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DISCUSSION => Electrical => Topic started by: MichaelP on June 20, 2010, 11:20:26 AM

Title: Where is main relay?
Post by: MichaelP on June 20, 2010, 11:20:26 AM

update: nevermind, I found it. Under the cover at the top of the firewall. Thanks anyway.

I'm embarrassed to ask this, but I've got a no start, and based on previous experience with other BMWs, the main relay is a suspect. But where is the thing? The BMW electrical diagram references it, but I can't pin down which one it is.

Edit: this a '91 E30 318ic, not an 'is, if that matters.

Title: Where is main relay?
Post by: DesktopDave on June 20, 2010, 01:08:15 PM

If you get a no-start and the relays are all good, test the crank position sensor resistance.  Should be ~600 ohms.  It will prevent the fuel pump relay from energizing, thus no fuel.  So don't toss an FP relay if the pump won't prime on start.

Mine had this trouble when I bought it...the crank sensor was very dirty and the AFM wasn't sending a signal.  Cleaned both up, it's run great ever since.

Do a stomp test too.  Sometimes it helps.