CO Specs Application - Please Advise

[Pawel66]

We have the following CO specs:

Idle       
750-800   RPM CO  3.5 - 4.5  =  AFR 12.80 - 13.20

Lower partial   
1500      RPM CO  1.5 - 3.0  =  AFR  13.40 - 13.95

3000+  RPM CO  0.2 - 1.5  =  AFR  13.95 - 14.50

Full load   

3000+  RPM CO  2.0 - 4.0  =  AFR  12.85 - 13.20

What I have access to is the good meter at the vehicle diagnostic station, where I can go and check/adjust the CO with car standing there in N or P being revved up to 1500 rpm or 3000rpm so that the CO can be measured. So the car is not on the rolls, not in gear.

Shall I set the CO to "Lower partial load" specs?

I know the proper adjustement is done during drive etc., but I do not have access to it for now. I need to start somewhere.

Please advise.

[jeffc280sl]

Been a while since I was into these issues.  The specs you reference are part of "Adjusting Injection Pump under Load" from the BBB.   Basically these are dynamometer tests that can be performed on the road as well.  Under load indicates the engine is under stress (load) versus in neutral or park.   Are you looking into fine tuning of the FIP?  This involves adjusting internal FIP screws (white and black) and is very difficult.  I ask because this is very time consuming and challenging.  I installed an intake manifold pressure sensor (to measure engine load), fuel ratio meter and used a data logger to to take fuel ratio data. Once you have the data you can make adjustments to the FIP.  This is described in our Tech Manual. 


I'll be happy to offer my experience if this is where you are.  The same goal can be achieved by sending your pump off for calibration.  (much easier)

[Pawel66]

jeffc280sl, thank you for attention and a kind advice.

Indeed I think my FIP will finds its way for check up and tuning in the winter.

The issue was always to find trustable service in vicinity. I used one of the Bosch shops, but I do not think any more  they know what they are doing.

What I was looking for was adjustment to be within some reasonable limits vs. Specs. Not a fine-tuning, I am far from it. i would not touch the black and white screws. I was after at least rough adjustment across range of rpms and then adjust idle and then warm up idle.

If I can have access to a proper meter at the inspoection station - what CO level shoukd I terget at, say, 3000rpm with car not in gear?

[jeffc280sl]

You're welcome.  I think we all share the same experience trying to find knowledgeable people to work on our cars.  FIP adjustment knowledge for a mechanical fuel injection system design that was superceded in the early 70's is very hard and expensive to find.

I can't answer your question about CO measurements without an engine load.  If you look at the profile of the space cam in the tech manual you can see the "programming" of the FIP is mechanical and the MB AFR Specs are written with engine load in mind.

You can buy portable AFR testers to take on the road.  Without a data logger it will be difficult to drive and see AFR under various loads like hills.   I think something like an average of 12.7 is what I would look for.  Without adjusting the white and black screws I don't know how to adjust the pump.  Maybe others can help out here.

Jeff

[Pawel66]

Thank you.

I was probably naive thinking that the properly adjusted FIP (as you describe) should produce a CO level reading, in the conditions I described, that can be taken as rough indication of where CO level should be...

[Benz Dr.]

Aside from the possibility that your engine simply doesn't run well or lacks good power, is what kind of seems like an obsession to perfection. This quest could get you into more trouble than you expect if you mess up your IP or burn a piston from running too lean.

If you can't adjust your IP from regular external means, maybe it's time to get it rebuilt or calibrated. These pumps are very sensitive to even small adjustments and you could easily damage things that are far more expensive than an IP rebuild.   

Just sayin'.

[Pawel66]

Thank you for the words of warning, I am taking them very seriously.

My FIP reacts to adjustments. I just do not know what CO reading should I get in the test I am able to do (stationary, 3000rpm) to be anywhere near where I should be (not an obsession for perfection - on the contrary, actually).

And yes, I will send it to check up, right after summer, just need to figuure out where...

[Benz Dr.]

Of course, I could be wrong. 

[jeffc280sl]

At this point I guess we are speaking about adjusting the external thumb screw used for idle range adjustment.  If your car runs well and the plugs are the right color maybe you leave it be.

Maybe someone here with a recently calibrated FIP that has been put on a similar emission test stand to what you have can share CO readings.  Long shot I think.  Absent any other input I would shoot for 12.7 to 13 AFR at 3000 rpm.   Maybe you can take data and post it here for comments. 

[Pawel66]

Of course, I could be wrong. 

It is quite rare that you are wrong... these are words of wisdom. I just need to know if I am close to where I should be and I came from being faaaar away.

[Pawel66]

At this point I guess we are speaking about adjusting the external thumb screw used for full range adjustment.  If your car runs well and the plugs are the right color maybe you leave it be.

Maybe someone here with a recently calibrated FIP that has been put on a similar emission test stand to what you have can share CO readings.  Long shot I think.  Absent any other input I would shoot for 12.7 to 13 AFR at 3000 rpm.   Maybe you can take data and post it here for comments.

Thank you again!

I am using the full range adjuster - accessed by removing the allen screw then turned with a thin long screwdriver understanding this is for adjusting across rpms. Then I am using the thumb screw outside of the rear plate and the air screw to bring idle to specs. I intended to add, say, 0.3mm oval shim as I have lean warm up, have not done that yet. I realize this may change idle a little.

I do not suppose the external thumb screw is for all rpms? There were posts saying that long time ago on the forum, but it looks like it was clarified that the thumb screw is for idle only.

Where I got with the adjustments is 3.3% CO (stationery, 3000rpm) and 4.7% idle. I came there from ca 15%CO and black soothy spark plugs.

