Well after hours/days of research at a time. Finding 4L80e problems all over the place. But nothing like mine. I gave up and took it to my specialist. The problem I've having is kind of excessive. You never know what your getting when you buy used. But I purchased yet another beautiful 6-5. This one is far different than my others. It's a 93 Chevy 2500 SRW, 6.5 TD, 1 owner fleet truck. But..... It's got 329k. Everything's still tight as a nut and everything functions perfectly, or did.

The guy mentioned "only odd thing is, the speedo doesn't work till it warms up" Yeah that's odd, but that's exactly the case. Transmission acted perfect with or without the speedo, on my way home (60 miles) occasionally the speedo would freak out and bounce around.

The next day, I replaced the VSS. And had no speedo at all, no matter the temp. So I put the old one back on, pulled the cluster, dusted it off, checked grounds (both dash and engine) and had a perfect speedo at all temps!

So I hooked up my trailer (2150 lbs) and headed to work, 20 miles later at 65mph on the hwy, I lost O/D. Pulled over, checked the fluids, all fine. Turned the truck back on and tried again, O/D was back, but no speedo. A mile later I lost O/D again.

Today (w/o the trailer) I took it to the shop, perfect speedo, perfect transmission. 5 miles before the shop, I lost the speedo, and O/D. Restarted the truck, O/D was back, but no speedo. The speedo came back 1.5 miles before the shop, but O/D decided to leave again.

I don't think my trailer messed up anything, he had a 6200 lb boat on it when I picked it up. Whats going on with this thing? Thanks guys!

 

Sounds like a fault with the TCM grounds or the TCM itself.

 

Where is the TCM located on this 93 model? It's going to its 3rd shop tomorrow morning. (A shop that's actually heard of this issue). They said it could be anything. But leaning towards the early 93 harness.

 

behind the glovebox

neutral safety switch could also be suspect

 

Oh what a headache. Ill pull the glove box out and inspect/clean grounds on the TCM. Make sure it has power going to it as well. Will the neutral safety switch play with the Speedo's function?

 

I haven't seen 1 for quite a while but I think the harness runs through the safety switch?

 

Now that I'm not sure of. That's going to take some digging.

 

Is the truck 4WD? the reason I ask is my wires to the VSS there is a pig tail extension for the transfer case hooked to the wiring harness, it fell of the mounting perch and rode on the front prop shaft until it wore in two.

 

Unfortunately not, this 93 is my "dirty work" 2WD work truck. I wish I had just bought another 94. I think I'd be better off. 93 was an odd year for these trucks from my understanding. Exterior transmission harness and connectors are all solid. I was under it an hour or so tracing wires and cleaning connectors to make sure there was no frays or dirt in places it shouldn't be.

 

92 and 93 were the only years for mechanical injection, and hands down they are way more reliable than the electronic and I have had both IMHO.

And get a piece of clear fuel grade hose to the IP this will save you time if you are having air in the fuel and you can see whether or not you are getting fuel to the IP.