No power to Fuel Pump Relay

[Komzorz]

Here's the situation: If I jumper the terminals at the fuel pump relay, fuel pump comes on and I can start / drive the car just fine. Put the relay in, and it never gets the signal to complete the connection. The car has always been this way, sat for a decade, corrosion is a possibility.

Where do I go from here? I can finally work on the car tomorrow, let's do this.

[dr.strangelove]

bust out some wiring diagrams!

are we talking a typical 4 pin relay? if so, it's usually 30 to 87 (hot in and power out) and 86 to 85 (power in and switch to ground, although I can't remember off the top of my head which is which)

If you are saying that you are jumping pin 30 to 87 directly and you can get the pump to work, then power isn't the issue.

It comes down to either a bad relay (does it even click? did you try swapping relays out?) or a bad pin 85 or 86. Bust out your ohm meter along with a wiring diagram and start back tracking.

Pm me if you are having trouble tracking down a wiring diagram for your car, i might be able to help.

[Komzorz]

I have the ETM and a Bentley..

Yeah, when I connect 30 to 87, I get power. Basically I can't get 85 and 86 to do their thing. I bought a brand new relay and tried swapping it; no difference. This terminal in particular doesn't look that bad corrosion wise, but it's a possibility I should investigate.

Should I be like, looking under the dash for something, or under the hood? Everything's stock and nothing has been screwed with, something just isn't working.

[dr.strangelove]

Do you have power at pin 85 or 86? one is definitely power, and the other is the switch to ground. If you have power, then you have an issue on the ground side. At that point, you just have to follow the wires, sucks.

[Komzorz]

I'd be getting power with the key in the on position, correct?

[jlevie]

The relay coil should have power from the ignition switch via C101. Coil round is provided by the DME when it sees timing data from a rotating engine. That should help you figure out where the problem is.

[Komzorz]

Okay, some chumps stole my multimeter out of my car so this got sidetracked for a while till I got a new one. (guess who fixed their door locks after that?)

Pin 30 always has power.
When I jump 30 to 87, the fuel pumps work and my engine starts fine.

Pin 86 gets power with the key in the on position.

When the relay is in, nothing happens.

Car, y u do dis?

[Komzorz]

Pin 85 of the relay should be grounded by the DME when the engine is turning. Since the engine runs, it has spark and thus the DME is seeing timing data from the CPS, which is a necessary codition for the DME to ground the coil of the relay. Since you don't see ground on pin 85 either the wiring between the relay socket and DME is bad or the pump control circuit in the DME is bad. A continuity check from DME connector pin 3 to relay pin 85 will tell which it is.

Performed successful continuity check which meant the DME was dead.

Upgraded from a 153 Motronic 1.1 to a 173 Motronic 1.3 DME, everything is working great now.

Thought I'd provide my solution so this thread can be useful.