1989 300e lambda problem, am i doing this right? - PeachParts Mercedes-Benz Forum

mespe · #1 03-24-2010, 02:27 PM

Well I just picked up a 300e for my daughter to drive, when she gets her license. PO played with lambda tower, looks like it's busted. All I get is 69.3 duty cycle, unless I open the throttle by pushing down on the big round flap.

First picture look at the tower on the bottom left.
second picture I'm fairly sure that this is where I check the duty cycle between 2 & 3

Question is, can a broken lambda tower as shown in the picture keep it from being adjusted?

Gilly · #2 03-24-2010, 06:58 PM

If you see the small hex adjuster inside the tower, you can adjust it. You have to push down with the proper tool (I think it's approx a 3mm hex (allen)) you may have to twist around a bit to get that hex to drop into another adjsuter, the upper hex is spring-loaded slightly. So in other words you don't just put an allen into that adjuster that you can see and turn to adjust, you push down with the tool, may have to twist around a bit, you'll feel it drop down a slight amount, THEN you are actually adjusting. Kind of a trick and a bear to explain. Just make tiny adjustments, like 1/4 turn. Blip the throttle a little and see if it changed. Sorry I don't remember what the duty cycle is on this car, I may have info somewhere. But a fixed position with the engine warmed up is a fault. FIRST thing to look at is the OVP relay fuse, as that puts you in a fixed mode like this. Make sure the O2 sensor is there and connected. Sometimes someone will save money on the exhaust and next thing you know the O2 sensor is in a landfill someplace instead of in your exhaust stream

I would investigate the fixed operating mode before doing much with that adjuster though, you can't really change anything until the engine is in closed loop.

Gilly
Gilly

Gilly · #3 03-24-2010, 07:00 PM

(The adjuster is quite a ways down but should be able to see it with a good light, you use a fairly long allen to get to it, an allen "T" handle works just fine. Not 100% on the size, but 3mm would seem to be close.)

sptt · #4 03-24-2010, 08:31 PM

You also need to make the adjustments with the air housing cover in place! The air temp sensor sends signals to the computer while you are adjusting. I had an issue with mine and was able to get a pretty close to perfect idle but not until I learned to adjsut with everything in place. You need to get a long 3mm hex wrench and quarter turns. Rich is clockwise!

Gilly · #5 03-24-2010, 08:45 PM

But not until it's out of fixed operating mode.......

mespe · #6 03-25-2010, 09:32 AM

Currently the car starts sometimes, and stalls within seconds. I get the 69.3 Key on engine off.

My concern is the crack at the base of the lambda tower. It also seems that the throttle flap sits a little too high, but that's from memory.

I'm not sure what the insides of the lambda tower look like, or if a crack in it will bind things up. I have another MAS Air flow, that I may end up swapping.

Here's a close up of the base of the lambda tower

Gilly · #7 03-25-2010, 04:20 PM

You are OK and correct to be concerned what that does and how it works. The main point I want to make again is that you should NOT be messing with it if you aren't getting closed loop. You have no way to know where it will end up when and if you ever get it in to closed loop, and if it isn't in closed loop, nothing in changing.

I'll try to explain it again;
If you look down in the hole where the anti-tamper ball or plug was, you will see a hex shape, that accepts an allen wrench. The other guy seems to confirm it is a 3mm. What that is is sort of like an extension down into the airflow meter and it is spring loaded in the "up" position. You insert your allen and press down on it, the lower end then goes down and engages into an adjuster screw. Sometimes you need to fiddle with it a bit to get that lower part to engage into the actual adjuster down below.
The only way to know is by trying to see if the crack is messing anything up. If it is you can buy a new adjuster tower.
First thing I'd check in regard to the fixed operating mode (ie not going in to closed loop) is the overvoltage protection relay (check fuse).
Gilly

sptt · #8 03-26-2010, 12:43 AM

Gilly is correct. Engine has to go into the closed loop operation first before you make any adjustments. The crack in the Lambda tower could have some effect on your idle but more unlikely. To check it out, run the car and spray some carb cleaner around the crack to see if it fluctuates or effects the performance. If not, you're probably OK. If it's not going into closed loop, replace O2 Sensor and check OVP relay fuse (I replaced my OVP relay thinking this was an issue but just wasted my money on it as the biggest changes came from O2 sensor and water temp sensor then lambda adjustment). I also replaced Coil, Voltage Regulator (won't effect idle) and rotor and cap. Recently I noticed my spark plug wires arcing to the engine case! This was causing a rise and drop in idle and lack of power. Replaced the suspect wire and problem gone.
To make the Lambda adjustment, put the 3MM hex into the hole and make sure it seats in there ok. Then push lightly until you feel the screw spring pushing back upwards and turn it until the two catch together. Then make your adjustments left or right. If you push down to hard your car should try to stall as this drops the throttle plate down and richens the mixture quickly. Again, it won't work right unless the air housing is on and the air temp sensor is working (which, it probably is).

400Eric · #9 03-26-2010, 03:34 AM

Sptt, if one spark plug wire was bad enough to be arcing, the others spark plug wires aren't far behind and should be replaced too!
Regards, Eric

mespe · #10 03-28-2010, 09:06 AM

Thanks for the help guys, I haven't played with the car for a few days. I didn't realize the tower is replaceable. Looks like it's welded in place. Will have to further inspect.

Thinking about the car, seems like it's only running on the CSV fuel.

I checked the OVP fuse (and swapped the relay) and same thing, start, run 2 s and stall, also when the air mass meter flap is pushed down lamda changes, which indicates to me that OVP is functioning and not a cause of the 69.3 lamda.

Maybe fuel pump relay?

Gilly · #11 03-28-2010, 02:31 PM

Closed loop and Lambda are essentially the same thing. Your meter might change, but you do NOT have Lambda until you see the meter oscillating (sp?).
Lambda is essentially the mixture changing in response to the O2 sensor; The sensor reads lean, the mixture drives rich, then the O2 sensor reads rich, so the mixture drives lean. THAT is Lambda and you ain't got it (yet).
It is a rather old fashioned system (although way advanced compared to a carburetor!).
Today what the mixture SHOULD be is guesstimated (OK, calculated) and the O2 sensor verifies that it is correct.

Gilly

Gilly · #12 03-28-2010, 02:33 PM

Oh, what holds the adjustment tower down are tamper-proof screws, you would back them out by getting them rotating (ccw like normal) with a small hammer and chisel. Once loose you can usually get them by finger or a small needle-nose pliers.
Gilly

mespe · #13 04-05-2010, 01:32 PM

Had some issues with getting the car started, then I saw about a pint of gasoline in the air intake. maybe leaking fuel distributor, or something else,,, anyway, I got the gas out of there and here is where I am,,,

http://www.benzbonz.biz/video/300estartstall.wmv

65K on the clock,,,

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