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Head Scratcher? - 2001 3.9L - No Spark, No DTCs.


Anti Federalist
12-01-2008, 12:11 PM
Hello all, I've done a cursory search of the forum, hopefully I'm not repeat posting on my first shot out of the gate.

Here's what I've got:

2001 Dodge 1500 Ram Van, 3.9 L X code V-6.

Died on the road, with no warning. Checked for spark, no spark, checked back to the coil. Checked and/or replaced the coil (had this problem once before, no/weak spark = bad coil)the distributor timing pick up, and have a crankshaft position sensor to try as well.

Now, here's the thing, there are no DTCs in memory, no MIL warning, and just for ha - hahs I cranked it with the CPS disconnected. Still, no trouble codes came up, I had my reader hooked up while doing it and nothing.

So, now I'm leaning towards a PCM failure, even though everything else seems to functioning properly, pre-start routine, warning light check, fuel pump pressurization, etc.

Before I spring for a new/reman PCM (I hate being a "parts flinger") what might some of your thoughts be? Anybody run into this kind of problem before?

I've been fussing with this thing for three days now and I'm :banghead:

alloro
12-01-2008, 03:22 PM
Did you check for voltage (12v side) on the coil primaries while cranking? If so, what did it read, if anything?

By CPS is that C for crank or cam? A crank sensor will not throw a code in these vans even if it's bad or disconnected.

Anti Federalist
12-04-2008, 03:05 AM
Did you check for voltage (12v side) on the coil primaries while cranking? If so, what did it read, if anything?

By CPS is that C for crank or cam? A crank sensor will not throw a code in these vans even if it's bad or disconnected.

The C is for crankshaft. Thanks for that tip, I didn't realize that you wouldn't get a code for a bad CPS. That seems odd, since that's a vital part of the ignition/timing circuit. What was Mopar's reasoning for this?

Yes, I had 12v at the coil primary while cranking.

So, in the meantime, I "rebooted" the PCM, disconnecting the negative battery terminal, and, viola', started right up...but, only ran for about 5 minutes and died in the exact same manner. Subsequent repetitions of this process led to start up but shorter run times each time.

This was enough for me to point to a PCM failure.

I've ordered a reman PCM from Auto Computer Exchange, should be here on Friday, I'll be sure to post the results.

Thanks for the reply.

bratt
12-05-2008, 06:38 AM
could be a bad TDC sensor.
I dont know how but mine cracked on my 94 dodge ram van and the van had no spark. It took a long time to spot the cracked sensor.

I replaced the coil *didnt help*. I was suspecting the ECU but it was not the ecu.

If the check engine light comes on when you turn the key. that is an indication that the ecu is being read and is still good.
If the check engine light does not come on when you turn they key, that means the ecu is not reading; which can mean a bad ecu!

Anti Federalist
12-21-2008, 10:37 PM
Sorry it took so long to get back to this.

Alloro, thanks, you saved me a ton of money.

After finding out, through you, that the CPS won't throw a code if bad on this model, I held off on the reman PCM and focused in on the CPS.

Turned out it was intermittent thermal failure at the CPS. Disconnecting the CPS and rebooting the PCM would get a start and run for about five minutes, then shutdown.

Replaced the CPS, which never did throw a code, and problem solved.

Well, make that replace the CPS twice, the first CPS, Echelin brand from NAPA, had a very slight bend in the bracket, allowing the flywheel to score the sensor. A second Standard brand worked correctly. Luckily, NAPA took the first one back after I was able to display the incorrect angle compared to the OEM part.

Thanks again.

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