Hello, all

Apologies in advance for the long, seemingly rambling post. I'm just trying to include as much relevant info as I can off the top of my head.

Some of you may be familiar with my project - a 1982 240D 4-speed. I bought the car in 2012 and was working on it until recently. I got it on the road, finally, on Sunday 10/18/2015.

Right now, the car's got 275,XXX miles on it. The car ran and drove VERY nicely until Monday of this week (so, for a week), when it started running roughly for no discernable reason - at idle. It seems to run OK when I drive it (took it for a test spin tonight).

Right now, I'm battling a few issues. I know the battery needs to be replaced, but I don't want to go ahead and do that until I have it running correctly again.

All the fuel lines (including the injector return lines) and the fuel filters are freshly-replaced (less than 2 weeks ago). I did a diesel purge just before driving the car on 10/18. This also includes the fuel tank screen. The tank itself - I cleaned it out last year while working on the project. In addition, I installed a

When I started driving the car, I had maybe 7-10 gallons of diesel in the tank - all bought from a Sunoco station. I brought it home in jerry cans and added it to the clean tank. I've driven the car maybe 200 miles locally so far, and filled up the car this past Sunday at the local Sam's Club. I added some Power Service Diesel Kleen to the tank, just to be sure.

The rough running happened right after the car's very first highway run. On Monday night, after driving the car locally for a week, including my 13 mile (each way) commute to work (top speed apx 50 MPH during commute), I decided to take the highway home. So, I had the car up to 65. It seemed to run, drive, and handle well. But, when I got off at my exit, I noticed the car was running rough. The timing of the highway run and rough running may have been coincidental, but I don't know for sure.

The car doesn't seem noticeably low on power, but I can't be sure.

When checking under the hood, I noticed that there was a slight fuel leak from the fuel filter banjo bolt (the big can filter). I'd neglected to replace the crush washer when I replaced the filter (I know, I know...). Thinking I was sucking air in from this point, and that it was a potential cause of the rough running, I decided to replace it.

I didn't have one on hand, so I ran to the store to get one. The only one I could find was a copper washer, as opposed to the original aluminum one. I replaced it along with the rubber seal ring on the banjo bolt (amazingly, I had a few of these new on hand). The car seemed to run a little better, but still not perfect. I took it for a drive around the neighborhood, and it seemed to run more or less OK. When I got home, I checked and the bolt was still leaking. I'm not getting a good seal with the new sealing washer, so I'll have to remove it and try to find another washer that fits and seals.

So, that may still be the problem. But, if I seal that leak and the car still runs rough, what's the next step for diagnosing the car?

The car has a new thermostat and temperature is holding steady at just below the 100 mark (the mark between 80 and 120), so I don't suspect a head gasket issue. The car also has a fresh valve adjustment - a couple of weeks back, just before I started driving the car.

I doubt a 15 minute highway run at 65 MPH in 4th gear was enough to cause any damage to a car that was running very well just a day before. It's odd that the engine's behavior changed so dramatically and so suddenly.

I'll try to get a new crush washer in there on Saturday and fix the fuel leak. If that doesn't help, I'll have to continue on with diagnostics. The car still starts very quickly, so I also don't suspect any sort of compression problem. If this minor fuel leak isn't the issue, I'm wondering what to look at next. Injectors? How would I diagnose bad injectors? Could one go wonky so suddenly?


Thankfully, I have other cars to fall back on while I sort this out. As I said, this 240D is still very much in shakedown.

First, get the car up to operating temperature and open your fuel filler cap. If the roughness goes away, then your tank breather is clogged. In that case, you may want to check if the tank is collapsing as well. If there is no change then move on.

If you have the original primer pump, crack the bleeder screw on top of the fuel filter assembly and then unscrew the primer to pump as if you're priming the system and listen for noise as well as feel for diesel escaping. This is a very common cause of introducing air into the system. If it leaks diesel or sounds like a kazoo or makes a vibrating noise, then replace it. If not, move on.

