Speed sensor needed???

[kcpaz]

I'm going to be using a Porsche 915 tranny so I won't have any speed sensors. I'm trying to use the stock engine management and I'm wondering if there will be any issues. I did a search and from what I've read, the speedo, and cruise control wouldn't work, but I won't be using either of those systems anyway. I know there will be a check engine light but I'm not too worried about that. will there be any drivability issues?

[b3lha]

I know the ECU does use the speed signal, but I haven't analysed it enough to see what it is used for. Generally, if a sensor is faulty or disconnected, the ECU will pick a sensible default for the data supplied by that sensor. I would recommend that you just try it and see - It will probably be fine.

If you run into problems you might be able to fake a speed sensor signal with a simple bit of electronic circuitry.

On my car I use a slightly fudged speed signal to overcome the JDM speed limiter and it doesn't cause any problems.

[kcpaz]

Originally Posted by b3lha

I know the ECU does use the speed signal, but I haven't analysed it enough to see what it is used for. Generally, if a sensor is faulty or disconnected, the ECU will pick a sensible default for the data supplied by that sensor. I would recommend that you just try it and see - It will probably be fine.

If you run into problems you might be able to fake a speed sensor signal with a simple bit of electronic circuitry.

On my car I use a slightly fudged speed signal to overcome the JDM speed limiter and it doesn't cause any problems.

Thanks b3lha. I think it should be fine, but if not, I can probably figure out what kind of voltage it wants to see and like you said "fudge" it.

You sound pretty familiar with these ECU's. can you think of anything else in the operating system that I won't be using that may cause an issue (PS switch, neutal safty switch,...)? I am modifying an engine harness and I'm trying to simplify everything so I'm only using the functions controlled by the engine ECU.

[b3lha]

It's not looking for a voltage. It's a 5v square wave. Four pulses per revolution of the sensor IIRC. There was a long discussion about it somewhere in the Aussie forum.

I am working on reverse engineering the ECU firmware, but I'm at a very early stage so I can't really give you a good answer. Potentially ANY missing inputs could cause you a problem. But it can't be too hard to overcome because the VW Vanagon guys have succeeded.

As far as things like the neutral switch and torque control signal, your best bet is to look at what the 5-speed conversion guys do with those wires.

[kcpaz]

Thanks, looks like I have some more research to do.

[kcpaz]

okay, so I figured out how to deal with the torque control, and I won't have to worry about the ignition lock because I'm using the 911 steering colum. The neutral safty switch will have to be addressed though. Does anyone what colors the wires are on the neutral safty switch and which ones need to be jumped?