250SL idle dilemma

[n/a]

Hello all:
      OK, I'm sorry that I started this task, but am into it now with both feet and need to be pulled out. I have been plagued by a loping idle and a marked hesitation on cracking the throttle for some time. Following instructions in a Chiltons manual to adjust the idle, I tried to adjust the air screw at the air inlet and the knurled mixture screw at the back of the injection pump. The manual clearly states that the knurled screw must be pushed against a spring to allow the adjustment (no more than three turns!) but did not mention that if depressed while the engine is running that it will engage a turning shaft. While pressing in on the knurled knob (while the engine was running), I felt the engagement and the idle immediately ran up to 1500 rpm and I am unable to get it to return to a normal level. Any hints, clues, verbal abuse will be accepted.
     By the way, the problem with the idle with slight throttle opening still exsists. Opening the butterfly about an 1/8 of an inch causes the idle to cycle up and down. Advancing past this point returns the idle to a steady, if rapid, tempo.
Thanks BB  :?:

BBAY

[k]

I would call one of the FI pump specialists and ask for their help (Pacific, H&R, a fellow in North Carolina as well). Chances are internal damage has occured; it might not be major, as I have been told the RPMs get up to 4000 and make a terrible whinning/grinding noise.

Unfortunately, the screw should never be pushed in with engine on.  An expert will tell you the next steps to repair.

[ja17]

Hello BBAY1,

Engaging the adjuster when the engine is running may cause the adjustment screw inside the pump to wind all the way in (revised 6-15-04). If you can no longer engage the screw the adjuster knob or the screw may be damaged. If so rear pump cover removal may be necessary. Get a little familiar with your injection pump. Keep us informed.

http://sl113.org/forums/index.php?topic=790,pump,tour

When you get the pump functgional again we can go through the adjusting sequence. A "searching" idle is usually caused by a lean fuel mixture.


Joe Alexander
Blacklick, Ohio

[Cees Klumper]

It sounds to me like the knurled nut, or rather, the screw that it engages, has turned to one of its extreme positions and is now 'stuck' there. I would give it one more go to turn with the knurled nut, inward probably, to see if it will come loose from that extreme position. If not, it should be possible to remove the plate that the knurled nut is affixed to.

If I were you, I would try to remove it with the pump still in the car to have a look what's going on behind and to try turning the screw with a proper screwdriver. There should be no oil leaking out or anything. If the engine still runs (although now with the adjustment way out of spec, too high), this would indicate to me that the pump is not damaged.

On the erratic idle I would, after you get the pump back into order, go through the idle fuel mixture set-up procedure (including the linkages, and in particular the air flap ("venturi") on the inlet manifold - it should be adjusted so that it is practically binding - oftentimes mechanics will mistake this for the idle air adjustment), make sure about my ignition timing, all with a CO meter at hand.

The hesitation could very well be caused by linkages that are loose / sloppy. Are the ball joints in good shape, are the brass bearings on the transverse rod ok, and is everything tight?

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[n/a]

Hi guys:
      Thanks for the input. I was feeling quite foolish when I read that the adjustment screw should not be depressed while the engine was running. I was sure that such vital information would have been included in the idle adjustment instructions in the Chilton Manual. I re-read the section carefully and was shocked and disappointed to find NO WARNING of the hazard of adjusting the idle in a running engine. It think it is intuitive for any mechanic to assume that idle adjustments are made while the engine is running. I will not use the Chilton Manual again for anything but washing instructions or toilet paper in the future.

    Naturally I want to have a look into the back of the pump to asses possible damage. Can the large nut that holds the adjusting screw be removed without damaging the unit or affection other adjustments? Could the internal adjusting screw have been completely unscrewed to the point of dropping into the pump sump? The sensation I have when pushing in the knurled knob and attempting to engage the screw is of a 3 or 4 position detent in 360 degrees of rotation.
Thanks again. I'll post my findings.
BB


BBAY

[ja17]

Hello BBAY1,
The large nut can be removed without any problem. You will find the screw in the rear governor chamber of the pump if it has backed all the way out. You may have to remove the rear pump housing to reach it.

Joe Alexander
Blacklick, Ohio

[n/a]

Hi BBay,
I would suggest that you consider obtaining either:
1.  a big blue service manual for your car.  These are available either on ebay, or, I believe, reprints are now available from MB Classics.
2.  a service manual on cd rom.

This manual is VERY detailed, but sometimes it is good to read Haynes or Chiltons as an introduction, and then go to the service manual for the details.  It is a worthwhile investment.
Best regards,
Don
Cleveland

[n/a]

Well, I removed the large nut that contains the knurled adjusting screw. Dumped about a half a quart of engine oil out the opening. There was no apparent damage to either the slot of the adjustable screw or the blade of the adjusting device.

