Author Topic: Can't set ideal fuel mixture  (Read 556 times)

Anosh

  • Associate Member
  • Junior Level
  • *
  • India, Maharashtra, Mumbai
  • Posts: 26
Can't set ideal fuel mixture
« on: December 09, 2021, 14:33:52 »
Hi Guys,
I have received the Fuel injection pump for the Mercedes 230SL from Fairchild and after fitting the same on the car these were the problems faced by us while setting the mixture. Please note we have installed the pump at 20 degree ATDC .

The car was idling too rich with a lot of black smoke coming out through the tail pipe and spark plugs becoming sooty within 10 minutes of idling.

I made the mixture lean by turning the Flower screw at the back of the pump ,anti clockwise, 3 notches at a time . When this did not help, I pushed the pin in the warm up device (under the thermostat ) to a lower position. This helped in cutting down the fuel and the car was running well except that the RPM could not be brought lower than 1200 RPM.

At this stage the idle screw on the intake manifold was fully shut, the flower screw behind the pump was fully out and the pin was fairly low in position. Cold start was an issue ... we had to crank 3-4 times to start the car but once started and idled for 3-4 minutes & engine was warm, she ran beautifully with idle at 1200 RPM. But there was a sudden jerk (engine rev) when moving the car forward from standstill position & was extremely difficult to drive in traffic.

In order to solve the above problem, I replaced the warm up device with the one from the old pump and noticed that on pressing the pin downwards, the RPM would drop.

Now my problem is that I'm unable to set her lean enough to run properly. When I set the pin of the wrd all the way down she becomes too lean. Upon moving the pin a little higher, she starts smoking. Now the RPM can be set at 800 using the idle screw on the intake manifold.

Please advise how to get a lean enough mixture to run her without any black smoke.

Would appreciate if you could please advise. Have gone through the linkage tour & the workshop manual but unable to find our mistake.

Many thanks.
Anosh Shroff
Anosh.shroff@gmail.com

Pawel66

  • Full Member
  • Platinum
  • ******
  • Poland, Mazowieckie, Konstancin-Jeziorna
  • Posts: 4674
Re: Can't set ideal fuel mixture
« Reply #1 on: December 09, 2021, 14:59:15 »
If the air screw is shut, it may be difficult to lean the mixture at idle.

There is a procedure we call Linkage Tour in our Technical Manual. You have to be Full Member to have access to it. It describes step by step the tuning process of the car.

Aside from that (I am not a mechanic, just bear it in mind):
1. If your engine is freshly rebuilt and these are its first minutes of work - there may be black smoke from the pipe.
2. WRD works only when the engine is cold. Then it does not work unless the air valve is leaking because WRD is not able to close it. Easy to check by unscrewing air filter and placing thumb at the opening - if suction is present when the engine is warm, air is drawn and WRD will be leaning the mixture when it should not.
3. WRD is not used to set the mixture value. For this we have
- the flower nut as you say, for idle, up to, say, 1500rpm
- the main adjuster - back of FIP, to the right hand side - across the rpms
- you can adjust mixture by adding or removing shims under barometric compensator - across the rpms
4. Before playing with mixture adjustment
- your injectors have to be checked if they work and not leak
- ignition timing and dwell properly set
- valve clearances checked and set
- engine is overall in good condition

I assume Fairchild properly timed the FIP.
If I were you I would:
1. Become a Member here
2. Study Linkage tour and how the FIP works
3. Review numerous posts on this subject (you are not the only one having this trouble, I was too)
4. Check out youtube materials on this topic
5. Check the points I mentioned above (injectors, valves, timing)
6. Unscrew the air screw mid way and take it form there.
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

Anosh

  • Associate Member
  • Junior Level
  • *
  • India, Maharashtra, Mumbai
  • Posts: 26
Re: Can't set ideal fuel mixture
« Reply #2 on: December 09, 2021, 15:21:51 »
Thanks for the prompt response. I was a full member and have the linkage tour & have followed the steps. But my engineer still can't resolve the issue.

BartSt

  • Full Member
  • Senior
  • ***
  • Belgium, Flanders, Antwerp
  • Posts: 121
Re: Can't set ideal fuel mixture
« Reply #3 on: December 09, 2021, 16:17:11 »
Check this video.

Solved similar problem I think

https://www.youtube.com/watch?v=F6sxlOFmoYw

Bart

mauro12

  • Full Member
  • Silver
  • ****
  • Italy, Sicily, Messina
  • Posts: 406
Re: Can't set ideal fuel mixture
« Reply #4 on: December 10, 2021, 22:19:15 »
Guys but how is possible that a freshly Rebuilt  injection pump is not working properly? I’m going to send my injection pump for a rebuild too and I’m scared about the same problems . Is not enough to set at the correct timing and that’s it ?
Usually when you put back a rebuild pump , what are the things that you have to set correctly ? What can go wrong ?
Mauro Pisani
250sl 1967 5speed zf manual

dirkbalter

  • Full Member
  • Gold
  • *****
  • USA, CA, Corona
  • Posts: 964
Re: Can't set ideal fuel mixture
« Reply #5 on: December 10, 2021, 22:39:32 »
Mauro, great question. Was wondering the same. I had my pump rebuild (locally) as well and the rebuilder color marked every bolt and told me:
Don’t touch anything, it will work as is. If it doesn’t, bring the car and I will look at it.
We will see I guess.
« Last Edit: December 10, 2021, 22:46:01 by dirkbalter »
Dirk
66 230 SL
70 280 SEL
18 C300 COUPE
05 HD FLSTNI

Benz Dr.

