CO Specs Application - Please Advise

[jeffc280sl]

on another thread we discussed adjusting afr with the barometric compensator.  adding a washer will enrich the mixture.  it easy to remove and add washers and its controllable.   you can play around and return to original washer selection easily

[Pawel66]

Thank you for your kind attention!

Yes, I know the drill. This is one of the ways. I bought the whole set of generic adjustment washers of various thicknesses to be able to do it.

Here I was after advise if, judging roughly just by the colour of the plugs, I should leave adjustment as is or enrich the mixture. Seems to me I should enrich it a bit.

[jeffc280sl]

I agree.  If it were my car I would enrich the mixture by adding a BC shim and see how the engine performs.  Your insulators look very clean and I expect a little tan color to make it perfect.

[Pawel66]

Yes, thank  you, will do. Probably with adjuster as I keep track from certain moment.

[Pawel66]

I thought I would close this, maybe someone in the future finds it useful.

The purpose of the exercise was to tune the mixture more or less across the rpms, then for idle, then for warm up. My car was running very rich overall. In the meantime, however, I found out that some of my cylinders were running much richer than the others.

It took some time to:
- check if FIP is delivering equal amount of fuel (with syringes)
- check the air inlet
- check if the inlet/vacuum system is tight (with e-cigarette and washer liquid pump)
- check/recondition/re-shuffle the injectors (the devise for that is priceless)

Having gone through the last point the second time - I am finally having the spark plugs having similar colours. They are all very light grey that tells me it is all a bit lean probably and also I will try hotter plugs (Bosch W9 instead of W7).

If the last point did not work, I would go into looking at and replacing check valves in FIP. I have the puller made, seals are available at MB, check valves you can find on ebay.

The rest is easy - need to make the car a bit more rich (probably 0.1 or 0.2mm shim under BC), then fine tune the idle (I have Gunson) and then warm up.

Hope this will work. Thank you for your kind advise!

[Berggreen]

Hi Pawel and All

I have read this thread with interest, as I have too been struggling with the adjustments on both my 280SL's - one automatic and the other manual.

I have not dared making any other adjustments to the FIP, than with the thumb screw on the FIP and the air-screw on the manifold, as well as the constant speed solenoid on the automatic. No load adjustments or measurements, only home garage adjustments at idle with a portable CO reader powered by the battery and going into the exhaust pipes.

However, one thing that puzzles me is the idle and load CO data from the MB service manual in relation to if the car is a automatic or manual.

On the automatic, what I have experienced is that there is a big difference in CO-readings at idle between P/N and then in gear (4/3/2/R), with the constant speed solenoid properly adjusted so that idle is constant in all positions of the automatic gearbox.

On the manual, here idle is always the same and not under load, as the car will always be in neutral at idle. So here it is much easier to adjust according to idle CO (I aim at 4.0%CO - ok?).

But how can MB make uniform CO data covering both automatic and manual cars, when their characteristics and load profiles are apparently different?

Or is what I experience with my automatic not normal? Should I see the same CO in idle no matter what gearbox selection I am in?

Currently, on the automatic, I have "played it safe", and adjusted the FIP to give around 4.0%CO at idle but in gear (4/3/2/R), and then I accept a much higher CO at idle in P/N and avoid leaving it in P/N for too long. But I think I am running a bit too rich, because friends driving behind me say that I am pulling a little smoke, when I push the car in acceleration.

Any views or advice would be great! 

Thanx,

Christian 

[GM]

It's been a slow weekend in quarantine, so I took the liberty of translating the German document that Hans provided earlier in the  "W113 280 sl" thread with Google translate. I didn't translate the items in the pictures. I'm not the expert that others here are, but hope I can help in other ways.

[Pawel66]

Thank you for translating this document!

I am obviously not qualified enough to raise voice on this, but reading the document sort of confirms what I read before (in much more detailed way) that this FIP is controlled by engine revs and gas pedal position, so all gear ratios related topics that would be the difference between automatic and manual are included in these parameters. Also - if you look at the parameters in the book and the tolerances, compared to a practical range of what the FIP can deliver, suggest that it is all not that precise, actually...

