Mongo

This is more of a technical question for those who are electronics gurus out there. What is the signal type for all 928 Speedometers? Is it Square wave type?

davek9

This thread just says it is switched signal 6 to 12v??
I never looked at it on a scope, what you trying to do/fix?

https://rennlist.com/forums/928-foru...ion-fixed.html

Mongo

I had a project mapped out a while ago involving a transmission swap from the factory auto to a 4L60E from a Corvette C5. I documented some of my findings so far on RL here and there, but with most of the electrical details sitting on my HD at home. I sourced a standalone TCU which will function with any type of EFI so long as there is a TPS, RPM/crank speed, Temperature and Speedometer signal. However, the TCU requires a square wave type signal input that is 12v in order for the existing speedometer to function.

4L60Es are all over ebay and wrecking yards in Socal at prices below $600. If I can get the electrics to work, it would be an interesting swap. While I am still about 2 years out from this swap. I have already sourced all my parts with the exception of the modified crossmember and bellhousing adapters. I last heard that Dinsdale Piranha and XSChop on here had some products that provide adapting solutions to get even the C5 torque tube to fit the 928's flexplate and adapt the C5 bellhousing to the motor as well.

dr bob

Andy --

The trigger is a magnet passing a reed switch, so a square wave. I haven't looked at the duty-cycle if that makes a difference. The switch has ground on one side, and a reference signal input to the other side. Su the pulse is reference voltage, pulled to ground when the switch closes (as a magnet passes).

Your aftermarket TCU probably needs a throttle position transducer rather than just an on-off switch to indicate idle position. Got a name or a linky?

Mongo

Thanks! It is a TCI Auto EZ TCU. Accepts TPS with a range of 0-5v. I know it is sacrilege, but it would be a pretty snazzy way of improving acceleration on a stock motor. Made some friends on LS1TECH who are willing to part with a 3.90 differential for the 4L60E along with a TT. Wife has to approve before I start hoarding parts for this LOL

The Forgotten On

It's only sacrilege if you can't reverse what you've done.

I've contemplated doing the swap with my 81 once all of the kinks are worked out.

dr bob

Normally, I'd cue up the MK diatribe on how gears don't make horsepower. Just for contrast though.

Carl has been working on a kit for the Corvette trans transplant, and I understand that there are several already installed and working. The 3.90 final drive looks pretty quick, but will need a pretty long-legged "overdrive" to make touring practical.

The 0-5V throttle position sensor or a switch? Take a look at Carl's setup and see what he does for this.

Rob Edwards

FTFY.

Mongo

Dr Bob their manual just says any TPS so long as its a 0-5v.

dr bob

Need definition of TPS. Throttle Position Switch (ala pre-GTS 928) or Throttle Position Sensor (with 0 - 5V linear position sensing). If the latter, you don't have one.

jpitman2

Didnt the speedo signal change when ABS was fitted? Early cars are reed relay on the diff cover; with ABS I thought the signal from one of the front wheel sensors was used. These would have a finer signal (higher frequency) than the 9 pulses per rev of the reed relay.
Dont know if that would change the waveform.
Re TPS, I have seen them with 0-5V linear signals (early 80s) and later they became a set of discrete steps, only 5-6 values, but these were on L-jet.\

jp 83 Euro S AT 57k

Mongo

It requires a sensor. I emailed TCI.

I am looking into Microsquirt's TCU which requires the use of a MAP sensor for load. Sensors are the same.

Mongo

Microsquirt TCU link

http://www.msextra.com/doc/pdf/html/...ntrol-1.0.html

Mongo

Microsquirt's TCU looks like it is perfect for a 928 application with one big caveat - NO SPEEDOMETER FUNCTION.

I checked the specs of the output speed sensor on a 4L60E and it is a Sine wave type, which will not work at all, much less trying to find something that will convert the pulses.

Don't 964 cars have ABS sensors that drive their speedometers? Could the ABS sensor be tapped into in order to provide a square wave signal to drive the speedometer on the 928?

FLYVMO

Did you look into this device? ---> http://www.dakotadigital.com/index.c...rod/prd126.htm