RAD951

I am currently having electrical problems with my car. The first problem is the dme relay, its not getting the signal to close the circuit and send power to the computers and the fuel pump. The way I have been running the car is by closing the circuit manually with a piece of paper to wedge it closed. Secondly on the dme relay fuel pump side coil, when does that relay come on???

And another question, after looking around and smelling for burnt relays, I found the cooling fan relay burned up. Could that be stopping the signal to the dme relay for the computers????

nh3

Is the coil inside the relay getting power? If it is then the coil is shorted and the relay is junk. No power to the coil? Do you have a factory alarm?

nh3

RAD951

I have power to all of the coils, the problem is that the coil isn't getting the signal to let the power go to the dme and fuel pump. Whats up???

RAD951

bump

nh3

If you have power going to the magnetic coil in the relay that will pull the contacts in thus suppling power to the dme and fuel pump. No power to the coil (or signal as you refered to it) equals no contacts being made. Think of a relay as nothing more than a switch. The coil is the mechanical means of throwing the switch. The coil is energized and pulls in the contacts and that will make the switch. Coil de energized and that breaks the switch or vise versa depending on what terminals are n.o. or n.c.

nh3

RAD951

I know what a relay is and does perfectly, I just need to know from where the small signal wires come from. Signal wires meaning the ones that activate the relay on and off, not the positive constant wires.

SoCal Driver

Let's see if this helps.

Pins on the bottom of the DME Relay
944.615.227.00

85 --> To Ground
86 --> From Ignition On/Cranking (has diode)
87 --> To DME Pins 18 and 35
85b --> To DME Pin 20
87b --> To Fuel Pump - Fused
30 --> 12 volts from Battery - NO FUSE!!!!

To: Run fuel pump short from 30 to 87b
Power DME short 30 to 87

Kind of how it works:

Turning on the key powers the coil (85/86) through relay pin 86 this pulls in the relay contacts 30/87 providing power to the DME at pins 18 and 35.

The DME grounds relay pin 85b through DME pin 20 to power the coil (85b/87) pulling in the contact 30/87b to power the fuel pump. NOTE: This is conditional on the contacts 30/87 engaging.

The DME also sees 12 volts on pin 4 when you crank the engine. This could be what triggers the initial pulse to the fuel pump.

I've been told that the input from speed sensor tells the DME to keep the fuel pump running.

There is a diode inside the relay between pin 86 and the coil. This has been reported to occasionally fail. Search Pelican or Rennlist.


I may have missed something here. If I have we shall soon hear about it.