W115 220D - Running rough, low power, stalling
 

I recently bought a 1972 220D. When the owner showed me the car, it idled rough. It had been sitting for a year or two, so I drained the fuel tank, replaced the rubber hoses and fuel filters, did an oil change, cleaned out the intake, etc.

Since doing this tuneup, it still idles rough. I've bled the fuel system the best I can. Usually I can get it to idle for 5-10 minutes, then it suddenly stalls and won't start up again for an hour or two, which I find strange. Once it starts up again, it does the same thing.

The part that worries me most is the noise that it makes when I rev it. It almost sound like a rod knock or something internal gone wrong. I did an oil change, and the oil is full, but the oil pressure gauge appears to be broken, because it reads 30psi all of the time, even when the engine isn't running.

I have a video of it running. Let me know what you guys think.

1972 220d running - YouTube

Yikes!

Being a fellow W115 owner, I'll take a stab.


I hear several things.

1. The pinging sound (like the shaking of a paint can) is your injectors nailing. At the very least they need cleaning so a diesel purge is in order, perhaps even new nozzles.

2. I thought I caught some belt squeal. So minor it's not worth mentioning in comparison to:

3. That clattery/knocking sound. From the video, I think that could be one of several things. Hopefully, it's valves out of adjustment. Next down the list could be a leaky exhaust manifold gasket. I say this because your engine sounds much, much louder than it should.

My worst fears, though, would be the same ones you have...an internal engine problem. Randomly stalling and then not restarting for a while sounds very suspicious. Can you give it a compression check?

What sort of shape is the car in? How much money are you willing to throw at it?

Without better quality audio (tough, I know) and compression figures, I'd say get ready to shop for another W115.

There is definitely a major exhaust leak where the manifold meets the midpipe. There is a lot of exhaust gas that escapes at that connection. I'll have to see if I can fix that so we can hear it better.

I have a compression tester that I've used on gas engines. I'll have to look up how to do it on a diesel. I'm assuming you just pull the glow plugs instead of the spark plugs?

I got the car for very cheap (few hundred dollars). The previous owner had the floors re-welded and there's no serious structural rust. The body only has surface rust, so it just needs a good paint job. I've already put a couple hundred in it for a new battery and tuneup. I really wouldn't be willing to put in more than another couple hundred to get it running nicely. I guess we'll see what it's worth after a compression test.

Thanks for your help!

Your petrol compression tester probably doesn't read high enough to work on your 220 (or at least you should hope not!). Although you can connect through the glow plugs, it's generally easier to remove the fuel injectors. If you wanted to spend the money, that would be the time to have them sent out for a proper cleaning. Don't forget the injector washers/heat shields. They're single use but aren't too expensive.

250 psi or better is the minimum compression needed to ignite the diesel, 300 psi or better means your engine should have some life left albiet with some oil consumption, and 350 or better would be most excellent. You'd want to see all pistons more or less equal as this would indicate even wear.

When you changed oil, what came out? Did you see any metal flakes or fragments?

My pressure tester reads up to 300psi, so I suppose I could use it to see if my engine is even worth working on. As far as the injector washers and heatshields, those will have to wait until after the compression test. Wouldn't want to replace them on an engine that is scrap anyway.

Exactly how hard is a valve adjustment? I assume you'd need some special tools? I'm good with a wrench, but have never worked on a diesel before.

I'm sure I could do an engine swap with these engines, if that is the better route. I guess it depends on the cost of a used engine. I've swapped newer BMW engines with much more hoses/wiring.

I didn't notice anything in the oil, but I didn't specifically look either. It's already gone, so I'm unsure of what could have come out.

You may blow up your compression tester ( maybe that would be a good thing). You are going to need a fitting for the glow plug hole or injector. Harbor Freight has tester kits pretty cheap.

Valve adjustment is pretty easy. Do a search here or check the FAQ- it is probably documented. You don't really need any special tools- just a couple of 14mm wrenches. You may need to grind one down to be thinner. Many people put a bend in them, but not really needed.

Probably going to be very hard to find a good used engine now. You should have been looking for one ...20 years ago....

Have you removed the oil fill cap and checked to make sure that oil is being thrown around the camshaft? With a broken gauge, I'd confirm oil flow before anything else. That's a noisy engine and it could be running dry.

OK, I'll probably get this compression tester. Somebody in the reviews said it worked on a Merc diesel.

12 Piece Diesel Engine Compression Tester


Sorry for the noob question, but does the engine have to be running when I check for oil on the cam?

Well, maybe not if you can tell its really wet up there. Best is to connect a working manual gauge at the oil filter and confirm it develops pressure, even if you can't start it.

On that tester, the parkerized plug in the center is for the Bosch injector on MB, VW and a few other cars.

Needs to be running to check oil on the cam. You could also disconnect the oil pressure gauge line and see if it pumps out oil when trying to start it. Dont let it run longer than a second or two to see if it's pumping oil up the gauge line.

Ok, I cranked it and it almost started. It probably would have if I gave it more gas. But anyway, there was oil on the camshaft, so we know the oil pump is working to some extent. Also, there is smoke in the crankcase when I open up the oil cap. I guess this means that there is some blow-by? Compression test is the next step, then.

Thanks again for the help.

Yes, smoke in the valve cover is a good indication of blowby. If you can get the engine to run, loosen the oil cap. The degree of movement is a quick way to gauge the condition the rings and an indicator of relative compression or the lack there of. If it stays in place, good. If it sort of hovers, not totally shot but certainly some wear. If it gets blown into the next county...not so good.

1982 Mercedes 300CD blow by - YouTube

Ideally, you want to do the compression check with a warm engine. But speaking from experience, it's somewhat painful to remove the injectors on a hot engine. In my limited experience, I've noticed about 50 psi difference between hot and cold compression with the el cheapo compression tester that was linked to above.

Remember, 250 psi is about all you need to be able to get the engine started from cold. Yeah, your oil consumption is probably going to be high, but theoretically it should run.

Cold compression test didn't turn out good. Now I see why it won't start. :(

Cyl 1: 290psi
Cyl 2: 240psi
Cyl 3: 260psi
Cyl 4: 150psi

Well, number 4 doesn't look good. But it could be a stuck ring. There's threads floating around about using Marvel Mystery Oil to work it loose.

It can't hurt to try.

Ok, thanks for the idea. I'll give it a shot. It isn't really essential that I replace the injector heat shields now, is it? Wouldn't be hard to replace them if the motor is miraculously saved.