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87 325is - Running - Removed Dash & Components - Dead sad smiley

Posted by EricM 
Hi all,

I'm building a 325is for 24 hours of Lemons. The car was running yesterday morning (once being jumped by another car) as the battery is dead. I decided it would be a good time to remove all of the dashboard as next week I'll be fitting in the cage; however, after carefully unplugging and removing everything per some instructions I found on a website, I went to test the gauges (as they'll be mounted to the center of the firewall.

Car really wants to crank over and nothing happens. I do not hear the fuel pump working and I didn't remove any wires that (I think) would be detrimental to the fuel system (from under the dash - but I could be wrong). Any chance you guys might know what happened? All wires seem to be for the AC system/Heater system/Stereo equipment. I checked the fuel relay under the hood (looks fine) and I lightly tapped on the fuel pump under the car to see if it would come to life... but nothing. Any idears?
Did your car have the OBC? If so, you may have disconnected the fuel pump lock out relay.
Quote
Archeo-peteriX
Did your car have the OBC? If so, you may have disconnected the fuel pump lock out relay.
I've never heard of that! Why would the OBC control that?

I know that I have run my 1989 325i without the instrument cluster (and driven it) without any problems what so ever. Outside of the radio/alarm/OBC thing I don't think anything on the dash would prevent the car from running.

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

The OBC "code" function activates a relay in the OBC relay box to...
a) in the 325e, interrupt power to the Main relay and hence the Motronic control unit.
b) in the 325i, interrupt power directly to the Motronic control unit.

Look for the OBC relay box up under the left side of the dash. It is item #7 in this RealOEM drawing, and it looks like this:



There are two flat connector plugs into that box. Find the Green wire (pin-3 on Connector-2). That one comes from the ignition switch and is hot +12v whenever the ignition is in the Run or Start position.

That Green wire goes through a normally-closed relay inside the relay box and comes back out onto the Green/Red wire (pin-4) on the same plug, leading either to the Main relay on the 325e or the Motronic control unit on the 325i.

If the "code" feature is activated on the OBC, among other things, the relay inside the relay box is held open, thereby interrupting power to the main relay or Motronic. Unplugging the relay box similarly interrupts the power.

If you want to remove that relay box for weight savings, you will have to connect the Green wire directly to the Green/Red wire to bypass the missing relay.
Holy crap, THAT'S what that little box is? It came in a "Box-O'-Parts" when I bought my car, but didn't have enough identifying marks on it for me to identify it, even with Google's help.
Apparently that whole system is bypassed in my car, because I no longer have that box in my dash. If not bypassed properly, this could very well be the OP's problem.

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

I don't think it is the OBC deal. I retrofitted my 318is with the full 13 button OBC including this box and although I've not tested the security feature, it has had no impact on things.

My money is on something with the ignition switch.
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