3 (E38) engine swaps/conversion's rev limiting at 5,500RPM's

[ScarabEpic22]

Dang, was hoping that was the issue and it would be simple to take care of.

Running a manual setup is probably easier going forward for swaps not using a factory-pared engine and trans, good to know the manual OSs let you input the VSS directly into the ECM. Didnt know that.

[GAMEOVER]

Yeah, I didn't know that either...just waiting to get ahold of a manual OS pinout & tune file...I went over the automatic E38 pinout that I have and there isn't a vss location!

[gmh308]

Yeah, I didn't know that either...just waiting to get ahold of a manual OS pinout & tune file...I went over the automatic E38 pinout that I have and there isn't a vss location!

If you cant find a manual OS drop me a line. Am pretty sure I have a fix for this. Limiting on a CAN failure. Just need to try it out on a willing field test candidate .

[tunedportcj5]

I was having the same issue last night on the dyno. I am running a E38/T42 with a 4L80e. I am still struggling with getting a VSS signal. We noticed we were hitting the rev limiter around 55-5700rpm and couldn't figure it out. Each time we would make a change, reflash and hit the limiter. We did back to back runs w/o any changes and it never hit the limiter. Very odd... after making additional mods and reflashing the tune it hit the limiter again. Another pull after that and it was fine...

I don't want to derail this thread but can anyone advise me on my VSS issues?

Thanks,
David

[Taz]

Hello David,

A little more information would be helpful. What is the problem with your VSS signal ? The T42 was intended for use with the 4L80, and should be sending a VSS signal to the ECM. Also, E38 and T42 pairings were common in GM trucks and vans - so I'm not sure what the issue is, without some details of your particular application.


Regards,
Taz

[GAMEOVER]

I noticed the same issue with the 5.3 truck engine...If I would try and hit rev limiter it would go to 5,500...but if I turned engine off and on real quick, it would shoot past 8,000rpm... But most of the time it would only go to 5,500rpms

[tunedportcj5]

Hello David,

A little more information would be helpful. What is the problem with your VSS signal ? The T42 was intended for use with the 4L80, and should be sending a VSS signal to the ECM. Also, E38 and T42 pairings were common in GM trucks and vans - so I'm not sure what the issue is, without some details of your particular application.


Regards,
Taz

The problem is that I have no signal in the scan tool - in addition, i'd like to hook up my speedometer. I have tried all of the relavent PIDs but no luck. Does the T42/E38 communicate over anything besides the CAN +/- connections that could be the issue? I do know that when new tunes are written to the TCM (upshift/downshift speeds) the changes work. The TCM has to know the VSS then....?

Thanks!

[ScarabEpic22]

In this setup, I believe someone on here said that the TCM sends the ECM the VSS signal on the CAN bus. So if you want to see VSS, log it on the TCM. Currently the only way to do this is via BBL as the V7.5 scan tool can only scan one controller at a time (V8 will be able to do both).

This is a weird issue though, wonder if Ross has any insight on it?

[Taz]

Hello David,

Are the ECM & TCM tunes from the same vehicle (i.e. matching tunes) ? Is the wiring harness from that vehicle, or a custom harness, and have you confirmed the pinouts / wiring connects to the components / locations that it should ?

If you need schematics to confirm the wiring continuity I can help with that. Also, some ECM & TCM pairings may have odd speedometer parameters to arrive at a proper signal (i.e. tire diameter of 6 inches, etc.). Looking at the stock, never altered tunes should provide some insight.


Regards,
Taz

[Taz]

... I believe someone on here said that the TCM sends the ECM the VSS signal on the CAN bus ...

Those were my comments … they are not completely accurate all of the time … they were intended more to get people thinking, and checking schematics and GM manuals, than to be taken as gospel.

I am still self-educating with respect to Gen IVs, so the following is merely my understanding at this point in time, and subject to correction …

Gen IV VSS communication is often platform or option (manual vs auto) specific.

Corvette’s output a direct VSS signal from the ECM to the IPC (Instrument Panel Cluster) – at 4K pulse per mile.

If the Corvette is a manual – the ECM receives a traditional VSS signal (high & low) from the T56. If the Corvette is an A6 (6L80) then the ECM receives the VSS signal from the T43 over the GMLAN / CAN BUS network.

Trucks are a hybrid of the above.

Truck ECMs output the VSS signal via GMLAN to the BCM, then the BCM sends this via GMLAN to the IPC (Speedometer).

Truck ECMs output a non-serial data VSS signal to the EBCM, and the Nav Radio.

Truck ECMs receive a Replicated TOS (Transmission Output Shaft) signal directly from the TCM. This is a single wire signal (high only) output roughly at 25 Hz per MPH.

As you can see, VSS signals with Gen IVs are very different than with Gen IIIs.


Regards,
Taz