Hi guys- just a few questions - M103 engine -

Should an air flow sensor test be performed on a cold or warm engine?

For starters, I performed this test on a cold engine, and I got the following results: when I measure resistance between pins 1 and 2, I show a reading of 1.02 ohm. Do I have a bad potentiometer? Or is this reading due to testing on a cold engine?

I've been told that the reading should be closer to 3.6 to 4.4. But again, I don't know if this is on a warm or cold engine or if it makes no difference at all. Thanks!

Temp shouldn't matter for the resistance of the potentiometer, however I feel that your test values are wrong.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

Did you disconnect the cable that goes away to the ECU?

Yes, I disconnected the cable.

On a side note- if I manually press down on the air flow sensor plate, the value on my multimeter rises (drops when I release), so at least I know that part of the potentiometer is working. But as far as the reading of 1.02, does that indicate a bad potentiometer?

Try this test procedure


Potentiometer adjustment;

3200 to 4800 ohms of resistance between terminals 2 and 3 when the airflow sensor is at rest.

560 to 1060 ohms of resistance from terminals 1 and 2.

The reading should increase to 3760 to 5640 ohms when the plate is at its lowest point.Adjust until this is achieved.

Goodness, now I'm really confused. What's the difference between our tests? I pulled mine right from the manual. On pins 1 and 2, I should get a reading of 3.4k - 4.4K Ohm.

Just to reiterate, when I performed the test I got 1.02K Ohm. So the test pretty much failed.

What's the range?

Readings between pins with flapper up and reading with flapper pushed all the way down.

I'm not sure what the range is. I'll test it when time allows. Do you know what the range needs to be?

I guess it's possible to calibrate these potentiometers. I'm basing that on Ivanerrol's comment about making adjustments. Work has stalled until I can get the special required to loosen the bolts on the pot.

I've just received a brand new Potentiometer.
I'll put in on later on today and give you some readings.

Hmmmmm....readings seem to contradict instructions I was given and posted

Heres some readings
1-2

2-3


1-3

here's an old pot next to a new one - notice the wear marks and "flat" spots on the older one

Ivanerrol, don't want to complicate the discussion, but I'm not seeing the tests for the results you're showing in the FSM. Test step 9.0 @ page 07.3.1122-121/115 indicates neg (-) probe on pin 1 pos (+) probe on pin 3 should read in the range 3.6kOhms - 4.4 kOhms (KOEO). I don't find any tests for (-) on pin 3 (+) on pin 1 or (-) on pin 3 (+) on pin 2. What do those tests indicate?

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

Tests between pins 1 and 3 on the example above reads 4350 ohms
within spec of what you have posted i.e. 3.6 - 4.4Kohms.
This is a static resistance test with an ohm meter on the unit with no voltage applied - so polarity is irrespective
(last image in the post above)

Oh yes, I see. Electricity is not my strong suit--business administration guy. Thanks for the explanation.

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

Higher planes, I think some of the confusion is in how the numbers are given. For instance 4.20K is the same as 4200. K means multiply by 1000. Does that help?
Paul

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84 500 SEL (307,xxx miles)