Factory ECU questions

[SHOoff]

I posted these in the tuning forum on j-body.org but nobody replied so assumingly noone knows an answer.

Will the factory ECU continue to keep the fuel pump in as long as the key is on, if it's not seeing an ignition pulse? Or does it simply turn it on for a second for the prime, and that's it until it sees the engine running?

I have a MS-II piggybacked into my car and was looking to possibly save on one of the outputs to use for something else by not having it turn on the F/P.

Secondly I was wondering about the ignition pulses. I know the crank sensor runs right to the ICM. What I was wondering about is what happens from there? Does the factory ECU see a pulse every time a notch passes the sensor? Or does it only see a pulse when the ICM discharges one of the coils?

Thanks much!

[bszopi]

Not sure on the fuel pump...

As far as the ignition goes, the crank sensor sends a 7x signal to the ICM. The ICM then converts that to a 3x signal, which is sent to the ECM for timing control. If the ECM is taken out of the equation, then the ICM takes over timing control by using a base "limp-home" spark table.

[robertisaar]

IIRC, if the bypass line isn't activated/deactivated by the ECM, i believe the ICM will only run on base timing at all RPM and MAP positions, which is like 9* i think.

[SHOoff]

Ok. I guess ill have to try to run it without the MS unit in charge of the fuel pump and find out.

With the ICM I'm going to assume that for a 4 cyl that it would send a 2x signal since only having 2 coils. I was looking into the tach signal for the stock ECU to run my gauge.

Thanks for the info guys

[robertisaar]

i believe the ICM tach out is a 1X signal.... regardless of being for a V6 or not. but i'm not entirely sure about that.

[SHOoff]

I'm going to make the assumption that since the car still runs in limp-home mode with the ICM unhooked that the ECU keeps the fuel pump on. But I'll find out for sure.

Then I guess on the whole tach output thing I'm stuck where I was before on having to figure something out.

Still though, thanks a ton for the answers.

[pocket-rocket]

I thought the ECM turns it on for a few seconds to prime, then the oil pressure sensor supplies power to the fuel pump relay to trigger the pump after oil pressure has been established- that way if you lose oil pressure the engine dies to prevent damage.

[robertisaar]

not quite....

you can disconnect the OPSU connector when running and it will continue to run.

the oil pressure based switch is a backup in case the regular relay fails.