Hi,
Hoping someone can help with this one. I have a 1996 low milege Ram 1500 in mint condition. It not my daily driver but but as such I like to start it often to keep it ready. Yesterday with temperatures in the upper teens in Indy, I went out early in the morning to start it. Although I installed a new batterly last fall it was dead and required a jump. After attaching the cables it cranked over and started immediately. I let it run for about 10 minutes and thenanddecided to drive it to where I purchased the battery to get it exchanged. As I have found from past expirience after a dead battery it didn't want to idle and as I was backing out of the driveway and it died. Apparently the battery was toast as it didn't want to crank over so I re-connected the jumper cables and attempted to re-start it. It turned over very fast but wouldn't even fire let alone start. After cranking it over for several minutes I decided to do some troubleshooting. I pulled a spark plug to see if by chance it was wet indicating the engine was flooded and it was dry. I then got my tester to see if it was getting spark and to my surprise, there was no spark at all. The other thing I noticed was that my engine light wasn't coming on when I would turn the ignition on. I pulled out my INNOVA 3100 OBDII code reader and to my surprise it wouldn't connect up to the computer and keep trying to read it and everytime would say ERROR. Just to make sure that there wasn't a problem with my code reader I plugged it into one of my other vehicles and it worked fine. I then checked all of my fuses in the cab and under the hood in the power distribution box and all were good as tested by a Fluke meter. I pulled a wiring diagram off the web and checked to make sure the 12 vdc + and - were present on the Powertrain Control Module (PCM) and they were. Next I checked and found that the Auto Shutdown Relay in the under hood power distribution box was not pulling in and according to the wiring diagram is suppose to anytime the ignition switch is in the on or start position. In fact, according to the diagram, if the Auto Shutdown Relay is not pulled in the fuel pump will not run and no power is available for the fuel injectors and oxygen sensors amoung other things. According to the wiring diagram, the PCM appears to use sinking instead of sourcing in that it's output circuits to the various controlled items switch on the common side.I tested the coil of the Auto Shutdown Relay and it appeared ok with an impedance of about 64K but just in case I switched it around witht the fuel pump relay and that made no difference, it still wouldn't pull in. I found a wiring diagram of the Auto Shutdown Relay and socket and checked and when the ignition switch was turned on 12 vdc positive was correctly switched to the relay coil so it would appear that the problem is on the other side of the coil which would normally be sinked through the PCM. I also was able to verify that the relay had 12 vdc positive to its contacts. Since the relay wouldn't pull in I jumpered the contact switching 12 vdc positive to the fuel pump relay and and fuel injectors but it still wouldn'nt start,indicating that the problem was the PCM was not sinking the other side of these devices to 12 vdc common as it should.

From what I've seen so far coupled with the fact the PCM won't communicate with my OBDII code reader tells me that the PCM appears to have gone bad. I am looking for someone who can either confirm my diagnosis or let me know if there is other things I need to check prior to condemming the PCM which I have found is a very expensive device to replace.
Thanks in advance for your feedback.

 

Don't these trucks not run right with a dead battery? I thought I read of others having them just not run right with a dead battery. I'd put a fresh battery in it and see what happens.

 

I read on some post that a person got a used PCM from a junk yard for around $25.

 

never personally experienced this, but i've heard from others it just flat won't run with a dead battery, unlike other vehicles where you just jump 'em and go. put a charger on it and either get it charged up enough to hold a charge, or swap the battery with a good one. i'll bet it does a lot better.

 

I installed a new battery and still no fuel or spark. Help, now what!

 

Is the coil prodcuing a spark?

You can sub out a PCM from another truck provided a few things are the same. This will let you at least check junk yards.

1. Same model year
2. Same engine size (5.2 or 5.9)
3. correct tranny (either manual or auto)
4. same security group (power locks burgler alarm etc.)

I think that's it but you can ask Silver_Dodge to be sure as I know he's used a used one before with success.

 

Thats correct.....If you kill your battery and then jump it, you need to hold your foot at 2000RPMS for about 5-10 minutes or the truck just stalls.....My truck does it along with my 2 friends who have 1500s....Or you can give it WOT run and that works also.

 

Thanks Aim4squirrels:

No spark from the distributor either. No engine light when the ignition is turned on, which I have been told is a classic symtom of a computer gone bad. I'll ask silver_dodge about his expirience replacing the PCM with a used one.

Thanks again.

 

No, not the distributor, I'm speaking of the coil itself. It may very well be the PCM, but it could be the coil and if that's the case it's much easier to procure a replacement coil than a replacement PCM.

 

You're right, I need to check for spark at the coil. I'll do that tonight. Thanks again.