240d misfire diagnosis - PeachParts Mercedes-Benz Forum

sethza · #1 07-09-2011, 03:40 PM

Hey guys,

This is my first thread on this forum, i've never really had a problem like this yet on my Mercedes. I've spent a lot of time on the Volvo threads, but my days with volvos are most likely done.....
Basically thanks for letting me on this forum in advance and thanks for any suggestions you might have to offer!

I have a 1979 240d, with a 1982 spec engine that was supposedly rebuilt around 140,000 miles ago, the total mileage on the engine is probably around 340,000. Three months ago, it began misfiring at idle. It smooths out somewhere around 1200 rpm and seems a little worse when the engine's at operating temp. Here's what ive done:

There was black gunk in the tank, i took the tank out and had it cleaned and I replaced all of the rubber fuel lines and fuel filters as well as cleaned out the metal lines with mineral spirits.
I ran two cans of diesel purge through the fuel system.
I adjusted the valves in the morning on a cold engine, then double checked them the next day in the morning with a cold engine.
Turned up the idle.
Put a can of fuel conditioner in the tank and drove to phoenix (from tucson) and back (about 300 miles).
Replaced the injector nozzles with monark brand nozzles (i did not POP test them however, i didnt think it would cause an all out misfire as much as a little nailing if they were off spec a bit)
I did a compression test, all above 350, cant remember exactly what they were but none were low.

Heres another thing; when the miss started it seemed as though the engine became noisier upon start up, but quiets down after a few seconds.

Perhaps this is a weak valve spring? There doesn't seem to be slack in the timing chain and the cam lobes look good, like I said supposedly the engine was rebuilt recently. I dont know what was replaced and what wasn't, so im suspect of the injection pump and fuel pump, as well as the valve springs. I'm not sure on the steps for diagnosing these parts as faulty...any suggestions would be greatly appreciated!

Thanks!

Seth

junqueyardjim · #2 07-09-2011, 04:11 PM

I would try hard to locate the miss. Try to pin it down to one cylinder. Then I would see if it stays at that cylinder when you move the injector around. If you can find it and it stays, then you can go on to things like valve springs and injection pump. Remember that injection pump is not built with the DIY crowd in mind and working on it means taking it to the shop.

Diesel911 · #3 07-09-2011, 05:45 PM

If you have the Old Style Hand Primer with an shinly Aluminum Body and when you pump with it it leaks Fuel there is a good chance that it is causing an Air leak into your Fuel System. Replace it with a new Style original Bosch one.

As in post number 2. Do the Injcector Cut Out Test (works on Volvo Diesels also).

Loosen the Fuel Injection Line Nut at at one Injector (this cuts off the Fuel to it). If the Injector is good you Engine should really notice the Injector not working and your idle speed should decrease.
If the Injector is not working well when you do that the idle speed will not change or not change very much. If this happens you have actually located a problem Cylinder.

Taking the Suspect Injector and swapping positions with one that is good and retesting them.
If the Problem Follows the Injector to the new positon you know you have a problem with the Injector.
If the Problem stays in the Same Cylinder you have an issue in the inside the Engine on that Cylinder.

Also an Injector with too low of a Opening/Pop Pressure can also cause a low speed Miss because the Fuel is not atomizing as well as it does when the Pop Pressure is correct. This means that the Fuel cannot burn as completely.

sethza · #4 07-10-2011, 03:52 PM

So I took a look this morning, following the advice above, and cracked the lines open to see if I could pinpoint which cylinder is being uncooperative...
when i cracked the lines open on #2, some fuel ran down to the bottom of the injector and little bubbles started coming out. The part of this that confused me was that the bubbles werent coming out in between the injector and the collar nut, but between the collar nut and head. Could this be? I thought they were put in pretty darn tight, is there some sort of damage to the pre cumbustion chamber that just appeared three months ago? A possible theory, my injector nozzles did need replacing, but when i took the injectors out i loosened the collar enough to cause a leak, replacing one misfire with another...

Any thoughts?

P>S I have a new primer pump on there, one of the new style bosch units.

Many thanks!

Seth

okto · #5 07-10-2011, 04:39 PM

I thought misfires were a gasser thing?

1980sd · #6 07-10-2011, 04:57 PM

Could be you loosened one of them up and you're losing compression. Doesn't sound like much but it shouldn't be leaking.