As for the difference in CO in gear in or N condition - when I measured it, they were very alike. The idle adjustment screw is responsible for revs up to 1500 - 1700rpm/min, so it should be within the Constant Speed Solenoid operation. The potential difference of 0.5% - I am not sure if my Gunson meter is accurate enough to nail. The longer you use it at one given "measurement session", the higher the readings are. You need to re-calibrate it.

What is fascinating to me is this 3D cam...

[Berggreen]

It's been a slow weekend in quarantine, so I took the liberty of translating the German document that Hans provided earlier in this thread with Google translate. I didn't translate the items in the pictures. I'm not the expert that others here are, but hope I can help in other ways.

Hi Gary

Fantastic, thanks a lot for your efforts in translating this document to English. I really look forward to read it in detail.

Cheers,

Christian

[Berggreen]

As for the difference in CO in gear in or N condition - when I measured it, they were very alike. The idle adjustment screw is responsible for revs up to 1500 - 1700rpm/min, so it should be within the Constant Speed Solenoid operation. The potential difference of 0.5% - I am not sure if my Gunson meter is accurate enough to nail. The longer you use it at one given "measurement session", the higher the readings are. You need to re-calibrate it.

Thanks Pawel, it is interesting to hear that you did not see any measurable difference in idle CO between P/N and the driving gears. Then something must be wrong with my FIP, so that it needs a re-calibration. Because when I read around 4%CO in gear, I read something like 8-10%CO in P/N - damn as it is not easy here in Denmark to get the FIP re-calibrated, and I don't want to take it out myself and send it to Germany!

But thanx for your help and input. At least I now know something is wrong with the FIP.

As a side note, the previous owner in Canada told me, when I bought the car, that the renovated engine has been set up to "racing specs". He could not tell me in detail what that meant, as he was not a technical person, and as it had been done years ago by an old Mercedes expert, it was not possible to trace down, as the expert was now senile and not able to remember anything. But some racing adjustments to the FIP could maybe be what was done to give it "racing specs". Do anyone know, if this is indeed possible to adjust the FIP to more racing-like specifications?

I must say that the car does pull VERY hard at higher revs - and sounds like a WW2 Messerschmitt when I take it on the highway and give it some pedal! It pulls MUCH harder than my manual 280SL, and people who have driven it say it is the most powerful "standard" 280SL they have driven. The question is then how "standard" it actually is!?

Cheers,

Christian

[Pawel66]

Look, I am by no means an expert on this, not even close. It would be best if someone more experienced commented on the idle vs. "fast idle" CO difference...

What I can say is that someone was kind enough and patient enough to advise me on this as I was doing it.

For myself I concluded that:
1. CO calibration in some detail can be done only on dyno stand or during the driving test with good portable device. I gave up on this and decided that I will calibrate high rpms just by driving and looking at the colour of the spark plugs - good enough for me. But you do not have to do that. I am sure you can find dyno stand or some shop with good portable device around you. What i would not do at all is to touch partial load screws and work only with BC shims, main screw and idle screw. You may not need to send FIP anywhere. This is if you want to chase the sweet spot.

2. For myself I concluded (right or wrong) that the order is following: broad range adjustment first (all rpms, high rpms - driving basically), then idle, then idle with CSS, then warm up. Otherwise it does not make sense to me. You will adjust idle for 4%. Then you will drive, say 100km, switch off engine (do not let it run on idle too long) and check the spark plugs. Let's say you will find them black. You then remove a shim from under BC to lean mixture. This minute your idle is gone, you will have it too lean. You have to re-adjust it again.

3. In your particular case, if it were my FIP, what I would suspect is not that the pump is wrong immediately. I would think that perhaps with CSS your linkage goes to the boarder of idle screw influence. So I would start making sure that your mixture is somewhere close to be ok on higher revs - now it looks it might be rich. Maybe it is too rich indeed, that is why you have 8% on "fast idle" with CSS?

4. What I heard form a person who helped me was that these devices work better if they are in the middle of their adjustment scales, rather than close to limits. From many observations of original cars, it was concluded that the factory amount of shims under BC was about 2mm. Could be this is this "middle of the scale". I indeed put 2mm of shims there and started form this place - and it helped a lot. But again - the all rpm adjustment first.

My car was also running like a dream when she was too rich. These engines like it. Now it is leaner, however, and runs great too!