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  #1  
Old 01-06-2003, 08:29 AM
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Anyone Know about Lambda Control?

I know that this is off-topic for this forum, but nobody on the tech board answered, and I know you guys will help if you can.

The Wayward Woman ('81 380SL) is running well with the exception of two problems that I think are related.

1. Running very rich at idle, but OK at other RPM
2. Surging idle in Park: bounces between 480-580 RPM

I ran the basic checks in the manual on the idle control, and that system seems to be working. My theory is that the lambda system is not working in closed-loop and sending bogus signals to the idle system.

By bridging the temp sensor, which simulates cold running, the idle went to a rock-steady 750 and vacuum stabilized at 16 inches.

I was able to verify that the lambda control is getting 12V, so the OVP is OK.

When I put a dwell meter on pin 3 in the diagnostic socket as it says in the manual, I got a steady reading of of 6 degrees, which is like 6% (very rich) when it should be fluctuating between 42-50 degrees.

So there are three components involved. The O2 sensor, the lambda controller, and the frequency valve. The sensor is a no-brainer at about $20. But the frequency valve is expensive and the controller is a budget-buster.

Does anyone know a bench-test for the frequency valve so I can tell if that's the culprit, assuming the O2 sensor doesn't do it? Other ideas or suggestions?

Many TIA

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #2  
Old 01-06-2003, 11:22 AM
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Location: San Jose, CA
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I think of the Oxygen sensor as a maintenance item that should be changed before a smog test, or when it starts running like yours!

Couldn't hurt...
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Ed
1981 300CD (Benzina)
1968 250 S (Gina) 266,000 miles!
1983 Alfa Romeo GTV6 (Guido)
1976 Jaguar XJS-saved a V-12 from the chevy curse, what a great engine!
1988 Cadillac Eldorado (better car than you might think!)
1988 Yamaha Venture (better than a Wing!)
1977 Suzuki GS750B
1976 Yamaha XS 650 (sold)
1991 Suzuki GSX1100G (Shafty Gixser)
1981 Yamaha VX920RH (Euro "Virago")
Solex Moped
1975 Dodge P/U camper


"Time spent in the company of a cat, a beer, and this forum, is not time wasted!"
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  #3  
Old 01-06-2003, 03:40 PM
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Chuck,
Have you checked the temp sensor to make sure it's providing the correct resistance throughout the temp range?

Happy Motoring, Mark
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  #4  
Old 01-06-2003, 08:32 PM
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Location: Evansville, Indiana
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Idle mixture needs adjusting, the O2 sensor is probably shot, and the temp sensor may also be wacked.

If the meter reading is off, mostly likely the O2 sensor is bad, but it could also be a disconnected wire (hehe) or a short.

There is a nice section on diagnosis, I think here on MErcedes shop, in the DIY section (I may have seen it somewhere else, though, getting a bit foggy upstairs....)

Make sure everything is in working order before setting the idle mixture.

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #5  
Old 01-06-2003, 10:07 PM
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Thanks, guys.

The temp sensor looks at oil temp and it goes to ground at 40 deg C. Will check this. Also picked up a new O2 sensor and will install it tomorrow.

George Murphy suggested a continuity check on the frequency valve's two terminals to verify that it is at least alive.

Stay tuned.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #6  
Old 01-07-2003, 06:46 PM
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Location: Falls Church, VA
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Replaced O2 Sensor

Took first step and replaced the oxygen sensor.

Positive results: better idle (480-520 in Park), engine seemed smoother, a bit more power, exhaust at idle did not smell as rich.

Neutral results: still getting lousy dwell reading, frequency valve still not vibrating.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #7  
Old 01-07-2003, 07:37 PM
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Join Date: Dec 2001
Location: San Jose, CA
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try giving the freq valve a tap...
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Ed
1981 300CD (Benzina)
1968 250 S (Gina) 266,000 miles!
1983 Alfa Romeo GTV6 (Guido)
1976 Jaguar XJS-saved a V-12 from the chevy curse, what a great engine!
1988 Cadillac Eldorado (better car than you might think!)
1988 Yamaha Venture (better than a Wing!)
1977 Suzuki GS750B
1976 Yamaha XS 650 (sold)
1991 Suzuki GSX1100G (Shafty Gixser)
1981 Yamaha VX920RH (Euro "Virago")
Solex Moped
1975 Dodge P/U camper


"Time spent in the company of a cat, a beer, and this forum, is not time wasted!"
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  #8  
Old 01-07-2003, 11:05 PM
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Do I Ever Feel Dumb!

