Changed OS Can't Enable PE

[Steve Bryant]

OS 12212156 has been flashed to the truck for a number of months. I believe that I have both the VE table (set up in SD only by failing the MAF) and MAF ({B0120} set for 400 RPMs) set up independently to track stoic pretty close. Here is the basic tune and a log plus a picture to illustrate this (at this point PE is delayed for 60 seconds to keep it out of the picture).

[Steve Bryant]

Here, I have changed B3643, B3644 and B3645 all to a value of 1 and the delay for PE is set to 0 seconds. The commanded AFR obeyed quickly, but the AFR did crazy things (tune and log included, see two pictures below, commanded AFR (green line) jumped right down to 13.0:1 then later right back to 14.68 when out of PE).

[Steve Bryant]

Right now, based on current symptoms I think that I have a partially defective PCM. Here's why.

I tried commanding an AFR of 13.0:1 using the BiDi controls and driving around. The commanded AFR jumps down to 13.0, but the WBO2 is no where near what is commanded. Also, my PCM will not include (add) the fuel from the aux tank into the displayed value on the fuel gage (even though it gets the proper voltage & A to D conversion as shown from logged data). I also had some crazy, inconsistent intermittant AFR problems on a long trip last winter when it was about 10 degrees F. The AFR could be around 14.6 and then suddenly jump to 16:1 for an hour on the WBO2 and it would set some codes for mixture too lean.

I'm about at the point of buying a replacement PCM as I no longer trust this one. It's more than just this PE issue which is frustrating enough. What do you think? Thanks in advance.

Steve

[WeathermanShawn]

Steve, your instincts are probably as good as anybody as to what is going on.

If it was just a PE issue, then I might suggest changing the TPS% Enablers to say 25-30% as a test. You could log FTC cells just to see what is happening as you 'enable' PE.

I have found PE Mode to be part 'voodoo' at times. I believe in the OS we are both using, that EVAP also becomes active during PE Mode. I had a dissimilar but equally frustrating issue when I attempted to set all PE TPS Enablers to 10%. I could not control Commanded AFR due to the excessive interference from the EVAP and its FTC Cell it 'shared' during PE.

You could always try a new PCM, but that is the only other thing I can suggest.

Let us know how it turns out.

[joecar]

It's hard to tell... sometimes the problem is solved by trying a new PCM.

[Chevy366]

Have you tried doing a "Full Flash" with your current .tun ?
Full Flash with the current .tun and see if it makes any difference .

[Steve Bryant]

Thanks to all who have responded. I'll try a few more things and get back with the results.

All my best,

Steve

[ScarabEpic22]

Hmmm interesting for sure, if you can pick up another PCM cheap and dont mind spending $100 on a license, that'd be my next step. You've done a TON of trouble-shooting and everything seems to point to a partially-defective PCM. Or if someone's local to you and already has their PCM licensed, full flash your tune into it and try that. Could even be a bug in the tune file itself, have you rebuilt the tune from a fresh 02 OS file with 0 modifications?

[Steve Bryant]

Erik,
I'm already in the process of doing what you suggest. I bought a used PCM at a salvage yard yesterday.

Thanks for your response!

Steve

[ScarabEpic22]

Let us know what happens Steve, troubleshooting a defective PCM when you've done a few other things gets to be a tedious process. But you sound like you're closing in quickly!