If you have an MW injector pump (and you do, I'm pretty sure), unscrew the little 10mm bolt just aft of the #4 cylinder line on the pump itself. It is the IP air bleed screw. Do this while the engine is running and just barely unscrew it till a tiny bit of fuel start bleeding out then close it.

Make sure all the nuts on the hard lines from the IP to the injectors are tight.

With the car running and up to temp, start at #1 cylinder and crack the upper hard line nut to bleed any air out. Do this with all four, one at a time. You should notice a very distinct change in engine behavior when the nut is slightly loose and diesel isn't popping the injector you're working on. If you loosen one and it doesn't change the idle, that is your bad injector.

Check the orifice or small hose that goes from your altitude adjustment on your IP regulator. If it is clogged, you'll need to unclog and see how this affects the car. Often there is a hose from this component which goes into the dash (in theory to suck in cleaner air than in the engine compartment.) This hose could be clogged somewhere in the dash. (When I bought my first Benz, this hose was capped in the dash and the car ran like a dog.)

If you do all this and can't find any leaks, you're going to have to get into your lift pump. You may have a slightly leaking lift pump which will definitely have an effect. There could be many more things going on as well but these are an easy start. Your diesel purge may have knocked something loose as well in the IP and that could be causing the problem inside one of the valve bodies.

Hope this helps.

Phil Forrest

__________________
1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

I did check out the tank breather when I cleaned/replaced the tank, but I have nothing to lose by checking this.


Alas, I don't have the original primer pump. I replaced it a few weeks back with the upgraded black plunger style pump. I wonder if the new one could have been bad right out of the box... Can you describe that kazoo sound a little better?

I have no idea which pump I have, but this is another one where I have nothing to lose by checking/trying this.

I've never disturbed these. I suppose I could/should check them.

Hmmm... very interesting. I'll definitely have to keep that one in mind.

Had to Google that one. I have no hose coming off mine. I'll check it out.


I hesitate to blame the diesel purge, as I drove apx 200 very nice miles after the diesel purge with no ill effects. I would think that if the diesel purge were to blame, the problem would have shown up right away.

Then again, if I was sure of anything, I sure wouldn't be posting about this issue.

That it does, Phil. It gives me a starting point for this weekend's diagnostics. Thanks much.

You have an MW. All OM61X-engined W123s, W126es, and W116s had them here in the US (in Europe, they used M pumps). Not so sure about the W115, since I recall some of them having some differences...

__________________
"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

If I recall correctly, all the 240D's in all the chassis variants had MW pumps. The 220Ds prior to 1974 had M pumps.
The main differences between the M and MW are the lubricating oil and the altitude compensation.
The M is the old style pneumatically-governed IP with a diaphragm that regulates fuel via a throttle body and venturi vacuum. Oil is internal, not connected to the engine at all. Kind of ingenius and insane design, if you ask me.
The MW is oiled by the engine, has a mechanical fuel governor and altitude compensator is a small vacuum can with diaphragm that reacts to ambient air temperature.

Phil Forrest

__________________
1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

Thanks, all. I'll report back the weekend with the results of my diagnostics (even if they turn out inconclusive).

"I'll try to get a new crush washer in there on Saturday and fix the fuel leak. If that doesn't help, I'll have to continue on with diagnostics. The car still starts very quickly, so I also don't suspect any sort of compression problem. If this minor fuel leak isn't the issue, I'm wondering what to look at next. Injectors? How would I diagnose bad injectors? Could one go wonky so suddenly?"

You should not see or smell fuel anywhere, anytime so fix the leak(s) first. The best diagnostic aid for air in fuel in any diesel engine is a clear return to tank line. In your Mercedes, it is at the filter tee on top of the filter housing (where the cigar hose connects to). You should see solid fuel there without bubbles at any time, engine running or off, otherwise, air is getting into the system.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Oh - fixing that leak is absolutely my top priority. I'm well aware that I shouldn't see/smell fuel. The car's parked until that happens. I'm just hoping I get lucky and that's the whole problem.

