VATS & PCM programming

[AWD V8]

Hi folks

I have a question to those of you who program PCMs.

I suspect that I may have a VATS issue. I'm doing an LS swap. The donor was a 2003 Silverado 6.0L. Before I pulled the engine I ran the truck and disconnected the BCM to disable the VATS. When the engine was out I successfully started and ran the engine several times with no issues. I installed the engine into a Jeep and it ran fine the several times I started it.

Yesterday I was playing around with it in the driveway and shut it off while I had dinner. When I returned I tried to start it. It would fire very briefly while "on starter" but not run. I actually held the starter on to see if it would continue to run, it did not.

I have experienced VATS activated before on my '99 Jimmy, but the engine would actually run about 2-3 seconds after releasing the starter.

Now I've gone though all my wiring and confirmed constant power and ground to the PCM at all times. Fuel pressure is constant at all times.

My question, is it possible that the VATS has somehow reactivated itself?

The relearn procedure is for the BCM, am I correct? This of course has no BCM.

Thanks

 

[Mooseman]

VATS can be deactivated in the PCM through a tune. It may be looking for the signal from.the BCM to allow the start. But if it was VATS it shouldn't even crank.

 

[AWD V8]

When the VATS was activated on my '99 Jimmy it would crank and start but dies in 2-3 seconds. This cranks and fires but dies before I release the key.


I planned on deleting the VATS among other things, but I wanted to get it driveable first so I could complete the swap, THEN get it tuned.

At this point I may just get a mail order tune, 100 bucks including shipping.

 

[Mooseman]

The way it works (crank/no crank) could be model or year dependent. I know that on our platform, I6 or V8, the starter, fuel and spark are disabled. Saw that each time I had to do a security relearn with different PCM's.

Even if just tuning a stock vehicle, VATS should be disabled because it always seems to rear its ugly head when you're alone on a desolated dirt road in the middle of the night with no cell coverage.

 

[AWD V8]

I am buying HPTuners tonight!

 

[Mooseman]

Will certainly be of use to you since you will likely be doing quite a bit of tuning just for your setup.

 

[AWD V8]

Well I've got my LS Jeep, and my Envoy, so yes, 2 for sure.

Now I can sell my Superchips hand held tuner for my Envoy and retune it with HPTuner.

 

[AWD V8]

Well my Jeep is running again. Got my HPTuners in the mail today. Downloaded the PCM's file to my laptop, disabled the VATS, saved it and uploaded it. Started right up!

Now back to work.

 

[prmoore]

Hey had a similar problem tour into all the wiring and turned out it was a fuse. So good luck.

 

[Mooseman]

Yeah, I'm pretty sure he got it figured out by now. Been 5 years.

 

[TJBaker57]

Here is a long shot question that I surmised would be best put here.

Having VATS tuned out of your PCM... Is there anything left there to reply to the deluge of BCM serial data traffic that otherwise goes unacknowledged??

I never thought about it until just today when tinkering and recorded serial data traffic with a BCM, DDM, CJ3 HVAC, LGM but no PCM on the imformation bus.

BCM spat out like 20 vehicle security messages per second for nearly a minute before giving up.

 

[Mooseman]

Well, it is called a "handshake" . I do know that when VATS doesn't detect the proper key or cylinder resistance, it will flash the security light constantly even while the engine is running because of the disabled VATS in the PCM. I guess in this instance it doesn't send the security message to the PCM which it is supposed to wait for before allowing the start.

Is there anything bad that could happen with ignored messages?

 

[mrrsm]

The only additional insight comes "Straight From The Horses Mouth" from the Mods over on the HP-Tuners Forum:

Vats

I am working on a 99 Z28 that has the security light on all the time. I went in and turned the vehicle security to none and programmed the car with write calibration only and the car will still not start. Have I overlooked something?

forum.hptuners.com

 

[TJBaker57]

Well, it is called a "handshake"

Yes, Normally looks like this....





But without the PCM participating I see this on a benchtop.... Looks pretty one sided! But what I wonder is if some level of participation from the PCM is retained after the tune.

Is there anything bad that could happen with ignored messages?

I am thinking no. When I have seen messages go unacknowledged the sending module eventually stops sending or asking for such messages. Perhaps in some cases the sending module reverts to using some default data?