And yes - this is what I was hoping for - someone will know the CO level at 3000 or 2500 rpm when stationery.

I think what I will end up with for the rest of summer - drive with what I have a little and check the plugs colour.

In the meantime will find a place to send my FIP to for the autumn. I will not send it to that Bosch service I used to work with any more.

[jeffc280sl]

I modified my earlier post.  Sorry for my mistake.  The thumb screw is for idle adjustment only.  Removing the allen screw permits access to the full range screw.  Sounds like you have good control tuning as results are improved.   Like you suggest I would drive it and check the plugs. 

I don't know how the FIP will respond under load.  If the fip richens the mixture a little under load (I suspect this is how it works) I'd say your in good shape.  You don't want to go the other way where the mixture leans out too much under load.  I'd pull the plugs and check color sooner rather then later.  I think you know what a very rich plug looks like

[Pawel66]

I can proudly say my thinking was exactly along the lines you described that is exactly what I am going to do before the FIP is sent out.

[jeffc280sl]

Glad to hear.  Good luck.  If you really want to learn about the details of tuning I suggest you turn to our Porsche cousins.  I believe they are more adventurous and enthusiastic about this matter.  Much of my tuning knowledge came from these guys


https://www.pelicanparts.com/techarticles/101_Projects_Porsche_911/30-Mfi_Info/30-Mfi_Info.htm

There is a lot of great information available on this website for Bosch fuel injection systems.  Poke around if you have time using their search engine.  This topic is discussed at length

[Pawel66]

Thank you, looks like a good lead!

[Benz Dr.]

It is quite rare that you are wrong... these are words of wisdom. I just need to know if I am close to where I should be and I came from being faaaar away.

Part of being wrong is knowing when you are getting close to being right. Only through hard work and experience will you know when you have it fixed and when to stop adjusting. Sometimes this means making small compromises when there's so much wear that the best you can do is to get something close or within the range that's possible. You seem to be going in the right direction.

Good work young man!

[Pawel66]

 

Wise words again...

[Pawel66]

Please kindly take a look at the pictures. This is after only 30km of driving (only so much I could make today).
Is it too early to say or you can say I am too lean already now, by the pictures?

This is 3.3%CO at 3000rpm, stationery.
Cold start, warm start, idle - all ok. Car runs like a dream.
The only thing I have found this morning - I may have a leaking air valve in WRD. I cannot blow through cloesd valve just with my mouth (1.5PSI), but when I blow 20psi from compressor, the air goes through (vacuum is 16mmHg, so ca 8psi, half of compressor, but will leak, I htink).

[Benz Dr.]

Those are some very clean plugs. I wouldn't go any leaner.

[Pawel66]

Thank you for an answer!

The worry is - am I not too lean? I do not know if 30km is enough to say...

I think the options are either enrich it a bit or wait for more kilometers to see if they get more brown.

[Benz Dr.]

They look pretty close to right.  The ground electrode isn't discolored or white and the shell is black so you are very close. If you have good throttle response and power then I would drive it for a while and see how they look. If you ever see small black specks on your plugs that's not good and indicates pieces of aluminum that have melted away from your pistons. That would be WAY too lean.

I burned up a 190SL engine about 35 years ago after I put 105 main jets in a set of Weber carbs I was running. I'm sure that the 90 MPH I was driving at the time wasn't a factor. lol   
It burned right through the side of two pistons - rings and all. I never go lower than 115 main jets now.

[Pawel66]

Ok, thank you. I would then give it next 30-50km and check again.

I do not usually rev up this car to 95Mph - I usually drive her mild...

My speedo once got stuck at 130 kmph. It was funny to see the car standing in the garage at 130kmph...

[Pawel66]

These are the plugs after 100km. Am I too lean? Please kindly advise.

[Shvegel]

Here is what I see or rather think.  You seem to be trying to optimize your settings so things are closer if not perfect.  The problem I see is that the Injection pump doesn't adjust for several factors that can affect your settings. Incoming air temperature, amount of air entering the idle circuit, Ignition timing and even fuel quality all affect the combustion temperature which affects the plug color.  Mercedes and Bosch have achieved settings through testing that take this into account.  They set the pumps up a little rich so when you drive the car on a cold day and the air coming into the intake is colder and therefore has more oxygen in it there is still enough fuel there to keep the engine from becoming overly lean and melting a valve or piston.  Without the ability to adjust mixture under load in all conditions I would leave the settings to a competent shop with a spec sheet and a test bench. 

Another thing to keep in mind is setting mixture to a loaded CO spec while not under a load probably isn't a good idea. Inside the governor there is a space cam that acts as the master fuel controller to the rest of the pump.  Different areas of the cam are at different levels depending on how much fuel is needed in that particular RPM/load point.  The cam is moved in two directions.  It is rotated on it's axis by the throttle position and it is moved in and out on it's axis by engine rpm.  When you set the mixture without a load you are on one point of the space cam and when you are actually under load you are on another. Since you have no way of knowing if those 2 points on the space cam are both going to deliver the same air fuel ratio (and almost certainly won't) I think you are on some dangerous ground.

I would find someone with a dynomometer to set it up and err on the side of a rich mixture or send the pump out to be tuned.

[Pawel66]

Shvegel, thank you - you are absolutely right in all you are saying. I will most likely end up with adjusting it while driving o on dyno in not-competent shop (unless I finally find it) or with sending pump to a competent shop (just got address in Germany).

One point yo may not be 100% correct is that I want it perfect - I am after a "more or less" setting by plug colour, for now, until I have time to find a shop or send the FIP.

To me my plugs look probably too lean, but I am asking here as most of Members are more experienced to judge by the colour: you can leave as is for now or make it a bit richer. For sure not leaner.

[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!