Go rich or lean?

[TheEngineer]

I put the new cylinder head on and installed a new timing chain. The head gasket cost more than the timing chain - ouch! Then I checked the valve timing: The 0,4 mm thing: It was close enough. Checked the ignition timing: Why would it be off? It was off by about 20º. Then I worried that I may have moved the sprocket when I installed the new chain. So I removed the injection pump just to check the timing: The marks lined up just fine. Germans must have small hands. My arthitis doesn't help. I adjusted the linkage from the gaspedal to the throttle plate - and to the injection pump. You're supposed to insert a 10 mm round into that hole to line up the ball. I have a stop solenoid on the injection pump and the time delay switch worked intermittently. I fixed that. I checked fuel pump pressure: It's 0,6 atü instead of 0,8. The start valve leaked, I lapped it in. I checked all the injectors for equal opening pressure and spray pattern. The result: The car runs (and leaks no oil at all) but: At mid range there is a "hollow spot" in the throttle response. It is most noticable when I drive uphill on a slight grade. It's not there on the level or downhill. And it pops in the exhaust. At idle it's very smooth (600 RPM) At nearly full throttle it runs very well with lot's of power. This midrange problem wasn't there before. So far I have leaned out the mixture at the rack 3 clicks to the right. I'm not sure I have improved things by leaning out the mixture. I'm running platinum plugs and points. If it pops, there may be combustible gas in the exhaust? Any suggestions anyone?

[Ricardo]

I think you've richened the mixture with 3 clicks to the right, but I doubt that would have any effect on the mid-range mix.....is your dwell on spec?
Richard

[ja17]

Hello Peter,
Since the flat spot was not there before be a little cautious. Make sure the vacuume part of the distributor is working. Just richening up the injection may actually disguise the problem.

You may want to double check the cam timing mark at TDC. It can be a little late but never even a bit early. Linkage seems the obvious problem but you have checked it. Can you replicate the problem with the car at rest you may be able to separate the linkage and actually find out if it is a lean or rich problem by increasing or decreasing the injection pump linkage movement.

Joe Alexander
Blacklick, Ohio

[A Dalton]

<< I'm running platinum plugs >>

 I would change them for stock copppers before doing any FI adjustments.

[TheEngineer]

I checked everything and forgot one item: What is different between the old cylinder head and the new one? The height! The new one is almost 2mm higher. This requires lenghtening of the rod down to the injecion pump. The BBB gives a 233mm dimension between center of the balls. Mine was 230mm. I adjusted that and turned the rack adjusting screw back 3 turns, to undo my earlier adjustment. I also had to adjust the other rods, so that the throttle plate moves together with the pump. It runs much better now and I think the hollow spot is gone. I'm getting picky now. Ricardo:The dwell is 38º. It's amazing that such a small thing makes so much difference. Tomorrow, I'll re-torque the head and check valve clearance and I'll put in the copper plugs. Thanks, Guys!
Richard: Please let's talk about your observation that "I think you've richened the mixture with 3 clicks to the right". I followed the instructions in the BBB,job 07-14/15 where is says:
 Adjusting at the head of the rack: Right turn-lean, left turn - rich. I'd hate to turn it the wrong way, even though - right now - I have undone the three clicks to the right by turning the screw three clicks to the left. My perception of the function of the injection pump is that the rack is pushed forward by a lever to increase fuel flow. That lever pushes on the head of the adjusting screw. When I turn the screw clockwise, the rack moves later, decreasing the quantity of fuel. But I may be wrong. Any body want to jump in here?

[George Davis]

Peter,

Lots of work, and I'm glad it's running better.  Sounds like your linkage bracket has the hole for centering the main linkage rod (you said you inserted a 10 mm round to line up the ball).  Later you said you adjusted the pump rod to 233 mm.  There are two procedures for adjusting the linkage, one uses the hole plus 10 mm centering tool to set the length of the pump rod; the other (used when the bracket doesn't have the hole) requires setting the pump rod to 233 mm.  These procedures are exclusive of one another, one or the other but not both.  Of course, some fine tuning is allowed, too.

George Davis
'69 280 SL Euro manual

[TheEngineer]

George: You are right! I first used the hole in the linkage bracket: I fabricated a slug with a tip,so that I could make a precise alignment. And I did, but obviously, someone made modifications because now that I have adjusted the rod to the pump to 233mm, the slug  and the ball in the linkage do not line up any more but the car runs nuch better. The ball is further aft in the bracket now. I found so many things wrong that this discrepancy does not surprise me any more. For instance: The previous owner gave me all the repair receipts and on one, I noticed: "Injection pump oil leak not repairable". I found that the bolt which carries the axle for the lever, the one which you have to back out to have access to the rack adjustment screw, had been backed out and not screwed back in. That's where the "unrepairable leak" was. I had the car for a 40 mile drive on the freeway yesterday and it appears to run fine. The hollow spot has disapeared. But I have a test light on the fuel cut-off solenoid to verify operation and it worked fine after I filed the contacts in the speed switch, but now it seems to be intermittent again. That feature doesn't do much, but I'd like to see it working. Maybe tomorrow I'll play with it.

