Transmission swap RPM issue

[montaillou]

Ok, so, I have a M1097R1. Now, according to the literature and the auction listing it was supposed to have a 6.5l, but it doesn't it has the 6.2l and it's still a 3 speed.
Bought a M1114 with a wrecked front end that came with a 6.5l, turbo & 4 speed. The plan was to grab whatever could be transferred and do that.

Well, there's no way to get the turbo on the 6.2 (sigh), but the transmission swap to 4 speed will still be useful and that has gone ok, except for a problem with rpm sender. Just so we're all on the same page, the NSN is 6880-01-148-8875. This is a new part, that I just purchased, the old part wouldn't respond at all.

Now, I'm not doing the work, a friend is and he sent me this text: It doesn't shift until super high rpm, the rpm sensor is not generating enough of a signal. I asked him what else I should write and he said: I want to know what input speed sensor people are using. The one on the back of the engine is throwing code 71.

Thoughts? Ideas? Recriminations?

 

[Retiredwarhorses]

First off, that signal generator puts out wrong signal for any of the aftermarket trans controller, but you did say what controller you’re using.
that generator is for STE/ICE, it’s a “K” band IIRC…anyway, in My shop, I’ve always used the H1 signal generator for the crank signal.
perhaps post a pic of the rear of your motor

 

[Mogman]

The original (yellow) RPM sending unit does not generate any signal, it is simply a reed switch and a magnet, the switch opens and closes 1 time per crankshaft revolution, it can be and I did use it on my 6L80 conversion but you have to bias the high side of the switch with voltage through a resistor and I was using an aftermarket controller that was programmable, After installing the GEP TD which cannot have a sending unit on the rear of the engine I switched to the crank sensor on the front of the 6.5L which gives a signal of 4 times per crankshaft revolution, this is not available on the 6.2L
If you are using an aftermarket controller then the instructions should include biasing a mechanical switch, if not consult with the manufacture of the controller.
If you are using a stock TCM then RWH would definitely be the one to tell you how to proceed as you need the correct generator as that TCM is not programmable.

 

[FlameRed]

Bought a M1114 with a wrecked front end that came with a 6.5l, turbo & 4 speed. The plan was to grab whatever could be transferred and do that.

I had to read this several times so perhaps I am still confused since I am a newbie. Why did you not take the 6.5L and 4L80 together to the other truck? Is the 6.5 shot?

When I swapped the TH400 with a 4L80 on my 6.2, I bought the US Shift tranny controller with their harness. I also got a new torque converter. I had three main issues. I just hooked up the US Shift harness to the 4L80 and connected a (GM) TPS to the throttle body in place of the fan switch. Also, I fabed up and jury rigged some linkage with the old fan switch so that still functions. The biggest issue I had was I could not get the old mechanical speedo to work at all so I ditched it. Those three things were a bit of a PITA, but aside from those things it worked well out of the box. Just supply power and ground and it was off and running.

If I had a spare 6.5 engine, I would have just swapped them as a pair, but I did not.

 

[montaillou]

Why did you not take the 6.5L...

So, the 6.5 had some issues, the least of which we discovered that this vehicle had spent some serious time at least partially submerged. There was water in places that weren't meant to have water and it was still there months (years?) later when I took delivery.