GP light does not come on the first time I spin the engine. If it fails to fire then when I spin the engine 2nd time then it will come ON. Also comes on with subsequent spin. All 6 GP check out good and measure 2 ohms or less at at the connector. I am stumped. Any ideas?

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Can you swap relays with another SDL? First swap the 80-amp strip fuse.

Sixto
87 300D

Are your glow plugs good? The light is designed not to come on when there are dead plugs.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

I think I know what is the problem. I suspect one or more plug is not drawing enough current at startup. It is kind of a 'lazy' GP. I did a few tests. When I glow it for 5-10 seconds ( no GP light ), no spinning of engine and switch off then try to start it again then the GP light comes on. It tells me the lazy GP fools the GP relay that it is not working initially.

Now the challenge is to find out which one. It could be a loose connection at the plug.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

IR thermometer at the GP contact post?

Sixto
87 300D

Checking a glow plug with an ohm meter isn't a sure thing. It's like a pretty good guess. If you want to really confuse yourself, and just for fun, do a continuity test on your glow plugs. Even testing with jumper cables with 12 volts isn't a sure thing as was reported recently on a post. Part of the plug got white hot while the tip didn't.

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2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900