As the shaft rotates anti-clockwise as viewed from the rear, I assumed the screw to be fully tightened (if std right hand thread)if my holding the knob in whilst running actually turned the screw. As the adjusting screw in flat sided and rubs against spring steel retainers, this would allow for the detents.

Now, the trouble is is that the screw does not want to turn in either direction. I am loathe to force it as obviously, if it was intended to be turn by hand with the tiny knurled knob, then it was designed to turn rather easily.

I did manage to turn it anti-clockwise about 3/4 of a rotation without effect on the 1600 rpm idle speed. So, before I do irreparable damage (too late??) can someone advise whether the screw is right or left hand threaded and what is the approx default (factory) setting (how many turns from fully turn in)?
Must I now refill the sump? (it is connected by two hoses to the engine oil filter but has a dip stick)
Much thanks

BBAY

[ja17]

Hello BBAY1,
You are right, engaging the screw when the engine is running will wind it all the way in. Yes the screw is standard right hand thread. Turn it counterclockwise to remove it.

Download Attachment: gov. low range adjuster screw.JPG
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View the screw removed. Notice that the six sided slotted screw is wedged between small leaf springs. The tension from these springs gives the screw the "click" feeling. As the screw is adjusted outward it may eventually move off the springs. At that point the "click " feeling is lost and The screw is free to move on its own!

Download Attachment: rear pump cover off.JPG
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I am sure the factory sets up the pump with the screw set down deep enough in the leaf springs so that there is enough room to adjust up or down. Start somewhere in that range.  The mixture of the engine will determine how much to adjust the screw after re-assembly as long as the adjustments do not take you past the limits.


A snap ring holds the entire adjustment assembly in place. The three coil springs are acted upon by the adjustment screws. Each coil spring effects a different range of the centirfical governor.
[
b]Download Attachment: governor adjuster mechanism.JPG
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Download Attachment:[/b] governor adjuster mech. 2.JPG
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The oil level on these "early" injection pumps should be checked periodically. It's oil supply is isolated from the engine oil. Oil should be added or drained accordingly. The level should be read after the dip stick is screwed all the way in. Later injection pumps had engine oil circulating through them and did not have to be checked. Carry on!



Joe Alexander
Blacklick, Ohio

[knirk]

Hello Joe,
Your "Injection Pump Tour" is excellent! I hope you have time to continue the story - and maybe eventually cover the complete pump. It's very hard to find any good information about this complicated subject in the manuals.

Per G. Birkeland
69 280 sl aut 834
Norway

[hands_aus]

Hey Joe,

You say that the "click feeling" is LOST if the screw is wound out.

If the screw is wound back in, will the springs open again and allow the "click feeling to return?

Bob (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[n/a]

Hi All:
    I appreciate all the sage advice. I will post this final report to advise  on the results of 'our' efforts. I decided to leave the screw in the position I last reported and re-installed the large nut. As the oil that had escaped had the appearance of old engine oil, I must assume that the hose from the oil filter assy feeds the pump and I did not add additional oil. I directed my attention to the air side and made adjustments to the linkage at the butterfly to allow it to close completely. I then tweaked the large air needle until I had a stable idle at approx 700 rpm. Amazingly it seems to run great and the fast idle and 'hunt' problems have disappeared. I have a steady, stable idle with no hesitation on take off. We should all be congratulated for a job well done (;-)
Thanks again to all the participants. I certainly learned quite a bit and will, no doubt, find the info useful if and when I put my 300SL (1963) back together and have to deal with the pump set up.
Regards and Happy Motoring.
BB

BBAY

[ja17]

Hellow BBAY, Knirk, Bob, and group,
Thanks Knirk, I am glad this information is useful to someone else.

Bob, the "click" feeling will return when the screw is turned back in. The leaf springs actually locks the hex screw in position until it moves too far outward.  

Hello Bob,
 Good job, it looks like you accidentaly richened up the pump enough to solve most of your problems. Or you may have disguised a fuel starvation problem. Make sure your filter is clean and your fuel supply is up to specs! Also check the oil level in that inhjecion pump. You probably have the injection pump with isolated oil supply. If this is the case you must maintain the level. If it is too high this can cause problems also.

Joe Alexander
Blacklick, Ohio

[rwmastel]

quote:Originally posted by BBAY1

As the oil that had escaped had the appearance of old engine oil, I must assume that the hose from the oil filter assy feeds the pump and I did not add additional oil. I

BBAY1,

Hi.  Please make sure which fuel pump you have.  Older pumps have their own oil resivoir that is self contained in the pump and they have an oil dip stick near the rear of the pump.  Newer pumps have small lines that circulate oil in and out of the pump and they don't have a dip stick.  Don't confuse the oil filter canister with the fuel filter canister!  They are the same size, shape, and material.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420