PCM power relay is chattering

Asked by Nov 03, 2016 at 12:48 PM about the 1999 Ford F-250 4 Dr Lariat Extended Cab SB

Question type: Maintenance & Repair

When the key is turned on ready to start the PCM relay chatters. The truck
will not start. OBD reader turns on runs through scan test but will not link up
sends back information to check various other  things that are working. I tried
another scanner with the same result. I have changed the CPS but noticed
the fuel pump is not coming on I have checked fuel interrupt on passenger
side. This is a 2002 super duty f250

8 Answers

78,375

Check the relays power and grounds feeds just too make sure the voltage is stable, if it is then replace the relay, I have seen this happen on the old MCU system but not on the OBD2 system, but anything is possible.

It's actually the relay below the PCM the injector drive relay I have switched it with others and it still sounds like an electric fuel pump it is chattering so bad

78,375

Then you still need to find out if the relays supply voltage and grounds are stable, if the are then you either have a high amperage draw on the ECM power feed wire or a short in the ECM itself, and either of those would explane the OBD link failure and the no start and no fuel pump.

I put a jumper wire to the pump it comes on with the new power source but still will not fire

78,375

That is cause the ECM is not sending any signals out. Get out the wiring diagrams and start tracing circuits, I would start with the main power and ground feeds to the ECM, disconnect power and use an ohm meter to check continuity on the wiring.

thank you but I think that you just went beyond my skill level. I'm kind of a plug and play guy I can remove and install but doing electrical diagnostics is beyond my capability I guess it's time to take it to a shop Thank you for your help

What does the injector drive module do

i hooked a jumper wire to the silinode on top of the motor and was able to start the truck the buzzing in the relay quit the truck started so it has to be a fuse some ware in this system that is not closing the Circuit

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