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Old 09-09-2010, 12:39 PM
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124.128/602.962/722.418
 
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Location: Raleigh, NC
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W124 OM602 Ring Gear Speed Sensor

I have a W124 OM602.962 and will be running through the “07.1-2006 Testing electronic idle speed control” as a starting step to track down my inoperative tachometer.

On page 5 is says to check for >2.8VAC signal at idle from the ring gear speed sensor but in other sections of the same document it says the minimum signal should be >4VAC.

Which is it? Thanks.
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1993 W124 300D 2.5L Turbo, OM602.962
2000 Chevrolet Cavalier, 2.4L DOHC
2002 Ford Explorer, 4.0L SOHC
2005 Toyota Prius, 1.5L

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Old 09-09-2010, 01:19 PM
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OW- having just diagnosed my OVP problem, it is fresh in my mind (thanks for the support, by the way).

Are there any other functions (A/C inoperable, or ABS light on) that might suggest an OVP problem with your car?

Regarding the tach pickup voltage, I don't have a specific answer, but I suspect that if the pickup is bad you will see Zero volts. My gut says that if you see any voltage at all, it's probably good.

SteveM
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'93 190E/D 2.5 Turbodiesel 5-speed (daily driver)
'87 190D 2.5 Turbo rustbucket - parts car
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Old 09-09-2010, 01:28 PM
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All electrical functions work correctly and I just had the Tachomer rebuilt, new capacitors and all.

I do have a 1600 Hz signal at the tachometer connection, which is correct at idle. But what I do not know is if the signal is "weak", or if it is even possible for it to be "weak".

So, I plan to test the source(s) of the signal the best I can.
__________________
1993 W124 300D 2.5L Turbo, OM602.962
2000 Chevrolet Cavalier, 2.4L DOHC
2002 Ford Explorer, 4.0L SOHC
2005 Toyota Prius, 1.5L

http://www.fuelly.com/sig-us/40601.png
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Old 09-10-2010, 01:41 PM
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124.128/602.962/722.418
 
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Anyone?
__________________
1993 W124 300D 2.5L Turbo, OM602.962
2000 Chevrolet Cavalier, 2.4L DOHC
2002 Ford Explorer, 4.0L SOHC
2005 Toyota Prius, 1.5L

http://www.fuelly.com/sig-us/40601.png
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Old 09-10-2010, 02:07 PM
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Have you had a chance to measure the voltage yet?

Steve.
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'93 190E/D 2.5 Turbodiesel 5-speed (daily driver)
'87 190D 2.5 Turbo rustbucket - parts car
'84 Dodge Rampage diesel - Land Speed Record Holder
'13 Ram 2500 Diesel
'05 Toyota 4Runner
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Old 09-17-2010, 02:03 PM
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I ran the tests and the VAC output and Resistance readings where within the acceptable limits set by MB. Although I'd like to get a answer to the 2.8VAC and 4.0 VAC limit discrepancy I stated in my original post. You can open the attachment to see what I am talking about.

Speed sensor measurements (per document 07.1-2006)
3.52 VAC at Idle
560 Ohm

When I removed the speed sensor form the EDS input, the idle speed dropped noticeably. When I reattached it the idle speed went up to normal. So it sounds like that part of the circuit working OK.

Does anyone have a W139 OM692.96 that can take a VAC measurement of the tachometer input to the instrument cluster?

Thanks.
Attached Files
File Type: pdf Testing electronic idle speed control 07.1-2006.pdf (654.0 KB, 126 views)
__________________
1993 W124 300D 2.5L Turbo, OM602.962
2000 Chevrolet Cavalier, 2.4L DOHC
2002 Ford Explorer, 4.0L SOHC
2005 Toyota Prius, 1.5L

http://www.fuelly.com/sig-us/40601.png

Last edited by Oldwolf; 09-17-2010 at 06:22 PM. Reason: Corrected VAC reading
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