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veg_svc 07-18-2007 12:51 PM

Engine Lope after warm up.
I hope that I am on the right track.

This problem showed up suddenly about a week ago.

I can feel the engine loping after the glow plugs turn off. While the glow plugs are on all is relatively smooth as soon as they turn off the loping starts. As an added bonus there is bluish smoke of unburned fuel more at idle than in higher RPM range, but always present. Again this smoke does not exist while the glow plugs are on. The loping is better when the car is in park, but in drive at idle is worse, and with the AC system running it gets unbearable. Loping is only at idle, the engine smooths out tremendously in the higher RPM ranges. Also from idle to moving there is from time to time a couple of knocks (similar to a gas engine with heavily advanced timing) but, not every time.

So far I have tested and or repaired several items. Nothing has caused any change in symptom whatsoever.

1 Cracked each injector hard line connection to verify all injectors are contributing to idle - They are.

2 Adjusted idle up to around 800 RPM - slightly better.

3 Changed both fuel filters and air filter - no change.

4 made adjustment to rack damper bolt, it was all the way in - symptom does not seem to change at all with any setting. It is a silver one and I have ordered a gold one, but can this part cause a sudden change or would the usual change be gradual as the spring wears out?

5 cleaned out the banjo and hollow bolt on the intake manifold - no change.

Is there anything else to test, Am I even close to being on the right track? This thing is driving me crazy! Thank you for any and all suggestions.

WINGAS 07-18-2007 01:01 PM

But I assume once its up to 60+ degrees C, it goes away?

THen, as I am facing same dilemna, prechambers. Actually I think I have one bad is all. Biodiesel is helping somehow.

BTW, when you cracked the injectors, did the stumble/lope mitigate at all on any particular injector?

Lastly, I dont have adjustible valves, but many of these do. It would be the next thing I'd eliminate as a variable.

Please reply with exactly which year/engine you;re working on.

veg_svc 07-18-2007 01:09 PM

1983 300D Turbo Not sure of the engine number. No above 60C it does not go away. Seems to get worse as it gets hotter, but I may be dreaming that. Had a similar issue in a ford diesel, turned out to be bad bio-diesel or so they said so i quit using the bio diesel and filled up with petro - no change am back on the bio now.

rrgrassi 07-18-2007 01:10 PM

Also what fuel are you running with?

veg_svc 07-18-2007 01:12 PM

bio diesel - tried petro diesel no difference.

rrgrassi 07-18-2007 01:19 PM

Try a valve adjustment, and also answer what WINGAS said about cracking each line. Mine loped like crazy also, and each time I cracked a line open, the car ran worse. Turned out to be beat up engine mounts and unattached engine shocks. The valve adjustment made the car run smoother.

Craig 07-18-2007 01:52 PM

Have you ever checked the compression? If adjusting the valves doesn't help, I would check the compression to rule out a weak cylinder.

the tenor man 07-18-2007 04:03 PM

Compression Test?
My first guess would be low compression on one or more thinking is that when the GP's are on, it is burning the fuel...once they turn off, there is not enough heat (compression) to burn all of the fuel that is injected into the cylinder. This could be caused by a cracked ring. You would get an increase on blowby with a cracked ring or even a small hole in a piston...

Just my 2 worth....

The Tenor Man

rrgrassi 07-18-2007 04:06 PM

Condition of engine mounts and shocks?

veg_svc 07-18-2007 04:28 PM

Well today I turned down the ALDA (Clockwise) about 1 full turn and a lot of the blue smoke went away. Now getting black smoke mostly at full throttle. The lope still exists and a little of the power is gone. Maybe there is hope yet. Will try to adjust the valves and install the rack damper bolt. Maybe I am on the right track.

When I cracked the fuel lines one at a time the lope seemed to get worse each time. I will try again and see if there is any mitigation to this lope.

toomany MBZ 07-19-2007 01:21 AM

I had similar difficulties, on dino. Try adjusting the RD bolt. If it is silver in color, consider replacing with a gold one. They are finicky at best. Make sure it is adjusted properly.

Mister Byrnzoil 07-19-2007 07:54 AM


Originally Posted by veg_svc (Post 1566276)
bio diesel - tried petro diesel no difference.

home made BD or bought? Did you ever run on WVO/SVO? Sounds like your rings aren't doing what they're supposed to.

Suggest valve adjust then dry/wet compressio test.

veg_svc 07-20-2007 11:01 PM

Home made bio, been brewing for nearly 2 years.

Will do valve adjust and comp testing tomorrow.

veg_svc 07-21-2007 12:42 PM

Valve Adjustment
Started the valve adjustment - so far so good 4 out of 10 done.

Something very odd, at least to me! All the valves so far have been far too tight. Average adjustment is 1/2 turn down (Away from the camshaft). Guess that this could quite possibly be the smoke source since the valves werent seating in some cases.

I would have expected the reverse, under wear the gap to open. Have the valves been adjusted wrong for a long time or does the MB wear in reverse? Would this be normal?

KAdams4458 07-21-2007 01:10 PM

They do get tighter as they wear. Half a turn doesn't seem so bad to me. I recently adjusted the valves on my newly acquired 300D, and while one valve was oddly loose, the others required six or seven complete turns each. Neglected? Just a bit, I'd say.

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