MustangConvert

I have a 2001 Convertible. I swapped out the engine and trans with a 2004 wrecked Mustang with low miles. I did not switch out the PCM.

The engine starts and idles fine, but when the car goes above 30 mph, the transmission does not shifts properly and the car lurches and would not accelerate properly.

Someone told me that the PCM needed to be reflashed or switched out. So I swapped out the PCM with the 2004 wrecked car. But, the car now won't even starts. The engine cranks but no ignitions at all.

I put back to the original 2001 PCM, the car starts just fine but still has the same transmission shifting problem.

Does anyone has any idea on how to fix this? Do I need to switch out the PCM harness and how difficult is that? Thanks for any inputs.

MustangConvert

Is the smart (chipped) linked to the PCM? Is using the new 2004 PCM with the old 2001 (chip) key caused the non-ignition issue? Or is the harnesses wired different for 2001 and 2004?

03shadow

thats what i thought, did the theft light flash like crazy when you tried to start it with the other pcm?

is ford able to flash the pcm to stock 2001?

jwog666

you cant just switch the pcm's due to the pats antitheft. sounds like the wrecked trans you swapped into the vehicle may actually be wrecked. any codes?

MustangConvert

Confirmed with the dealer that the old key won't work with the new PCM and so the engine will crank but won't start because of the anti-theft system described above. They can reprogram the old key to work with the new PCM for $125. Will try that.

The trans does not seem to be damaged. Below 30 mph, the car drives fine, except that the speedometer is way off...showing like 80mph. Above 30 mph, the trans shifts up then down, and speedometer goes wild. Seems to be a communication problem. Several mechanics said the corresponding 2004 PCM must be used with the 2004 drive train. Made sense...since the 4 digits codes for 2001 and 2004 PCMs are different, TBX3 and CAX0 accordingly.

LilRoush

Did you stay with the same style trans? (Auto to auto swap?)
You need to retain the stock computer for the car - as posted - and not swap the 2004 computer in.

I'd say the trans you have is messed up or one of the sensors in the trans is shot. VSS would be the place to start since you mentioned the speed is reading way off.

jwog666

the transmission shifting problem may be caused by the vss reading so far off. if you are going 30 and the car thinks you are going 80 the trans will shift all sorts of crazy. this may be caused by a difference in speed sensors between the 2001 and 2004. if so, swapping the 2004 pcm in and programming the key should fix your concern. if not wiring or the trans and sensors are suspect.

RyansQuick6

The ignition and charging system are different between those years, it changed it 02.