Next step, pull the head?? - PeachParts Mercedes-Benz Forum

Stevo · #1 05-04-2005, 11:53 AM

Heres the deal, 82 240D, idles rough, smokes & nails, seems to be worse when warm. Has plenty of power and runs smooth (no nailing either) when NOT at idle. It always fires right up

What I've done,
changed injectors
changed the IP & retimed
readjusted the valves
I can hear its missing at idle and haven't done a compression test (gauge is loaned out)

I'm thinking it wouldn't be poor compression in one cylinder due to bad rings because it has plenty of power and runs great
above idle without any nailing or smoke. When I readjusted the valves yesterday I tweeked each valve around this way and that, thinking there might be carbon hanging one up. To me the symptoms point to valves?? One other thing, one of the valves on # 4, exhaust, I think, SEEMED to rotate easier than the rest. The spring was intact and I couldn't see any reason why it shouldn't rotate as easy as the rest. Any ideas on what could be going on before I pull the head ?

dmorrison · #2 05-04-2005, 11:58 AM

Don't want to burst your bubble. We had a 300SDL that knocked at idle but ran fine. Low compression in the #1 cylinder. I think the previous owner hit the oil pan pretty hard and messed up the crank shaft front bearing area. At 150,000 miles had a new piston and rings installed. Drove it for another 100,000 before it started to "knock" again.

Do the compression test and see what you get.

Dave

Pete Burton · #3 05-04-2005, 12:11 PM

definitely do the compression test. Also, look for leaks around the fuel pump/prefilter/primer pump area.

leathermang · #4 05-04-2005, 12:41 PM

I think all our engines have valve rotators on the exhaust...and most on the intake also... those should keep carbon from hanging onto anything in that area... if not then they may need replacing...
I suggest you pull the precombustion chambers and look at them ....
If one valve seemed to rotate easier than the others you need to check all of the springs... they DO wear out at some point. I suggest new springs and rotators if you take the head off.... or even if you don't given your symptoms...

Stevo · #5 05-04-2005, 12:45 PM

" knocked at idle " No knock, nailing, and I am sure the compression IS low in #4 although it would be nice to check it if I had my gauge.

Pete.....no leaks as I had the eng really clean, with a new primer pump before I installed it.

I was thinking about one of those little rotatie gizmos under the valve spring but I would think if it failed or collapsed it could be felt when rotating the valve.

Stevo · #6 05-04-2005, 12:59 PM

Greg

Ya, all the valves have those rotaters. I was thinking of just swaping the head as I have one in good shape off another engine. I guess it could be a PC chamber, never had a problem with them or messed with them at all. I peeked in there when the GPs were out, balls there but I guess that doesnt mean there OK........ That one valve definatly wasnt as stiff too rotate as the rest, maybe it needs a shot of viagra in the lub oil

samiam4 · #7 05-04-2005, 08:11 PM

Steve,

Just a suggestion, but I would check things a little more before changing a cylinder head. You must determine if it is a valve or ring problem?

Beyond that, it is well known that rebuilt injectors are not always great. Have you checked the pop pressures and spray pattern of the rebuilt injectors. It could be just a defective injector.

Prechambers are fairly easy to pull with a few tools. If the ball is there- that is a good sign. Beyond that a bunch of carbon inside can give hamering too.

Obviously, call for your diesel compression gauge to be returned.

Michael

bullwinkle · #8 05-04-2005, 08:51 PM

Sounds just like mine when I had mismatched bad injectors-its a whole lot easier to have them tested than pulling the head!!!

t walgamuth · #9 05-06-2005, 06:59 PM

definately do compression test. in my experience, new injectors have never solved any problem that i have had.

Stevo · #10 05-06-2005, 08:37 PM

Ya, I think you guys are right, a compression test should be the next step, now if I can find that special 12mm end for the compression gauge that fits in back of the IP.

This engine sat around for a couple of years before I put it in the car its in now. In reality I think its more likley a ring is gummed up

than something wrong with a valve.

P.E.Haiges · #11 05-07-2005, 02:15 AM

Stevo,

Try to find which cylinder is causing problem by loosening injector nuts one at a time. Then switch injector from bad cylinder to another and see if the problem moves with the injector from the bad cylinder. If it does, its a bad injector.

P E H

Stevo · #12 05-07-2005, 10:31 AM

PEH

I swaped out the injectors and changed the IP,..no change. When I crack the fuel lines it heard to tell but I think its in #4. Like I said, past idel it has plenty of power, sounds quite healthy, and almost no smoke. I've run it around here for the last coulpe of months with my foot in it, maybe what she needs is a long freeway drive.

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