need help from gm mechanic

[boatguy19]

hello all, i have a 95 chevy van g20 with a 350 engine. the problem is when i start the truck 80% of the time it runs real ruff and blows black smoke out the exhaust until it warms up then it runs great. i had to put a new converter and oxyagin censor on cause it burnt it up a couple years ago. havent had a problem with that part since. forgot to mention i had to put a new ecm in it about five years ago,i take good care of my stuff as i can not afford a new truck at all, only once in awhile does the engine light come on and only for a couple of seconds and thats it. im stumped on this one i checked the egr valve and thats ok also checked all the wiring and nothing seems out of place not loose or corroded, like i said when it warms up it runs great and some days it starts up with no problem at all. new plugs and new gm wires and new gas cap, no difference. thanks for any help in advance i appreciate it.

 

[TilliamWe]

Re: need help from gm mechanic

Since the light does light up from time to time, go to Autozone and see if they can read the codes that are there. That might give you an idea.
It could be an Idle Air Control issue. Or, since that TBI doesn't have a choke, it has to richen the fuel at start up somehow. I don't know exactly how it does it, but I'll bet that's your problem.

 

[puddle jumper]

Re: need help from gm mechanic

My guess would be the coolant temp sensor is reading wrong. Its telling the ecm that its colder than it really is. Now saying that your MAP sensor may also have a problem i have seen where the vacuum hose will freeze to the MAP sensor causing the same run problem on till it thaws out.
Just a guess i also would get the codes read ,it should help point you in the right direction.

 

[puddle jumper]

Re: need help from gm mechanic

One more thing, check you throttle body to see if it leaking fuel from the gaskets or injector o'rings. Take your air cleaner off and turn you key to the run position . Then look for any leeks around the injectors.
PS that's if you have a thoughtal body and not multi port injection.

 

[MrBigStuff]

Re: need help from gm mechanic

The throttle body base gaskets are known to develop leaks over time and it can act just like this. Try spraying some carb cleaner around the TB base gasket when it's cold and acting up. If it smooths out, you found the problem. They're cheap and easy to replace. Might just want to try it regardless.

 

[flashback]

Re: need help from gm mechanic

black smoke = rich mix..too much fuel....thats all I know...

 

[guy74]

Re: need help from gm mechanic

I agree with puddle jumper on the coolant temp sensor. Also the throttle position sensor may not be reading that the throttle is closed. It would seem that the problem goes away once the ecu goes into closed loop operation, and can read the rich condition, and correct for it. The engine uses fixed values to maintain idle and run until it reaches operating temp, then the system goes into closed loop operation where it gets feedback from the O2 sensor(s) and corrects the rich condition. It might be hard to get the codes out of it since it is an OBD1 computer system. Those old OBD1 systems somtimes require checking componants one by one with a multimeter. Thats how I keep my '93 Poniac Trans Am going.

 

[JCF350]

Re: need help from gm mechanic

See if your data link connector is OBD or OBDII. If OBD you can pull your owns codes with a paper clip or jumper wire. OBDII requires a scanner.

For OBD codes.
http://www.troublecodes.net/GM/

For OBDII codes. See the "zonies" for free scan.

 

[dolluper]

Re: need help from gm mechanic

Getting the code would help but some fast checks you can do Check the MAF [mass air flow] that all the hosing is tight not leaking and give it a couple of taps with the wooden end of hammer ,vehicle will stumble if right.Check injectors if TB just turn key, don't start if you see fuel at either injector it's leaking replace,fuel rail type remove rail out of intake only insept nozzels ,same thing turn key on if fuel at any injector it's leaking replace Also check fuel pressure regulator pull vac hose off if fuel present it's bad Or do a fuel preesure test to determine if regulator diaphragm is leaking

 

[Benny1963]

Re: need help from gm mechanic

have seen that prob a few times .usually the throttle position sensor
if loads up bad at idle .i willsend false sig and add to much gas
god luck benny

 

[boatguy19]

Re: need help from gm mechanic

i will look at some of the things suggested here, i cant look at it till sunday want to get it fixed as it is driving me crazy. thanks for all your help so far i will post back after i look at it.

 

[dolluper]

Re: need help from gm mechanic

One thing I forgot to ask has this been your trouble since you changed the computer if so you may have the wrong PROM [chip}

 

[dolluper]

Re: need help from gm mechanic

It's Monday did you pull the codes or find anything??