Hot Rod Forum banner

1 - 4 of 4 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
I have a Chevy 350 TBI in a p/u truck that has set up for about 3 months. When I started it the motor will run fine for 3 - 5 minutes then begin to run rough and cut off. It appears to run very rich and gray black smoke comes out of the tailpipe. I have checked the gas tank, sending unit, fuel filter, etc. Once the motor is hot it does not want to start again. After the engine is cool it will start again and run well for 3 -5 minutes and shut down again. The motor will turn over once it is hot but will not fire off.

The spark is good and I just recently put in new plugs, new distributor cap and button. I thought it might be the computer and swap it out but have the same problem. Someone told me it could be the map sensor. The check engine light is on from the get go once I try starting it. Is there any way to test the map sensor?

Can someone offer any other assistance as I claim to be no mechanic (but am not afraid to play with it). Thanks......jack
 

·
Registered
Joined
·
36 Posts
TBI motor question

Jack,
The map sensor can be checked . It is used to monitor your manifold vacuum.If it has no vac. as in a broken hose from the manifold etc. it is going to run rich .It thinks it is running in full throttle so it needs more fuel.You can take a vacuum pump and apply 15-18 in of vac. to the MAP and see if it will stay running.If it does then this is possibly the issue.If the check engine light is on then the ECM should have a code stored to give you the direction needed for repairs.Another thing to look at is the EGR it could be stuck open causing a vac. leak .Also the TBI gasket is know to fail .It will usually decay around the front closeing off the PCV vacuum port .You could spray some carb clean around the TBI and see if it smoothes out.Good Luck
 

·
Registered
Joined
·
6 Posts
Discussion Starter #3
Thanks a great deal for the information. I will try these things and let you know. Thanks again for your time and help as it is greatly appreciated.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #4
Thanks a great deal for the information. I will try these things and let you know. Thanks again for your time and help as it is greatly appreciated.
 
1 - 4 of 4 Posts
Top