[Ricardo]

Peter
If you have a Haynes manual it states on page 70 section 24 item 7 that the idle speed screw should turn "clockwise to richen the mixture and anti-clockwise to weaken"... and I thought that was the same in the BBB, but I'll pop over to the shop this evening and check my BBB's (both versions)....I know that Haynes manuals are not more reliable than the MB manuals, so this may yet prove to be wrong and I'll eat some crow and promptly go adjust my mixture which is at the max. "anti-clockwise" and still too rich at idle, though with perfectly colored plugs.....
Richard

[A Dalton]

<<I followed the instructions in the BBB,job 07-14/15 where is says:
Adjusting at the head of the rack: Right turn-lean, left turn - rich. I'd hate to turn it the wrong way, even though - right now - I have undone the three clicks to the right by turning the screw three clicks to the left. My perception of the function of the injection pump is that the rack is pushed forward by a lever to increase fuel flow. That lever pushes on the head of the adjusting screw. When I turn the screw clockwise, the rack moves later, decreasing the quantity of fuel. But I may be wrong. Any body want to jump in here?>>

 Turning the screw CW increases the foward position of the rack at idle, thereby richening the fuel..CCW lets the rack recede back further, decreasing fuel.
 The confusion you have from the BBB is I believe you are looking at adjustment on the 2 plunger ZEA pumps , which are the opposite of 6 plunger PES pump.

[ja17]

correction 9-27

Hello Guys,

First of all don't, get the rack adjustment screw (full load screw)confused with the idle control thumbscrew for low range (idle mixture and up to 1700rpm). The rack adjustment screw is internal and must be accessed by removing a cover screw on the back of the pump. The idle control thumbscrew is external.

I know the exposed mixture control thumbscrew richens the mixture by turning it clockwise ( as you sit in the driver's seat looking forward). I do not remember which way to turn the internal full load screw (rack adjustment) refer to the manual at this point.  For those of you with the 1968-on BBB page 07-14/16 gives a nice run down with photos.  I am posting my own photos for those who do not have a BBB.  The idle control thumbscrew,  controls mixture up till around 1700 rpms. The rack adjustment screw and other speed range screws are internal and normally are not tampered with by the inexperienced.



Download Attachment: inj pump1.JPG
50.92 KB

Download Attachment: inj pump2.JPG
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Here below is more than you probably want to know;
The IDLE CONTROL KNOB (external) adjusts the tension on the low range spring in the centrifugal governor of the injection pump, which changes the position of a three dimensional cam which in turn moves a lever which moves the rack, which rotates the heliocentric plungers controlling the amount of fuel delivered to the injectors. In other words it changes the mixture at low range engine speed (up to 1700 rpm). In addition to these inputs, the warm up device, altitude compensator, linkage position and engine rpms, also input through a complex maze of springs,  levers, etc.

The FULL LOAD ADJUSTMENT SCEW (rack adjustment) is internal and adjusts all speed ranges by changing the tension on a spring which changes the rack position slightly. The same "all range " adjustment can be achieved more easily by removing or adding shims under the warm up device.

Joe Alexander
Blacklick, Ohio

[enochbell]

I know this one has been just about beat to death, but I still have a few questions:

Is the adjustment a continuous circle, in other words if I go three clicks to the left, is that always going to get me full adjustment, or does it depend on the orientation of the screw before making the adjustment?  If you go four or five clicks in one direction, does that bring the mechanism to the other side of the adjustment range?  In other words, does 5 clicks left equal two clicks right?  And is there any way to know the orientation of the adjuster without removing the cover plate and without a CO meter?

The reason I ask is that I can't really tell any difference when I adjust mine, and I just want to get it right.  And yes, I am making the adjustments properly.  I have had the pump apart (5 years ago when it was rebuilt) and the mechanism looks like it kept a dozen engineers busy for a year, what a beauty.

Thanks,

g

'64 230sl, fully sorted out...ooops, spoke too soon

[Ricardo]

G
I'm pretty sure this is simply a screw type adjuster, in that it will turn in until it reaches the end of it's threads. We have had a discussion previously, relating a situation where if the adjustment screw is backed out (CCW) too far, that it can engage the spring loaded plunger/adjuster and turn it self out completely when the engine is running. You can tell this has happened by checking the plunger, if it is engaged with the adjustment screw without pushing in then the screw is too far out (CCW).
Dr. Dan showed me the innerds of this mechanism last time I was there...very clever design, where one spring serves to tension 4 different screws....
Richard

[A Dalton]

