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Discussion Starter #21
I am familiar with the intake air heater and this is a seperate deal from that. It is a senser and it is just below the IAH...I was told it is an input to the computer like the engine oil temp senser that the ECU uses to determine things like the injector pulse width. I did get another IDM from a friend this evening and will try that hopefully tomorrow
 

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There's no sensor below the IAH on the turbo wye. But there is an actuator solenoid for the EBP valve at the front of the turbo pedestal. Unplugging that won't affect how the engine runs, but will just disable the EBP valve. It has the same type of wiring connector as the IPR.
 

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I will leave the two experts to troubleshoot your problem and I am not suggesting this as a cause but just curious what your ICP pigtail looked like when you had it unplugged. You have quite a few miles and years on that original ICP and I just wondered if it had started seeping oil yet.
 

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Discussion Starter #24
This is the senser I was told was a MAT manifold air temperature sensor...below the IAH and above the pedestal. When I changed my ICP...the pigtail did have a little oil on it...I cleaned it and checked the wires and they all seemed to be in good condition
 

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This is the senser I was told was a MAT manifold air temperature sensor...below the IAH and above the pedestal. When I changed my ICP...the pigtail did have a little oil on it...I cleaned it and checked the wires and they all seemed to be in good condition
You are correct. That is the MAT and it does communicate with the PCM along with the IAT sensor at the airbox. I forgot about that little gem in the spider.

I did some reading last night on it and found very little for what it actually effects and it isn't considered an input for Diesel Controls to the PCM. Kind of strange, but I will see if I can find more on it today.

Did you get to install the IDM yet?

Also, the rough running is happening as you bring the RPM up right? Does it go away? Is it RPM based or HPO based? I was pondering the throttle position sensor being the issue since everything has checked out. Thinking a dead spot in the pedal.

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My bad. I forgot about the MAT Sensor down on the turbo outlet wye. I must have been thinking about the tubing connection there that goes to the MAP sensor. Sorry.

I believe that the PCM uses MAT as an input (would have to check my resources to be sure), but again, don't think it would affect your intermittent problem.
 

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Discussion Starter #28
You are correct. That is the MAT and it does communicate with the PCM along with the IAT sensor at the airbox. I forgot about that little gem in the spider.

I did some reading last night on it and found very little for what it actually effects and it isn't considered an input for Diesel Controls to the PCM. Kind of strange, but I will see if I can find more on it today.

Did you get to install the IDM yet?

Also, the rough running is happening as you bring the RPM up right? Does it go away? Is it RPM based or HPO based? I was pondering the throttle position sensor being the issue since everything has checked out. Thinking a dead spot in the pedal.

I did install the other IDM...no change...still does the same thing. Actually when I first put it on it seemed like the engine was idling smoother but within a few minutes I could hear it changing and getting in my worse. You can hear the pitch of the engine begin the change. As that happens the hpop numbers are usually getting higher. If u try to rev the engine it starts chugging worse and then when returned to idle it is even worse. So I wouldn't think it would be a dead spot in the TPS. Out of curiosity I unplugged the MAT and EOT sensors and it got better. Wasnt running perfect but definitely better...according to torque this put my EOT at 210°. It had been about 120...now keep in mind the truck had been plugged in and running for about 10 minutes at this point. It definitely acts like something is getting hot or the pcmr "thinks" it is and is changing something. Any ideas?
 

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What about just unplugging the EOT? It doesn't make sense, but it could be reading faulty.

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What about just unplugging the EOT? It doesn't make sense, but it could be reading faulty.

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The PCM responds to the EOT signal kind of like a switch. It changes the HP oil pressure based on whether EOT is above or below 140F (IIRC). Higher oil pressure below that and "normal" lower pressure if above. If the EOT sensor is unplugged, the PCM uses higher pressure for starting, and lower pressure for running. Unplugging it would be a simple test, although I doubt it would affect an intermittent problem. Once above the warmed up temp, the signal would have to switch back and forth around the switch point. The EOT sensor is an RTD (resistance thermal device) and they're typically pretty robust, and unlikely to fail. Might be a wiring issue, possibly an intermittent short.
 

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Discussion Starter #31
Messed with it some more today...I really thought I was onto something with having the oil temp sensor unplugged. It ran the best it has the longest today. Had it running about half and hour. Then took it for a drive up the road. Made it to the next town and was still running pretty good, turned around and started heading home and it began to lose power. Wouldn't make boost, like about 5psi on the gauge and wouldn't go over about 60 on flat ground. Made it home and still wasnt running right but did clean up a little. Shut it off and plugged in the EOT. within about 2 minutes it was missing so bad it wouldn't go over 2000rpm and eventually died. Unplugged the EOT...it started up and cleaned up for a few minutes before it started missing again. So while having it unplugged helps, it isnt the whole problem. Got bored and decided to change the oil since it had been several months, even though it hasn't been ran that much. That so made no difference. Ran smooth a few minutes and then just like u throw a switch it starts running rough and dropping cylinders...I dont know what to think or where to look anymore
 

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Have you run a Cylinder Contribution Test?

Here is some information on the EOT.


 

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Given the intermittent (possibly high heat) nature of the concern, it may be worth going back and checking every pertinent wire for continuity. klhansen helped me with a similar issue a while back where my 7.3 Ex was throwing P1280 codes (https://www.thedieselstop.com/forums/f24/help-w-icp-differential-diagnosis-526873/), it turned out to be a badly soldered ICP pigtail. On a separate occasion a few months later, again with a P1280 code, I ended up ohm'ing every wire from the sensors to the block connector at the driver's side valve cover, then again from the block to the PCM. As the readings were taken a helper moved each wire gently to see if we could isolate a break. Finally, after removing the wrap on the big wire bundle going from the valve cover block to the PCM we were able to isolate a positional wire. Once bi-passed with new wire, all was well again. Just a thought...
 
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