Clicking the Fuel Adjuster Left

[Pawel66]

After fixing the fuel delivery issues last year my idle somehow got out of tune.

Did the linkage tour by the book. Checked again WRD closing and CSV not leaking.

I am clicking the adjuster left, I lost count, the split linkage test still indicates the car runs rich on idle. Exhaust fumes smell, exhaust pipe gets black on idle, engine hesitates a bit when pedal pressed to start...

Will I screw the adjuster screw out of thr FIP when I click to the left too many times?

By the symptoms I should lean the mixture more.

[ja17]

Pawel, also do the split linkage test at higher RPMS. If it is still rich at higher RPMS then you may need a rack adjustment or a baro compensator adjustment.

[Pawel66]

Joe, thank you, I will do this. I got access to CO tester, I will know exactly.

I checked the baro compensator before - it works and there are no more shims to be removed.

When I was struggling with mixture before I did the rack adjustment - many clicks to the right to lean the mixture. Exhaust pipe is grey after ride.

How far left can I go with idle adjuster or how far right can I go with rack adjustment? Will there be a stop or I will just screw them out of where they are causing trouble?

[ja17]

The idle adjuster can be turned a lot of clicks. Eventually the clicks become less pronounced.  This is your warning. The clicks might eventually feel very faint or disappear altogether. This is definitely too far. As the screw clicks it moves rearward and moves away from the leaf springs that create "the click". The screw may move so far back that it can fall out of its threads or trap the adjuster knob and cause it to stay engaged.

[Pawel66]

Clear, thank you!
i think I am not there yet. In my FIP the adjusting screws are behind the plate, so it is relatively easy to get there (did that before to replace the oring on adjuster screw).

What I feared was that I will mess something internal up.

Thank you for your kind attention!

[PeterPortugal]

Guys,
This might be a dumb question.....but how do you do a split linkage test at higher rpm?
Regards
Peter

[stickandrudderman]

Simple. (if you have two hands).
You rev the engine to 2000rpm and disconnect the rod to the pump. Push the rod down (to add fuel,  let it up to reduce fuel) with one hand whilst maintaining the position of the rest of the linkage with the other hand.
If the engine runs better as a result of either of these two actions you have identified a fuel delivery problem.

[PeterPortugal]

Thanks Colin.....luckily I have two hands !

[Pawel66]

I think if you had three hands it would be even better...

That moment of revving up to 2k and disconnecting linkage - I would have a hard time holding the linkage steady and disconnect the rod with one hand.. unless you disconnect first the rod and just press the ball joint against the ball (to have it centered) while revving up...

Anyway - the idea and way to do it are clear - thank you! The rest is just a matter of a number of hands.

[PeterPortugal]

Pawel - if you didn't know either then it wasn't a dumb question...so here's another.

Does it matter if you choose to keep the fuel steady and give it less or more air?

[Pawel66]

I was also trying to imagine how to do the split linkage test at 2 or 3k rpm and I am happy you asked and I appreciate stickandrudderman paid attention and advised.

I really appreciate experienced Members' patience and devotion to explain to people like me the same simple things again and again.

I was always told there are no dumb questions and I agree with it. However, when I read some of my questions I asked, I begin to hesitate...

I am not sure if there is a clear recommendation on what to keep steady and what to add. I think you need to manipulate both to determine hypothesis and to verify it.

I think the purpose of the exercise is to broadly (!) determine if there is more or less balanced amount of fuel and air in the mixture or too much of one of the components (which would mean there is too little of the other). So when you add fuel a bit (air steady) and the engine stalls, this suggests the mixture is rich. Then to verify this, if you add a bit of air (fuel steady) and engine revs up - this confirms the mixture is rich.

And vice-versa for lean mixture.

When I had a good (more or less) mixture - the changes in the way engine was running were not significant and they were more about how even it ran rather than revving up or stalling.

[ja17]

I think you have the general idea Pawel. Note that with the split linkage test at idle warm, the RPMS should be able to increase by opening the venturi slightly (200-300 rpms). In this way the air screw on the intake manifold can be used for minor idle rpm adjustments at any time.

[Pawel66]

Joe, yes, clear, thank you!

On the other hand, if the engine revs do not react to the idle air screw - the venturi is set wrong, it is not closed.

Thanks again! I will be fighting this uneven struggle during the weekend. I hope the CO tester will come handy. My biggest wprry was the clicking left with idle adjuster or right with the rack adjuster - with mixture still too rich... which would indicate other issue in the system (CSV, baro, WRD), which I checked before and they seemed to be ok, with a note that there was no more shims to remove.

