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Old 04-23-2003, 03:22 PM
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Ruined glow plugs

I recently had an unusual experience -- first time in many years driving
Mercedes diesels. The car, a 220D which had recently received a new set of
glow plugs, was running great when one day -- shortly after I had filled up
the tank at a local Conoco station -- I went out to start the car and the glow
plug indicator on the dash didn't light. I waited a few minutes, and it lit
up ok & started. Next day same thing, but it did eventually glow & start &
seemed to run ok. Then next day -- nothing. Couldn't get it to light up & had
to have car towed -- ended up replacing glow plugs & injectors. Not cheap.
Mechanic said fuel was probably bad. My question is, is fuel the likely
problem, does this kind of thing happen very often, and is there anything that
can be done to prevent it?

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Old 04-23-2003, 05:08 PM
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I have heard of water in fuel giving injectors a problem but don,t know why the glow plugs would have a problem but then again I,m a new guy. I'll be watching to see what the goo ruz are going to say.

1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
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1964 Allice Chalmers D15 tractor
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Old 04-23-2003, 05:40 PM
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I'd bet all you needed was one GP. The 220D GP are in series so when one GP has an open circuit, then the entire GP circuit is open like a string of series Xmas lights. I used to carry a small jumper wire in my 220D to jump a bad GP to get started should one of the GP go open. Worse, I once had one GP that got a short so I had to disconnect it and jump across it.

Even if you did get bad fuel, I would not believe it would damage the GP or the injectors. The only thing that might damage injectore is water if left in them for a while which could rust the precision parts inside. However, you said the car ran OK after it started which it wouldn't have if there was much water in the fuel.

Did you have the injectors tested at a Diesel injection shop? If not, how did you know they were bad.

I think you need a new mechanic more than all new injectors and GP. How did he determine that the injectors were bad? One bad GP and he replaced them all? Do you replace all the light bulbs in your house if one burns out?

Why was a new set of GP put in your car recently? Same mechanic said you needed them? I think you got ripped off twice. You didn't say how much you total "NOT CHEAP" cost was but it would have only cost me about $10 for 1 new GP.

Yes this "thing" happens often: People get ripped off by mechaincs that either are dishonest or incompetent. Learn a few things about your car and you will save yourself a lot of money. The 220D is the simplist engine ever made to service.

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Old 04-23-2003, 09:09 PM
jcd jcd is offline
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Join Date: Jun 2001
Location: Northern New Jersey
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PEH is correct. I'm sure you only had one bad glow plug.

I broke a key rule this fall and replaced all of mine as preventative maintenance. (rule broken, if it ain't broke, don't fix it)

As the winter wore on, I had two of the new ones go bad,,,,all were Bosch. I later found that the fuse was bypassed, replaced the fuse and have not had an issue since (not sure if this led to the bad new plugs or not)

Bottom line, a bad glow plug is easy to diagnose and replace. I now see no real need to replace them unless you know they are bad. My problems started when I replaced the original 26 year old GP's. NEVER AGAIN.


PS, the mechanic should have replaced the GP first. If the problem was solved, then he should have left the injectors alone. I'm still a relative newby, but I can't make the connection between bad fuel, injectors and glow plugs.
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Old 04-23-2003, 09:21 PM
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A bad injector can take out one of the old loop type of glow plugs. It seems unlikely that all 4 injectors would go bad at the same time though. Maybe there is some way that a load of bad fuel could do that, but I have never heard of it. I suspect it just had one open glow plug and the mechanic had a boat payment coming due.

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Old 04-24-2003, 12:24 AM
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rewood, you can choose: phillips, slotted, or torx. Give one to your old mechanic enroute to the new.

For general FYI, a drippy injector can wreck a series glow plug in two ways. First is faster accumulation of carbon, which shorts the plug to the pre-chamber. Second is the drip on a red hot loop which will eventually cause the loop to break. Keep the fuel clean and dry and a series plug should last a very long time.

P.E.Haiges: I think lunch is on you, regarding why changing one plug can make the difference and changing another plug makes no difference, at least in a parallel system. My money says your engine (and most others) shut down in a repeatable fashion, providing you turn things off the same way every time (as most people do). The odds are that a particular cylinder gets set up for a compression stroke (the plug that makes a difference) and another cylinder gets set up for a power stroke and another for an exhaust stroke (the plugs that makes no difference). And you'd have to have a really boring life to check that 100 times in order to do the statistics!
daBenz - 1970 220D
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Old 04-24-2003, 02:08 AM
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I have no idea what you are talking about.

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Old 04-24-2003, 11:30 AM
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P E H, in a few previous postings you stated that you had engines where it didn’t seem to matter if a couple of glow plugs worked or not – the engine still started. And for the same engines if one plug went then the engine wouldn’t start. And it seemed to be the same cylinders that acted the same way. Swap plug from one of the cylinders that didn’t matter and off you went. Now let’s say the crank stops close to the same place when you shut the car off. In the short term it should, as long as you shut down the same way – heat/AC off, radio off, same gear, low idle selected, etc.- due to cylinder compression ratio imbalance and different clearances in main bearings, wrist pins, etc. If this is really true then a particular cylinder should be set up for a compression stroke the next time you start the car, and just about every time you start the car. Glow, fire the starter, the crank compresses that cylinder and the cylinder fires. This is the cylinder where the glow plug matters. Now let’s say that the crank sets up another cylinder for a power stroke. Glow, fire the starter, the crank expands the cylinder then exhausts then intakes then compresses. That cylinder isn’t going to fire as easily as the cylinder that was set up for a compression stroke. All this on a cold engine. And all a moot point in a series system. And a moot point if you keep the fuel clean and dry.
daBenz - 1970 220D
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Old 04-24-2003, 12:02 PM
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I think you know what you are talking about but I disagree. The next cylinder in the firing order, and it is unlikely it would be the same one each time, would be slightly before TDC because it stopped on the compression stroke and maybe even backed off slightly. So the 2nd cylinder coming to TDC on the compression stroke in firing order, would be the first one with a chance to fire.

Anyway, the problem I had was that 2 GP were bad: #3 and #5 which are next to each in firing order. The engine didn't fire at all. It was like the GP weren't working at all and originally that is what I thought the problwm was. I would have thought the other cylinders would still fire, even if it wasn't enough to keep the engine running without the starter's help. After I replaced both bad GP, the engine started on the first crank and it was below 30F. I think the one GP was bad for a while and the second one failed on my way home from New Orleans LA. AM I going to replace the other GP, hell no. In fact one of the ones I put in was a used one from another engine.


Last edited by P.E.Haiges; 04-24-2003 at 04:42 PM.
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Old 04-24-2003, 02:18 PM
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had the same problem

I had the same problem when I first bought my 77, it has those same filament type glow plugs. I bought all new Bosch glow plugs, but that didn't do the trick, what was actually the problem for some reason is that my fuel filters needed to be replaced. I got a new primary fuel filter, and I looked at my secondary fuel filter. My secondary fuel filter was all black and gunked up, because I guess algae was growing in my tank since the last owner didn't drive it that much. Well anyway, I replaced the fuel filters and everything has been great since. I would also recommend looking at your glow plug relay behind the dash, because that goes out sometimes, and it is worth checking just to be safe

1981 240D/297K/4-spd/OM617 (mine)
1982 240D/241K/4-spd (wife's)
1979 240D/291K/4-spd/OM617 (father-in-law's)
1983 300DT/240K/4-spd (brother-in-law's)
1985 300DT/???K/5-spd Intercooler conversion (brother-in-law's)
1985 280TE/160K/5-spd (father-in-law's)
1963 UNIMOG (brother-in-law's)
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