Relays

[FEP]

I am changing my engine loom / ECU from pre to post facelift.

I now have a handful of relays - think some may have been in the fuse box. Can anyone tel me how to identify relays and which one goes where?

Cheers

[rich318i]

wiki mate

http://www.e30zone.net/e30zonewiki/index.php/Fuse_Box

[Brianmoooore]

All relays in the fusebox are orange, except for the two nearest the bulkhead (K4 and K8) which are black. All have plain sides to their cases with no retaining lugs.
The fuel pump relay, if original, is orange as well, but with retaining lugs on the case.
The OE DME relay is white, and with retaining lugs.

[FEP]

OK - thanks for that. Raises a few more questions! (And bearing in mind that mine is a pre-facelift Tech 1)

I have a metal bodied relay - looks quite old but it does have lots of numbers on it - how do I interpret these numbers?

What exactly is the "main relay"? What does it do?

From the whole car map on the Wiki relay page, the ECU/DME has it's own relay? Where exactly is it?

Are the fuel pump and O2 sensor heater relays on the n/s inner wing or somewhere up near the base of the windscreen?

What is a "motor relay" and what does it do?

What are the low speed, high speed and un-loader relays all about?

Sorry to ask so many dumb questions, but I never really have understood the whole relay business.

[Grrrmachine]

Remember that a relay is a device that allows a low-power circuit to turn on a high-power circuit.

So the main relay (also known as the ECU or DME relay) turns on all the high power circuits to things like the ICV, the fuel pump and the injectors, when the ECU decides to. Effectively, the ECU can turn on or off a lot of its own functions - that's why it's got a 55-pin plug

Relay location depends on car. For six-pot engines, the 3 relays (DME, O2 and Fuel Pump) are on the inner wing, next to the suspension turret. On four-pots, they're on the bulkhead.

A motor relay is exactly that; a relay that turns on a motor. Considering electric motors use a LOT of power, you don't want that much current going through the wires under your fingertips, so things like the starter motor and the windscreen wipers have relays.

And the unloader relays disconnect all other circuits when you're cranking the engine, so that the car's electric system is "unloaded" and diverting all available power to the starter motor.

[Brianmoooore]

If you're changing from steam age to post facelift management, then there won't be any metal bodied relays involved. The only metal cased relay on any facelift E30 is the ABS protection relay fitted above the glove box, and this is only found on early facelift cars.
Assuming this is a six cylinder car, the DME (main?), fuel pump and O2 sensor (probably not fitted) are all fitted to a panel under a cover, fitted between the air meter and the inner wing.
Low speed and high speed relays are associated with air con. only.
Unloader relays disconnect parts of the cars electrical system when the starter motor is engaged, to provide extra power for the starter system and to prevent damage caused by things trying to operate on reduced power.
No idea what the 'motor relay' is.

[FEP]

Brilliant.

Well the metal bodied relay was doing something before I started. It says 0 332 014 135 on it which is see matches the picture of the main relay on the inner wing in the photo on the Wiki relay page. Should I not be using it now?

Motor Relay is as per item 17 on the map of non-fusebox relays on the relay page on the Wiki. Not really critical - just wondered.

[Brianmoooore]

Motor Relay is as per item 17 on the map of non-fusebox relays on the relay page on the Wiki. Not really critical - just wondered.

This is the relay for the ABS pump motor.
There are two relays under the plastic cover of the ABS pump assembly, and I'd better revise my earlier comment. One of these IS metal bodied.

[FEP]

Thanks for the answers all.