Also: someone here mentioned to me that when you remove the breather tube from the valve cover, you will get a different (lower) reading of the CO. I saw no reference, however, to it on the forum and I assumed that, even though it makes sense (as there must be carbohydrates coming to intake from the breather), in the properly working engine it should be negligible or taken into account in the norm.

[ja17]

If the warm engine does not react to loosening the large, slotted air adjustment screw on the intake, then a slightly too lean condition exists. This may be caused by a venturi not closed, incorrect IP mixture setting or incorrectly set engine linkages etc.

[Pawel66]

Ok, thank you, clear!

[Pawel66]

I think I might have identified the issue for rich mixture (low and high rpm) - it looks like my WRD seems not to shut completely when warm. It used to be ok couple of years ago, but it may not be ok now.

I feel a slight suction when engine is warm (thumb, with filter removed). It is slight and it goes away once in a while, but it is there. It is slight regardless of rpm.

Please confirm kindly, if I may ask, that even slight suction should not be there, before I dig into posts figuring out how to fix it to get leaner mixture.

[Pawel66]

I did some studying on the WRD and wanted to wrap up conclusions and the next steps (not re-inventing the wheel, just trying to be a bit systematic and hoping for your input and kind advise):

1. I am working on overall rich condition of the engine, during idling and on higher rpm as well.
2. Before getting to rack adjustment, checks on several parts (CSV, barometric compensator, WRD) revealed small air leak through WRD when the car is warm (this was garage warm up, I will verify this after driving warm up).
3. This air leak may be caused by
a. only air valve leaking/not closing while the WRD pushes lever in FIP to decrease fuel supply after warm up - this may not cause the rich condition
b. both fuel and air increase supplies are not completely cut off (as the whole assembly of thermostat pin, air valve, spring and plunger does not move down enough) - this would cause the rich condition
c. separately - as I do not remember exactly the oval shim situation I checked in the past - I need to verify again how many and how thick shims I have there - this may cause the rich condition too

So what I think I need to do:
1. Disconnect and plug the coolant hoses, disconnect the air hose.
2. Remove the upper and lower WRD assembly together and take it to the bench (seems to me the best way to avoid coolant pouring to the lower WRD part)
3. Note the oval shims configutration
3. Disassemble the WRD, check the movement of parts, note the round washers configuration
4. Check the thermostat in a pot with water (how many mm extension - need to look up)
5. Check the plunger rod travel (I did not note how many mm it should extend in hot water, 7mm? not sure, I will try to look  it up), I saw 1.1mm for older type pump

I have the R25 pump.

Any watch outs from you, any advise?

[Pawel66]

Please kindly advise what should I do.

I have the WRD out.

I do have the oval shims: 2x 0.5mm and 1x0.2mm

I have 1 round shim 1mm.

The pin at the bottom was moving freely with travel ca 9mm.
Pushed in: 22mm from housing base
Extended: 30mm, which gives travel of ca 8mm

The air valve is relatively tight in its cylinder, but moves with some resistance and it holds air very tight.

Thermostat
Ambient: ca17mm from its collar
80 degC: ca22mm from its collar, giving travel 5mm

When assembled back together for test:

Ambient:
Pin sticking out 22mm from WRD base, 8mm from bottom

ca 85C
Pin sticking out 27mm from WRD base, 13mm from bottom, 5 mm travel
Air is cut off completely.

So travel due to temperature change is 5mm.

Air not cut off when pin sticks out 11-12mm (75-80C).

What do I do?

It seems to me I could use one more round shim 0.5 to 1mm to have air cut-off at lower temperature.

My rich conditoin is ca 8% CO at idle and over 15% at 2500rpm.

However: I was looking for the proper travel of the pin driven by thermostat and I found what BenzDr was saying: "The 230SL thermostat has a very short travel at about 1.5 mm while the 280SL has about 7 or 8 mm of travel. If the late system won't shut off at a fully warmed engine, you can add  round shims at the top of the slide valve until there is no longer any vacuum with the air filter removed".

Shall I then assume my thermostat is bad (too short travel) and replace it first? That would mean I do not need round shim and I may not need to remove oval shims.

