98 torque convertor not staying locked up, neighbours truck is acting up, what can it be?

 

Plenty of reading if you search it.
12 valve or 24 valve?


12 valve sometimes is the tps.

24 valve is noise in the electrical system.

 

As j-fox stated, it depends on what year truck you're working with, as to what the root of the problem can be.

Here's a couple quick tests (94-01)...

1. Start the truck, take a DVM (Digital volt meter), set it to DCV, and measure across the battery. should be 12-14VDC..
2. Now set the DVM to VAC, and measure across the battery, again, as before. VAC side should show less than 0.100 volts. Anything higher than that, and the alternator is causing RF induction, or AC voltage waveform.

You can use a BD RF filter to band-aid the problem. Or, you can fix the source: The alternator.

If your trans kicks in/out consistantly, try test to for verification (note*: Best to do this in daylight hours, as you'll not be recharging the batteries during this test) :

1. Remove the alternator fuse from the PDC, and test drive it. See if the trans stops doing the in/out crap. It most likely will.
2. If trans acts as it should, then the noise is being induced by the alternator.
3. Re-install the fuse. If the trans goes back to acting ignorant, you've now further enforced the issue.