Rough Cold Start - Glow Plug Question
 

When I start my '83 300D after it has been sitting overnight, it starts right up and runs smooth for probably three seconds before it starts to miss a bit and expels a fair amount of grey smoke. It will do this even if it is 80 or 90 degrees out, but it gets worse as the temperature falls. Unless it is REALLY cold (i.e. below 40 - that's really cold for Houston), the problem goes away after 30 seconds or so.

If I let the glow plugs run a full cycle, the problem is reduced but not eliminated. That is, I have the missing/smoking problem even in August after a full cycle of the plugs, albeit not as badly as in the winter.

I replaced all five glow plugs in May (I used Bosch), which was about 22,000 (almost entirely highway) miles ago. I reamed out the glow plug sockets when I replaced the plugs.

I just removed all the plugs and hooked them up to 12V. After a few seconds they all glowed white-hot.

After that I tested the resistance at the relay, and all of the sockets read between 1.7 and 1.9 ohms. Based on other posts, shouldn't this number be lower, like under 1? And what exactly does it mean if every single plug reads high - that I installed five brand new but faulty plugs, or that the plugs are already wearing out?

Oh, and the valves were adjusted around 6,000 miles ago. I did it myself and am confident in that I did it correctly.

Next time you replace main fuel filter,fill it with atf.That should unstick a injector.

The resistance sound high but you might check on Diesel Giants web site, he has a write up on testing them.

Diesel Giant says that the resistance should be 1 ohm or less. I guess I'm having trouble interpreting exactly what it means to have them all test 1.7-1.9 when 1 or less seems to be preferred, at least according to DG.

As I remember testing mine 3 of them were under 1ohm and 2 above so I change out the 2 and have had no more problems.

The aforementioned statement is all that is required to rule out the glow plugs. If the engine starts and runs, the glow plugs have done their job.

On engines with marginal compression, extended operation of the glow plugs will serve to mask the symptoms, but the problem remains.

In your specific case, I'd be looking to see if one of the injectors has a marginal pattern that doesn't perform well when the engine is cold.

This would be more compelling if the engine developed the onset of the problem relatively quickly which would rule out low compression as the culprit.

Answer
 

Above 1.0 they are junk..

You need a glow plug reamer to clean the hole.



Glow plugs link thread All diesel models
http://www.peachparts.com/shopforum/diesel-discussion/137732-glow-plugs-link-thread.html#post1019018

Where does one purchase a good, reasonably priced glow plug reamer? I see one on eBay for $39. Surely there are cheaper ones out there that still do the good job...

..and I never reamed when I put my new set in this summer.. The old ones came out easily (Beru), they were all good by the way, but what the heck, a couple of the new ones (Bosch) went in "stiff" as they were inserted. At first I wondered if they were correct part, but triple checked and yes. Am I doomed next time I try to get them out?

I agree the GPs are probably OK, and if they are all reading the same I would suspect the meter is a little off. It seems very unlikely they are all really at 1.7 - 1.9 ohms cold (you did test them cold?).

These are the same symptoms I had with a couple of bad injectors.

Cross the very tips of your meter probes together, get the ohms for that, then subtract that from your plug measurement!

Typically just probes and their wires alone add 0.5 ohm to every reading you take.

Yeah, it sounds more like a fuel delivery issue. I agree with those suggesting you check the injectors. You should also try to verify that you aren't getting any air in the fuel lines.

Answer
 

The reason you use a glow plug reamer is that there is carbon buildup around the tip.
This causes a carbon (insulation) sock to form over the electrode.
The reamer breaks up the shell to powder that will pass through the pre-chamber and out the exhaust pipe.

Here is a thread that should answer the rest of your questions.

glow plug reamer - pic
http://www.peachparts.com/shopforum/diesel-discussion/76490-glow-plug-reamer-pic-post1756147.html