G,
  As R states, it is a screw and does not rotate back to a full circle/original setting position.
 The screw has a hex head where a flat spring holds it in place. That is the 'Click' you feel when turning the screw . Because the hex head has 6 sides/flats, each click is a 60 degree turn of the screw. If you go 6 clicks CW, you have enrichened the pump low speed by one full screw turn . To get back where you started , you have to turn back a full turn. [6 clicks]
 This screw rotates when  the pump is turning, so orientation is dependant on where the slot is when the pump stops..that is why you have to turn the thumbwheel to find the screw slot before getting it to click and that is also why you do not try to turn the thumbwheel while the engine is running..
 Without a Co meter , the setting combination of the fuel [by thumbwheel] and the air [ air bleed screw]  are fairly correct when the idle speed is correct and smooth .  This takes a little back and forth adjusting, along with a good ear. A vac gauge helps here .
 The main point is to make this final tweak after all other things are considered. [ ign. timing , link adjustments, etc]
 Your chassis has the earlier style pump, so you can also test the rack posistion with a test screw from an access port in the front of the pump.
 I have a detailed article on that and other adjustments that you may want , so send me an email and I can send the article out to you . I still have your addy....
A

[Benz Dr.]

The screws inside of the pump don't work directly on the rack. These screws change spring pressure on the governor fly weights and it's the fly weights that control rack position. There are 3 springs inside of a cylinder and as the fly weights open, mechanial linkage moves the fuel rack forward. Speed and load determine how far the fly weights open as well as spring pressure against this movement.
Reduce the spring pressure and the fly weights open a bit more and more fuel is injected. This is VERY sensitive and you should NEVER open the back of the pump and start moving the screws around. Anything you do should be recorded so it can be moved back to an original setting.
There are so many things going on inside of the injection pump that any adjustment can put it far from right or improve it greatly ( if you know what to do ). Aside from basic aadjustments I leave them alone. Ask me why......

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[enochbell]

Thanks this is really helpful, and yes, Arthur, I would appreciate the articles.  My email is gbellware@yahoo.com.

Since I don't know where the screw is relative to it's "original" and, presumbably mid-adjustment position, then it could be anywhere in the rich or lean position.  The idle and performance are fine, but I suspect it is a bit rich from the color of the tail pipe residue (black).  This gives me an excuse to get a CO meter.  I told my wife it was a safety issue, I am sure all would agree with that...

g

'64 230sl, fully sorted out...ooops, spoke too soon

[TheEngineer]

Joe: That's a really nice picture of the adjustment screw for the rack. They should have that in the BBB. I've saved it in my file. you also moved the actuating lever out-of-the-way by swinging it up. Very nice! I also liked your poster and it gave me an idea: I still think my #3 cylinder gets more fuel than the others. I can clamp the pump in a vise and turn it as you show in your poster. I can attach six small syringes to each outlet and thus measure if all plungers deliver the same quantity. Thank You!

[hands_aus]

http://index.php?topic=790

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

[enochbell]

Bob, thanks for the post on the old thread, this is an amazing piece of engineering.  At the risk of exposing even further my ignorance...just what, exactly, is the mechanism of varying fuel delivery volume.  Is there a source I can access to read up on this?  I understand that the volume of fuel pushed by the pistons would enjoy a linear relationship with the pump camshaft speed, which in turn is directly related to engine RPMs, but that can only be the beginning.  I assume that the rack and flywheel mechanism somehow controls the pump inlet volume, but it must be INCREDIBLY complicated...there is only fuel in the line at this point of the delivery system, so everything must work with the laws of fluid-dynamics, pressure and vacuum in an anaerobic system.  Yikes, how did they do that.

g

'64 230sl, fully sorted out...ooops, spoke too soon

[ja17]

Hello Peter,
Yes this is basically how the pumps are metered on a test stand (with more sophistication of coarse). They are metered at different rpm, manifold pressures, coolant temperatures, and linkage positions. They have all the factory specs. Sounds like a lot of trouble, maybe you can meter the fuel with the pump on the engine?

Joe Alexander
Blacklick, Ohio

[ja17]

Hello Greg,

Good question, it actually shows a deep understanding.  It seems that the early manuals go into the injection with more detail. The 300SL manual is very detailed on fuel injection operation and theory.  The early W113 manual (Passenger Cars Starting August 1959)also gives some details not seen in the later W113 manual.

For those of you who have the early manual (Passenger Cars Starting August 1959), refer to the diagrams at the top of page 07-10/6.

Yes the fuel pressure is constant and the volume produced by the electric fuel pump is also basically constant. The volume metered happens in the cylinders inside the injection pump. Fuel is supplied by a  hole (inlet bore) directly in the side of each cylinder of the pump. The piston has a receiving groove which accepts fuel as it passes the inlet bore in the cylinder. This much is fairly straightforward. Here where it gets a little complex; This receiving groove in the piston is cut at an angle and is referred to as a heliocentric groove. One unique feature of these pistons is that besides moving up and down these pistons also rotate! The rotation causes the heliocentric groove to accept fuel earlier or later in piston travel which increases or decreases quantity pumped to the injectors! Now the "rack" is a toothed rod which is responsible for rotating the pistons and thus changing the volume injected. Factors such as engine rpms, altitude, coolant temperature, linkage position and the starting solenoid influence the position of the rack.


Joe Alexander
Blacklick, Ohio