Its a Mystery - PeachParts Mercedes-Benz Forum

Gregory · #1 05-15-2014, 08:30 AM

1983 300DT engine

In the last week or so the engine has been running much better. It used to buck and stumble on cold idle until it warmed up, blowing white smoke, then it seemed better. My diagnosis was retarded timing of the IP.

Now it runs great. It starts cold with smooth idle and little if any smoke. I never touched the IP timing, or did anything to the engine that would change things.

Could this be the difference between winter and summer diesel blend? I can't think of anything else.

Maxbumpo · #2 05-15-2014, 08:38 AM

Could be you need a valve adjustment, and the weather has finally warmed to the point that the symptoms are masked?

Change in fuel is also a possibility.

Dan Stokes · #3 05-15-2014, 09:40 AM

That excorcism has finally kicked in?

Dan

rscurtis · #4 05-15-2014, 10:20 AM

Quote:

Originally Posted by Maxbumpo

Could be you need a valve adjustment, and the weather has finally warmed to the point that the symptoms are masked?

Change in fuel is also a possibility.

Very good possibility. It could also be a burned out G
P. A well-tuned 617 in good condition will make a smooth, smokeless start even at 0*F.

Maxbumpo · #5 05-15-2014, 10:50 AM

Yes, forgot about glow plugs.

Gregory · #6 05-15-2014, 12:01 PM

The engine has 5 new GPs and 5 rebuilt injectors. I put them in.

The car had only ten miles on it with the engine transplant when I bought it.

The PO gave me two home-made valve adj wrenches when I bought the car. I haven't checked the clearances, I've just assumed they are correct for now, because the PO probably set the valves about 3k miles ago, when he installed the engine.

The PO also swapped the IPs, that is why I was thinking the IP timing is off. But now it runs good.

It does seem like it doesn't have enough power at highway speed. But my last 300 was an SDL, 1987, so I might be a bit spoiled by the 6-cyl.

eatont9999 · #7 05-15-2014, 02:10 PM

It could be timing. Did the PO know how to properly install an IP? Did he actually install it properly? I guess you would have to check the timing to be sure.

Are the GPs still good? What brand were used? Some only last a few GP cycles before they burn out.

crashone · #8 05-15-2014, 02:54 PM

It is a self healing Mercedes.

uberwasser · #9 05-15-2014, 03:01 PM

What brand glow plugs? Cheap brands have sometimes failed rapidly.

Did you bench test them before install? It's not totally unheard of to have a bad one out of the box.

I'd not assume the valves were adjusted. If he installed the engine just pre-sale it may have been low on his list of things to do if it ran OK upon install.

Gregory · #10 05-15-2014, 03:08 PM

I don't remember the GP brands. I bought 2 at one store and 3 at another.

When it starts running bad again, I'll check the valves first.

Simpler=Better · #11 05-15-2014, 03:45 PM

Quote:

Originally Posted by Dan Stokes

That excorcism has finally kicked in?

Dan

Sometimes it takes a couple months

cooljjay · #12 05-16-2014, 02:12 AM

I give up attempt to figure out my smoking cause, one day it seems good....other days not...assuming i am burning fuel, but fuel mileage seems to be 20mpg city...right on the mark...so why smoke? and only at idle? why am i not getting bad mpg? I give up....least it keeps the bugs at bay lol

ah-kay · #13 05-16-2014, 02:25 AM

I hope it doesn't but nothing mechanical will heal by itself. It is all to do with compression, stuck rings probably. I would recommend a compression test.

Similar thing happened to my 300SDL, ran like a champ for a few days, then idle rough and ran like crap. I did a compression test and 2 cyl had very low readings. The problem was a broken ring in 1 cyl and stuck/semi stuck rings in others when I opened up the engine.

Mxfrank · #14 05-16-2014, 05:49 AM

Let it go. If it's a problem it will be back and be worse. If not, then it won't. Really...it could have been something as simple as moisture in the fuel. Not good, but if it's digested, done.

OTH, when I rebuilt the head on my 190DT, I was in a hurry to get it going. I had an old set of Autolite GP's on the shelf, which I had decided never to use. But I needed plugs and I used them. Started getting what you're having. Thought it might be timing. Thought I might have a cyl with low compression. Thought the shop might have botched a valve. Thought I might have a sticky tappet. Thought the one India built injector was bad. Within 12K miles, a plug failed, which made the problem clear. New plugs and no problems. But I wouldn't bother unless it was consistent, too many possibilities.

eatont9999 · #15 05-16-2014, 08:34 AM

Gregory,

If you have 5 minutes and an ohm meter, you can test the glow plugs. Pull the GP harness from the GP relay and test for ohms at each of the 5 terminals. Ground should be touched to the engine. Your symptoms match what a glow plug or two would do if they failed. The rise in ambient temp making the problem go away is your first clue.

My newest 300SD only had one working GP. The car would start just fine in 70F or above temps but anything below that would have trouble.