[wwheeler]

Hi Pawel,

If I read your post correctly, your engine is rich at idle and at higher RPM hot or cold? Not sure if the function of the WRD shims has been explained. The oval shims change the mixture ONLY when the engine is cold. The round shims changes the time when the WRD shuts off. The round shims do NOT change the mixture of a cold running engine.

If you want to change the mixture over the entire range hot or cold, I have found shimming the B. compensator to be the easiest. Be careful as it is super sensitive. A .003" shim makes a world of difference. The WRD affects the mixture for a cold engine and only at idle. It serves the same function as a choke on a carburetor. 

Does the WRD air shut off at around 70*C (160*F)? I believe that is near the correct temperature. I read that yours has a slight suction. If slight means you can barely feel suction, then that can be normal. The air valve does wear over time and will not seal 100%. What temp engine coolant thermostat are you using? If it is a cold rating, the engine may not be getting hot enough to completely shut off the WRD. That happened to me.     

Hopefully that helps.

[mrfatboy]

To add to Wallace's explaination, since you have an overall rich condition you must remove shims from under the BC to lean out your pump. Like he said it is very sensitive.

[Pawel66]

Gentlemen, thank you for your kind replies!

I have no shims to remove from under the barometric compensator. The BC pin extent dimension seems to be within specs. It is not that that makes the mixture rich. It is not the leaking CSV either.

Yes, I know WRD and its elements are for cold running (and I have rich mixture when warm, I do not look into cold running mixture at this stage). But what if the pin at the bottom of the WRD is not long enough to cut off additional fuel with thermostat fully extended?

I understand that in the WRD when the thermostat is shrunk, the lever in FIP pushes up the pin at the bottom of WRD and this lever is in its up position. This is causing additional fuel is supplied and additional air is delivered. As the thermostat expands, it pushes down the plunger/spring/air valve assembly. What happens now is - the air valve closes the air holes, cutting additional air delivery and the pin (bottom end of plunger) pushes down on the lever in the FIP - cutting off additional fuel supply.

Is this how it works?

Then what if the pin at the bottom of the WRD does not push down enough to cut the fuel supply?

[Benz Dr.]

I would add round shims in the slide valve or replace the thermostat for the WRD. All air should shut off and any vacuum leaking is a sign that you may not have full shut off on the slide valve. You must be sure that you have obtained full movement to final stop on the slide valve or you will always have a rich running condition.

My guess is that you may have to do a lot of reverse tuning if you replace the thermostat. I can't emphasize enough how important it is that you have 100% shut off on the slide valve.

[mrfatboy]

pawel,

You are correct about the operation of the WRD. 

How about this theory?

There is also a rack adjustment screw that is accessed located by the solenoids.  It does the same thing as the BC adjustment. I'm wondering if someone has adjusted it so far out if range causing your rich condition that the BC adjustment can't even compensate.

[stickandrudderman]

My guess is that you may have to do a lot of reverse tuning if you replace the thermostat. I can't emphasize enough how important it is that you have 100% shut off on the slide valve.

Dan, I have to respectfully disagree.
A small bleed at the auxiliary air slide is just the same as undoing the idle screw half a turn and can be easily compensated for in tune-up.
Obviously a large and unchanging bleed is a different matter but as long as there a big noise at that orifice when cold and a little or no noise when hot I'm satisfied.

[Pawel66]

Dan,

Thank you - I have to proudly say my thinking was along the lines you stated. Yes, I may be chasing the correct settings once the thermostat is replaced. I am not sure if then I need to add a round shim as valve will be pushed further down than today. When I was pouring water from the kettle to the thermostat tower and blowing in the pipes I htink I was missing a 1mm or so to be sure the air is shut off. If I follow your statement from years ago, that the thermostat pin travel should be 7-8mm, I am short there and a new thermostat should solve the issue or move me forward at least towards the shims.

Stick,

I am not competent enough to get in the discussion between two Gurus, but my simple thinking is: I am not worried so much about the leak as such, but rather a leak that is a symptom of WRD not shutting down and continuing delivery of both fuel and air. A leak because of the valve not tight - fine, but a leak as the valve is not pushed down enough - that may be a different story.

mrfatboy,

Yes, this is very likely. This someone could be me a couple of years ago or the Bosch service. I think it is more likely to be a Bosch service as a couple of years ago I was after leaning the mixture like today. Othr place who touched the FIP was where it was re-built - Bosch service. But.. the rack adjustment is counter-intuitive (especially after adjusting idle screw) clicking right is leaning.

Priceless posts from all of you, thank you!