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1976 280SL, 1979 450SL
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26 Posts
Discussion Starter #1
So my car 1979 450SL is running insanely rich, and I was wondering if there was a quick way to tune the air/fuel ratio on these cars for a short term type of thing. I'm not looking to perfect it just yet (unless it's "easy" and "quick" to do), but I just want to tone everything down a notch so that I stop choking people with my gas fumes everywhere I drive. If there's a link I could check out, please do post. I'm new to this car (I had a rotary with a stand-alone ECU before), so I wouldn't know where to start, and typing "tuning" and "tune" in search engines didn't exactly give me what I was looking for. Thanks!
Erik
 

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1976 450 SLC. (working, in need of paint)/1987 300E/1989 635 CSI/2004 Honda Element (appliance)
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142 Posts
I would take the car to a reputable MB shop that knows about the CIS injection system.
That said, there is a way to make your car run leaner, but there are a couple of questions that you need to ask before tinkering with the mixture.
Was this something new, or has it always been like this?
Is there something else wrong with the car, I.E, a cold start injector that got stuck on open? (if so it would explain the car running rich)
Is your cat clogged?
You have an O2 sensor... When was the last time it was changed?
How about the distributor cables, rotor, cap, spark plugs, coil? Did you pull a spark plug? How did it look?
Your car is a mechanical fuel injected engine, with mechanical compensation, and very little in the way of electronics. Your diagnosis will depend upon close inspection of the CIS components and their functions. There really is no easy quick fix, that is if you want to drive the car for any amount of time.
And probably you know, but it is best to remind everyone, that a lean condition in a car is deadly, and will eat through your pistons in very short order. Better rich than lean.
 

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Premium Member
2010 Mercury Milan Hybrid, 1993 BMW 325i convertible
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Just a correction: your car doesn't have an O2 sensor. They didn't add those till 1980.
 

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1976 450 SLC. (working, in need of paint)/1987 300E/1989 635 CSI/2004 Honda Element (appliance)
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142 Posts
I was unsure of the start date for the O2 Sensor. Thanks.
There are a lot of variables that could lead to the car running rich, that I feel that unless you are very familiar with them, that you should take them to a reputable shop, or learn how they work intimately.
Also of concern is that if you adjust the mixture, and then fix the problem, your car will be running lean, leading to a premature death (the spare parts for pistons, heads, etc, can be very expensive).
This is the reason that I converted my car to Megasquirt. Troubleshooting got a hell of a lot easier!
 

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1976 280SL, 1979 450SL
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26 Posts
Discussion Starter #5
wow, smolina, thanks for the input :)

i changed the spark plugs and the spark plug wires within the past few weeks. the spark plugs looked pretty good, a tad bit orange on the tips, but otherwise within normal standards i would say.
i'm changing the transmission and motor oils and filters today.
everything runs, but you could smell gas a mile away when my car's on, and the gas-mileage is horrible.
i hear what you're saying with taking it to a professional, but that'll be when i get down to la (i'm driving from sf to la in a few hours), and i just wanted to tune everything down just a tiny tad bit for the drive down.
as for the condition of anything else, i have no idea what condition they're in, or what they're supposed to be (i have no idea what to make the comparison to).
i'm going to be selling this car and i have a euro "grey market" 280sl i'm going to pick up soon, so that one for sure i will be putting a megasquirt or some other ecu into...how do you like yours? more power? more gas-mileage? better running? i've read a lot on those, but others' input is always nice :)
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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32,359 Posts
What color is the smoke? I am surprised your plugs did not look black and sooty if it is running rich.
 

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1978 280slc
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3,203 Posts
I hope you know megasquirt isn't CARB approved. I'd love to squirt my car but damn it is both expensive and time consuming, and the end result is a non-smoggable car.
 

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1976 450 SLC. (working, in need of paint)/1987 300E/1989 635 CSI/2004 Honda Element (appliance)
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142 Posts
I made the decision to install the Megasquirt based upon the fact that the 3 most expensive components of the system had died. I am talking about the fuel distributor (1200 or more at the dealer) the Warm Up Regulator (no Idea how much) and the air slide valve.
As my car is not one that is driven often, I can not say how much better the fuel economy is, but I can say that the car starts easily, idles very nicely warm, and has plenty of pickup. You can "dial" in the amount of Horse Power and Torque that you want, and I found that my car runs really nicely with about 215Hp and 270 lb/ft.
With that said, the process was not difficult, just time consuming. I had to make new fuel injector rails, made from AN3 racing stock, and a special drill bit to make the chanfered fuel rail holes, used a variable fuel pressure regulator (any one can do, I used this one because it was an AN3 fuel pressure regulator), and used 2 adaptors at the fitting side of the fuel lines.
The sensors that are needed are commonly found GM sensors (so if they die every 3 years instead of 30 like a MB sensor, it will be $7 and not $70), like the Intake Air temperature, and the Engine temperature sensor.
With the sensors, and the laptop it is easy to diagnose things. For instance my car was running too retarded, and MS gave me the ignition timing that would work best. It does work very nicely.
You only really need those 2, although an O2 sensor is generally regarded as a good idea, and is my next project with the car, as I have the awful catalityc converters under the exhaust, so I need to remove those, and probably replace the manifolds with something better, but that is another project in itself.
 

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1976 450 SLC. (working, in need of paint)/1987 300E/1989 635 CSI/2004 Honda Element (appliance)
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142 Posts
I feel for you guys in California. I mean, how many 1970's vintage cars are out there?
It seems to me that a cutoff date would be in order, I live in the other Peoples Republic on the Right coast (Ma), and we do not have to smog our cars if older than 1996. With that in mind, very few 1990's cars are on the road due to the salt.
I think that there are a couple of options concerning ECU's for cars that have to meet the CARB standard, but they are far more expensive, and you guys would have to go to the BAR to get them legalized. Not fun from what I hear.
Although the 280 Euro might be rare enough, that it might not be a known car, and therefore minor mods like a fuel rail, and a new bundle of cables going into the cabin might go un-noticed.
Here is part of the MS conversion.... See what differences you can spot...
 

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1978 280slc
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3,203 Posts
Cool to hear you done did Smolina, that is cool. You have MS controlling both fuel and spark then? That's the proper way to do it.
 

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1976 450 SLC. (working, in need of paint)/1987 300E/1989 635 CSI/2004 Honda Element (appliance)
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142 Posts
At this moment I am just controlling fuel. My Ignition is pretty good, and works well and is the later rather problem free one. I am running MS from the coil, as that way it triggers according to RPM.
 
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