I kinda sorta think I have this figured out.

Keep this in mind. WW failed the emissions test right before the chain jumped. Not running very well at all then compared to now. I am fairly sure that it had a vacuum leak of some sort then which seems to have gotten fixed with the head replacement. And I think the new chain helped the valve timing.

So anyway, I disconnected the new oxygen sensor and put my DMM on it and started the car. As the car warmed at idle, the voltage came slowly up to .27 and stabilized. By holding the RPM at 1500, the voltage came up to about .78. When I dropped it to idle, the reading gradually dropped back to .26 volts.

Now you need to read Steve B's dialog with Cap'n Courageous on the Tech forum to understand this and I am not sure I have it totally right.

The oxygen sensor generates a current as the mixture richens. The computer measures the current and leans the mixture by telling the valve to open and divert fuel from the injectors. As the mixture leans, the voltage drops and and the computer responds by closing the valve. All of this is happening in milliseconds. But here is a quote from Steve B

"[The] system will correct mixtures less than .5v by adding fuel (within the 10ma correction range we have already tested) till the mixture becomes richer than .5v at which time the current will reverse and the system lean out till it switches the other way. Once the O2 sensor is hot and everything is adjusted then the .3v to .7v O2 sensor swings will be kept in check by about a 4ma total mixture correction."

The light comes on! At idle with .27 volts, I WAS NOT GETTING ENOUGH VOLTAGE FROM THE SENSOR TO PULSE THE VALVE. The mixture is a bit lean. So I am gonna run up tomorrow and get the idle re-tested with my slightly lean mixture and then richen it up a bit so the lambda controller can regulate it.

So my theory is that before the chain jumped I had some basic problem, possibly vacuum related, causing a rich condition that the system could not deal with because the O2 sensor was bad. With that now fixed, the mix at idle is lean enough that it does not need "help" from the mixture valve.

The other point that Steve makes which I did not fully grasp is that the lambda system only "trims" the mixture - it cannot cure basic problems with the injection system.


Hope this makes some sense.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #9  
Old 01-07-2003, 11:28 PM
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Chuck:

Bingo!

I suspect the idle mixture was set with a vac leak, with the result that you are now running rich with the leak fixed. Double check everything for leaks, including the idle control valve hoses if you have idle speed control (I think you do). Also check the condition of the idle control valve, they get dirty and cause rough idle and/or idle speed hunting when the valve overcorrects, sticks, comes free, and then sticks again.

Make sure all the accessory vac systems hold vac, too -- leaking door lock or climate control systems can cause funny idle, too. Ditto for EGR and tranny control stuff. I replaced ALL the connectors in the engine compartment on the 300TE -- eliminated most of the stalling problem (sticky idle control valve) and the serious throttle lag. Also replaced the idle control valve hoses -- big pain on the six, but it runs better!

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #10  
Old 09-30-2003, 07:26 PM
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Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
Fast Forward to September

I still have the problem with a lumpy idle and disfunctional lambda. A few months ago, I installed new injectors and seals and air hoses and checked all vacuum connections. This improved matters somewhat. I decided to have another go at the problems this week starting with the lambda system.

Here is what I have determined.

1. The computer is getting power
2. The O2 sensor is putting out at least .4V at the computer connection.
3. The ground on the computer is good
4. The oil temp sensor is working correctly
4a. The coolant temp switch is working correctly
4b. The throttle switch is working correctly
5. The frequency valve is vibrating
6. The on/off ratio sits at about 8%
7. Changing the mixture has no effect on the ratio.

The mixture seems about right. I can turn it 1/4 turn in either direction and it runs worse.

I am running out of options here - I think I have verified all the inputs and it is looking like the computer is dead.

Other thoughts?

TIA
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #11  
Old 10-03-2003, 09:21 PM
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Location: Evansville, Indiana
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Chuck:

Sorry I've been so late in answering this, I've had a couple projects here keeping me busy.

For whatever reason, you do not have closed loop lambda control. I'm not real familiar with that version of KE-jetronic, but either you don't have the closed loop "message" getting to the computer (oil temp or coolant temp) or you have a fuel distributor problem.

When you change the setting on the mixture screw, how long do you wait to see what happens? At idle it will take 20 sec or so for the O2 sensor to work, and it may in fact NEVER be in closed loop at idle unless you have a heated O2 sensor -- the older ones are only in closed loop with the throttle open and the sensor heated by exhaust gas.

The other thing to look at is basic fuel distributor operation -- control flap centered and at the correct height, plunger moving freely, pressure regulator working, no restrictions in the return line to the tank, etc.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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