Does anyone on this site know exactly what the pressure sensor does when it detects too much pressure? Does the voltage go up or down? How EXACTLY does it cut the fuel to the rear rotor? Injectors or spark?

Thanks,
~Rob~

 

The pressure sensor does nothing but send a signal corresponding to manifold pressure to the ECU. If the ECU sees that manifold pressure has exceeded 8.6psi it stops firing the injectors on the rear rotor until boost drops below 8.6psi.

 

When the output of the brown/red wire reaches 3.70volts, the ECU cuts FUEL to the rear rotor.

You can do this in your driveway. Just put a source of pressure to the nipple on the pressure sensor while the car is idling. The fuel to the rear rotor will cut off when the output of the brown/red wire is at 3.70 volts, and the engine will get the wobblies til you let the pressure off. Been there...done that.

 

This raises an interesting point. After 15 odd years it's unlikely that all FC MAP sensors will output 3.70V @ 8.6psi anymore. Most will probaly be higher or lower, so fuel cut could be at a quite different boost level for every car.

Perhaps a "Hailers driveway test" should be performed. My stock boost sensor always reads a little below zero with the engine off, so who knows what the ECU thinks the engine's doing.

 

will the fuel cut off cause the engine to stall?

 

****My stock boost sensor always reads a little below zero with the engine off******

Try removing the vac line to the sensor, blocking that line off, then starting your engine and letting it run. Then look at your boost gauge. Does the needle now come closer to ZERO????? Mine does and I have wondered on this site if others have the same results??? Takes but a couple of minutes to do. It's a curiosity of mine.


****will the fuel cut off cause the engine to stall?*****

If you meant doing the fuel cut in the driveway....no my car does not. But I can see where a not so well running car might drop dead. Bottom line.....no it should not die.

****This raises an interesting point. After 15 odd years it's unlikely that all FC MAP sensors will output 3.70V @ 8.6psi anymore*****

I doubt if all are the same either for the same reason. Also as you let the pressure off the sensor the thing does not come back online at the same voltage/pressure it went off at. It comes back a bit lower, something like 3.5, I forget the exact figure.

The driveway test was just a fun thing to do, it's not useful for much except seeing approx where to set the voltage on a home built FCD.

Did I mention I passed Emissions testing yesterday with flying colors?
So I don't have to avoid the coppers with my two months out of date sticker anymore.

 

That makes sense, since battery voltage is a little higher with the engine running.