I need a good PCM mine went out and for now I'm using an external regulator but my transmission doesn't shift in low and won't shift in high but all gears in between works fine . Also my tach won't work and interior lights don't work either .

 

Send a PM to one of our members Oliver Foster, he usually is hanging out on the first gen side.

I am sure he has one laying around, great guy to work with as well.

 

Does anyone know what this could be ? What is wrong with my truck .

 

I'm not sure you need a pcm.. Maybe it's just the engine speed sensor on the front of the engine.

If that does not work the PCM assumes that the engine is at standstill, and won't give you a reading on the tachometer, will not energize the alternator, and will not give you overdrive or converter lock.

With this sensor shorted to ground you also lose governor pressure information and will have 2nd gear starts.

HTH

 

I have already replaced the crank sensor and checked voltage to alternator and no voltage but alternator checks out good also my transmission starts out in 2nd and my tach does not read . I searched every ground on the engine and gram retightened and also cleaned every terminal to every connector including the transmission. After doing all this I put an external regulator on my firewall and the alternator now charges at 16 volts which is plenty but I still have no tach but it does jump but soon as it cranks the tach goes back to 0 and the transmission still starts out it 2 nod and also will not shift into high gear . So my only option now is new PCM unless anyone has any other idea please let me know . Also I did set the Crank sensor at .045 and tried .050 and about everything in between .

 

Did you check for +5V on the crank sensor supply? Check for ground on sensor ground?

16V with the external regulator is much too high, you are cooking your batteries.

 

Thanks Alpine I'm going to check them in the morning I'll get back with y'all as soon as I check it .

 

Ok I have 5v coming to crank sensor and it is getting a good ground I don't know what else I can check but it still seems I need a PCM I wish I didn't though cause they are expensive.

 

Let me give a little history on this truck . I bought it with a blown 12 valve engine and I replaced it with a 1996 12 valve with 160,000 miles on it . But first the truck sat out in the weather with hood off of it for 4 months before I decided if I was gonna build or buy a used engine . So I'm sure the PCM got a little wet or even soaked at times but I didn't think about PCM being in the weather so this could have played a factor .

 

 

 

You could check the signal cable from the crank sensor to the PCM pin..

With the soaked PCM it makes sense now. I have seen a lot of PCMs being bought where the problem was in the wiring or with a sensor.

 

Before you get crazy, make sure the PCM isn't bringing in the ASD relay.

I would much more believe the weather corroded the relay terminals before I would bet it hurt the PCM, that seal is pretty well weatherproof.

If you don't have a factory service manual, let me suggest you get one now.

Dodge Factory Service Manuals - DODGE RAM FACTORY SERVICE MANUAL - CD ('98)

Cheapest 35 bucks you will ever spend and is absolutely invaluable for diagnosis.

Anyway, the PCM brings in the ASD relay ( ASD is Auto Shut Down ) and will also cause the conditions you describe.