91 Silverado TBI problems

[texastruckjunky]

I have a 91 Chevy 1500 with the 350 700r4 combo. having problem with black smoke coming from the exhaust. Pipes are cut off after the muffler so it's leaving a black residue all over the rear end. But that's not the problem, truck spits, runs rough and dies, it's hard to start after words. If I let it sit for 30 to 45 minutes it will start. It runs for a little while then dies again. I've changed the fuel filter, fuel pump and rebuilt the TBI. Now black smoke is coming from the exhaust. And it's even harder to start. I've done some research on the problem and from what I'm understanding, it could be a O2 sensor or the MAP sensor. Any help would be appreciated. Thanks.

[edhtrd71]

Hey, it sounds like its running really rich, which you probably already know. Definitely can be the o2 sensor or map sensor. It could also be the coolant temp sensor also. Quick checks you can make are checking the connections and related wiring to those sensors. Make sure the map sensor vacuum hose running from the throttle body isn't cracked and leaking. After that I would invest in a data reader so you can see what the sensors are doing. Also I have seen ignition modules cause funky drive ability issues on those. Good luck.

[edhtrd71]

Hey, it sounds like its running really rich, which you probably already know. Definitely can be the o2 sensor or map sensor. It could also be the coolant temp sensor also. Quick checks you can make are checking the connections and related wiring to those sensors. Make sure the map sensor vacuum hose running from the throttle body isn't cracked and leaking. After that I would invest in a data reader so you can see what the sensors are doing. Also I have seen ignition modules cause funky drive ability issues on those. Good luck.

[88Ironduke]

91 TBI should have an ALDL port to check for codes. Granted its ODBI but if the map or O2 sensor is dead it will flash out a code. Make sure the vacuum line for the map sensor hasn't cracked and isnt leaking. Another fail that's hard to find is failing fuel pump relay, the old ones can quickly cycle on/off causing all kinds of havoc. It is the same as the AC relay and can swapped to eliminate systems.

Good luck.