So, on Monday I purchased my first MB diesel, a 1986 300 SDL with 350k, 200k on the engine. On the test drive it started a little rough, and I figured it was due to old glow plugs, most of which were original. After a minute or so of idling it was purring beautifully. Pulling out of the driveway it had plenty of power, and I drove it at a sustained 55-65 mph for about ten minutes. Everything seemed good. I talked the owner down to 1300 bucks, he signed over the title, and I headed home with my beat up tank of a luxury automobile. And that's where everything went to hell.

Unlike the test drive, this time the car seemed to be taking its time getting up to the 55 mph speed limit. Within a minute or two, I had the pedal completely floored and was only limping along at forty. No matter what I did, I just could not get the RPMs above 3000. The engine did not seem to be struggling at all, just slowly losing more and more power. After staggering up a tiny hill, it was going 25, and I pulled over with the hazards on just as the engine up and stalled altogether. By then it was spewing pretty big clouds of blue-black smoke that smelled really greasy and sooty, not at all like healthy diesel exhaust. On restarting it was really rough and farted out another huge cloud but would idle okay until I cut it off. I probably made it a whole twenty miles before I had to call a tow. Thank god for AAA. Now its sitting in my driveway and every time I try to start it it gets rougher and rougher.

So the question is, what went wrong?

I found a few previous threads with 603 owners getting power loss through a plugged up trap ox or catalyst (my car's trap ox has been removed). I took out a bolt in the exhaust manifold to reduce backpressure and starting seemed a little easier, but the idle was still pretty rough and revving the engine killed it. For about five minutes after stopping the same thick smoke was pouring out of the bolt hole. So I figure that I probably do have a pretty plugged up cat, but that's only the tip of the iceburg.

Is it a fuel system issue, or perhaps the fuel itself? The PO said he barely drove it 60 miles a week in the last year, so for all I know the diesel that's in there is a year old. He says he rebuilt the injectors but after talking to him I kind of doubt the guy really knows much about these engines. I ordered a diesel purge kit from dieselgiant, and hope running that plus changing all the filters and putting fresh fuel in the tank will get it up to at least a smooth idle. Until that comes in the mail, is there any thing I can do except wait and think about all the other, potentially far more expensive, things that this could be?

Do you guys think it could be the turbo? It seems to me that if the turbo was seized that would explain why taking the bolt out of the exhaust didn't do much. Is that right, or a I missing something?

Finally, I worry that I cracked the head or blew the head gasket. Yes, the engine does have the dreaded #14 head. But while I was driving it the coolant temp never got anywhere near a dangerous level, and the nasty black stuff coming out the tailpipe seems more like the thing's burning oil or bad fuel rather than coolant. It does seem that the oil level has dropped since I purchased the car.

Well, that's all I've got. What do you guys think? I've been a long time lurker on these forums, and am really impressed by the depth of knowledge here. Any help would be greatly appreciated. Thanks!

Two basic easy things to do. Replace the fuel and air filters and see what happens. Could be that mice built a nest in the air cleaner and you simply aren't getting enough air. Black smoke is unburned fuel, so when you see it, immediately think, 'not enough air'.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

also find a long uphill climb at interstate speeds hold pedal to metal.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Is there something blocking the air intake?
Replace BOTH fuel filters, and the air fliter!
make sure you are getting complete throttle from the linkage

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1981 300TD 4 speed manual
Euro bumpers, zender valance and skirts, H&R springs, billy HD's, leveled sls, real AMG Pentas 16x8 et11, vdo boost/egt gauges intergrated into ash tray, eurolights, led 3rd brake light

I agree with Kerry.

Fuel filters will need changing out of good diesel-owner habits, but are not your problem. When fuel filters clog you have no smoke, no power.

It is a lack of air, pull the air filter and see what you find. Could also be a seized turbo, you can pull the rubber boot from the intake side of the turbo and spin it by hand, if there's no obvious drag it is probably fine, move on to the next item.

The sudden onset is a bit odd, but could happen if a nest in the intake horn or laying beneath the air-filter element was lifted to the filter under highway acceleration.

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Gone to the dark side

- Jeff

Well do you know if the motor has ever been rebuilt? If all the filters check out ok, then i would think you have a compression issue or something. Especially if you are seeing all the smoke. Usually blue smoke is not a good sign. When oil is burning it will give a blueish smoke. I would do a compression test just for ****s and giggles.

Well, I pulled the filter and didn't find anything out of the ordinary unless you count a fairly dirty filter and one dead wasp. Unfortunately I wasn't able to pull everything off up to the turbo because of lack of time before work... I'll see if I can do it tomorrow morning. I just checked the oil, and it seems like its a lot dirtier and at a lower level than when I first took it for a test drive. Is there a chance its a problem in the engine block itself?

without going through all the far-out possibilities, the likely issues are turbo and/ or headgasket.

I can't make sense of why the issue would worsen as the engine warmed up if it was the lower block... they aren't known for cracking.

If you are certain it is oil burning, start with the turbo and rule it out before checking the head. The cheapest way to figure these things out is process of elimination.

*A cheap way to test the head gasket is to re-torque the head bolts. This is not the greatest advice, but I suggest it b/c of the car you bought. It is not a fix, only a temporary adjustment to reseal the oil supply from block-to-head. And if you're going to go through all that work, you might as well throw a new head gasket on there and do it right.

The compression test is a good idea after you inspect the turbo as well.

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Keep us informed! This is a great resource and this forum has the kindest members around.

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Regards,
Ian White

1995 E300 Diesel w124 OM606
2014 E550 w212 M278 biturbo

2001 BMW 740i E38 M62 (past)
1981 300SD w126 OM617 (past)

How do you re-torque a head when it's supposed to be torqued using a stretch-bolt? There isn't a spec for that, it'd be a WAG at best.

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Gone to the dark side

- Jeff

So I started on pulling the turbo yesterday, and when I disconnected the connector from the turbo to the charge air, I found that they both were nearly clogged with extremely dirty, gunky oil! Did this oil blow out of the intake valves or was being blown in by the turbo? I haven't had the chance yet to check the turbo out - I'm going to go finish the job right now.

If it is the intake manifold that is clogged with that mess, that is caused by the EGR valve. Clean it all out and see what happens.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Should I just use carb cleaner on the thing and scrape it out? I read about people just block up the vacuum line to the egr to keep the valve closed, wouldn't that work just as well?

I had to scroll back to your first post to see what kind of car you are repairing, it helps a great deal to put it in your signature line.

Clean it out any way you see fit.

A BB in the vacuum line to the EGR is all that's necessary, another BB in the ARV line while you're in there is also common. As long as the EGR isn't stuck open, there's no reason other than cosmetics to remove it.

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Gone to the dark side

- Jeff

The blocking of the vac line is to be done after you've cleaned out all the gunk from the manifold....it will prevent it from happening again.

I'd probably remove the manifold and clean it out away from the motor. Scraping + carb/brake cleaner should do the trick. Might want to get some stainless brushes to feed up through it too to get everything out.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)