fouled as well.

...just a thought

mikie1

will do thanks mike

mikie1

theguardian

A neighbor 3 doors up recently got a '91... I also have one. He stopped down to talk w/me about a similar problem... Seems he'd never been told to disconnect the little brown wire from the ECU... the EST? wire (Electronic Spark Control) prior to setting the engine timing. Once he disconnected, checked/set timing and reconnected the EST wire, it ran like a top.

Simple, but not something that's always obvious.

Hope this helps.

JM

bogus

There is a huge difference between an unloaded revving and a 3000 rpm bog under load...

mikie1

well i bought a new 02 and new plugs again had the car running about 10 minutes in the drive way and still not running correct still seeing a tad of black smoke from the pipes on idle shut it down pulled a plug and FAT as can be not wet just black .
now i lifted the intake went for the egr valve passage is clear and sucked on a hose and pulls the egr fine so now whats left map and air sensor in the intake not sure if the function of the air sensor in the intake would make this car run fat ANY IDEAS??????????

Cherry6speed

Are you certain fuel is not the problem? Fuel pressure may be good but, the injector pulse or fuel supply quantity may be waay off. You may have a sloppy, leaking injector, Bad throttle position sensor, O2 sensor flipping out, for example. Bog, sounds like inadequate fuel supply or lean condition. Diagnostic testing equipment will go a long way to solving this one. Hooking-up to a OBD-1 scan tool would be worth the $$. Real live data will determine the problem rather quickly. Tell us what you find

Cherry6speed

Oh yeah, Check for a Vacuum leak. the brake booster comes to mind. This will definately throw your ECM into Havoc.

mikie1

thanks rubyred i will get back a friend has a high dollar scanner and will check this out so i can stop the torcher and i will get back when we find the problem .
as far as fuel pressure i had the manual gauge hooked to the fuel rail and ran the car on the street and i could read the gauge even when it boggs still had 40 psi
but like your saying maybe the injector pulse dies.
very strange the car idles fat and then boggs at 3000 when under a full load and from a stop or roll it takes off and reves right up but always in the same place 3000 to 3200 rpm under load it will shut down and if you dont lift it will stall and start right back up and from what i can tell its lean when this happens not loading up and fat.