Hello all,

A few weeks back, all of a sudden my OM603 GP light stopped working and consequently I had rough cold starts. Went through the process of checking out the GP relay and the glow plugs. I found #3 GP was open, aaha time to replace that one, the resistance on the other five showed good and all were in line with each other between .9-1.0 ohm. I must say replacing #3 GP with the intake on the car was not the easiest thing in the world to do, but with patience I got it swapped out in about an hour.

After that the MB started up easier and better than before...but not quite right. She still has a little roughness at cold start-up and I can see a little white smoke when I gun it the first 10 secs or so and then she settles out nicely.

So I've checked the GP's again just to see if there was one more out of whack but the resistance still shows the same (good) for all of them, the wires to the GP's also tested fine and they are all getting the proper voltage. I know that the relay works I can hear it click and the timer shuts it down after about 20 secs.

I can't figure this one out. Has anyone had a similar situation or have ideas as to where to check next?

TIA
Bill

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

Did you use a glow plug reamer to clean out the carbon?

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1977 300D Lost coolant while someone else was driving
1983 300D Can't run without oil
1985 300SD (gone but not forgotten)
1990 300TE 4matic Sold
1991 Yamaha Venture
1975 Kawsaki 250 triple
1974 Honda 200CL
1951 8N Ford
2008 Wildfire 650C

No I did not use a reamer, I couldn't get a mirror in there to check it out the hole but the GP that came out was very clean with no signs of carbon build up on the edges. I also purge the system regularly and have not had smoke or soot issues so I just assumed that the fuel was burning fine.

Outside of reaming, will purge or another product work to remove the carbon build-up if it exists?

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

The '86 has a full set of "functioning" glow plugs.

With that said, the engine won't start cleanly when cold unless I use the full 35 seconds of available glow time. This is in ambients of 50 degrees or so.

The plugs are old and the tip temperature is probably far less than desired.

If you want some snappy performance on startup.........change the other five.........even though they check out OK with a meter.

If you do it........please post your results on this thread. Maybe I'll get some desire to do mine............

Brian,

Thanks for the comments. I had posted a question to the forum few weeks back regarding the different types of glow plug tips and their potential impact on running order.

Here's a shot of the two plug tips in question:

[IMG][/IMG]

The one on the right with the bullet shaped tip is the bad GP pulled recently, the one on the left is an old possibly original Beru round tip plug of which I have 5 spares and used as the replacement for the bad bullet tipped one.

I wounder if the only performance difference between the two styles would be that the bullet shaped ones glow quicker than the round tipped ones. If so then could I have 5 GP's warming up quicker than the sixth leading to a situation where the cylinder temperatures are hotter in 5 and cooler in the sixth, somewhat mimicking a a near bad GP?

If it was number 1 or 2 I'd just get another bullet tipped one and swap out, but #3-5 are such a pain to get to.

Any opinions?

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

I think the shape of the tip matters little.

I think the age of the tip matters greatly.

Thanks,
Oddly enough all five spare Beru's tested at .9 ohms, the other newer ones tested OK but worse than the Berus. Your point on age though could explain a performance difference between them leading to the condition I'm experiencing.

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

Not odd at all.

Cold resistance is not relevant in any way to the hot resistance. The hot resistance determines the current flow and the resultant temperature of the tip.

The temperature of the tip is directly related to starting performance versus glow time.

As always you explain it so well. The ones I thought were good may not have been based on how I tested them. Well I guess it's time for new ones all around when I work up the gumption to dive in and remove the manifold.

I'll post the results of that on this thread.
Cheers

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)