1997 L-31 VCM Problem

Bluesman123 · December 29, 2003

This looks like a great forum, and I'm hoping someone can help me out a little. Let me give you a brief background:

1. I swapped a 1998 5.7 Vortec/4L60E into a 1991 Sonoma. After it was in, I discovered that year had the passlock system installed in the VCM.

2. I bought a 1997 VCM, supposedly from the same engine, and using my Helms manuals I rerouted the 1998 C1-C4 wires to match the 1997 C1-C4 connectors.

3. To my amazement, it runs. It actually runs fine in open loop with no DTCs.

4. But when it goes to closed loop the 2 banks show wildly different fuel/air mixtures. Bank 1 (drivers side?) is really flooded with O2 voltages (HO2 #1)around 0.9 and fuel trim around -30%. Bank 2 (passenger side?) is way lean with O2 voltages around 0.1 (HO2 #1B) and fuel trim around +50%. The plugs from 1, 3, 5, and 7 are seriously carbonned, and the plugs from 2, 4, 6, and 8 are actually pretty normal looking. Oddly, the plugs from 1 and 2 are the cleanest from each bank.

5. This condition gets worse and worse instead of self correcting, until the engine dies when it goes closed loop.

Here's what I have tried so far:

1. I installed the CSFI to MFI conversion according to the tech notice.

2. I rechecked the Helms diagrams for the VCM connectors and I believe I have made the correct changes (although if it ever stops raining today I may try swapping the HO2-1 and HO2-1B connectors just in case the manuals got it wrong)

3. I've replaced all of the O2 sensors

Here's what I am wondering:

1. Could it be that the junkyard sold me a 1997 VCM for the 4.3 V6? Would it even run? I'm suspicious because the front 2 cylinders seem to be the leanest.

2. Does the VCM need to just be reprogrammed? Does it take a dealer to do this? Would they need anything more than a VIN ... like do they need the RPOs? I can probably cook up a VIN, except for the check sum, and could find similar RPOs from this site.

3. Is there any way to clear the stored fuel trim data that keeps making it run worse and worse? I'd really like to go back to the original factory settings.

This has been a long posting...and I thank you for your patience. Do you think I am heading in the right direction? Can you suggest anything else?

Thanks for all your help,

Bluesman

Import Hater · December 29, 2003

Wow. In all honesty, I'm a little aprehensive about electronics from a junkyard, but it's probably OK. You'll have to see if the part numbers on the PCM match what a 1997 engine would use, or you're wating your time. If that's good, I would reflash the PCM. You can bring the PCM in all by itself to either the dealer, or the handful of shops out there (like mine) that have the equipment.

And I'd make d**n sure that the connectors you swapped are indeed in the right places. Maybe a factory service manual would be more accurate?

Rob

Bluesman123 · December 30, 2003

Thanks for the advice!

My local GM dealer says the VCM (PCM) has to be installed in a vehicle with an OBD-II plug (DLC) before they can do anything. It took FOREVER to find an OBD-II plug. It's installed now but I'm not sure I can get it down there without a tow-truck! Can anyone other than a dealer reflash it? I am delighted to hear that. The guys at the parts counter are GREAT but the service manager leaves a bit to be desired.

What info would I need to bring in to get it reflashed? Anything more than a VIN that I could cook up? (I don't think the Sonoma 2.4 VIN would do much )

Bluesman

Import Hater · December 30, 2003

My local GM dealer says the VCM (PCM) has to be installed in a vehicle with an OBD-II plug (DLC) before they can do anything. It took FOREVER to find an OBD-II plug. It's installed now but I'm not sure I can get it down there without a tow-truck! Can anyone other than a dealer reflash it? I am delighted to hear that

The dealers should have all the tools, but they need the off board adaptors to program PCMs off the car. My shop has them. We of course have the in car cable that reflashes through the DLC, and we also have about 6 or 7 different cables to plug directly into the different PCMs and flash them on the bench.

I'd call some auto parts stores... When they sell a replacement PCM for a newer GM, the computer needs to be flashed. Someone has to be doing that for them. See if they'll refer you to that shop.

Rob

Bluesman123 · December 30, 2003

This has really been helpful, Import Hater! I've learned more in the last 2 hours than in the last 2 months!

