Hey all, new to the forums post wise and need some help. So, I have a customers 97 Dodge B3500 van with the 5.9L, customer called and said it cranks but wont start. We started with the simple stuff, checked the under hood fuses, and also made sure we could hear the fuel pump running, which it does. So we moved to spark, which we pulled a spark plug and noticed we had no spark, so we pulled the coil wire off the distributor and we had no spark there as well. Checked the voltage at the coil, and no power going to the coil. So we decided to plug in our scanner- we have a nice tablet Launch scanner that will run full diagnostics, but wouldn't recognize the van, so we thought maybe it just wasn't compatible with the van, so we plugged in our generic bluepoint scanner as well, and it kept saying it could not establish a connection with the PCM through the OBD port, which is a problem I've never ran into, and stumped me. I will say I didn't check the in cab fuses super well(I did look) but I did not see any bad ones, or any that are specifically labeled for the port, and there isn't anything else not working. So to shorten heres the symptoms:
No spark
Scanner cannot communicate with OBD Port/PCM
No lights in the dash(CEL or the other smaller round lights by the speedo/odo) come on when the key is turned on for a bulb test, or to indicate there is any codes, so right now I have no way of knowing if there is any codes.
So basically I just need some direction on what to check, some possible causes/solutions, etc. because it is beyond me. I should also note its not my van and so I'm hoping to get lots of ideas/what to check since I don't have the van accessible at all times. Thanks for any help!

 

You will only see power at the coil for about three seconds at initial key on, after that, the PCM won't energize the ASD relay, unless it sees the engine turning. (crank sensor)

I *think* there is a fuse in the inside fuse block that also powers the pcm/obd port. Can't recall which pin it is.

 

Yeah, I checked the the voltage at the coil while spinning the engine, which is what makes me think there is another issue causing the van not to fire. But the problem is, I can't connect to the PCM through the OBDII reader to see if there is codes or any other issues, heck the CEL never illuminates, even when just turning the key on to run so I'm not even sure where to start, or what the issue is to cause either of my scanners to not be able to connect to the PCM to see any data whatsoever. Its got me caught between a sensor issue, or a PCM error of some kind.

 

Probably don't have another PCM layin' about you can try.....

You can find wiring diagrams for the van here. See what does what on the obd port, see if anything is missing/obvious. Also verify you are getting power TO the pcm.......

 

I wish I had an extra PCM lol. I think I’m going back out there today if the rain subsides so I’ll see what I can find. Thanks for the info!

 

Alright so I thought I would share what I found. Huge shoutout to HeyYou, the site you linked for wiring diagrams was a HUGE help! So, I started by checking the red/white wire that is fused power going into the PCM, in which it was feeding the power into the PCM. Next I checked to see if the coil driver wire(solid grey wire) coming out of the PCM, and had no power coming from that wire to the coil. Next I checked to see if the crankshaft position sensor was sending its voltage signal to the PCM(grey/black wire, next to the solid grey wire), and it was not sending any voltage with the engine spinning. I then discovered it also had a 5 volt supply wire going into the crank sensor to power it coming out of the PCM, which I believe was violet with a white stripe, and it had no voltage coming from the PCM to power the crank sensor. So essentially, the PCM was not powering the crank sensor, so in turn it was not sending a signal back to the PCM, so the PCM was not telling the coil to fire, so the coil had no power, thus would crank but had 0 spark. I also checked the power wire(pink wire) for the data link connector(OBDII port) and I had no power there as well. Going to get a new PCM ordered and hopefully get this van going again for the customer! I have to add I usually dont like electrical, but that website had such nice & clear and easy to read diagrams, so it was actually kinda fun figuring out how to read the diagrams and tracing wires- the PCM being easily accessible on this van helped alot with that as well. I hope down the line this forum helps someone!

 

Awesome. Let us know what happens.