Keep us posted!

leathermang · #7 07-10-2011, 05:00 PM

You need to check with Whunter..
as I think I remember there being the potential for some real damage if left....but I do not remember the specifics of it...

sethza · #8 07-11-2011, 12:14 AM

I took out the injector and replaced the heat shield after cleaning everything out. This seems to have somehow gotten rid of all of the bubbles, but the miss persists... driving me insane. I may have unwittingly driven the car about 300 miles with this issue, what kind of serious damage might we be talking about here? Im not driving it anymore until its fixed, even though its 110 degrees here. Biking sucks. Anyways, it doesnt seem like this is coming from any one cylinder specifically. When the lines are cracked, the rpm drops for each cylinder, albeit for 2 and 3 a little less than for 1 and 4... maybe me being hyper observant."

Thanks again for ideas.

Seth

sethza · #9 07-14-2011, 02:07 AM

One more thing, when the car is misfiring, it's MUCH worse when the engine is warmed up. I think that's gonna be the biggest clue my car's going to offer... It also smokes alot when warmed up, and this car never used to smoke excessively. ALSO when its warm its noisier. It shakes so bad when its warm, my friend said it made him "sea-sick". And like I said, all injectors are working and the valves are adjusted. Is there a way to check the pump or the valve springs? Or could it be anything else.... And one more thing, the car sat for awhile, the problem started after I started driving it after it sat. I did all of this work after it sat, also, so I'm not worried about the injectors fuel lines or fuel etc. Would it sitting increase the odds of something 'hanging up' in the injector pump? Do valves or push rods get sticky from sitting but would free up at higher rpm? Im dumbfounded.

Thanks a million

Seth

Codifex Maximus · #10 07-14-2011, 02:57 AM

You still need to isolate WHICH cylinder (if it's only one) that is causing the imbalance. Once you find the cylinder, it was suggested that you move the injector to another cylinder to see if the problem follows the injector or stays with the cylinder.

The fact that you have 350 or better on every cylinder tells me that the engine's mechanicals should be solid.

sethza · #11 07-14-2011, 03:20 AM

yeah I did crack the lines on each cyl., doesnt seem like any one cylinder stands out. I just realized I still havent tried to adjust the rack dampener bolt on the back of the pump, this seems worth looking into. Im going to adjust that and replace the motor mounts as well as inspect my primer filter and see what that does for me. Really feels like its running lean to me, dont know if thats actually the case. Even though the filters are new, since I just cleaned out the whole fuel system I suspect the possibility of loosened particles still working their way out. I'll post an update tomorrow.

Thanks again!

Seth

kerry · #12 07-14-2011, 10:46 AM

You could check the pressure on the lift pump to see if it is providing adequate fuel at idle.

Zacharias · #13 07-14-2011, 11:42 AM

Hey Seth,

You don't have a rack damper bolt. It's only a feature on the five-cyl turbodiesels.

Was this car ever run on WVO? I had a 240d that exhibited exactly these issues.

I think I remember you from the old days on Swedishbricks? Welcome to the forum.

barry123400 · #14 07-14-2011, 02:13 PM

When running any air bubbles processing through the primary fuel filter? There should be none other than a permanent static one in the filter.

A primer pump that is leaking air as well may be an issue. To eliminate that as a source if it is the older white one stretch a ballon or condom over the top of it and squeeze the air out for a test. Make sure to run the engine long enough to eliminate any residual air in there before deciding.

sethza · #15 07-14-2011, 05:43 PM

this car has run on b99 biodiesel, is running on about 50% now. I never had a problem before, but im going to run on full diesel just to eliminate any possible issues from that. And yes, I looked at the back of my injector pump and saw no rack damper bolt. There aren't any bubbles in the primer filter besides one large on. I did replace the primer pump, but it was with one of the new bosch numbers that's just a black button that you don't have to unscrew. I'm not sure that these are biodiesel friendly, actually, and Im going to look into that. Also, a friend gave me a special tool for checking pump timing, so Im going to give that a shot using my manual. One more thing: how do i check pressure at the lift pump?

And yeah, i was on the bricks forums! My friend who I was renting the shop with, where I had my 740, ended up being a drug dealer... the super kicked him out while my car was in a million pieces. Welcome to Tucson. I made the conscience decision to give up on that one, and the trans burnt up on the 240 my roommate and I were working on. All these cars and I have to ride my skateboard to work.

Thanks again!

Seth