1. I found that the bar codes on the VCM can be decoded by the dealer and...as I was suspecting...the '97 VCM I have came out of the 4.3 V-6, not from a V-8. So just in case anyone ever asks you, yes a V-6 VCM will run a V-8. All the cylinders fire and all 8 injectors inject, but the fuel map is just way way off...too much to be corrected by fuel trim adjustments.

2. The dealer (I haven't found another non-dealer shop yet that can do this stuff, but I've just started looking) cannot re-flash a VCM that already has been flashed. They are also unwilling to let me cook-up a VIN to use on a bare unit...apparently according to GM rules.

Has your shop ever reflashed an existing OBD-II unit? One that already had code flashed into it?

Bluesman

Import Hater · December 30, 2003

Has your shop ever reflashed an existing OBD-II unit? One that already had code flashed into it?

What we use came from Cardone. They are one of the largest remanufacturers of ECM/VCM/PCMs, so it's only fitting that they got into reprogramming. Cardone's setup essentially takes the place of the Vetronix Tech II Flash that they use at GM dealers in line to the PC based TIS2000 Expertec SPS software on a PC.

Lot of fancy names huh? The short of it is, we can reflash in service PCMs to update the firmware when there's new updates, correct corrupt data, or even change tire sizes. We can also flash new or used PCMs so they "match" the vehicles they are going in. Setting options (like keyless entry, traction control, etc), VIN numbers, and emission certification.

Rob

Bluesman123 · December 31, 2003

Man this has been so helpful!!

I found (after a day of searching) an auto parts place that can reflash VCMs. They can't do all the things your outfit can do (they can't change tire size, etc.), but they can reflash the original set of specs. Unfortunately, they also need a legitimate VIN and the particular code from the VCM that was sold with that vehicle. So now I need to get the numbers for any 1997 2WD 5.7L 4L60E light duty truck, Suburban, Tahoe, etc. I'm goin to open a new thread and go beggin!!!

I see your location is San Jose. I'm in Walnut Creek. If your system can reflash without using all those numbers (a VIN and the VCM number) I'll drive the VCM down this weekend and buy the job.

Have a great and safe New Year!

Bluesman

Import Hater · January 1, 2004

The PCM will need a VIN to be flashed into it. So make sure you use one that will match the engine and transmission you're using.

If you want to use us to do your flash, just shoot me a PM. The shop is in south SJ, right with all the dealers on Capitol auto row.

Rob

Bluesman123 · January 2, 2004

Thanks for all your help, Rob (and everyone else who posted and sent emailes). I found a guy in Martinez who can do it and 99-2DR was nice enough to send me the info for his truck which has the right RPOs (even down to the gear ratio in the pumpkin!). We'll try reflashing it next week and I'll let you know how it works out.

Thanks to everyone for your help...this is a great forum!

Bluesman

Bluesman123 · January 8, 2004

Here's an update on my VCM problem. Thanks to Rob and Larry on this board, and to TurboS10 and others on the Hotrod board, I've got it running. Here's the info for those who may be facing the same problem I did:

1. Yes, you can get your GM VCM reflashed (reprogrammed). It doesn't matter whether it is one from a V6 or from a V8 (except for diesels I would guess) they are both the same computer and only need to be flashed correctly to work fine.

2. To get it reflashed, you need BOTH the VIN from a vehicle with similar RPOs AND you need the Service Number from the VCM THAT WAS SHIPPED WITH THAT VEHICLE. That is important, especially for anyone buyng a used VCM from a junkyard. Be sure you get the correct VIN or you are going to have problems.

3. you can get all the VCM upgrades from this web site:

http://vci.ecomm.gm.com/vci/

Just type in the 17 digit VIN followed with no spaces by VCI. This will generate a page with all the factory upgrades for that vehicles VCM.

If you really want to start messing with your VCM, check out this site:

http://tunercat.com/tnr_desc/do_tc.html

These folks are very helpful and sell software and hardware that will let you mess with your VCM. DO NOT expect to easily get a performance upgrade like you would with an OEM reprogrammer such as Hypertech. They make their changes on a dyno and you aren't likely to beat that. However, if you want to just have a little fun why not give them a try.

Once again...MANY MANY thanks to Larry, Rob and all you others who helped me through this problem. This is a great site!!

...and hey! It runs GREAT!!

Bluesman