Defeating the torque limit request on the Volvo 850 Turbo

[northernlights]

I no longer have a car with this setup.
You are looking for the green with yellow stripe wire that is a jumper between rear of ECM base and TCM base.
IT requires removing TCM and ECM and then pulling the box apart so you can get some access. None of this is hard. You take the bolt out behind the washer reservoir filler and look for the tabs down on box base and the box lifts straight up.
There a 4 or amybe 5 wires that go between the bases for the two control modules. All the other wiring leaves the box to the front engine and trans harnesses or to the rear for car body harness wires.

Fair enough, but that is the wire which he said he cut. What is you opinion on his observation of no change?

[Bondo1]

i saw the green and red wire but not the yellow and violet, probably cause i wasn't looking for it. tempted to try the green and red. As far as the reverse burnout.... I can't bring myself to do that to my car. boost is still the same after the shift since i have a boost controller. on another note i found a manual tranny that if i can afford it and its good would solve the problem of these sluggish starts.

[northernlights]

I just came into possession of a 1996 vintage service manual for the AW50-42LE. There is an interesting twist to the torque limit request issue. If I am reading the literature correctly, it looks like one must supply battery voltage (e.g. 12 VDC) to the ECM connector B42 aka the green/yellow wire in order to NOT have the torque limit request. This appears to be what the TCM sends the ECM during normal operation when no boost limit request is in place.

In many ways that makes sense. Control systems should be as fail-safe as possible. A cut wire is more likely to happen by accident vs. a powered wire, hense the ECM is looking for a low signal to enable the request.

Note the laundry list of when it (the torque-limit request) can happen:

1st gear is engaged
Reverse gear is engaged
Winter Mode (W) is selected
Oil temperature in the transmission is too high

[jimmy57]

No, the 0-2 V below Ubat is the reference voltage, Vref, on the wire from ECM. The TCM grounds the Vref to signal the ECM the desire for torque reduction via boost capping to the base setting. No TCV operation is the way the boost cap is enacted.

On every car I ever did this mod to, 6 or maybe 8, I got noticeable difference. Ready front wheelspin on take off and much worse torque steer.
There are two wires of the colors used for this function, maybe the wrong wire was selected.

[matthew1]

I'm going to try this tomorrow, meaning I'll cut the "green with yellow stripe wire that is a jumper between rear of ECM base and TCM base". I'll know one way or another, and report back within minutes.

[matthew1]

I'm knee deep in this now. Printing out the TCU PDF so I can take it into my garage for reference.

[matthew1]

No change . Oddly, I can't feel any change, but there should be something to be felt. I disabled something.

[northernlights]

If you're feeling really brave, would you care to kludge together a 12V jumper from your battery (or something close) to the ECM side of the now cut wire?

[matthew1]

Maybe, NL. Anyone care to comment on this?

I have an R ECU in there, but that shouldn't make a difference. If it does, I can swap my stock ECU.

[northernlights]

No change . Oddly, I can't feel any change, but there should be something to be felt. I disabled something.

For what it's worth, the harness looks like it matches the wiring diagrams, at least what I can see in the pics. #1 is green and yellow, #12 looks somewhat pink, and #22 has two wires, a violet and a white, just like the diagrams claim.