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Old 03-22-2010, 05:05 PM
esloc esloc is offline
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Join Date: Dec 2009
Location: Wisconsin
Posts: 10
Voltage Drop at Glow plug Relay

So I have been messing around a little bit trying to figure out what's with a rough idle and varying amounts of smoke at startup. During the winter months I figured no big deal--at least it was starting--but now as its getting warmer the issue almost seems to be getting worse.

I did the normal glow plug checking procedure and they all check-out fine (they were replaced last fall) at about .4 ohms. The peculiar thing is that with the ignition off, the relay is getting full battery volts (~12.4) but when I turn the key to start the glow plug cycle the voltage at the relay drops to 10.4 volts, slowly climbs to about 10.9 V during the cycle and that after the relay shuts off hops back up to 12 V.

It seems to me like a bad ground somewhere, but I don't really know where to start. I tried replacing the battery ground cable but that didn't make any difference. I'm hoping someone who has also experience with this issue on an om603 knows some other grounds to check. Where does the relay ground to? The wires all just disappear back into the fuse box area.
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