L67 swap PCM issue

[Quaraxkad]

According to the schematics I posted:

I have confirmed that all of these are properly hooked up, except for C2-23 which I have not yet tested

I do have some 3800 Series II experience so maybe I can help. Flashing a 2004 bin file to a 1998 PCM won't work. There is some interchangeability between PCM's, but not in that case. Your tuning software shouldn't have let you write the bin file at all, it should have have some internal tables of what PCM model numbers and what bin file OSID numbers are compatible and prevented you from creating a brick.

I am assuming that when you did the swap you used an L67 harness. What year/make/model did it come from?

The reason I ask is that PCM pin assignments changed over the years. For example, 1996-1997 PCM's are totally different internally, but are pin for pin compatible. A 1998 PCM will physically plug into a 1996-1997 car, but the PCM connectors have to be completely rewired for it to work because the pin assignments are different on the 1998 PCM. On top of all that a 1998 PCM and wiring harness would use a drive by cable throttle body, and a 2004 PCM and harness would be a drive by wire throttle body. The PCM, harness, and all other components on the engine have to be compatible.

I am using a wiring harness from a 1998 Lumina LTZ. It is not an L67, all but 2 or 3 of the harness connectors are in the right place, making it the easiest to use and requiring the least amount of modifications. The C100 firewall connector was the only thing that really needed to be altered, and I am confident that I have all of those pins moved to the correct locations.

I have mapped out all 160 pins for the PCM on both cars, based on Mitchell's wiring diagrams. There are of course pins that are populated on one side and empty on the other, but all pins that are present on both ends are the same. The names for each pin does sometimes differ in the chart but I have verified in the diagrams that the wires still lead to the same place. One difference I noted that I don't think matters, the Impala PCM has separate ground pins for a few sensors, for example C1-10 is a MAP sensor ground, whereas the Lumina harness has all of those sensors grounded through C1-17. I would like to cross-check this chart with the factory service manuals, although I don't have a 04 Impala manual. I do have the 98 Lumina/Monte factory manual.



Do you see anything here that's missing in my Lumina harness, that would prevent the car from running on the Impala PCM but run just fine on a 98 Lumina and 00 GTP PCM?

[scubasteve231]

Do you see anything here that's missing in my Lumina harness, that would prevent the car from running on the Impala PCM but run just fine on a 98 Lumina and 00 GTP PCM?

I compared the pin assignments, and the things that stick out to me aren't any differen't than what you've already said. C2 19 on the 2004 is an oil pressure switch input and not present on the 1998. I don't know if that is required for the engine to stay running, but it sounds like it won't even start in the first place.

One thing to consider is the MAP sensor. An L67 PCM expects to see a 2 bar MAP sensor. An L36 PCM expects to see a 1 bar MAP sensor. I once put an L67 PCM into an L36 car without changing the MAP sensor. I had purchased a 2 bar MAP sensor but I just forgot to swap it in. It would not start. Once I removed the 1 bar MAP sensor and replaced it with the 2 bar, it started right up.

It's possible that your tuning software never actually disabled VATS in your 2004 PCM. I know when I've done it, several values had to be changed and it was not intuitive at all, but I'm not familiar with the software you are using.

[Quaraxkad]

but it sounds like it won't even start in the first place.

It will start and run for a coupe of seconds on the 04 Impala PCM. It will start, run, and drive on both the 98 Lumina LTZ and 00 Grand Prix GTP PCM. Unfortunately I need the Impala PCM due to the transmission incompatibility.

One thing to consider is the MAP sensor. An L67 PCM expects to see a 2 bar MAP sensor. An L36 PCM expects to see a 1 bar MAP sensor. I once put an L67 PCM into an L36 car without changing the MAP sensor. I had purchased a 2 bar MAP sensor but I just forgot to swap it in. It would not start. Once I removed the 1 bar MAP sensor and replaced it with the 2 bar, it started right up.

I am using the MAP sensor that came on the engine, 12580698, google search suggests it is in fact 2bar.

It's possible that your tuning software never actually disabled VATS in your 2004 PCM. I know when I've done it, several values had to be changed and it was not intuitive at all, but I'm not familiar with the software you are using.

That's very possible. However if that's the case, then both TunerCAT and TinyTuner are incapable of disabling VATS. I have tried both. Are you able to download the 2004 Impala SS Stock.cal attached to my first post and disable VATS in whatever software you use?

EDIT: I forgot to mention, I did try hooking up C2-23 to a hot-on-crank source, and that had no effect.

[delcowizzid]

When you are flashing it do you have a separate switched ignition to the ecu so it has both solid 12v and switched 12v because you need to key off the ignition power while retaining the constant 12v feeds for the tune to stay flashed or it will revert to the old vin number and old vats on tune

[Quaraxkad]

When you are flashing it do you have a separate switched ignition to the ecu so it has both solid 12v and switched 12v because you need to key off the ignition power while retaining the constant 12v feeds for the tune to stay flashed or it will revert to the old vin number and old vats on tune

Oh... no... I don't have that! I'm using a bench harness, I had no idea that was a requirement! That explains the VIN number resetting itself. However, when I read back the program and check it in TunerCATs, it still has the same settings I chose for VATS so it *seems* like that setting is being saved properly. I will definitely modify my harness now though. How long does it need constant power to stay on after switching off ignition power?

[Quaraxkad]

OK, I've done that. Reflashed the PCM and wrote a new VIN. Disconnected only ignition power and let it sit for a minute or two. Unplugged it completely. Plugged it back in, and read the VIN. This time it *didn't* reset the VIN back to default, which is good! So I went out to the car to try starting it up and the battery is dead from all of yesterdays cranking attempts. I've got it on the charger so I'll be able to try again later today or tonight.

[dave w]

EFI Live ... Bench Harness Tutorial .pdf is attached below.

dave w