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  #16  
Old 12-27-2006, 01:09 AM
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Injectors tested

Richard took #2 and 3 Injectors and had them tested. They are good. They were just replaced in the beginning of October. He did change them around and I think there was no change in one cylinder when he opened the injector, can't recall which one. I had a used engine that I purchased from ASAP Motors in Houston dropped in at the end of February this year. Engine cranks right up when cold 20 degrees without block heater plugged up and she uses very little oil. The old engine consumed huge amounts of oil and and was very hard start in cold weather. I had to use the block heater. This leads me to believe that the engine is good. Is there something else other than a complete rebuild of IP if one cylinder is bad on IP. Was told by independant MB mechanic that cylinder 2 and 3 are weak. This rough idle is just too rough! Thanks for any input
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  #17  
Old 12-27-2006, 02:06 AM
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"Engine lopes while idling..."

I was doing some casual reading of a new book I just purchased, the Haynes manual for "Mercedes-Benz Diesel 123 Series"... so let me quote you from it's troubleshooting section for the likely causes for this symptom:
(1) Air filter clogged,
(2) Fault in the fuel injection pump or timer,
(3) Clogged fuel injector,
(4) Leaking head gasket...,
(5) Timing chain worn,
(6) Camshaft lobes worn, AND
(7) Contaminated fuel.
Q - What do you suppose is meant in (2) where it says "... or timer"?
Regards,
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  #18  
Old 12-27-2006, 02:19 AM
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Quote:
Originally Posted by Samuel M. Ross View Post
Q - What do you suppose is meant in (2) where it says "... or timer"?
Isn't the IP timed?
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  #19  
Old 12-27-2006, 02:54 AM
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I think you are right... but let me check!

Quote:
Originally Posted by justinperkins View Post
Isn't the IP timed?
I just remembered, these Haynes manuals usually have a section titled "Use of English" that serves to translate "English" to "American"... but NO, they don't show "timer". Maybe it was a "typo"!
Sam

Last edited by Samuel M. Ross; 12-27-2006 at 02:55 AM. Reason: correction...
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  #20  
Old 01-05-2007, 12:10 PM
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Not the injector

As you suggested, Jimmy L., We switched injector 1 and 4. There was still no change in the idle in the #4 cylinder. What would be the possible culprit of that cylinder not firing? Thanks!
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  #21  
Old 01-05-2007, 01:42 PM
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Have you done a compression test? How did you confirm that #4 was the problem?
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  #22  
Old 01-05-2007, 03:17 PM
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Worn Cam Lobes

We pulled the head and both #4 Cam Lobes are worn. At this point, I guess it is...replace the Cam Shaft! This was on a list of possible culprits posted by Samuel Ross addressing this post. No, I have not done a compression test. Engine does not use much oil and starts right up, never using the block heater. We eliminated it being an injector by doing what Jimmy L suggested...when you bleed the #4 injector there was no change in the idle. There was a change in all of the other injectors. We switched #1 and #4 and the problem was still in #4 indicating a problem with the cylinder. I am hoping the worn cam lobes are causing the rough idle and not the IP. Thanks!
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  #23  
Old 01-05-2007, 03:21 PM
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Wasn't 1979 the last year where some of the cams would wear due to inferior metals used???? Seems like I remember this being an issue with some W116's.
However, memory is not my strong point.....
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  #24  
Old 01-05-2007, 08:46 PM
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I posted a new thread Camshaft 1979 or 1980-81. What year did MB start with Pencil glo-plugs? I have pencil glo plugs. Any ideas?
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  #25  
Old 01-06-2007, 07:55 AM
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Unfortunately, probably the IP.....

On my previous 300DT (an 85), I chased every possible cause of the rough idle to no avail, although all these things are important for good engine performance...

1) injectors ...bought new ones and before installing, brought them to a shop and had the release pressure and spray pattern checked, all OK...installed to torque spec. with new crush washers

2) compression...all cylinders tested within 310 to 350 psi

3) timing (start of fuel delivery)...adjusted using drip tube

4) new timing chain

5) cleaned banjo bolt and line off of manifold

6) cleaned injection valves on top of IP and replaced copper seals

7) adjusted rack damper on IP (adusted all the way in, with no effect)

8) adjust idle speed (I think somewhere between 750 and 850 rpms)

9) adjusted valve clearances

10) new engine mounts, transmission mount, engine shocks

In the end, and after lengthy discussion with a guy from a company that rebuilds injection pumps (vary candid, no BS), I concluded that the notorious rough idle common to almost all of the 123 5 cylinder diesels, is caused by IP. This is a very complex (ingenious) mechanical device that will wear over time and go out of calibration, resulting in noticable symptoms (rough idle) after a few hundred thousand miles. Rebuilding involves replacement of various parts (sleeves, plungers, seals, rings, etc..) finished by bench calibration. At high speeds, the slight variation in fuel delivery characteristics between cylinders is not noticable given the total volume of fuel delivered, but a idle, these differences become more significant and result in rough idle. If you can live with the rough idle (easier said than done!) these engines will still perform admirably at higher rpms for many more thousands of miles ....just avoid stopping at red lights and such!

That said, my second 300D (84 wagon), had real bad front end shake at idle (if I set a glass of water on the dash, water would splash out), and when I adjusted the rack damper in, the idle smoothed right out (engine still rocks a little), but at least the front end isn't doing the Irish jig. What really fries me about these cars is the rough idle in combination with the design of the air filter housing....on both of my cars, I replaced and/or welded broken air cleaner mount brackets a few times!!!!! Damn, that is a pain!!!

Perhaps someone can comment on inherent characteristics of 5 cylinder turbo engines vs. 4 cylinder (240Ds) and 5 cylinder non turbos....I have seen a few nice 5 cylinder non turbos and 4 cylinder cars at idle, and they seem to purr with a nice evenly spaced clatter (music to my ears). The 5 cylinder turbos all seem to have that characteristic dink, dink, dink, dink. I don't buy the argument of the odd number of cylinders causing an imbalance...that seems kinda dumb to me...but I heard from someone that the turbo has an impact...I just don't know enough about how inherent engine design features result in performance characteristics.

Mark
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Last edited by MarkM; 01-06-2007 at 08:06 AM.
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  #26  
Old 01-06-2007, 12:58 PM
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I had already priced having the IP re-built, but had still not pulled the valve cover. Mr. Ross posted on this thread stated that that was 1 of 7 things that would be the likely culprit of the rough idle. We had put in new engine mounts and injectors. My 300D is a non-turbo so it does not have a rack dampener pin. Will post if the cam shaft solves the problem
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  #27  
Old 01-12-2007, 07:03 PM
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Let me assure you...

Quote:
Originally Posted by tc art View Post
We pulled the head and both #4 Cam Lobes are worn. At this point, I guess it is...replace the Cam Shaft! This was on a list of possible culprits posted by Samuel Ross addressing this post. No, I have not done a compression test. Engine does not use much oil and starts right up, never using the block heater. We eliminated it being an injector by doing what Jimmy L suggested...when you bleed the #4 injector there was no change in the idle. There was a change in all of the other injectors. We switched #1 and #4 and the problem was still in #4 indicating a problem with the cylinder. I am hoping the worn cam lobes are causing the rough idle and not the IP. Thanks!
... assure you that IF my previous POST [ #19 above ] you refer to turns out to lead you to the proper solution... PLEASE DO NOT anyone think I'm anything but lucky and that my suggestion was purely coincidental.
I just had read this new reference I had purchased!
Regards,

Last edited by Samuel M. Ross; 01-12-2007 at 07:05 PM. Reason: minor correction/addition...
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