I hope you guys will be able to help me out because I'm at a complete loss.  So i have 2002 dodge 2500 with 174k and it has a rough idle when the motor is at operating temp.  The truck idles just fine when it is cold, only when it is hot does it start idling like s**t.  It almost sounds like it is missing, but I don't think it has a miss,  I don't know what else there is to replace on this thing, everything is all new.  This is a daily driven truck, it does not have a programmer on it, just 100HP injectors, 60/67/12 FPI turbo, 4in exhaust, BHAF, gauges.  Here is a list of everything that have been done to the truck in the last 3k miles and it has not solved the problem.  

New Vp44 about 1k miles ago

Air dog 100GPH about 500 miles ago

New MAP sensor

New IAT sensor 

New CPS

New injectors (100hp DDP)

New connector tubes

New batteries

All new battery cables( cleaned and checked all grounds)

New alternator

 

Please let me know if you have any ideas about what this could be, just need ideas about where to start next.... APPS? ECM? Dodge wiring? 

 

Thanks,

Did you have any trouble codes that were pointing to any issues?

The only codes that i have seen, pointed to a bad VP, so it was replaced, i don't remember what they were. There was one code that had something to do with BUS communication, but don't remember the number. Since then, there has not been any codes. 

i remember now, it had a P1694 code.

 

The more i think about it, could it be a "heat soak" issue with something in the ECM? 

more brain storming here.. could the keyway be off on the VP, causing the timing to be off, but wouldn't it idle bad when cold too....or does the VP change timing when the motor is cold? 

The VP timing does change when cold.

 

Sure sounds like an electrical issue, but before sending off an ECM I'd make sure most other possibilities have been exhausted.

 

Have you checked valve lash? Since you have problems with it when hot, maybe one or more cylinders were set too tight.

 

Any odd smoke or other clues?

I adjusted the valve lash when I installed the injectors and set to cummins specs.  There is some slight idle haze when cols started, but that's normal. Truck runs great, plenty of power and go-go, just a crappy idle. 

13 hours ago, Krlspokane12 said:

only when it is hot does it start idling like s**t.  It almost sounds like it is missing,

 

• Injectors are not properly pop tested.
• Injectors installed incorrectly causing pressure leaks in the head. 

When you installed the injectors what did you tighten first the cross over tube or the injector hold down cap?

 

Correct Answer is Crossover Tubes always first light seat the tubes into the injectors before pinning the injector down with the hold down cap. Once you tightened the hold down cap first then the injector can't self center to make a good seal on the cross over tube.

 

Did you have the injectors pop tested and flow matched?

 

Good idea to have them all tested and flow match for that group of 6 injectors instead of 6 random injectors toss in a box and not verified.

 

As for misfire hot is a sign the pop pressure is typically too low or there is high pressure leak inside the head from installing incorrectly. 

Injectors would be my first  thought also. I had the same miss you speak of many years back and it was injectors. DDP injectors are known to be hot and smokey and its possible one may have been popped improperly, happens to the best of folks. I darn sure would not just replace the ECM hoping that fixes it. 

 

I wasn't thinking it could be injectors since it did the same thing before i put these in.  In regards to the injectors, i had them all pop tested and flow checked prior to install.  This is the procedure i followed when installing the injectors.

 

Once the injector was in the hole, I tightened the hold down to 40in lbs to seat the injector and then backed off the bolt.  Then i inserted the connector tube until i heard a "click", and then double checked the tube was seated all the way.  Then the hold down was retorqued to 89 in lbs.  

 

So is it incorrect to seat the injector first and back off the retainer? 

 

I also used new Bosch connector tubes when i installed the injectors. 

Another thing, it only idles like crap when its in park.  If there is any load on the engine, the idle smooths out.  

1 hour ago, Krlspokane12 said:

Another thing, it only idles like crap when its in park.  If there is any load on the engine, the idle smooths out. 

 

Now that's a little gold nugget of information

Is neutral the same?

yes, neutral is the same as park.

I noticed that when in gear the tach is dead steady at 800rpms, but in park or neutral it bounces between 800 and 900rmp,

I was thinking ECM because a local company was in it a few months back.  Something happened with the ECM when the VP failed.  I'm not sure what they fixed.  Also, it started running better after i had it re-flashed by dodge 2wks ago, then started running crappy again.  So not sure if that is related, but ive heard stories about these ECM's doing weird stuff after some one has been in them...just more food for thought. Also today it started idling funky while i was sitting at a stop light, not as bad as when it is in park, but off enough to notice.. 

ECM is in control of idle rpm when apps is at 0

So it might be the ECM or maybe a bad APPS?  

 

I spoke with a mechanic I know and he said it might just be a s**t reman VP or the wrong VP for the truck or the keyway was reversed.. i dont know enough about it.  But he said that it might be why it smokes so much and the idle is all funky.

 

This thread is like Perry Mason or Columbo, but for 2nd Gen, 24V guys.

I'm sorry you're the victim!

LOL, you have no idea man, i appreciate every ones input, but i cant for the life of me figure this out.  Its getting old loading up the "parts cannon" and just throwing money at it.  I dont know what else there is to replace. 

Have you put an ohm meter (volt meter) on the APPS to see if it's smooth (when hot)? How about checking or replacing temperature sensor? ECM cares about temp, and sensors can be affected by temperature (weak solder joints, etc)

 

Just throwing stuff against the wall to see what might stick or jog loose another idea from someone else.

I checked the APPS a few weeks back and it was out of spec, so i reset to the specs listed on it.  So, its funny that you mentioned temp sensor, my temp gauge is messed up, it reads 190 when cold and 220 when warm, but was 192 from OBD.. more mysteries. 

 

So here's a thought, could I hot wire the VP and see if that changes the idle?  Wouldn't that eliminate the ECM from being the issue? 

3 minutes ago, Krlspokane12 said:

So here's a thought, could I hot wire the VP and see if that changes the idle?  Wouldn't that eliminate the ECM from being the issue? 

Yes I believe so. 

It sounds like you got electrical gremlins, maybe some ground slices are weak, losing 5 volt reference. Some models had issues with oil senders shorting out internally and messing with 5 volt reference so other sensors go nuts. Not sure on years from top of my head but worth looking into. If you did WT mod you got most of ground splices, but there is more, in wiring harness close to ecm there is a splice that I need to still get done myself and by passenger battery few quick connects that could lose connection. 

I'm just throwing ideas out, shouldn't cost much but time to get done.