Just a simple question and probably not your problem, but do you have a cigar hose on the return fuel line?

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1980 300D 300K KM - parting out
1979 300D 375K KM - parting out
2 300Ds for sale

About $4,500.

I didn't buy it, but I have the receipt. Apparently, MBNA was offering an "engine exchange" program in 1998. The former owner, an elderly gentleman, purchased the motor complete - with alternator, starter, and PS pump - basically a turn key engine. I have the literature on the "program". The engine was purchased through MBNA in Northern New Jersey and then delivered to your local dealershipwhere it was installed. He then paid a Mercedes dealership another $1,500 to install it. Ouch!

He loved the car but only drove it for 1 year before it failed inspection for rust. The floor pan rusted and unbeknownst to the owner, the drivers seat was falling out the bottom of the car! He parked it for a year or so and called some body shops about fixing it, but no one wanted to touch the car.

Finally in 2000, he listed the car for sale in a local free classified newspaper as a "parts car". I was the only person who came out and looked at it. I was reluctant to buy it at first, but the engine only had 12,500 original miles on it and still shined when you opened the hood. I offered $500. He called me a few weeks later and agreed to let it go.

The car sat in my garage for 5 years until I got around to welding a floor pan in it. I started driving it in 2006 and so far I have put about 12,000 miles on it myself. Really a great car. People say these 240D's have no guts, but I'm not complaining. It's plenty fast for me. Maybe cause it's a stick shift. I can cruise at 95MPH all day long with the AC on and still get almost 30MPG. Not bad for a 3,300 lb. car.

Yes I do have the cigar hose. It's skinny on the ends and fat in the middle.

I'm quite sure that IP timing is not your issue. It affects engine rpm and efficiency but not idle quality.

One of the owners of a 617 recently had the identical issue. The engine ran fine when cold and started to develop a rough idle when warm.

Turned out that the rack damper was not adjusted properly.

I'm not sure if the 616 has a rack damper or not, but, if so, that's likely your issue.

Pretty sure there is no rack dampner bolt on the 616.

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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

When troubleshooting a problem, you try to start with the simple and cheap things first if you don't really know what's causing the issue.

For example, if you want to choose between temporarily running on a bottle of diesel under the hood - and pulling the engine to do a ring job, you should try the bottle of fuel first. That's an extreme example just to illustrate the point.

So, the suggestion is for you to get a container of something, either Diesel Purge or just plain diesel, and switch the car over to that when it starts to run poorly. Doing that eliminates the whole tank and fuel line as a cause.

I also want to mention that the primer pump can cause fuel/air leak problems. The old style is a white plastic plunger that you unscrew and pump like a little bicycle pump. The new style is black with nothing to unscrew, you just push down on it and a spring returns it for the next push. Which kind do you have? If the old style, try to tighten it down more tightly.

I did the same floor pan weld work on a 240D some time ago. That was a nice running and shifting car. About a year after that work I started getting a tapping noise a little louder than usual. Shortly after that, it threw a rod.

Did you fabricate your own floor pan or use a pre-pressed replacement? I did patches on one side and the driver's side needed the pre-pressed complete replacement.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

Ken,

I have the white plastic primer pump, which I have never used by the way. I'll check that too to make sure it's tight.

I didn't know they made pre-pressed floor pans for the 240D. I called a few restoration shops, and they said it was N/A for the 240D.

I went to a machine shop and took home a 4 foot square piece of 16 guage steel. I made a template out of cardboard and then cut the metal to my template. From there after it wasn't too hard, just lots of time with the Mig welder. The section that was rotted out wasn't too big, but I figured while I was there I would replace the entire floor under the driver's seat. I made brackets for the seat as well and welded them to the floor.

After I was done I coated both sides with black roofing tar which I thinned with a little kerosene and applied with a paint brush. This worked VERY WELL as a cheap undercoating.

IIRC, it might leak air in without leaking diesel out. Don't try to open it/use it... will only cause it to leak. Next time you make a parts order go ahead and get the updated one.

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John Robbins
'05 E320 CDI - 240k
'87 300TD - 318k

I dunno if it would be the primer pump. Mine would leak out fuel all over the place when I used it but the engine still started up just fine. I eventually replaced it just because it was a huge mess to use.

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1985 CA 300D Turbo , 213K mi

Let the engine run till idle gets good and rough and try to localise it to one cylinder by loosening off one injector line at a time. Also look for air going through the prefilter in a steady stream of bubbles.

Lubro Moly - Diesel Purge?

I went to 4 different auto parts stores today, and not only did they NOT carry the stuff, not one person working in any of the stores even heard of it.

Where do I get this stuff? I live in Southern New Jersey. The closest major city is Philadelphia.

Can I only buy this stuff online?

Unfortunately, thats the only place I've ever found it...

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John Robbins
'05 E320 CDI - 240k
'87 300TD - 318k

Olympic Auto has a good price on it along with reasonable shipping.

https://www.olyonline.com/Lubromoly.asp

LM2005

Also, to comment, I had a primer pump loosen up on me on the interstate and kill the engine. Took a few moments to figure out - tightened it down with pliars and took off again. One of the first items bought for that car was the new style pump.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

Air leaks can occur anywhere in the fuel delivery chain. I had a loose bolt on top of the secondary filter, not hold down bolt, did not leak fuel, just let air in. Diesel Purge, as noted, available by mail. I would replace that primer with an updated version, a black one that does not need to be screwed down.

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83 SD

84 CD