any ideas?

[TXsilverado]

a buddy of mine bought my old truck from me about a year and a half ago. in the last week hes been having electrical problems but cant figure it out. while hes driving down the road, for no aparent reason the speedometer will start to go crazy, the transmission wont like shifting, and the engine will start to sputter. then as mysterously as it appears it disapears...

its like the truck thinks its turned off for a few seconds. the doors unlock like you turn the truck off, and when it goes back to normal the doors will lock back like you just started it. it seems like i remember something about a bad speedometer cable being able to do all of those symptoms on new trucks but im not sure. any ideas?

[RedHeartbeat]

That sounds like a bad battery cable, most likely the ground. Bad contact for body and engine grounds. It's that or the battery is getting ready to bite the dust, shorting out internally.

[TXsilverado]

brand new battery. and why would the speedometer go crazy when a ground went? seems like it would just go dead instead of shooing back and forth from 100 to 50 to 84 to 35 to 69 etcetcetc

[RedHeartbeat]

Chassis ground sending voltage off and on from high to low. I would not think it would be an alternator voltage regulator unless lightbulbs started blowing out. A bad ground in the dash caused that in my old 73 truck.

[RedHeartbeat]

I guess the question would be what year was the truck and is the speedometer cable or electronic. My 92 is electronic and all newer trucks are too.

[TXsilverado]

00 silverado. electric

[RedHeartbeat]

Could also be a short in one of the coil packs firing coil voltage through the wiring harness. Imagine 40,000 volt spikes hitting the wiring harness, needles would be bouncing all over the place. If I had one known good coil pack I would replace one at a time and see if the problem goes away, then move to the next coil for replacement and repeat until I ruled them all out.

[TXsilverado]

its a v6. i didnt think v6's have coil packs. do they?

[RedHeartbeat]

It does have a coil. One coil is all it takes. My 97 Vortec V6 did something similar when the distributor cap and rotor needed replacing. I replaced the hall-affect sensor while I had it apart since it's quite a chore to get into the engine compartment.

[TXsilverado]

i talked to him and he replaced all of the distributer stuff about 20k miles ago so all that should be fine. electrical systems are no fun