PCM Issues??
 

Been fight issues with my 7.3l since I got it and now have reached the end of my rope. The first and most aggravating issue has been happening since I bought the truck. It is a random check engine light that turns on and off at seemingly random times. Codes pulled read P1670 usually and occasionally P1668. I have swapped in 4 IDMs and checked the wiring between the PCM and IDM throughly. The truck has run great up until recently where as now it is dropping the RPM's when the TC unlocks coasting/decelerating from highway speeds. I am thinking the IDM codes are probably not related to the RPM drop issue, but anything is possible.

My question is I have a Phoenix burnt for my PMT1 PCM (DPC-422) and I have read (I think from Cody) that any DPC-422 would work with my chip. Is this correct? I am not concerned about getting the same PMT1 PCM if something else will work with my chip.

If anyone has any ideas and/or suggestions that would be helpful. :help: I have an AutoEnginuity but currently having laptop issue so unable to do any driving tests. I have tested it thoroughly sitting in the garage idling and things seem ok there from what I can tell. Still trying to learn the AE and all it can do. Thanks!!

Prepare to be more aggravated.....

I'm not going to go into any diagnostic bits on your P16xx codes because there's no way to pinpoint in what way you should spend your money (and I loathe "throwing parts" at vehicles in hopes that it will resolve a problem).

I will, however, tell you that your RPM drop "problem" is mechanical. It's transmission mechanical. Sorry for the bad news. It's not going to hurt anything, but as you've found out, it's really annoying not having any engine braking. I've found it in two transmissions now (one was my own, the other was one I rebuilt for a guy). The coast clutch snap ring pops out of its groove and you lose much of the clamping force on the frictions and steels.....and they eventually burn up. The only way to fix it is to take the transmission apart. The tuning on the chip doesn't change and I can guarantee that wasting money on another PCM won't fix your transmission problem.

Well, damn, that does suck. Kinda not shocked though as this did kind of start happening all the sudden. Any idea how long I can drive it around like this? And my "drop" in RPM is quick and momentary and does bounce right back up to idle. The cause for the dip, I would guess, is the transmission engages when the TC unlocks and loads the engine (??). Just a SWAG there. Please feel free to fill in any gaps or incorrect info. Thanks.

Now I have to start tracing those P16xx codes. Extremely aggravating. Done so far is a nearly complete ohm of the PCM to each sensor (tracing something that wasnt a problem to begin with), ohm from IDM to each injector, to each VC inside and out, and from each VC to each injector.

The dip in RPM before bouncing back to idle is caused by the lag in the IPR/ICP relationship. It's not a problem, but impossible to tune out without being there (and once you write tuning at one temperature for one brand/weight of oil, it will change again with a different brand/weight anyway).

As far as the transmission problem, you can drive it forever that way. It's not going to hurt anything. Mine took a dump at about (I want to say) 80K and the transmission needed rebuilt at 140-ish when my ex wife broke the intermediate one way clutch.....it would have gone farther.

Just pmd you nicmartim

Ok, now confused.... The RPM dip is IPR/ICP related? I have heard this before and the coast clutch thing is a new one to me. Is it both?

What Cody is saying is that the overshoot past base idle is often related to the ECM trying to control ICP when coming off higher RPMs and it opens the IPR too much. This cause a slight drop in ICP and a subsequent dip in RPM. The convert won't have anything to do with it since it doesn't normally engage at anything below 1100 RPM.

So, my transmission is fine? No worries about the coast clutch as Cody mentioned in post #2? I did recently replace my ICP and pigtail (old one was oily in the connector). How would a new OEM part make this start or would it? Wonder if I should take the IPR apart and clean it as the PCM is getting a strong/correct (presumably) signal from the new ICP.

I am guessing this is a non-issue going forward as it concerns to drivability. Thanks guys!

Probably since I read it as a new issue where wherein the RPM had just begun dropping when the torque converter clutch was released......as it should in OD. I had mistaken your first post to mean that it was a new issue that appeared regarding engine braking (which would occur in 3rd gear with the TCS or OD "OFF" light on).

My bad.