Ok, that basically eliminates the fuel. So now the only thing left is spark. Gotta be something electrical. I'm wondering about throttle position, and, mass airflow, and MAP sensors... Maybe a module in the distributor? Did you change the cap and rotor?

Try unplugging the mass airflow sensor and running it. If it gets worse, it's not that. If it gets better or stays the same, it might be something to try. Don't know how to test anything else...

 

I did the cap and rotor, throttle position, plugs, wires, idle control motor. Haven't done mass ariflow or map sensors. I will try those next...

 

Ok. i unplugged the map sensor and the truck stalled. I looked up in the Hanyes manual how to test it and I performed all the tests. The voltage was reading quite high - much higher than it should, indicating low vacuum in the truck. I performed a vacuum test and when it starts doing the idle problem, it drops from about 20 pounds of vacuum to about 10. The map sensor is reflecting this change properly.

So... what's making my vacuum drop suddenly? As soon as the idle returns to normal, the vacuum is back to normal. I know there is no vacuum leak. I tested the entire system. Even after the truck is off for a few minutes the vacuum holds.

Any next steps? Thanks.

 

what do you mean when you say "when the truck is off, the vacuum holds"? when the motor is off, there should be no vacuum. 1st thing that comes to mind is the cad unit for the 4x4 engagement, I've heard of there being problems with vacuum leaks on the lines going down to the CAD unit. have a look at that.

Does anyone know if there are any vacuum switches on these motors? I don't recall seeing any when I've had mine torn down. I'm wondering if there is a vacuum leak on the other side of one of these switches and when it's being engaged when cold, we're getting a vacuum leak... (not even sure I have the same problem as you but it sounds like it... stumbling when warming up).

 

The truck was off. I traces some vacuum lines to find a good test port - the cruise control T. I unplugged the cruise control, and PSSSSSSSSSsssss..... Vacuum pressure released. The engine was off, and the vacuum was still present.

No vacuum leaks anywhere, at least as far as I can tell while the engine is off, and when the engine is on running smoothly.

Um... i was told today to check the EGR (valve and controller)? Could that be affecting it?

Thanks.

 

For what its worth, according to my Chiltons manual, there is NO EGR fitted to the 5.9L Gas engine (nor have I seen one on the engine anywhere). Only the Diesels have an EGR system. Someone asked about vacuum switches. The only one that comes to mind is the solenoid for the Evap Canister (fuel System). Now I'm wondering if something is hinky with the solenoid or the canister, but that's a Wild A$$ Guess.

 

couple of other threads that are similar...

Idle problems #1
Idle problems #2

I didnt get a chance to mess with my truck over the weekend so I have nothing to add... mine still acts up but it's not predictable like I'd hoped.

 

Looks like they have been having quite a problem with these. I'll take a look at mine tomorrow. I've got a couple other things to look at too. I WILL SOLVE THIS PROBLEM.......

 

Yah, now that you mention it, I've had vacuum problems like this before on a couple other rigs (Non-mopar). Turned out a couple lines were dry rotted. If they got in just the right position the motor would lose vacuum and run like hell, then it would fix itself if the line would shift just a little bit. I replaced all the vacuum lines and everything was hunky dorey after that.

 

Checked everything we've talked about. I looked the entire vacuum system over. I took out the hanyes manual and double checked everything. I checked the EVAP system. No EGR system on the truck. There is nothing mechanically wrong with the truck. I'm guessing the problem is going to be a computer problem. I didn't see any recalls or anything related to the problem, but I did see some TSB's for it, and I see that one of them is a computer upgrade. I'm thinking that's what it is going to be...

Any thoughts?

Thanks.