SPD signal ECU

[ambiorix]

I have a question about the SPD signal for the ECU.

It concerns a 4A-GE 7rib engine ( non TVIS ) built into a kitcar. On the ECU there is a connection for the speed of the car ( not the revs ), which is deliverd by a speedsensor inside the combination meter.
As the kitcar doesn't use the speedo of the Corolla AE92, I don't have this signaal and I get the faultcode is 42 from the ECU.
I also do not use the blue idle-up VSV valve to raise the revs at idle, all vacuum ports on the throttle housing are blocked.

Is it possible to run the kitcar this way, using no SPD signal ? What are the concequences driving the car in this mode ?
Why does the ECU need the speedsignal from the car ?
Does anybody know a way to suply the ECU with a proper signal that it can use ?

The last question is directed at the Westfield and Caterham builders who will encounter the same problem when using a Toyota fuel injected engine.

[firehawk]

In our AE82 FX-GT race car, we also had a smallport 7-rib engine ("red top") and had removed the dashboard completely - didn't have any problems at all. We had also removed all the idle-up and cold start features so the car needed to be started with a bit of throttle applied when the engine is cold.

I think that the signal is mostly used for the 180km/h speed limiter on JDM engines - can't think of any other use for it. Using it, for example, to compensate against wind drag at speed wouldn't make sense as the effect can be seen also in the manifold vacuum as increased load.

JMR_AW11 might be the guy to ask about the internal secrets of the ECU - he's disassembled the code contained in the CPU chip and knows a lot about how it all works.

[banpei]

AFAIK the speed sensor within the combination switch is at 100 km/h for the dinging device. The one on the ecu is meant for a speed limiter. I don't think it would be wise to connect them together.

[firehawk]

The actual sensor which generates the signal for the ECU is behind the combination meter, as this is where the speedo cable comes to. On some newer cars, the sensor is directly on the gearbox and the speedo is driven electrically.

Anyway, I found some info on where the SPD signal is being used in addition to the 180km/h limiter. The ECU uses it to keep the idle speed control system disabled when it detects that the car is moving, even if the throttle is closed (IDL signal is low). So if the SPD signal is missing, every time you let off the throttle, the car will think that it's idling stationary and use the idle VSV to adjust idle speed.

However, since you've removed the idle-up VSV from your engine, this shouldn't cause any problems. If you'd still want to generate the SPD signal yourself, a simple reed switch which connects the SPD pin to ground four times per wheel rotation will do the trick.

[ambiorix]

Thanx Jani for the info about the SPD signal for the ECU.

The info you are talking about as being used as a 180kmh limiter, where did you find this info. On the net ? Can you point me to the website ?

After a long search I seemed to have found someone who knows what he is taking about.

[firehawk]

The 180km/h limiter is mandated by japanese traffic law which requires that all new cars sold in the japanese home market are equipped with it. So if your engine is imported from Japan, it most likely has the limiter. This is usually overridden (well, raised to 360km/h - should be enough) with a simple frequency halving circuit which loses every other pulse. If you generate the SPD signal yourself with a reed switch, it'll be even easier - use only two magnets per revolution.