RPM Diffrence on AVC-R
 

The RPM display on the AVC-R is different then the tach. At idle they're very close but the higher I rev, the more off the display shows. At around 6500 RPM the AVC-R shows about 5500 RPM. Is this a grounding or voltage problem? Or some kind of wiring problem?

1000 seems a bit high. but the stock tach is most lily off some. you are just comparing a 15 year old analog gauge to a brand new digital one...

the AVC is most likly right. my safc is off by around 300-400.

Bringing this back from the dead as I have the same problem. The only thing is, I'd like to solve it. How can I get my stock tach to read correctly? Let me explain the current setup:

This is a GTUs tach(0-9k rpm) with a turbo engine and stock turbo ecu, with an AVCR wired in, coincidentally, by Neevosh. My problem is exactly the same, except it's about 400 rpms off at redline, and maybe 0-20 rpms off at idle.

I plan on going Haltech in a few months, is there any chance this will solve my problem and I should just tough it out until then? Or should I try and get the Tach calibrated now? Thanks guys!

Steve

No oem tachometer gurus? :p: Ka-bump!

Steve

P.S. The AVCR is set to 4 piston mode, which I believe is the correct setting for our application.

I have this problem too, anyone using the turbo ecu on an s5 n/a guage cluster is going to have the tach off. I first figured it was off when I hit the rev limiter at 8600 rpms ;)
I doubt its possible to calibrate it without modifiying the circuitry somehow, since its off by a different amount at different rpms.

After a bit of searching: apparently, because the aftermarket electronics tap the rear trailing coils, and the stock tach taps the CAS, there's a discrepancy between the two. But nothing I've read so far offers a solution. Not even which is more accurate(although I'm guessing the newer electronics are). I'd really like to have an accurate tach, there must be some way to fix this.

Steve

I dont think the problem we're seeing has to do with the rpm being read from different sensors, rather the computer is expecting to output the signal to a tach with an 8k range rather than a 9k range. The tach in the guage cluster isnt a real tach, its just displays what the ecu tells it to.

That would make sense if Neevosh had a 9k tach, but he doesn't, he has the stock 8k TII tach. I don't think it's because of the difference in tachs/signals, everything I've read/been told says that there shouldn't be a problem. I think it's a problem in the tachometer unit itself. Question is, can it be fixed?

Steve

Bump. :drool:

Steve

That would be wrong.

The tach in the dash gets its signal from a summed signal from the trailing coils

the stock tach does not tap into the CAS. It gets its signal from the trailing coils.

Only the stock ECU get's its speed from the CAS.

actually the trailings are fired on a "toggle" there is a "tach" signal that the ecu sends for every trailing event and everyother one it also sends a second "toggle" or switching signal which tells the trailing ignitor to fire t2. the 20b cosmo also works this way except its got 3 toggle signals, one for each rotor

mike

I know nothing about the ACVR, but there are numerous wrong posts in this thread.

In your case Steve, what does the ACVR tap into to get its tach signal???

I normally have to set most aftermarket electronics (like remote starts and the like) to 6 cyl when using the trailing coil signal (which I am figuring that is what you are using). Your 4 cyl setting may be off- again though, I don’t know enough about a ACVR to tell you for sure.

The stock tach has about a +/- 500 RPM window (depending on RPM) for calibration. At 1000 RPM the stock tach is in limits if it is reading between 880-1060 RPM. At 7000 RPM, the stock tach can be reading between 6965 and 7455 RPM and still be within factory limits. In theory it is possible to increase the accuracy by building a buffer, but I have not tried to do one on the FC stock tach before.

either way, with his problem, if the ACVR and the stock tach were using that same trailing coil Y/L tach output wire, they would be getting the same signal and reading the same thing.

Which suggests that one of the two devices are not calibrated as well as the other.

yah thats my thought, i bet money on the tach being slow/fast vs the avcr. unless the avcr gets its signal from the cas, then it could be off.

i just threw out the info for info cause we need clarification here.

mike