85 911, no fuel pump, injector pulse or spark

[scottsmotowerx]

Hi all. New to the forum & looking for some answers. Got a customers 1985 911 in my shop. Have a crank no start condition. Vehicle has no pulsing ground @ coil, no injector pulse & the fuel pump doesn't energize. Dme relay has been replaced but pin 86 doesn't energize pump. Manually tested pump, both speed sensors, maf etc & all test within acceptable ranges. Possible dme failure?? Thanks in advance

[steely]

Welcome!

I was leaning towards the old decrepit sensors until you said they were A-OK.
DO they change values as you move them around while measuring (stable?).
I would fault them before the DME, but if you trust your measurements, then yes, the DME could be suspect.

[ischmitz]

Fuel pump needs to come on (with good DME relay) when only one of the following conditions is true: So either (1) or (2)

1. START terminal energized (engine cranking)
2. Motion detected at the flywheel with both sensors functioning

Bad sensors alone would not prevent the fuel pump from coming on during cranking. In your case if the fuel pump doesn't come on during cranking AND there is no spark/fuel pulses this makes me think there is no power to the DME. Does the car have an alarm system. The way the factory alarm is implemented is to cut the +12V to the DME. This could be your issue.

First check is to feel if the ICV is vibrating with the key in the RUN position. This indicates the DME is alive and powered. The ICV is the silver can on top of the intake.

Also, try to listen for the faint click of the 1st stage of the DME relay under the drivers seat when you move they key to the RUN position. If the relay doesn't klick and the ICV isn't vibrating you have no power to the DME.

Let us know what you find,
Ingo