A little background - I've been around W123s since my parents bought their 240D new in 1980 (they still drive it). I got my first 240D in 1996 and drove it in to 2005. I've had other diesel Mercedes on and off since then. I just haven't daily driven one since 2009. So, I'm pretty well in tune with what should be normal for the car.

I'm a little suprised the brand new copper washer last night leaked right away. I'm going to take it back out tomorrow and heat treat/anneal it and see if that makes a difference. I'm having trouble finding the correct size sealing washer at the local stores. To get the one I have now, I had to buy an assorted pack with a bunch that I'll probably never use.

Just in case other things do not repair the issue.

If the valves required quite a bit of adjustment to get them right when you did them. You might want to check that the clearances are still there. I doubt this is a problem but is a slight possibility.

You could have lost some old deposits on the face of a valve then closing the lash gap or gaps. Especially on the highway run.

Also when you are loosening each injector line to bleed them. Pay attention to the sound of the engine. You are listening for any cylinder that does not make the engine drop in rotations as much as the others when doing this. I think you already know this though.

Hopefully it is just getting something like too much air in the fuel though. The 616 is a much easier engine to check out than the turbo 617s in many ways.

Since it ran really well initially I do not expect there is much really wrong.

Incidentally, glad to see another rocket ship hitting the road again. We 240d owners seem to have one end of the automotive speed and performance spectrum solidly tied down.

Was the brand new copper washer the correct part # or something close from the autoparts store? I'd use the old OE washer over the incorrect part by cleaning it up (anneal with heat then 400 grit wet/dry paper). Put some magnifying glass on and inspect all mating surfaces and clean them up if necessary.

edit: I missed that you wrote that the copper washer was the incorrect one.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I have always thought installing this clear line an excellent approach. Personally I would not think a bad injector all of a sudden. That does not mean it is impossible. Just pretty far down on the list of probabilities.

It sure is! I have a permanent clear return to tank line on every diesel I own. Makes life with a diesel so much easier.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Interesting theory... The valves did require adjustment, but I don't recall it being that bad. I'll likely leave the valve cover on for now, but will keep this in mind if the other diagnostics don't pan out. Like I said, as the engine didn't seem to work any harder on that highway run than in the previous week of driving, I'm hesistant to see that as a source of my problem. But, as that 15 minute highway trip MAY have been to blame, I mention it.


I think someone already mentioned that, but it bears repeating.


Yeah, I'm thinking (and hoping) based on what I'm seeing that the engine is just sucking air. Like I said, I drove it 200 miles or so before this happened. I definitely had the ENGINE up to speed before the highway run. The only reason I delayed a highway run until then was that the alignment was way off. I had the car aligned after work on Monday and that's when this (unrelated) problem started.

Past experience tells me not to drive it until I fix it, though, as (knowing my luck) it will quickly get worse and strand me. As I have other cars, there's no reason to take that risk. So, I'm hoping that's all this is. If it's NOT, though, then I want a solid plan for diagnostics.


The question is, what WOULD be the correct part number on that? Peach/Pelican doesn't seem to list it.

Also, it's a sealing washer. My gut tells me that we don't really need the official Mercedes part on this (then again... mine is still leaking).



So, like I said, my plan for tomorrow is to pull and anneal the washer before reinstalling it and take it from there.

Call the dealer, they'll order one for you and give you the part number. If you don't want to wait and have an old correct washer, clean that up and use it instead of the wrong copper washer.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

While at suggestions. In the process of elimination if it goes on. Pump the primer pump. Since it is new it probably is good.

You want to see substantial increasing effort as you do this until the relief valve opens. If you do not the relief valve needs attention.

Or the check valves in the lift pump are leaking too much. Usually you will see a back and forth surging in the pre filter if this is the case as well.