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1982 240D Mercedes Benz---Skips

My 1982 240D Mercedes Benz skips especially when accelerating. While it doesn’t do it all the time, when it does it really loses power and comes almost to a crawl (at least 10 mph decrease in speed) and is quite annoying for me and probably for the drivers behind me who have no idea what’s going on. My guess is that the fuel injectors are clogged as they have never been changed since the car’s creation. When idling it does not skip; only when engaging and shifting through the gears (this is a manual transmission) especially when going up into third gear and fourth. I hope someone out there can shed some light on this as I really want to get it fixed as soon as possible because this is not safe.

Several possibilities, including worn injectors, clogged filters, low compression (worn engine), and valves out of adjustment. You’ll want to find a good ‘old MB diesel’ mechanic to check it out.

If this diesel car has no in-tank fuel pump assist like my older VW diesel, then the line from the tank to the injection pump must be perfectly sealed or else it can draw a little air into the fuel line which can make the symptom that you describe. I can’t explain how it could be intermittent, however. If you have a section of clear fuel line under the hood like my VW has, you can see any air bubbles that may have entered up to that point. The other obvious thing is a plugged fuel filter but in my estimation, that is unlikely. I have inspected some of my old fuel filters and none were clogged; appeared easily good for another 30,000 miles. I have never had my fuel injectors out of the engine at over 250,000 miles so far and have never heard of clogged diesel injectors. Worn, yes but not clogged.

Your benz is 30 years old and it is a diesel. You really need to go to a benz forum to find folks who know about these cars. You must have a mechanic for a car this old, so that is the 1st person you take this problem to. Other options are a German car specialty shop, or an MB dealer. You need someone with diesel expertise.

Fuel pump and fuel pressure are critical with these old diesels. There are filters, and perhaps even fuel separators that keep water from getting out of the fuel tank and into the motor. It is hard to say if you have a routine lack of maintenance issue or a significant fault somewhere in the fuel delivery system. I don’t see this as a clogged injector issue. If it was the idle would be off, and the problem would be consistent as in every time you start off from a stop.

The FIRST thing I’d check is the cap or plug on the #4 injector.

See this picture: It’s nice because someone painted all four injectors red. Going from each injector to the next injector to its rear (right) is a braided line, about 3/16" in diameter. See them? There is no such line going from the #4, because there is no #5 on a 240D. That injector has a plug instead. The one pictured looks like it might have been fashioned from a piece of the hose that has been plugged. If that plug is degraded, the car will not run right. I might not call it skipping, but it is a factor in drivability. Back when I had a series of 240 and 300Ds as my daily drivers, I used to keep a spare plug in my glove box. They came in 5-packs from the dealer.

I’ve never found a Benz forum that was filled with anything but stuffed shirt Benz owners bragging about their latest new cars. Questions? Forget about it… Anybody know one?

The plug that MG McAnick mentioned is the end of the fabric/rubber injector internal leakage fuel return line that returns fuel to the inlet side of the fuel filter. If the plug leaks, it might suck in air which will degrade performance. My VW plug degraded but it did not suck air, just leaked fuel. Air bubbles in a diesel injection pump result in a badly running engine.

Thanks everyone that has responded to this post. I don’t know how to respond to each person individually so from MG McAnick and above I do appreciate your taking the time to respond. Seems like I have a little work to do. I do have a MB mechanic so I’ll take it to them. Just wanted to know if there was something I could do before taking the car in. It has 270,000 miles (probably more) and aside from the skipping it runs fine. Thanks again and Happy New Year!

270,000+ miles = worn. If the simple stuff isn’t it, have a compression test run.

I’m no Benz expert at all, but experience with VW diesels has me agreeing with texases about having a compression test run.

If there’s a problem with compression then the valve lash could possibly be considered as a cause of any compression problem.

@benz240d, I used to work at a Benz dealership.

Many owners had low compression and were unaware of it.
After adjusting valves, there would often be a marked improvement in performance.

Hi guys! Thanks again! Yes, I’ll have the compression test done. Also, I decided to take a closer look at the fuel filters and one of them is solid black (the smaller prefilter). It was clear about 3 years ago so I’m guessing that I failed in the area of routine maintenance. Should have changed these a long time ago but this is my first diesel and I’m learning a valuable lesson. So, I’m having both fuel filters changed and will update you all on how that part went and if it affected the performance. My guess is that it will but we’ll see.

Ok here’s the update…changed the air filter, both fuel filters and NO SKIPPING! The Pre filter was clogged I mean really clogged. This is my first benz and I while changed the oil on a regular basis I changed the fuel filters and air filter only once in 4 years which is how long I have owned it. So, to make a long story shorter, I have learned my lesson with a diesel…the fuel filters especially need to be changed on scheduled intervals (including the air filter). I appreciate the comments and will take them to heart. With the number of miles the compression will be checked soon. But in the meantime, the skipping has subsided. That is a HUGE relief!

@benz240d, thanks for the update.
Sounds like you got it fixed on the cheap!

In his book “What You Should Know About Cars”, the late Tom McCahill said that most car problems as far as the engine running properly is concerned are pretty simple. This book was published about 50 years ago, I think it still holds true today. You just proved it.

Yes! Fixed it for cheap! So glad too. Who would have thought something so simple. Now I have to watch my speed because while it’s still slow, it’s a lot faster than it was even picking up speed going up hill. Now, I just need to get the cruise control fixed so any ideas about that will be good. Thanks guys!