6 degrees outside, but the truck has been in the 70 degree shop for 3 days today makes day 4. This truck will run for 20 or 30 minutes on the first start of the day. will run longer if it is in the 6 degree weather. Then after each consecutive start the run time gets shorter.

 

I would be checking the map sensor and the intake air sensor.These 2 work in conjunction with each other.You obviously know that the 14 lbs of boost at idle isnt possible.

 

If I unplug the map sensor my boost drops to 0, if I run the truck with the map unpluged there is no change.

 

As it's a "temp" related thing, what about the IAT?

 

Ok I am getting close here I think. I took my lab scope and the DRB3 and hooked up a low amp probe to the FCA and monitored the voltage on channel 2 of the scope. At idle this truck is pulling about 1.5 amps and my voltage is switching from 8.5 to zero. When the truck dies the voltage gets pulled down to 0 and the amps go to 0 also. I am leaning toward this new ECM being defective. I am going to play with the FCA that came off of this truck tomorrow. If it works like I think it works then the ECM is bad. I will keep you all posted.

 

I agree it could be an ECM, golden rule is when there are no faults indicated by the computer, it's usually the computer that's at fault as it doesn't know there is something wrong. However I think the ECM sends out a low voltage signal to various sensors, they modify the voltage and send it back to the ECM. The MAP and IAT are two of these, the latter being the one for temperature. If it was sending a false indication (one that was too hot) back to the ECM, the ECM would fuel for that temp, possibly to the point of not enough fuel to keep running.

 

Here is what I am thinking. I have 14 # of boost when the truck is not even running. I tried another map sensor and I still have 14# of boost. I took the old FCA and tested it with a 9 volt battery and it works. I checked the wiring for both of these and it is fine. I put a lab scope on the FCA circuit one channel with a low amp probe and the second channel monitoring voltage to the FCA. When the truck dies the computer is pulling the FCA circuit to ground and this shuts off the fuel to the injection pump and the truck shuts off. When I turn the key on it takes a long time for the ECM to energize the FCA circuit once it gets hot. I think the computer is miss reading the map sensor and when the circuit for the FCA gets hot it is failing. If the rebuilder puts this in a test stand it will pass because cold this truck will run for 30 or 40 minutes. I will have another computer here in the morning. I should know by tomorrow night if I was right.
Thanks
Eric

 

let us know what you find out

 

dumb q? but what's an FCA?

it sounds like you have put your voltage Meter on the fuel pump, and you are seeing the ECM remove the voltage for the fuel pump,

so the pump quits running and it dies.

if the MAP sensor is not bad, and you are showing 14lbs boost, and the FCA (?) is functional, then it sounds like a software problem.

would a Bullydog or Smarty not re-write the ECM?
can a Bully dog dealer still do the "3 day free trail" like they used to?

side note on what i thought about after readin your first post, was put your multimeter across the fuel pump (like you are taking a resistance reading of it's windings)

set it to resistance (unplug harness) and check the windings are good
and set it to voltage, and plug it in, energize, and watch the voltage drop across the pump.

if the voltage supplied is staying the same (i am assuming you checked this prior, due to the detail in your posts)
but the voltage dropped ACROSS the Fuel pump goes up as it runs (as it gets hotter)
then the internal windings could be bad
(the old chevy starters used to heat soak, and the armature would expand and contact the case)

dunno, but hth?

 

FCA is the Fuel Control Actuator. It determines how much fuel goes into the injection pump. The more fuel the more pressure. My thoughts were that the ecm is shutting off the fuel with the FCA and with no fuel the pressure drops until the truck quits. To confirm this I tried testing the old FCA that came off of this truck and it works, then I went to the map sensor and checked the wiring and replaced the map sensor and it still reads 14 lbs at all times. So my thought was that the ecm was reading it wrong. I replaced the ecm today and the replacement made NO difference. I still have 14 lbs of boost and it still quits when the fuel pressure drops off. The only computer that Chrysler sells for this is a reman. If they put either one of these in a test bench they will test good because it will take 30 minutes or more on a cold start to fail. If they had a bad bunch of these then I will go nuts trying to fix this. I find this unlikely because no one else seems to have this problem. The good news is I am learning a lot about these common rail trucks and I also learned that I will keep my VP44 truck forever. Changing a VP44 is a piece of cake compared to these common rail trucks. lol.

 

It looks like the map takes a 5 volt supply and a B+ from the ECM then sends a signal back to the ECM. That B+ is the same B+ the IAT uses and also the eng coolant temp sensor,oil press sensor,water in fuel sensor and APPS. Any one could be pulling down the voltage from the ECM but I would try the IAT first. It just dawned on me.. did you calibrate the APPS after replacing the ECM?

 

I did not calibrate the apps, is it done the same as my 01?

 

I think so.. so I did a little research and it looks like it's the same procedure. The APPS should still be on the side of the engine for 2004, 04.5 it seems it was relocated under the batter tray. You may want to ask in the 3rd gen section though. good luck!

 

Thanks
From what I have found it is just disconnect the batteries, wait, and re-connect
I will try it tomorrow
Thanks
Eric

 

So do you know the atomospheric psi in your shop? Your scan tool does key on!