Last years of KE CIS - was it so different? (STUCK with error code problem) - PeachParts Mercedes-Benz Forum

Stretch · #1 02-13-2016, 09:46 AM

G'day Folks,

I'm back pulling out my hair trying to get my M102 to behave properly.

The problem is this:-

The air flow potentiometer has been changed. I have been helped out by someone who sent me a bit of information out of CIS saying that with the engine off - ignition on you should have between 0.2 and 0.5 volts.

Simple enough eh?

Other information on the interweb says you need to have 0.7 volts (all DC readings!) when the engine is at idle (about 750 rpm) =>

SG-Motorsports Air Flow Meter Potentiometer Replacement

OK - also simple enough - well it is a pain in the arse but it can be done.

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Trouble in paradise (1)

If I adjust the potentiometer with the engine idling (as most people seem to do) then all is OK until the engine temperature gets about 60 degrees C when the switch over valve for the timing kicks in and things get even worse when the engine temperature gets to "normal operating" of 80 degrees C =>

I get a 80% duty cycle error code on my multimeter (which in Mercedes speak means 20% error code - typical eh?) which corresponds to a WOT sensor problem (==20% error code). Now I've had that sensor in bits and checked it over so many times (with and with out dodgy leads) - I am sure there's nothing wrong with it.

So I don't believe this error code in terms of a problem with the sensor or the wiring.

On a warm engine >80 degrees C - Idle is high => 1200 rpm as though the air idle control valve is disconnected - but I this is due to the error code

Adjusting mixture screw has little effect (until you turn so far that you starve or flood engine)

*******

Trouble in paradise (2)

If I ignore the "on the fly" setting it at idle advice in the link above and follow the CIS instructions I get a different kettle of fish.

Ignition on - engine not running - set air idle potentiometer to 0.2 volts (or the other end of the range at 0.5 volts) and I get about 2 volts showing with the engine running at idle.

Engine runs at a good idle for all temperature ranges. 750 rpm - a bit jumpy

The duty cycle is at about 50%

BUT

It is like the computer is stuck in warm up phase so it thinks the engine is colder than 60 degrees. The duty cycle always seems to be at 50% during warm up.

Adjusting mixture screw has little effect (until you turn so far that you starve or flood engine)

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So questions

1) Should I believe the error code with the air idle potentiometer set at 0.7 V with the engine at a cold idle?

2) Should I believe the CIS instructions and carry on looking for reasons for why the ECU seems to be stuck in warm up phase?

3) Was the last generation KE CIS system so different from the slightly earlier KE systems?

If anyone can help - that would be great - I'm running out of hair to pull out on the top of my head - I don't want to start yanking out stuff "downstairs" too!

Stretch · #2 02-13-2016, 12:29 PM

Update:-

Additional reading in the CIS information I have states that at idle the air flow potentiometer output should be between 0.55 and 0.95 volts dc.

So an additional question comes to mind =>

What would make the potentiometer output change from 0.2 volts dc - engine off - ignition on - to 2 volts + with engine at idle at 750 rpm...

...the answer of course is the position of the potentiometer measuring the air flow plate motion but that much for such a small movement is mad.

I think I might have to piss about with the "do not touch this adjustment screw" screw on the potentiometer...

duxthe1 · #3 02-13-2016, 06:43 PM

When you adjust for .7V it needs to be at operating temperature 750 RPM idle without any accessories on.

If you had the WOT / idle switch apart I'd make sure you don't have the leads reversed. Disconnect the 3 pin connector and jump one lead to the center lead. Give it a bit, disconnect it, and connect the other lead to the center lead. One of the two conditions will be correct for idle. If you get a stable idle in one state then make sure the switch correlates.

Ivanerrol · #4 02-13-2016, 07:08 PM

Unfortunately there are many ersatz air flow potentiometers out there on the net that can be bought for as little as $15.00.
I have had one of these and never been able to get it adjusted properly.
Better check that the one you have on is a decent Bosch or knockoff - this could be your problem.

Stretch · #5 02-14-2016, 06:14 AM

Quote:

Originally Posted by duxthe1

When you adjust for .7V it needs to be at operating temperature 750 RPM idle without any accessories on.

If you had the WOT / idle switch apart I'd make sure you don't have the leads reversed. Disconnect the 3 pin connector and jump one lead to the center lead. Give it a bit, disconnect it, and connect the other lead to the center lead. One of the two conditions will be correct for idle. If you get a stable idle in one state then make sure the switch correlates.

Getting the engine to operating temperature has been a struggle! But I think the setting is more or less correct. My CIS information gives a limit between 0.55 and .95 so I'm certainly in that range.

As for that pesky WOT switch - I have measured it a hundred times but I'll measure it again just to be sure.

Quote:

Originally Posted by Ivanerrol

Unfortunately there are many ersatz air flow potentiometers out there on the net that can be bought for as little as $15.00.
I have had one of these and never been able to get it adjusted properly.
Better check that the one you have on is a decent Bosch or knockoff - this could be your problem.

I most certainly have a knock off. The Bosch was silly money. I ended up getting one that was "meant to come from the same factory". I actually think it is OK at the moment...

...having slept on the problem (again) I'm going to check the voltage sent to the sensor from the ECU.

