Originally Posted by Skybow23@gamil.com
I have a 87 gmc Jimmy and I just put a new motor in it. It's a 350 not sure the year. But it's bored over 60 and rv pulling cam. Forged flat top pistons and full release values, e five heads. Not sure about how big the cam is tho, but I am losing oil pressure and it wants to die when I am at idle and when I give it a real quick shot of gas, at idle. It Boggs down and if I do that and stay on the gas it back fires and shoots fire out the tbi. And I have good pressure in all cylinders. It dies down when it gets hot. When I drive it and come to a stop I have to keep on the gas at a stop light. I changed the oil sending unit. And has a new pump put it in when I put the motor in, well before i put it in. But I am just lost. I don't know what to do. Do I need to make it a carb motor or what??
TBI is very sensitive to manifold vacuum as a relationship to throttle position and RPM. This is contained in a map of relationships within the computer. Anything that changes these relationships in the physical world cannot be resolved by the computer in its logical world without a new map of these relationships.
The TBI now needs to feed a larger size engine with a cam having more duration and lift than what the computer was mapped to. These and the other changes you did require a new chip with a new map see these people: http://www.tbichips.com