TRM tune, rev limit went down to 6k

[sludge1300]

I have an M52 in my e30. I finally installed my TRM tune a couple weeks ago, replacing the m50 chip/19 lb injectors with my TRM chip/21lb injectors.

I tested it on the road, and the rev limit was up to 7000, like it was supposed to be.

Once I started driving on track last weekend, the rev limit started kicking in at 6k. occasionally it would shoot up to like 6300 and then go back down, but otherwise, it was always stopping at 6k.

Any ideas what could cause this? It seemed to be running well otherwise.

Guess it's worth noting that i have a Race Tech Dash2. I don't see how it's possible that it could recalibrate the tach on its own, but perhaps somehow the scale changed? Doubt it tho since it read idle at just under 1k, which sounds right.

[FredK]

Do you still have your stock instrument cluster installed, behind your Race Tech Dash 2?

I am 99% certain that your DME is no longer receiving a vehicle speed signal since you have an aftermarket dash. Ordinarily, the sensor in your diff would pass on rotational speed information to the E30 instrument cluster. From there, a signal would be passed to the DME from the instrument cluster, called the vehicle speed signal. The signal is absent, either because you don't have the stock instrument cluster, or even though it's installed behind your Race Tech Dash2, it has become corrupted, or something flaky is happening with your wiring.

[sludge1300]

Pretty sure you're correct, I wired the sensor into the dash. It was however, disconnected before I bought the car. So, no road speed signal, i believe has ever run to this DME.

In other words, i don't know if it's ever had a rs signal, and yet the rev limiter worked fine last week.

I think i might need to pull out some wiring diagrams and stuff though, kinda forgetting how all that stuff is set up

[328ijunkie]

Vss.

[FredK]

Yes, sorry, I meant VSS. Vehicle speed signal. That originates from the instrument cluster to the DME.

[sludge1300]

So what you're saying is that the tune requires a vehicle speed signal...and it took a while for it to figure out that it's not there?

I guess i can believe that, I only tested the high rev limit in the first 10 minutes after installing the tune.

I have the vss wire running straight into the dash, can't think of why I couldn't just splice that and connect it up to the harness going to the DME

[FredK]

I think the soft cut is only in 1st and 2nd gear? Not sure though.

[sludge1300]

I think the soft cut is only in 1st and 2nd gear? Not sure though.

kinda losing me here. I can tell you that my issue is for all gears, but i guess without the vss the DME wouldn't be able to tell that anyway.

[e30rapidic]

VSS applies in all gears. I know firsthand!

[sludge1300]

Ok, well I'm going to check this out tonight, but I can say confidently that I have the VSS running into my dash with a pull up resistor.

If i:

-splice the VSS wire coming from diff, into a Y
-connect one half into the dash, through resistor,
- connect the other half to the black/white (?) wire going into C101
do you think the dme will get the type of signal it needs?..or is the resistor going to screw it up?

Sorry, I can never remember too much electrical stuff at once :)

[FredK]

Sorry I confused you earlier. The sensor in the diff is the road speed signal. The VSS is a signal that originates from the e30 cluster.

If you had a handheld scope, you could easily find out what type of signal the DME is looking for. It is likely that it is looking for a square wave signal. The signal from the diff should be a sine wave. You will have to find alternate means of conditioning the sine wave so that it appears to be a digital signal.

[sludge1300]

Sorry I confused you earlier. The sensor in the diff is the road speed signal. The VSS is a signal that originates from the e30 cluster.

If you had a handheld scope, you could easily find out what type of signal the DME is looking for. It is likely that it is looking for a square wave signal. The signal from the diff should be a sine wave. You will have to find alternate means of conditioning the sine wave so that it appears to be a digital signal.

Ahh, ok. Interesting. The reason I'm running a pull up resistor is for that exact reason. The dash requires a square wave voltage signal. The question is, without a scope....how could I know what the dme needs?

I suppose i could just try it out. Split the wire after the resistor. The question is, what voltage does the DME want? I'm pretty sure I'm running 12v from the sensor into the dash now.

[FredK]

There's no harm in trying, for sure. If it works, great. If not, it's probably best to borrow someone's scope and check the output at the cluster. This sounds like a race car, so maybe you've already deleted the cruise control. But the cruise control would be a good place to intercept the VSS, with the cluster in place.

I think that you might need to install a small VR to square wave circuit, like http://www.diyautotune.com/catalog/z...ers-p-378.html

[sludge1300]

There's no harm in trying, for sure. If it works, great. If not, it's probably best to borrow someone's scope and check the output at the cluster. This sounds like a race car, so maybe you've already deleted the cruise control. But the cruise control would be a good place to intercept the VSS, with the cluster in place.

I think that you might need to install a small VR to square wave circuit, like http://www.diyautotune.com/catalog/z...ers-p-378.html

Yep, I'll just give it a try. I have no cluster, no cruise, no nothing. Here's my circuit:

[sludge1300]