Is your tower still intact? Are you pressing the spring down then turning the adjustment? Open the attachment and take a look at the design.

Attached Files

Idle adjustment.pdf (50.2 KB, 317 views)

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Thanks for the schematic! If by intact, you mean still in one piece then yes, but internally it *might* be a different story (I hope not!). From what I am experiencing, it's as if #61 isn't even there anymore or #'s 3 and/or 4 aren't engaging #61. When I was turning the screw to max LEAN there was no problem at all, even turning clockwise to rich was ok. As soon as I got to max RICH, it was like the screw just went awol, weird. Worst case scenario, how does one take the lambda tower off?

Question: When the round throttle plate is pushed down, does gas enter the a non-running engine? Well, the remaining gas in the fuel distributor since the pumps aren't on, I suppose...

So, the reason the lambda tower wasn't engaging the adjustment screw at the bottom was due to me screwing it in too far clockwise, or too rich. To fix this I removed the lambda tower and turned the adjustment screw with a plain 'ole 3mm allen wrench all the way to lean, or counterclockwise. The tower gasket broke in the process of the removal, so I had to make a new one. Also, the screws can not be used again because of their unique head, so 2 M5-.80x12mm hex head screws were used, worked like a charm!
I then began to en-richen the mixture with 1/2 turns from max lean at a time. I actually got it after about half an hour of tinkering. The engine turned over, over and over until it finally fired up. I then went to adjust the mixture since the engine was running very rough only to have it die on my again! After that, I couldn't get to that sweet spot again, even after another 30 minutes of tinkering. However, I did keep track of how many turns and what not, in order to have a reference point. Now, how do you adjust the lambda tower with the car running?!

Once you get the engine running, a 1/2 turn is a lot of adjustment.

Why did you start adjusting the air/fuel mixture to start with? What was your problem/issue before messing with the adjustment? I ask this because you might be compensating for another problem.

To properly adjust the air/fuel mixture, you need a Volt Ohm Meter that reads 'Duty Cycle', like Sears model #82139. Your engine needs to be in the 'Diagnostic Mode' to get the duty cycle readings.

Try doing a search on the forum for "Measuring Duty Cycle", this has been discussed many times.

http://www.peachparts.com/shopforum/search.php?searchid=3773073

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Well, the car has always ran rather rich since I purchased it in September and recently failed smog (obviously). So I tried leaning the mixture out. Oh, when the plugs were pulled they were badly carbon fouled, rich mixture indeed!

The car is now running, however, not as before. Also, I tired to take it for a run around the block, but its lacking all power. Idle seems fine, its just when I step on the accelerator in D or R that the car doesn't even acknowledge it. I have my pedal at WOT and nothing... The EHA was also tinkered with, could that have something to do with this problem?

One thing I have noticed since getting the car running (and right before making the adjustment that killed that car about 4 days ago), is that the vacuum gauge is more to the left in all positions (P,D,N) now more than ever before.

EDIT: I just caught this mistake. It should have read,"is that the vacuum gauge is more to the RIGHT in all positions..."

Are you sure the plugs were fouled from rich mixture or do you have a problem with your valve seals and guides?

If you have the latter problem, screwing around with the lambda adjustment will not help you. Been there done that.

You may want to use a scope to test as you tweak the air/fuel mixture.
Here is a sample view of a rich mixture:



And here is a sample view of a mixture properly adjusted:



You need to do this on a test port where you can measure Lambda. On my 190E it's on pin 3 and 2 of the test port near the driver side fender.

You can also use a voltmeter on the same pins on that test port to measure the duty cycle.
Here is a sample view of a rich mixture at idle (notice the rpm meter above) and the higher voltage than reference on the meter below:



If you can't get it with air fuel mixture tower (which seems to be your problem) you will have to adjust the EHA. First make sure it's working properly by measuring the fuel pressure differential between the upper and lower chambers, then measure the current to the EHA and it should be near ZERO Amps + or - 1 mA. If it's too positive then it's rich and you will need to adjust the EHA screw COUNTER CLOCKWISE and please , pretty please DO NOT MOVE more that a hair at a time or you can kiss that one goodbye too. Be very very gentle

It's been many years since I worked on a CIS car... as I recall when you adjust it you have to be careful not to apply any downward force on the adjustment as it will push against the airflow sensor and screw up the mixture strength. I never worked on anything that had this extra "tower," so I don't know if it behaves the same way.

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1987 W201 190D

Good point JonL. The mixture / duty-cycle measurement will only be accurate after the adjustment screw has been allowed to spring up away from the AFM arm and the mixture allowed to stabilize for a few moments.

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Gone to the dark side

- Jeff

Well, there we have it I'm assuming that this is also true for pins 3 & 2?

Absolutely! The CIS computer will generate a nice steady square wave if you just turn the ignition on without the engine on. That signal will stay steady as it is a reference signal. Once you turn the engine on, you will have to wait for operating temperature so that your reading is reflective of what the O2 sensor is detecting. At this time you will see the signal drift a little, the top of the signal gets wider when there is a rich mixture being called for and the bottom gets fatter when a leaner mixture is called for ( you can see these on the scope of course, otherwise use a voltmeter and watch the voltage increase for a richer mixture and decrease for a leaner one). The ratio between the upper side and lower side of the signal is your duty cycle. Basically how much of the whole cycle was dedicated to the upper side. If the signal is exactly the same at the top and bottom then you have a 50% duty cycle for example. With a voltmeter you should get half of what your battery is generating if you are at 50% duty cycle.
Does that help?

Doesn't the CFI Module have to be in the 'Diagnostic Mode' from '88 up to read duty cycle? On my '93, I use the homemade LED Tester to check for DTC codes and also to put it into diagnostic mode to check my duty cycle. Otherwise, all you'll read is battery voltage across pins 2 & 3.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Great explanation, really Helps to understand how things work in these cars!

Now,As SLK was saying, doesn't the car have to be in some sort of 'diagnostic mode?'

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'89 300E - 153k miles - California car - Black/Palomino

I see you are in California, doesn't your car have the built-in LED and button on the Diagnostic Block in front of the battery?

@1988 California and
@1991 with diagnostic trouble code
storage:
The CFI control module must be switched over
to output of on/off ratio because the signal for
the diagnostic trouble code (DTC) display is
output as priority.
The output of the on/off ratio is performed once
all the DTCs have been read out and the start
button of the impulse counter scan tool or the
non-locking switch on the diagnostic connector
(California version only) is then once again
pressed (see section m).
The % readout now fluctuates when the engine
is running at normal operating temperature and
there are no DTCs.

On/off ratio
in %
Possible causes of fault
- No voltage or ground at diagnostic connector (Xl 1)
- Cable from diagnostic connector (Xl 1) to CFI control module (N3) has open
circuit
- Lambda control tester defective
- Mixture setting too “rich”
(on/off ratio 0 - 8 % also possible)
- @ California model year 1988 and @ 1991: CFI control module not
switched over to on/off ratio output.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Never even tired looking for that LED and button by the battery. When I do find it, all that is reguired is to turn the key to the 'on' position and then press the button for 2-4 seconds and record the pulses, correct? After that I should be able to read the lambda @ pins 3&2 of the X11 connector if everything is all good?

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'89 300E - 153k miles - California car - Black/Palomino