GrampasBuick

I picked up a cream puff Burb with a 5.3 and a really strange problem. It starts and runs fine. Step on the brakes and put it in gear, no problem. As soon as the truck starts moving, the truck dies. Even in neutral if you get out and push the truck 2 feet it kills the engine. Disconnect the VSS and it will drive around the yard just fine. So it is definitely not a mechanical problem.
I did have to put a junkyard transmission in it, but it had the problem with the old trans (also not original) and the new one. The new one is from an 02. The 4l60s over the years had electronic differences but I believe 00-02 are compatible.
Now, according to the PO, the truck was stolen and recovered and he thought it might be stuck in theft mode. But my code reader did not show any antitheft codes, and I have seen antitheft codes on a similar truck, so I know my code reader is capable of them. Also the truck that I saw that was in theft mode had shut it's fuel pump down and would not run at all. So I don't really think it's that.
I swapped the VSS hoping it was grounding out and shutting down the system, but that wasn't it.
The ignition switch was swapped too, but I think (not sure) that was an attempt to fix the stalling problem.
I'm wondering if it has something to do with the VATS. Is that easy to bypass?
Anybody have any ideas?

codyvette

iTrader: (24)

VATS is easy to bypass with tuning software but it should not run but for a couple of seconds max. The rolling of the truck should make no difference. That is definitely a strange issue. Please update when you figure it out. Is is posSibley there is some aftermarket alarm mounted around the steering column. Sometimes they hide those things pretty good.

GrampasBuick

I haven't really dug around for an aftermarket security system. I cross posted this on a few websites and a guy on CK5 said he had the same exact problem in a 2000 motor home and it was the vats. I don't have easy access to tuning software but I am seeing vats bypass kits with resistors. Any experience?

bigdaddy350

Old school remote start installers still use resistors to bypass the VATS system. No issues there. If it was a VATS issue, the car would die a few seconds after starting. To me, if it drives with out the VSS hooked up, you can probably rule out the VATS system

GrampasBuick

Well, I made some phone calls, I can get the ECM flashed at a local dyno tuning shop for under $300 with no guarantee that it will change anything. Way better than $600 at the stealership.

So I went to the U-pull junkyard down the street and paid 40 bucks for an ECM. Figured what the hell, if it doesn't fix it I'll just return it. They never ask questions about returns.

Put it in, went through the 30 minute anti theft relearn, and fired it up. Got the wheels off the ground and threw her in gear, and no more stalling! Ran like crap though. Great, fixed one problem to create another. But after 5 minutes or so it cleared out and ran great. I guess it had to learn all the sensors and stuff. I'm gonna road test it right after I get my little boy to bed, but so far so good.
Fingers crossed!

1FastBrick

iTrader: (16)

The Idle relearn process is 10 minutes.

I suspect the throttle body needs to be cleaned and the IAC passage is getting coked up.

Being a theft recovery, It's also possible the OP replaced the ECU and it does not have the correct calibration in it.

Glad you got it running though.

truckdoug

iTrader: (25)

sounds like you oughta put a turbo on it

GrampasBuick

Yup.

I bought the truck super cheap and figured worst case scenario I'd turbo that 5.3 and drop it in my Skylark.
Guess I'll keep looking for a deal on a 6.0