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#1
04-16-2023, 11:03 AM
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How much current should the glow plugs draw?
My little diesel isn't starting nicely if it's not plugged in. I assumed I had a bad glow plug, so I popped the connector off and measured resistance from the four wires, through the glow plugs to the battery negative. It reads 1.2-1.3 Ohms on all 4. A new glow plug reads ~0.9 Ohms.
I got out my cheapie chinese DC amp clamp, and read ~15Amps on each individual gp wire, rapidly dropping to ~12A as they warm. All those readings were taken with the engine warm. Since all the gps are reading the same, I am starting to think they're working, but 15A seems crazy low. What current draw should I see? Also, what other issues might cause it to run rough or just die for a few seconds after starting, before it warms up? This just began recently.
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'75 John Deere 450C (times 2) '83 240D plus parts car '87 F350, 6.9L IDI '89 F350 crewcab, 7.3L IDI '89 F-Superduty, 7.3L IDI '91 F-250, 7.3L IDI '91 F-350, 7.3L IDI '94 F-350 Crewcab, 7.3L IDI '94 E-350 Ambulance, 7.3L IDI 
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#3
04-16-2023, 02:09 PM
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Agreed.
It doesnt mean the plugs are good though. Thw plug is supposed to heat nigh instantly at the tip, and worn plugs will be slow, and heat further from thw tip, causing hard starts. A new set of bosch plugs wont hurt.
__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 560SL convertible 1987 190D 2.5-5SPEED!!!  1987 300TD 2005 Dodge Sprinter 2500 158"WB 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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#4
04-16-2023, 04:32 PM
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__________________
2012 Mercedes ML350 Bluetec 102K (hers) 2005 Corvette 55K (fun car) 2002 VW Jetta TDI 238K (mine) 1998 Volvo S70 T5 Turbo 211K (kids) 1994 Ford F150 4WD 246K (firewood hauler) 1983 Mercedes 300D 384K (diesel commuter)
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#5
04-16-2023, 06:27 PM
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My trucks draw about 50A/plug, so I was expecting to see a lot more inrush current.
Oh, well, it's getting warmer every day. I'll definitely get new plugs in before next winter. Thanks, all!
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'75 John Deere 450C (times 2) '83 240D plus parts car '87 F350, 6.9L IDI '89 F350 crewcab, 7.3L IDI '89 F-Superduty, 7.3L IDI '91 F-250, 7.3L IDI '91 F-350, 7.3L IDI '94 F-350 Crewcab, 7.3L IDI '94 E-350 Ambulance, 7.3L IDI
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#6
04-16-2023, 06:29 PM
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12 A initially sounds reasonable, which is 144 W, and matches your ~1 ohm reading. The wiring may not tolerate much more current. I don't fuss over the exact ohm readings. If bad, you read infinity at the GP Relay connector. I often find one or two glow plugs bad. I'm keeping a log. So far some Chinese brands (VSP, CP something) only lasted ~20K miles. I recall that Autolite lasted longer, but not pulling it up since not the question.
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1984 & 1985 CA 300D's 1964 & 65 Mopar's - Valiant, Dart, Newport 1996 & 2002 Chrysler minivans
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#7
04-17-2023, 07:31 AM
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Quote:
__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 560SL convertible 1987 190D 2.5-5SPEED!!! 1987 300TD 2005 Dodge Sprinter 2500 158"WB 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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