Thanks for the add, I bought an 88 model 4.9 that is baffling me. Cylinder 5 and 6 get no spark until I get the RPM's up. I've changed plugs,cap and rotor,wires,swapped the coil and module with a known good one and swapped the Hall pickup in the distributor with a known good one with no change.The original computer was laying in the seat,I tried it but it won't power the fuel pump.I ran the numbers on the ECM in the truck and it is a 2.3 Mustang unit and I also tried one I had from an 86 F150 with 302 and still did the same thing.I'm under the impression that any ECM should run on all six since it's receiving a signal from the module to fire but the fuel map will be off.I'm stumped on what to try next.

 

It sounds like you have the incorrect pcm for that motor. I would hit up a local picknpull and try to find the correct one; or order a new one from online

 

Yes it's definitely the wrong one,i'm sure at the least the fuel tables are screwed up due to the higher pressure of the 4.9 but it seems like it would spark correctly since it relies on the module to tell it when to fire.

 

rockauto.com sells them reasonably cheap.

 

i also concur that you have the wrong PCM. you need one specifically for the big six.

 

But do you think that would keep it from firing on all six cylinders until it builds some rpm?.It'll smooth out as if a fouled plug all of the sudden starts firing if I crank it up in first and second.

 

yes because the timing is all off.