Need help with 1987 Chevy 350 TBI

[Iceman]

This is my sons truck.
It is a 1987 Chevy 350 TBI.The engine only has about 20,000 miles since rebuild.The truck has about 200,000 miles.
The problem it is running real rich.It blows black smoke.Idles high then idles low.It acts like it is flooded.Have to hold it on the floor to start.He has checked for vaccum leaks,tps,o2 and timing.It is not putting out any codes.
Help!
Anyone know of any good TBI boards?

 

[G-boz]

you can try some of the F-body boards www.thirdgen.org www.transamgta.com

 

[Scott King]

A friend of mine has an'88 GMC that ran like that. The vacuum line to the MAP sensor was plugged with carbon. It caused a rich condition. No codes ever set because the sensor hadn't failed, it just thought you had it floored 'cause of the low vac signal. Other things to check would be fuel pressure and check for leaking injectors.

 

[myclone]

High then low idle is classic MAP sensor, MAP sensor vacuum supply line, or other vacuum leak symptoms.

Make sure the vacuum hose going to the MAP has been replaced. The stock GM stuff deteriorates after a while from under hood heat giving the symptoms of a vacuum leak but they still look "ok".

The MAP sensor itself could be going bad. It may not be "bad enough" to throw a code (yet) but out of range enough to cause the engine to run rich none the less.

Check the TPS while youre under the hood too to make sure it hasnt developed a "bad spot" which is sending an open throttle signal to the ECM even though the trottle is closed. With 200k on the truck Id say the TPS is getting a little worn. Especially in the first 1/3 of its movement as thats prolly where 90% of those 200k miles were spent (unless you do a LOT of WOT driving. ).

 

[Iceman]

Thanks guys I will have him read this!

 

[steve hughes]

Not only check the vacuum line to the map but also the port in the throttle body for carbon. The fuel pressure regulator in the tbi could also be bad or leaking.