dantheman92

We have recently perfomred a motor swap on a 94' mustang, froma v6 to a v8 5.0 HO engine. We have the 5.0 wiring harness, computer, gauges, the whole 9 yards...besides a transmission. This car has an auto transmission by the way. but to the point, we have installed everything correctly and have the new computer hooked up, however the engine will not run at 100% efficiency, in fact it barely runs at all, but the trans shifts. With the original computer we bought with the engine built for a 5 speed the engine runs great but the transmission will not shift.

This new computer is manufactured for the V8 engine, but will not mae it run right. What could be the problem?

projectresto83

Many things can be the issue. What do you mean by it barely runs? What does it do? Timing is usually the first thing that gets messed up with engine work. What cam is in the motor?

AdderMk2

lol... transmission wont shift with a 5 speed computer.

maybe thats because the transmission is controlled by the computer.... DUR

You need to go back in and verify your wiring. There are changes to the harness that are required to run an auto trans. You have likely fried the ECM by not having stuff hooked up correctly.

Blown408

Absolutely true. Get a schematic book out. Harnesses are wired differently from an automatic to a manual. If the car you got all the harnesses from was a manual and you are trying to use the harness for an automatic then you are going to have to redo some of the wiring. A Chiltons book will give you correct wiring diagrams. Or just google the wiring diagrams and print them out and compare.

02WhiteGTVert

Fail. What did the computer come out of?