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Mysterious Glow plug Problem..good dectective needed
So here is the situation. My 85 300td has been running great. I was monkeying (with ignition turned on) around with some wires to my frybrid (WVO) control panel and I shorted some wires (sparks flew). I'm not sure what wires got crossed but the only 2 power sources in that area are: 1)directly from battery and 2) from cigarette lighter wiring ("ignition on" power source). Anyway, this caused my WVO contol unit to sense that the ignition was turned off (it beeps at when when ignition goes off without purging), this indicates to me that the "ignition on" power source was interupted. This was followed by a mysterious lack of power to cigarette lighter wiring and radio. This is mysterious because if the fuse for circuit blows then the glove compartment lights also go out, but in this case the glove compartment lights WERE still working. The fuse was OK and power was mysteriously restored to the cigarette lighter and radio. Also, this whole time the glow plug indicator light started NOT coming on and the car won't start. I haven't had time to do a thorough diagnosis of the Glow plug system, but I can tell you this: 1)there is voltage >12v to relay, 2) relay is clicking on and off and voltage >12v is coming out of the relay to the glow plugs when relay is "on". I charged the battery up real good (thought that might be the problem) and heated it with a block heater and tried starting it tonight but no luck. BUT there was a development....the glow plug light began coming on. It would work for a few cycles and then it would stop coming on. Does this sound like a bad relay??
Does this add up to anything to any of you all. Sorry for the long story, the whole electrical short circuiting thing could be unrelated (as those circuits aren't connected to anything too critical to the cars functioning). Thanks for reading all this..please help. Brett
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'85 300td Frybrid WVO Kit |
#2
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Unfortunately, most of us have these cars due to a minimal amount of electronics. Such issues are staggering in my VW TDI compared to my MB's.
Having said that, the electronics are sure mysterious. By dinking around, I have burned out glo plugs before, resulting in the disappearing of the glo light. I thought it was coincidental, but actually by running the starter hard, wearing down the battery, swapping batteries and going again, I killed a glo plug and the car wouldn't start I've also shorted out the starter wires before (loss of rubber coating). That sent a disaster through the system in terms of how the VR, Alt and Battery were interacting. diesel don
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DAILY DRIVERS: '84 300DT 298k (Aubrey's) '99.5 Jetta TDI IV 251k (Julie's) '97 Jetta TDI 127k (Amber's) '97 Jetta TDI 186k (Matt's) '96 Passat TDI 237k (Don's '84 300D 211k Mint (Arne- Undergoing Greasecar Conversion) SOLD: '82 240D 229k (Matt's - Converted-300DT w/ 4 speed |
#3
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The real mysterious part to me is why different components work and then don't without (knowingly) fixing anything.
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'85 300td Frybrid WVO Kit |
#4
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Have you checked resistance across the plugs? Pull the wiring harness that leads to the plugs (it has 6 holes but only 5 have connectors in them) and check continuity from each hole to ground. Resistance should be less than 1 Ohm. If they pass that test, the only further test is to pull them out and apply voltage and see if they glow.
When I had 1 bad plug, my light quit working. When the rest of them went bad, the light worked just like normal again. So I just take it as a suggestion.
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1985 300TD-euro 352,000 mi 1974 240D (1?)52,000 mi - has a new home now |
#5
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Yea, the part about the radio not working and then working again, you got me there. Does the frybrid controller work normally? It has relays in it and I don't know how sensitive to spikes in current they are...I know Chris Goodwin brags about how bomb-proof his controllers are, but I don't know about surges...
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1985 300TD-euro 352,000 mi 1974 240D (1?)52,000 mi - has a new home now |
#6
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Did you mess up your fuel supply somehow? Spray a little wd-40 into the intake while cranking to find out. After all sparks flew around It's control panel.
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All electrical components work the same way. Smoke is implanted at the time of manufacture. You let the smoke out and now they won't work!
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How would I use this test to determine if the fuel supply has been switched? Alsi, I don't think there should be a problem with fuel supply because when the system is OFF there is no current to valves and the default is diesel.
