My '87 300D is not running like it used to, and I need some advice before I take it to my mechanic for some serious work. Following is a brief synopsis of what's going on. I'm not much of a wrench, so please excuse my weak understanding about the symptoms and previous repairs on my car. All I know is that I really like this car and would love to continue driving it if it doesn't break the bank.
My previous car, '85 300D, would start easily with a cold engine and run quietly with minimal exhaust. Much of my experience with my "new" car is based on what I remember about my 123. Since I bought it, the 124 has run rough when the engine is cold, even if the weather is warm. It starts okay, but until the engine warms up, it kind of sputters and the "diesel knock" is pronounced, and exhaust pours out of the tailpipe. Later, I started to notice a hesitation. It's not turbo lag. I would step on the accelerator and the engine would kind of bog down before accelerating normally. The problem started as intermitent, but got progressively worse and more consistent. My mechanic thought it might have a bad turbo, but found that some vacuum hoses were clogged and replaced a switchover valve. I've found lots of posts on this site related to this. It would run better (hesitation gone, other symptoms still occurring) for a while, but then would reappear. Last time I took the car in for maintenace, I mentioned the problem again. My mechanic perfomed a leak-down test, and told me that he thinks my car has worn valve guides, but it would be impossible to know without taking apart the motor (top end? - I'm a mechanical dunce). Since then, the hesitation has come back (seemed to clear up a bit the other day, strangely) and the rough idle and heavy exhaust have remained. I think they've gotten worse. Several of my more mechanically inclined (though not diesel enthusiast) friends have suggested that something "ain't right," after hearing my car at idle (warm.) My mechanic has told me that it would cost about $1400 to open things up for a look, plus whatever it costs to fix whatever is wrong.
I like this car a lot. Maintenance is due again. Should I buck up and tell them to proceed? Or should I unload this beaut and go back to the seemingly more reliable 123? Any advice would be much appreciated.

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'87 300D Turbo 220k (for sale)
'03 Dodge Sprinter 3500 tool body (shop truck)
'98 Ford F-150
'04 Subaru Forester 2.5X (wife's car)
'86 BMW L7 (for sale)
'69 Alfa Romeo Spider

$1,400 just to take a "look" is a little disturbing!

But if your willing and trust this Mechanic go ahead. I hope some master mechanic replies to your post and suggest whats best. Sorry I could not help, but that $1,400 is harsh.

a few questions

1) fuel filters - r they due for a change
2) air filter - is it clogged ... due for a change
3) clean the boost switch (next to the air filer housing)
4) is delivery line from intake manifold clogged. clean it.
5) have u replaced all rubber connectors in ur engine compartments. With the car this old, it is a something u need to consider doing.
6) have u replaced the vacuum check valve ( yellow unit that connects to the vacuum from the engine compartment into car).
7) when is the last time u ran diesel purge or something similar
8) get hold of a mityvac ( or someone who has one ) and check the kind of vacuum ur car is generating. U may have to rebuild ur vacuum pump.

Work ur way methodically and we may come closer to solving the problem. Do let us know what u find.

Thanks for your responses. I service the car regularly, so surely my mechanic checks and changes these at the prescribed intervals. I do not live on a dirt road or anything, so I wouldn't think that the air filter would be getting prematurely clogged. I will look at it though. I have not replaced all the rubber connectors. Would these be on vacuum lines and such? I will look at the vacuum check valve and the boost switch. I have never used diesel purge. I will also see if I can locate a mityvac to determine if I have weak vacuum.

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'87 300D Turbo 220k (for sale)
'03 Dodge Sprinter 3500 tool body (shop truck)
'98 Ford F-150
'04 Subaru Forester 2.5X (wife's car)
'86 BMW L7 (for sale)
'69 Alfa Romeo Spider

Most of what I know about the 603 I've learned here and messing with my '87 300D, so my advice isn't the authority answer. Would start with the glow plugs, and make sure they are working correctly. For the nailing, would clean injectors with Lubro Moly and/ or fuel additive cleaners. Check for a plugged air filter altering air/fuel ratio, which may cause strumbling and exhaust smoking. Also check timing chain stretch which could throw timing off causing smoking. Faulty EGR valves have also been blamed for some of your symptoms. Keep us posted on what you find, so we all can learn.

I will look into all this stuff and post what I find. A thought just occurred to me: not to badmouth my mechanic or anything, because I like him and trust him, but I wonder if he just kind of wants to keep it simple. There's a lot of stuff to look into here, which may or may not lead to an answer. Maybe when you're doing it for a living, it's easier to perform the maitenance (on which I'd assume profit margins are relatively high) and get the guy with the old oil-burner on down the road, rather than spend all day tracking some elusive problem when you could be doing $300 services on newer cars at one car per hour or whatever. I know when my customers come in and want some kind of special solution, I usually try to steer them toward a standard product rather than spending hours tailoring a custom solution that may or may not turn out to be profitable to me. Just a thought....

