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#1
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what did i do to my glow plug relay?
so ... in my weekend of over-repairing (i love the compulsion thread, btw) ... i decided to dust off my multimeter and decided to look at my glow plugs ... AKA how diesel giant did them.
my dash glowplug light was fine ... everything worked great ... (i think), but was compelled to learn a bit more while i had an hour in the day battery voltage: 12.5 running: 13.2 turned everything off, and checked each plug from the relay connector everything was fine. less than 1Ω on all 5. plug the only plug back in ... nice and snug go back into the house to deal with other things. come back about 4 hours later to give it a cold-start .... and the glow plug light on the dash no longer illuminates i double checked the tightness of the connector try again nothing .... i have not had time to look at anything else since then. and I'm not even really sure where to look did i fry something? what testing should i do? one solution finds 3 more problems. geoff
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'81 300SD ---> '46 IHC Metro (some day) |
#2
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Pull the cover off the GP Relay and check the 80 amp strip fuse.
It may look good, but could be cracked. I keep a spare taped to the inside of the Glove Box door. Charlie
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there were three HP ratings on the OM616... 1) Not much power 2) Even less power 3) Not nearly enough power!! 240D w/auto Anyone that thinks a 240D is slow drives too fast. 80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works |
#3
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could i have cracked it (or been the final straw) by opening the cover and pulling the connector?
i'll give that a look at lunch. thanks g
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'81 300SD ---> '46 IHC Metro (some day) |
#4
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The odds are severely stacked in favor of the connector being the culprit.
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#5
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are you saying the connector from where the GP wires come into the relay?
does that need to get R&R?
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'81 300SD ---> '46 IHC Metro (some day) |
#6
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I'd pull the cover, and turn on the key to the glow position, and quickly measure voltage to ground on both screws in the fuse. if 12v on both, it's not the fuse.
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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 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
#7
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Take the connector out again and look for green or whitish corrosion on the contacts. Use 600 grit wet dry paper rolled up lubed in soapy water to clean the contacts, rinse, blow dry, coat it with some Nolux (or any grease will do in a pinch) and see it that fixes it.
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
#8
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Quote:
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w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded next wish/project: w114 coupe OM603 powered |
#9
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As you should. The glow plug timer is "hot at all times."
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#10
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Did you plug it back properly?
On the E class the connector need a good push, its a tight fit.
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E300TD year 2000. RUSTY SOLD cost a fortune to maintain on the road but run well on WVO Second Merc died due to corrosion ( NOT rust) How can mercedes get away with that for so long? Third lasted a month then went away... Fourth now... Corroded too... |
#11
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the drama continues...
Hi Everyone:
here are my findings from lunch...
is there anything i can rule out? any more diagnostics? why the heck did i open the thing in the first place ... it was working fine! sorry for that scream ... as always, any help/ideas are appreciated geoff
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'81 300SD ---> '46 IHC Metro (some day) |
#12
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If you were getting 10.5 volts at the Glow Plugs the Relay is working. You were also hearing the Relay Click off.
Could it be that the Bulb in the Glow plug Light is no good? Also does you 81 300SD have the Glow Plug Relay that is connected to a Temp Sensor?
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84 300D, 82 Volvo 244Gl Diesel |
#13
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pre-glow system...
here is a diagram of the 300SD pre-glow
there appears to be a temperature sensor... the diagram says 'as temperature increases, resistance decreases' i also find the coincidence of the light going out at the exact same time as my messing-about to be tooooo coincidental. anything else to check?
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'81 300SD ---> '46 IHC Metro (some day) |
#14
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On your car assuming that is the correct schematic, the thermal sensor is inside the relay body.
The only external connections are the 4-pin control plug and the 5-pin (6 position body with 5 holes used) connector for the glow plugs. The control plug on your car does not have any thermal sensing wires. Later cars had external sensors so they had more external wires. You can do a quick check by jumping pin 1 to 3 on the body side of the control harness. With the key in II you should have a glow light. The glow relay does 2 things with the light. First is the light turns on to help you know how long to pre-glow based on ambient. Note that the relay continues to supply current to the plugs after you crank, that is known as "after glow". That is why there are 2 power wires in the control plug. One is hot in II and III, that triggers the pre-glow, and the other hot in III only, that is the after glow trigger. The light does not illuminate during the after glow interval. The second function is that the relay has a current sensor built in. It compares the current draw from plug #1 to the sum of the current draws from the other 4 plugs. The approximate mathematical operation it is doing with the sensing coils is (plug 1 current * approximately 3.5) - (sum of currents in plugs 2 - 5) = 0. If the result is not zero then there is a plug not drawing current. If the summing circuit is not satisfied then the glow light will not illuminate. Unfortunately the design of this circuit had enough room for error that it is possible for 1 bad plug to get through. Also there are documented cases on this forum of members whose glow plugs passed the ohms test but did not glow hot enough to do their job as verified by bench testing with jumper cables. (Danger- extremely high temperatures - almost 3k *F - and risk of short circuit - battery explosion likely if you short the cables - so proceed with extreme care on this if you decide to try this test.) If you had a plug that was on the way out maybe it just failed while you were testing. If your bulb passes the jumper test I would go ahead and change out the plugs. Be sure to use only Bosch or Beru plugs. Auto lite is bad juju. And use anti seize paste on the threads, you will thank yourself next time.
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The OM 642/722.9 powered family Still going strong 2014 ML350 Bluetec (wife's DD) 2013 E350 Bluetec (my DD) both my kids cars went to junkyard in 2023 2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles) 2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles) 1998 E300DT sold to TimFreeh 1987 300TD sold to vstech |
#15
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Quote:
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