Because:

Ignition ON engine not running you can set the potentiometer in the range between 0.2 and 0.5 volts quite easily. Start the engine - plate deflects slightly (not by a massive amount) value at potentiometer jumps up to about 2 volts. Way too much.

This sudden jump could be because the potentiometer is a POS

But this could also be because the ECU gives too much juice to pins #1 and #3 when the engine is running / in the final warmed up phase. So I need to check this.

Stretch · #6 02-18-2016, 06:09 AM

Today I spent 30 minutes of my life with a multimeter. Ug...

...anyway I made measurements from the throttle valve connector back to each and every pin on the ECU plug.

(I did this because I've still got random stalling and a fixed 20% error code via duty cycle measurements once the engine / coolant is warm)

Grasping at straws but found some potentially weird ****.

The green coloured results are the correct specifications according to the FSM / WIS information I have.

Blank spaces are a measured "infinite ohms" reading

Dashes are not applicable

Here's what I think I have found.

1) Pin #1 (idle sensor wire) is connected some how (slightly) to ground
2) Pin #3 (WOT sensor wire) seems to only be connected to itself

Now I would expect the WOT wire not being connected to anything else would be a good thing but the ECU is telling me there's a problem here. What the ****?

I can also measure high resistance connections between the throttle position ground and the road speed sensor, the OVP, and the fuel pump relay.

Strange.

Anyway if anyone knows if 2.3 KILO ohms or 12 KILO ohms is worth getting up set about (when I'd expect things to be not at all connected to each other) please let me know.

Those in the know please enlighten me

Stretch · #7 02-18-2016, 06:09 AM

Suggests there's nothing wrong with the WOT switch to me

pmckechnie · #8 02-18-2016, 09:13 AM

Stretch, looking at post 7 I would think that the WOT switch is connected wrong.
Just to help me get it straight in my mind would you please do the following checks?
With the battery disconnected and the ignition off and everything else connected:

Check resistance between pin 2 and pin 1 with the accelerator at idle position.
Check resistance between pin 2 and pin 3 with the accelerator at idle position.

Check resistance between pin 2 and pin 1 with the accelerator at WOT position.
Check resistance between pin 2 and pin 3 with the accelerator at WOT position.

Check resistance between pin 2 and pin 1 with the accelerator at 1/2 position.
Check resistance between pin 2 and pin 3 with the accelerator at 1/2 position.

It will take longer to read this than it will to do it.

PaulM

Stretch · #9 02-18-2016, 11:09 AM

Quote:

Originally Posted by pmckechnie

Stretch, looking at post 7 I would think that the WOT switch is connected wrong.
Just to help me get it straight in my mind would you please do the following checks?
With the battery disconnected and the ignition off and everything else connected:

Check resistance between pin 2 and pin 1 with the accelerator at idle position.
Check resistance between pin 2 and pin 3 with the accelerator at idle position.

Check resistance between pin 2 and pin 1 with the accelerator at WOT position.
Check resistance between pin 2 and pin 3 with the accelerator at WOT position.

Check resistance between pin 2 and pin 1 with the accelerator at 1/2 position.
Check resistance between pin 2 and pin 3 with the accelerator at 1/2 position.

It will take longer to read this than it will to do it.

PaulM

Thanks for your input Paul.

I've done something similar that shows that everything is working as it should

Stretch · #10 02-18-2016, 11:12 AM

Mini update: I was trying to find a different cartoon but this one will do

See this post Achtung - Das schweinhund baby benz thread

I don't know why but after a bit of bad language I managed to get the mixture adjusted to 50% - or so it seems. I don't think I've fixed it - "it" just decided to play ball for a little while and I took advantage of the situation.

Stretch · #11 02-18-2016, 11:27 AM

I also measured this =>

Pin #7 must be linked to the other grounds inside the ECU. I'll check that tomorrow (ish).

Why the measurements change on pins #16 and #20 when I switch on the ignition is beyond me.

201.028 · #12 02-21-2016, 08:26 AM

Quote:

What would make the potentiometer output change from 0.2 volts dc - engine off - ignition on - to 2 volts + with engine at idle at 750 rpm...

...the answer of course is the position of the potentiometer measuring the air flow plate motion but that much for such a small movement is mad.

The system pressure, which is constant, balances the "air-flow force" on the sensor plate via pressure on the plunger in the distributor - with the engine ON (at idle). The 0.7 V output should correspond to a small deviation from 0 degree deflection of the plate (approx. 5 bar system pressure on the plunger and "idle air force"). 2 V corresponds to about 3 or so degrees of deflection of the plate.

201.028 · #13 02-21-2016, 09:38 AM

This might illustrate it in a more comprehensive manner (se picture).
So, one of 3 things (or a combination of the 3) is possible in my mind:
1. Wrong sensor plate zero position or incorrect clearance between sensor lever and the control plunger (the basic position = the 1-2 mm of free travel from zero position until resistance [with ignition/pump ON]) .
2. Wrong potentiometer zero position/misalignment.
3. Bad potentiometer.

Stretch · #14 02-23-2016, 03:28 AM

I think the data in WIS I have for the "switch on ignition engine not running and adjust to between 0.2 and 0.5 V" is a factor of ten out of whack!

I'll check it later on (in my life) and see if my feeling about this is correct.