I have a 1999 3500 4x4 QuadCab Dually Auto, with ~230k miles, bought earlier this year. It had a bad APPS when I bought it, and I got a new one at Autozone and installed and adjusted it with an analog multimeter following instructions I found online. This fixed the intermittent dead pedal instantly. It also has slightly-larger-than-stock tires, 235/85R16, as opposed to the stock 215/85R16, speedometer doesn't appear to be adjusted for this. It also has all new clean battery terminals, along with one brand new battery and an old one it came with. I mention these things having no idea if they have anything to do with the problem.

Now sometimes when I am driving it, *usually* when it's under a slight load, like starting to head up a hill, after keeping a steady speed, it will act like it is going to shift, and the tach will jump 100 or so RPMs. It does this repeatedly though, in quick succession. Kind of hard to explain with typing, but even my wife can hear the resulting vr-vr-vr-vr sound. It only stops if I let off the gas some, or press it down harder, changing my speed a bit. It seems to be happening more often now that it is getting colder outside, though I don't know if it's related to the cold or if it's just getting worse as time goes on.

It isn't just a problem with overdrive, because if I turn overdrive off, the problem will still happen. The transmission fluid is full (dipstick says ATF+4 or Dexron/Mercron III, dealership(s) said ATF+4 only, so that's what I used, who knows what other people put in?), but I don't know anything else about the truck. What can I do to troubleshoot this and hopefully fix the problem?

 

kind of sounds like torque converter locking and unlocking. heres a good link on it.

Torque Converter Lock / Unlock Issues

 

My truck was doing that turns out my alternator was going bad. Maybe take a look at that. Just my .02

 

I appreciate the pointers, after reading a few other threads on torque converter locking/unlocking that seems like exactly what is happening.

They also all seem to point to the alternator, however, I disconnected the alternator by removing that fusible link, and it didn't change the behavior. Does this rule out the alternator? Or are there more things to disconnect?

Also I asked autozone about testing the alternator and they said all they test is whether it puts out power or not, which it is doing, since my batteries stay charged. They said they couldn't test whether it was going bad or whether some diodes were out. Any pointers on where I CAN get this tested?

 

Mine kept it all charged but it was sending out bad pulses to my TPS.

 

How did you determine that though? Like I said, I've pulled the fusible link supposedly disconnecting the alternator, and it still does this.

 

The alt interferes with the apps wire through electromagnetic interference (emi). So unless you pull the belt the alt will still produce emi.

 

Hmm, and with a serpentine belt that's not really an option to drive it. So is there any way to tell if the alternator is bad in that way? :/

 

Not really. I've been through the lock/unlock problem too and the only fix that worked for my truck was installing a BD apps noise isolator

 

its different for everyone. the only thing I had left to do was replace my alternator so I did and it was fixed, if I done that in the beginning I would have saved $400 on parts.