240d rough idle in park - PeachParts Mercedes-Benz Forum

va240 · #1 05-21-2018, 03:19 PM

My 240d is idling rough in park only after a long drive on the highway. The car only has 112k miles and runs perfect other than that. So far I've replaced all 3 fuel filters, ran 2 cans of diesel purge through it, rebuilt the injectors with new monarch nozzles and new return lines. As far as the fuel system the only thing I haven't done is timing. The timing chain has very minimum stretch. I also just recently adjusted the valves. Any suggestions what to look at next?

va240 · #2 05-21-2018, 06:47 PM

When I say rough idle it sounds like a slight miss not a vibration or shake.

Diseasel300 · #3 05-21-2018, 09:21 PM

Compression wouldn't be a bad thing to check. If you have a significant difference in compression values, you'll have a rough/lopey idle.

pj67coll · #4 05-21-2018, 11:55 PM

Quote:

Originally Posted by va240

When I say rough idle it sounds like a slight miss not a vibration or shake.

So you're saying the problem is purely one of sound. No physical shake at all? Get a stethescope and try to pin point the sounds location.

- Peter.

va240 · #5 06-07-2018, 09:52 AM

Sorry for not posting a reply but I wanted to do more research and do a compression test before replying. Right now I'm not sure I am still having the miss when idling only on warm days, I haven't driven it enough to see but it does have a rough/lopey idle as Diseasel300 described. You can feel it in the steering wheel. More then a 240d should have. Other than that it seems to be running perfect, plenty of power and smooth going down the road. So far I've adjusted the valves, replaced all 3 fuel filters, ran 2 cans of diesel purge through it, rebuilt the injectors, new return hoses, set injection timing (was only of by a degree), stretched the Fuel Pressure Relief Valve spring to 25mm and did a compression test. Numbers are from 1 to 4; 330, 370, 350, 380. I did the test on a cold engine. I have read on here about 240d's having low compression numbers on #1 cylinder. Could this be causing the engine to shake? I read a theory that low fuel pressure could cause issues with the #1 cylinder, could this be a problem. Alone 330 cold is good but there is more than a 10% difference. If there is a problem I want to address it now not 100,000 miles from now.

Diseasel300 · #6 06-07-2018, 10:44 AM

A difference greater than 10% between a pair of cylinders is enough to cause a rough idle. The low compression cylinder(s) contribute less of a power impulse to the crankshaft and give that "soft" miss. The less cylinders the engine has, the more pronounced the "lope" due to less overlap between power impulses.

You might drive it for a while, then recheck your valve adjustment. You could have a tight valve on #1 or a buildup of carbon on the valve face causing the valve to fail to close all the way. Drive the snot out of it and check/adjust the valves and see where that gets you.

If your engine mounts are old or worn out, they can conduct the vibration/shake to the body. If they're old or collapsed, you might consider replacing the 2 engine mounts and the rear transmission mount. It goes a long way towards isolating some of the harshness.

Trying too many things at this point can be a money-losing proposition. Without a definitive direction to go, you can throw a large number of parts and time at the engine and get nowhere. It's highly doubtful that you're risking anything by driving it as-is so I'd suggest driving until you have a new development that sheds further light on what's going on.

va240 · #7 06-07-2018, 11:29 AM

I figured the rough idle I'm feeling was due to the difference in compression. It's good to here it from someone with a whole lot more experience than I have!

I drove the car about 800 miles after the last valve adjustment before doing the compression test. It doesn't take that long so I'll probably do a valve adjustment again this weekend just to check.

I'll eventually replace the engine mounts to see if it helps any also.

Thanks!

Diseasel300 · #8 06-07-2018, 12:08 PM

Another thing that can exaserbate a rough idle situation is the injectors. You recently rebuilt them - do you have a combustion knock/clack/nail accompanying the rough cylinder? When I redid the injectors on the SDL I would get some fairly obnoxious nailing at times that accompanied a "lope" at idle. One of the injectors was hanging up intermittently. Swapping it out ended the problem. If you have a spare with a good spray pattern it can help to an extent too.

The underlying issue of the compression imbalance will always result in a less than perfect idle. If it's really annoying, you can try playing with the idle speed adjustment and see if you can find a "sweet spot" where the shake is at a minimum.

va240 · #9 06-07-2018, 12:40 PM

I did kick the idle up a little and it helped. I've been having problems with 4 of my 8 injectors which I have another thread started but basically I've had a couple sets of injectors with both Bosch (India) and Bosio nozzles and the problem hasn't changed. The Bosch may be slightly noisier (nailing) but I can't tell a difference in vibration or rough idle.

Diseasel300 · #10 06-07-2018, 01:01 PM

I have a set of Bosch India nozzles and they're sat around as spares. The spray pattern and pop pressures were very unsatisfactory with them, when in the engine they were noisier and produced significantly more smoke. The final straw was when one started leaking down overnight and causing rough starting.

Sometimes the injector bodies wear out and you simply cannot get them aligned properly anymore. I have a couple of them that I have as "backups" that will weep and "pee" prior to popping. Nothing I've been able to do to them will stop the behavior regardless of what nozzle is fitted. Having an injector like that in your engine will result in a noisy idle and very rough running at low/idle RPM's.

va240 · #11 06-07-2018, 01:08 PM

You just answered my question to my other thread about rebuilding injectors. You say you have injector bodies that weep and "pee" prior to popping, that is exactly what 4 of mine are doing regardless of what nozzles I put in them. I thought I was doing something wrong. The injectors I have in the car right now are testing fine but they do have the new Bosch nozzles in them. I also have a new set of Monarks I may try to see if they smooth things out.

va240 · #12 06-07-2018, 05:23 PM

Just drove the car home and it seems to be getting worse. It was a little wormer then it has been the last week or two and when I got home and put it in park it runs rough, seems like fuel starvation. Could the lift pump be going?

Diseasel300 · #13 06-07-2018, 05:36 PM

You could have air in the fuel system, it could also be those craptastic Bosch India nozzles. Mine would get worse the hotter the engine got to the point it was almost like a dead skip at idle. Knocking and clattering like hell as the engine warmed up. I replaced the POS India nozzles with Monarks. Once the engine is warmed up, you hardly even hear the diesel clatter, most of the engine noise is the DV's popping in the IP.

Checking for air in the fuel system is fairly easy, forum member Funola advocates the use of clear tubing in place of the return fuel hose and it's an excellent suggestion. If you have a solid column of fuel, you're golden. If you see bubbles or form a big bubble, you have air ingress problems you need to address.

va240 · #14 06-07-2018, 06:07 PM

It does sound like air intrusion, I'll check that first.

va240 · #15 06-09-2018, 10:05 AM

Update, this morning I ran a couple cans of diesel purge through it and changed the filters. No change. I pulled the injectors and put the Monark nozzles I purchased off ebay and they tested perfect. Even in the injector housing's I thought may be bad. Put them in the car and it runs great.