My 19 year old son has swapped his 3.9 for a 5.9 in his 1998 Dakota. We have ran into a problem concerning his PCM. We took the PCM off the donor vehicle along with the wiring harness and many other parts. The engine would not start with the donor PCM, however it would start with the original PCM (V6 PCM). Ran but didn't seem quite right. ( We are assuming that the old PCM won't accomadate the 2 extra cylinders ) We have done a ton of reading and have a few questions.

1. Will a PCM from another Dakota work without reprogramming ?

2. Does it need to be the same year as his truck?

3. Can the V6 PCM be reprogrammed to work with the V8 wiring harness?

Thanks in advance to any help!

 

Welcome to the forum Sandman.

You need to match the options for the PCM.

What year was the donor engine from? Some years will swap and others won't. After '01 will not work - period. Dodge changed the bus communications.

No. You can't reprogram the PCM.

 

Ok. We found a PCM that will alow the motor to run. The new problem is that the transmission doesn't seem to be acting right. Doesn't seem to have any giddy up. Any suggestions?

 

Is this the original transmission, from the 3.9? Did you use the flexplate off of the 5.9? They balance different.

What's in do in manual low?

 

Yes it's the original, and yes I did change the flex plate. In low gear it doesn't seem the wind out.

 

Does the engine rev OK in neutral or park?

Check the throttle valve cable adjustment.

This is from a 2000 but it should be close:

THROTTLE VALVE CABLE ADJUSTMENT CHECK
(1) Turn ignition key to OFF position.
(2) Remove air cleaner.
(3) Slide cable off attachment stud on throttle body lever.
(4) Verify that throttle body lever is at curb idle position. Then verify that transmission throttle lever is also at idle (full forward) position.
(5) Compare position of cable end to attachment stud on throttle body lever:
(a) Cable end and attachment stud should be aligned (or centered on one another) to within 1 mm (0.039 in.) in either direction.
(b) If cable end and attachment stud are misaligned (off center), cable will have to be adjusted as described in following procedure.
(6) Reconnect cable end to attachment stud. Then with aid of a helper, observe movement of transmission throttle lever and lever on throttle body.
(a) If both levers move simultaneously from idle to half-throttle and back to idle position, adjustment is correct.
(b) If transmission throttle lever moves ahead of, or lags behind throttle body lever, cable adjustment will be necessary. Or, if throttle body lever prevents transmission lever from returning to closed position, cable adjustment will be necessary.