Okay.. so here goes with my attempt to explain what I tried so far (and why):
To start off, I feel I have some excellent (or would be..) tuning from Codi Pitock of Pitcock AgTech (great guy to deal with, wonderful customer service so far). To each there own on tuning, but Codi and I seem to share the same thoughts on how these trucks should run. That said, we have been running into a bit of an issue with my VGT not wanting to follow his Air/Fuel tables (VGT does not want to open to 0% under light load), getting some codes after tuning that he says shouldn't be occurring, and just some Iodd gremlins generally. I have tried all of his recommendations, such as making sure the batteries are good, fully charged (I have even tuned it while jumped to one of my old truck to keep volts above 13), etc etc etc. I had it re-flashed at the dealer (both the ECM and TCM). That made a huge difference with some minor bugs I was having with the AISIN, particularly shuddering in 1st/2nd gear and a screwy shift that had been occurring between 3rd and 4th (other threads said updates would cure that and it seems to have done so for me)' trans feels wonderful now.
I re-loaded my tunes, and I am not convinced I am any better off after the updates... The "demanded" and "actual" positions are in sync, so I hesitate to think it is an actuator issue. So, I have been trying to hunt down anything that might be amiss that would cause the truck to follow a default table, or something that might skew the air/fuel tables of my tunes. In that effort, I found that my IAT-M reads almost exactly 35 degrees higher than my IAT (which I assume is the combo sensor at the intake horn) under all operating conditions (at least so far).
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So, that's about when I started doing some experimenting. I started by simply unplugging the IAT-M sensor. The IA-TM dropped to -5 (by the time I could make it back around from the engine bay to the driver seat) but the truck ran fine. The weird thing is, after the IAT-M reading dropped, it switch over to some other reading. Not sure if it was calculated or picking up another sensor, but it was about 10 degrees warmer than the IAT (which again, I assume is the intake horn sensor). I took the truck for a drive, and aside from a code for the sensor being unplugged it ran fine. It may have been my imagination, but it seemed like the VGT was opening a little more than it would before.
I then jumped online to see if anyone else has had this problem. The only thread I found about this particular issues is this one. I asked MM3 about it, they weren't much help, but did say that the MM3 will only display what the truck tells it to. The dealer seemed to think it was odd as well, but didn't have an answer. (Some of this may not be in order).
I then tried a sensor of an identical type. I had one left over from the EGR crossover tube (Same numbers, same exact sensor, same plug). I didn't bother pulling the old sensor, just plugged the 'new' one in and let it dangle.. Guess what, SAME READINGS ! 35+/- hotter than every other temp sensor and reading, even during cold soak.
I then decided to try a completely different style sensor, thinking maybe the sensor doesn't start giving a real value until it reaches a certain temp.. and a more sensitive sensor would do the job, after all it is just a 5volt two wire simple sensor. So.. I cut the factory plug off and wired in the old water temp sensor... That's when things got weird
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Not only did my IAT-M give a skew reading (engine was cold soaked in this picture), but the IAT was 419 degrees with the truck off.. It was about 55 degrees in my shop. I decided to drive it anyway....
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Boost was high, fuel was high, airflow was high, and VGT was more closed than it should have been for the driving conditions. Also, both IAT and IAT-M were super screwy looking.
So I took it home, and wired the old sensor back in, or so I thought. I think I may have had the wires backwards (i wasn't really paying attention to wire colors because it is a simple two wire 5 volt system, didn't think it would matter), but that is when I got this:
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Yep, that's the IAT reading -40 and the IAT-M which might actually be accurate as I had just drove the truck and it had sat long enough for me to wire in the old sensor. NO CODES! By this point, I had some butt-connector problems and the factory plug wires were getting shorter and short... for all I know it wasn't even making a connection and the truck just decided not to throw a code (it was pretty quick to do so when disconnected though, so I am thinking I had the wires backwards).
I drove it like this (sorry no picture) and again, unless it's my imagination, it seems like the VGT was quicker to go to 0% and was staying open more than when all the readings were "hot". Thus, supporting my theory that this wacky temp sensor may be the issue I am having with my tunes.
So.. after some cussing and fussing, and long story short.. steeling a plug from where the old EGR probe use to be (because i had accentually cut some things too short), I finally have the original probe wired back in (with corresponding wire colors) and I am back to "normal":
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As you can see, I am back in the same boat as before.. 35+/- hotter than IAT sensor. During all of this I did found an Intercooler outlet temperature (I have been told this is a calculated value and means nothing). I don't think anything I did helped me figure this issue out whatsoever. All I can say is this.. 35 degrees is being superficially added to the IAT-M by whatever means. It is NOT the sensor. Also, type of sensor matters as the readings were even screwier with the water temp sensor inserted.
I have though about posi-taping into my MAP/Temp sensor, but at this point I am not sure how much more butchering I want to do to my factory wiring harnesses.
All I can say I this.. if any of you go pulling that sensor and have an AISIN, good luck getting to everything without moving the oil and transmission dip-stick tubes. I did find I could run my arm under the mast cylinder area and get two hands back there, but what a major PIA to try and do anything with the wiring or the sensor because of obstructions.
I'm taping out on this one for now. Hope my write up helps someone, or motivates someone to diagnose things further than what I have done. Best wishes!
V/r,
James
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