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'85 300td Frybrid WVO Kit |
#9
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Quote:
You might also get a quick check by removing the tank return line from the injection pump and check for fuel escaping when cranking. Just an easy test or two to make sure of what you are chasing. Either one only takes a couple of minutes to perform. Heavy unintentional current may have opened or burnt something out. For example you might now have gelled vegatable oil in an unheated area because of a control failure of some sort. Sure it concievably could be a sudden glow circuit problem but your 12 volts to the plugs usually means they are working. That is providing they were functioning properly say an hour earlier. Last edited by barry123400; 02-22-2008 at 12:50 PM. |
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Thanks Barry, Sounds like some good advice for troubleshooting. Does my intermittently working glow plug light suggest anything?
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'85 300td Frybrid WVO Kit |
#11
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Yes and no in my mind. Monitor the voltage at a glow plug and see what kind of duration time you have and voltage under load. This at least can exclude or condem the relay generally at this point.
It sometimes pays to have a helper to turn something like the glow circuit on on when you are checking things. . The quicker you become familiar with diesel issues the more comforatable you will be. Like most things it is more difficult or time consuming the first time in a new area. The upside is it may become a walk in the park the second time you experience difficulty in the same area. The boost to your self confidence is priceless. For what it is worth as a general statement it was almost impossible to burn out a glow plug itself when you had the arcing around the fuel selector control panel. With 25 years heavy electronic experience and more than a smattering of straight electrical work damage to a glow plug was just highly unlikely in my opinion. Yet there is always coincidence to consider. Divide and conquer is a very old valid concept. Again in only my limited opinion you have a primary choice of only two possible type of faults plus a little spin from the car being set up for alternate fuels. Fuel supply or glow circuit. As soon as you qualify one you will know the area to concentrate on and the helpful suggestions on site will multiply. My last comment is also to never bypass a friend to help out as well if you feel he has superior knowledge in what you are doing. |
#12
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Thanks for all the advise. It looks like I've identified the issue. 3 of my GPs are reading Open when I test the resistance. Other two test well (<.5ohms). I'm really surprised these are out, because the car was staring up very well in some very cold weather (10F) previous to my incident. I also checked my GP resistance 2 months ago and they all checked out fine. Any ideas on what could cause 3 GPs to burn out seemingly simultaneously? I guess I need to read up on GP replacement!! Nothing like working on your car, on the street, in 20 degree weather.
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'85 300td Frybrid WVO Kit |
#13
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Good you seem to have it. I have gotten too old to enjoy working outside in the cold. Come to think of it age is not a requirement either.
Multiple plug failure in cold weather is really not all that strange. Probably at least one has been burnt out for a little while anyways. Usually I do not replace all the plugs if only one fails. In your case a complete new set might be worthwhile. Do not buy an inferior brand. Buy bosh or beru. Usually money well spent. Mercedes are about the only cars I have owned that faults seem to correct themselves sometimes. Best of luck on the electrical thing. |
#14
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May have just been the last one that created the start issue. How did it run before after starting? kind of miss, or a little sluggish at first, or extra smoke? These could be signs of a cold cyl?
Changing the GP is remove wire, rempve gp, clean hole if you wish, a lot of people use reamers, a little antisieze on the plug threads only, plug in, wire on. Test again, Good to go!
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83 300SD Dark Silver Dark brown inside |
#15
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Okay I thought about this. Why are three plugs open? As mentioned I suspect perhaps one might have been out a little earlier. If you remember doing multipal glow cycles reciently in the cooler weather the stress may have been too much on the remaining plugs and a couple of others let go as well for arguments sake. Or when working on your car the plugs might have got too many cycles one right after the other.
As there is no way to have applied more than 12 volts to them in your car the arcing itself cannot have taken them. One last thought was the arcing just might have locked the relay up and left the plugs on burning out a couple. Then your battery should have dropped off though. It was not one of your concerns so I think not. What is important is you located the problem and generally speaking again it was not the worse thing it could have been. . Also for what it is worth if I were you. It is fairly safe not to buy a lotto ticket this week in my opinion. I would love to see you prove me wrong. Last edited by barry123400; 02-24-2008 at 06:26 PM. |
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