This my first "problem post". I got a 98 ram 1500 4x2. with 125,000 miles. Mods include: M1 intake, K&N Cai, one size cooler plugs, Mallory coil, PCM re-cal by KRC perf., shorty headers, cat-back system. Problem is I have a problem with the engine running rough ( stumbling) 2 mins. into a cold start. All appicable sensors have been replaced. It does it also with a stock PCM. Afterwards it smooths out. Its been doing this before any mods were done. Also once in a while, at operating temp., It will stall and not start for a while. Or stall repeatedly...When i ran the cooler spark plugs, the cold start stumble disappeared and the stalling. Yesterday at work, I started it. It ran for 10 secs., stalled and wouldn't run afterwards. I checked the dist., timing, cam and crank sensors, all fine. I unplugged then plugged the hareness to the PCM and then it started without a problem.
Barring a compression test, would a head problem cause the cold start run-ability problem?? What would cause the stalling problem ?? Any input would be appreciated

 

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The coolant temp. sensor provides info to the pcm for injector pulse width, O2 open/closed loop mode, spark advance, among a few other things...find some specs if possible and ohm the sensor...there may be a chart somewhere that has the ohm specs for the corresponding ambient temperature. My first thought.

 

Now it got worse. The truck started, ran for a few minutes, then stalled. It would crank, but not run. I changed the cam and crank sensors about a year ago. I'am wondering if the crank sensor might've failed again. It did ran for a few seconds at a time then stalls again. Then it didn't want to run at all...I'am gonna grab my scanner and see what happens tomorrow......

 

Crank & cam sensors...they would be the 1st place i'd look. also make sure your fuel pressure is up around the 49psi spec you should ALWAYS hear the pump turn on for 2 seconds on each key on to the run position.

 

I did the scan and came up with a code for "Ign. circuit failure". WHich means there's a strong possibility that the PCM is shot to hell. Coil is not even 6 months old. Connections are good. When it dies, the coil stopped firing. Not a sensor issue, every sensor on the truck been replaced already...Need to do more research on it....

 

Just a thought before you start replacing expensive parts, try an isopropyl drygas. I have to put one in mine every couple months, it acts about like yours does. I have also fixed a few friends vehicles after they spent hundreds of dollars at the dealer to no avail.
Brian

 

Update....While getting the truck home, the CEL light came on also for a #1 injector circuit problem. First, I did the testing procedure outlined in the factory book for the Ign. coil circuit failure code. All the wiring checked out fine with a multimeter. The testing procedure tested wiring resistance between coil and pcm plug, coil itself, and voltage check from coil to ASD relay output. A friend also suggested a wiring issue. Once again, all checked ok. Last item on the flow chart was PCM replacement. I'am thinking possible driver circuit failure (thermal related) inside PCM....
Regarding the #1 injector problem, I replaced it with a "known" good injector that I kept is a spare. No good. I'll update more on this later...

 

ive had a temp sensor go bad...i couldnt find the suggested ohm reading for cold-hot .. but if you just stick it in a boiling pot of water and meter it that way and then cross reference it with a brand new one then you should have a good idea.. then again you could just swap it out and call it a day lol i think advanced had the gp sorensen brand for 6 bux when i got my SECOND one (they first sold me a diesel one... morons)

 

Update.....Performed same testing procedure on #1 fuel injector circuit. Everything checked out ok. A friend suggested a bad ground issue, which might be a good possibility. So, I'am gonna add more ground between battery, engine , and body. In the mean time, waiting on a second hand "good" PCM from local person. Still looks like a PCM failure, but gonna check every other possibility before buying one......

 

I did some research, apparently dodges had some issues with bad grounds. I decided to clean all my ground connections to the engine and frame. I added a ground from the battery to the body located on the passenger side firewall ( there's a ground strap going to the firewall to the engine). I added two more; one to the front radiator support and a second to the engine. There's a ground between the A/C and P/S pump on a stud. This ground is especially important, since it also grounds the ECM. I ran the engine, still no #1 injector activity. I used a graphing multimeter because it also shows a pattern that indicates when an injector is firing. Vaguely similar to what you see when checking Ign. coils.
I swapped out the original ECM with the spare I picked up. After 2 secs. of running, #1 starting to fire. I cleared all the codes, then let the engine run for an hour. Everything worked fine. I sprayed all the grounds I cleaned with an Ignition sealer spray I picked up at NAPA's. It coats everything with a shellac-like compound. I talked to a Master Tech friend of mine at a dodge dealership about my problem and what I did. He said its a strong possibility that due to a bad ground, that the #1 injector circuit burnt out in time. It would also explain why my Ign. coil would cut out, stall, and not re-start. It could also make the ECM run "hot", operating temp. wise. Which also was something I noticed while doing all of this. I'am gonna do local runs with my truck for a while, until i feel comfortable that the problems are fixed. As difficult as this was to diagnose, its not always a sensor crapping out that causes problems of this nature. I was guilty of thinking that. Knowing that I, ever time, already replaced all of them ruled out the possibility of a sensor failure in the first place. Knowing that, made it harder to figure out the cause of the problems to begin with. Its was a learning experience. I hope this helps any and all.......