  • Full Member
  • Platinum
  • ******
  • Canada, ON, Port Lambton
  • Posts: 6718
  • Benz Dr.
Re: Can't set ideal fuel mixture
« Reply #6 on: December 10, 2021, 23:29:01 »
The pump will be set to factory specks but it may not be set to work on your car. Most of the time it will be a small idle mixture adjustment or similar. Every engine runs a bit differently and some have better compression or are fresher than others. In other words, don't panic because your rebuilt pump needs to be dialed in to your engine.
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

Pawel66

  • Full Member
  • Platinum
  • ******
  • Poland, Mazowieckie, Konstancin-Jeziorna
  • Posts: 4674
Re: Can't set ideal fuel mixture
« Reply #7 on: December 10, 2021, 23:39:28 »
The shop where I had my FIP finally tuned properly, the only one I found in my country, have the policy: we do not set the mixture values without the car in our shop. I think there may be some sense in it. They did my FIP because I did not ask to set the fuel mixture, I asked to calibrate fuel delivery to be equal between sections.

If in the US or Western Europe you have knowledgeable mechanics who send their FIPs to be rebuilt and adjusted and then they know what to do to tune the mixture - it works. Here, I can only imagine people calling back after FIP installation and claiming it does not work. So they say: bring the car, we will install it and tune it.

That is because:
1. The engine needs to be in tune
2. You need to be quite fluent in these systems and you need to know what you are doing when you install a calibrated FIP in your car - because every car will run a little different
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

mauro12

  • Full Member
  • Silver
  • ****
  • Italy, Sicily, Messina
  • Posts: 406
Re: Can't set ideal fuel mixture
« Reply #8 on: December 11, 2021, 15:10:50 »
Im going to send my injection pump to Hans Fritszche in Germany. I guess is probably one of the best around Europe and of course I cannot bring the car to Germany for a simple idle adjustment . My idea is that is not possible that a freshly rebuilt unit is working worse than before the overhaul. For what I have read around this forum and in other forums , the most critical thing is the correct timing of pump. Sometimes you can set 180 degrees off and the result will be a very very rich mixture .
My thought is that less you play with a tuned and freshly rebuilt pump and better is it. I already asked Hans fritszche this question and he told me that I need to set the idle mixture only , I don't have to touch anything else. If I have a co analyzer is even better but is not critical .
Why do I need an overhaul of the pump? my car is running ok but is very very rich and the co level are over 9.99 and there is a bit of petrol dilution in the engine oil, I guess this is the worst enemy.

if somebody has some other advices about the process of putting back an overhauled pump, please let us know.

thank you
Mauro Pisani
250sl 1967 5speed zf manual

Pawel66

  • Full Member
  • Platinum
  • ******
  • Poland, Mazowieckie, Konstancin-Jeziorna
  • Posts: 4674
Re: Can't set ideal fuel mixture
« Reply #9 on: December 11, 2021, 18:12:09 »
Mauro, if I may - a very quick way to see if you can lean the FIP is to remove all shims from under barometric compensator and see if you went any leaner.
The other way would be to turn the main adjuster right in a controlled manner (so that you can come back) and see if you can lean it.
The number 3 quick check is the injectors.

But of course sending a FIP for check up and adjustment is not a bad idea at all.

I had my FIP out of time for some period. The symptoms were not rich condition, but rather uneven work of engine and lower performance of the engine. It is intake injection, I think timing has a fairly broad tolerance here. It is, again, an easy check with tooth picks.
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

mauro12

  • Full Member
  • Silver
  • ****
  • Italy, Sicily, Messina
  • Posts: 406
Re: Can't set ideal fuel mixture
« Reply #10 on: December 12, 2021, 13:09:20 »
I guess that by removing shims you solve partially the problem . You remove one symptom but it is not the cure .
Having the pump calibrated to factory specs should solve the problem for at least 50 years . My concern is that in 10 years , the injection pump market will increase its value and less specialists will be around this buisness.
Especially with electric cars.
Please let us know if you solved the problem .
I remember that last year I thought that my rich running issue was caused by defective injectors so I decided to buy a set of 6 new from mbclassic.de.
The result was terrible because these injectors were defective from the factory and they have refunded me.
Mauro Pisani
250sl 1967 5speed zf manual