swapping pcms now wont start

[Trevor]

Well new pcm didnt help anything truck still runs like crap and nothing works. Idk what else to check

[RedHeartbeat]

Something tells me you're not telling us the whole story here. We need more details to help you out with your issue. Tell us what you have, what you did and describe to us what the problem is. From your first post it sounded like it just ran a few seconds and dies. Now it sounds like you've done some stuff to your truck and it isn't running correctly.

[Trevor]

No the truck has just been a problem ever since ive owned it and has always ran like crap becasue of fuel problems and has wring issues or something. Its had 5 fuel pumps in the past year. Half the cluster works half doesnt.

[RedHeartbeat]

where did you get the replacement PCM from? Did you have your tune written into it? A V6 tune will not run a V8 engine. Just having the right PCM is not enough, it has to be programmed for your vehicle type if it had an incompatible tune in it before. Are you sure you're not having fueling problems due to dirty fuel injectors or a leaking fuel pressure regulater on the fuel rail?

[Red03SilSS]

Do i need to do a crank relearn? I suspected my stock pcm of needing a reflash so i got another stock pcm with same service number and same motor for free. trying to swap them now truck tries to crank but wont run.

Everytime I put a new PCM in my truck it does this. I always have to do the security relearn like Mel said.

[Trevor]

i put the new pcm in and got it running. there is no tune its a stock pcm. That was to try and rule out a bad pcm. Im having BAD fuel problems 7 fuel pumps in a year and a half. Not sure why. Runs good when the pump is replaced but the pump will only put out pressure for a few months and i have to get another one. I have a 4.3 so the FPR is under the intake manifold on the spider injector.

[zebra]

just curious... if the message center never says 'security' - it just shows the red battery light, can you or do you need to do the security relearn procedure?

i have a 99 NBS sierra 4.3 swapped to a 5.3 from a 01 tahoe. the old PCM from the V6 was the black one with 4 connectors & the new one with the V8 is the silver 411 PCM with the red & blue connectors. the motor turns over & fuel goes to the cylinders, but none of the coils are firing. i bought the engine from a scrapped tahoe that had the roof smashed in & the junk yard said they started it right up & ran it when they got it (early august). i've checked over every ground & connection - all are solid. i installed new plugs & wires and then went in with a probe & each coil is getting power, all fuses & relays are good, each ignition/fuel/start/ecm/etc fuse is getting power at the fuse block, and the crank position sensor is getting power, so my guess is that it's the tune

[trx2stroke4life39]

The pump is probably shorting out due to a bare wire or a bad ground.

[George C]

These don't have VATS. VATS is the old school system that uses the square head key with a pellet.

Anyway...you can swap but at minimum you need to do a theft learn as already stated in the topic by Melly. Even then option content and therefore the stock tune can vary greatly.

Why are we swapping PCM's again?

up till least 02 they still had VATS in the program. It was under the system block of the program and says VATS and you have choice of 3 settings. None, PWM and serial

[PitchBlackC3]

up till least 02 they still had VATS in the program. It was under the system block of the program and says VATS and you have choice of 3 settings. None, PWM and serial

You are correct

Technically they do have VATS, since VATS just means Vehicle Anti-Theft System.
The early chip on the key was PASSLOCK, the 98-up trucks have PASSLOCK II and I think the GMT900 trucks have PASSLOCKIII.

They are all a form of VATS.