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'87 300D Turbo 220k (for sale)
'03 Dodge Sprinter 3500 tool body (shop truck)
'98 Ford F-150
'04 Subaru Forester 2.5X (wife's car)
'86 BMW L7 (for sale)
'69 Alfa Romeo Spider

Talk to Matt Cama at Old World Auto in Lawrenceville, GA, 404-550-8000. He is a good friend of mine and he won't steer you wrong. I bet he can tell you more by laying his hands on your machine for 5 mins than your guy can after $1,400!! As you can see by the picture on his website he pretty much deals excusively with older Benzs.

http://www.oldworldauto.com/

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Bill Reimels
Now down to one:
1972 300SE 3.5 W109 (Euro delivery)

Bill's ideal makes sense. A shop that has kind of a specialty function may take a far greater interest. Why not give them a call and have a chat. Ask them if they do a lot of diesels of your type. Familiarity with a model really does help. Pretty certain valve rubbers and guides do not account for all your problems anyways. Plus if 1400 just to basically remove head you may want to go to another place or at least I would be tempted. Oh yes try to get the results of the compression and leak down test before phoning if you do not have the numbers already. Could save you some time and money.

While your mechanic may be correct, and the vehicle may need valve guides, this won't explain the hesitation when you step on the pedal and it won't explain the very rough running while cold.

The symptoms point strongly to a bad fuel injector(s) and/or improper injection and/or valve timing.

Ask the mechanic when he last checked the injection timing and valve timing on the engine. If you don't get a definitive answer, get another mechanic.

Additionally, I would determine if he has the proper M/B tool for reading the timing electronically. It is a small box with a couple of lights on the cover. Without this, he probably is the wrong man for the job.

I would definitely not remove the head to "look around" at this point in time.

I would go with Billrei's advice!

By the way you described your mechanic, and pointing you towards valve seals, and $1,400, just to see, sounds to me like he has overlooked many easy checks! You should ask him if he's checked for chain stretch, as well as all the other item's your fellow members here have pointed out, and if he hasn't checked these before he said valve seals, then I would know he's screwing me, and with a smile! Some mechanics love to take advantage of others ignorance, and I don't mean that in a bad way, but less knowledged I guess would be a better way to put it.

Change air filter anyway! Even if you don't live, or drive, on dirt roads. You'd be surprised how much dust you don't see is in the air around roads.

You didn't say, but what is the milage on the car? .........BB

My car has a little under 185k miles on it.
I'm going to do the simple checks myself asap. I'm also tempted to go ahead and take the car up to Lawrenceville for a look by Old World. While I trust my mechanic, I must say that he doesn't do such a great job explaining things to me. Like I said before, I'm not a real mechanic like so many people on this site, but I feel like I'm intelligent enough that a little explanation helps my comfort level when I drop real dough on my car. He's never been real forthcoming with explanations.

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'87 300D Turbo 220k (for sale)
'03 Dodge Sprinter 3500 tool body (shop truck)
'98 Ford F-150
'04 Subaru Forester 2.5X (wife's car)
'86 BMW L7 (for sale)
'69 Alfa Romeo Spider

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Never hurts to have a second opinion!

Is your car burning oil? Or blowing blue smoke on start up? If so then maybe the valve seals are getting weak. If not move on, it is something else.

I would start with getting the injectors spary pattern and pop pressure tested. Also replacing the glow plugs and cleanout the intake manifold. On a 603 the EGR is a useless, don't spend a dime to "fix" it. In fact plug the vacum line at the very least. Or buy one of Brians egr removal kits.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

You are getting some great advice from the guys on the forum. The only thing that I can add is that your vacuum pump is probably not the cause of your rough running problems but while you are in there you may want to look into replacing it. At 185,000 miles it may be a ticking time bomb. It is a known defect in early 603 engines.

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Tom Hughes
St. Louis
84 300SD
92 300D
86 300SDL

I had crappy diesel performance issues for a while, till I took my 300CD to Hatch and Sons in Mass for an unrelated repair. They said "By the way, your car isn't running like it should, we can adjust the fuel pump timing if you want." I'm glad I had them do it, because it feels like a completely different car. WAY more pickup! No other repair shops, not even dealers, have ever even suggested this. The constant mantra was "Well, you know, those cars were never all that fast to begin with, yadda yadda..." They either didn't know or care what to do. Thank you, hatch!

http://www.hatchandsons.com

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Gil

2004 ML350
1984 300CD; Ivory (sold)