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#1
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Tach works sometimes and sometimes not! 1995 300E Diesel
I have 1995 300E Diesel and the tach works sometimes and sometimes not
Back in Oct Or Nov of 2010 I posted that the tach did not work and with help from this forum I finally got it working. It worked until I started having alternator troubles and now it will work if you "fool" with the sensor cable and the wires going to the over-voltage protection relay. If you "kill" the engine and start it again the tach will not work. It will temporarly work going down the road if you "race" the engine-that is it will momentarly work and then go back down to zero when you let off the gas and run normally. I have checked most of the connections and fuse in the over-voltage protection relay. I also have a new sensor cable 'which I don't think I needed'. Any one out there experienced a similar problem? Thanks: L L L |
#2
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The flywheel sensor should generate 4-6Vac with engine at idle.
__________________
MERCEDES Benz Master Guild Technician (6 TIMES) ASE Master Technician Mercedes Benz Star Technician (2 times) 44 years foreign automotive repair 27 Years M.B. Shop foreman (dealer) MB technical information Specialist (15 years) 190E 2.3 16V ITS SCCA race car (sold) 1986 190E 2.3 16V 2.5 (sold) Retired Moderator |
#3
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Have you verified that the problem is not your OVP? Also like mbdoc says, verify the output of of flywheel sensor.
Go to page 7 of this FSM document for testing the flywheel sensor. http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/602_603/07.1-1120.pdf
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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 http://www.fuelly.com/sig-us/40601.png |
#4
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Thanks for the info mbdoc!
I checked the voltage thru the signal wire to where it is connected to the other wire behind the battery and I got only 3.3-3.4 vac. What would you recommend I do next? I am going to take the signal wire off from the flywheel housing and clean it. Also try to locate the flywheel sensor and clean it. Is the flywheel sensor replaceable and if so where do I find one if it has to be replaced? Or did I get a bad signal wire? Thanks: L L L |
#5
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The flywheel sensor only needs to be greater than 2.8VAC, so it is OK.
What troubles me is that you say you can fool around with the wires going to the OVP and the Tach will work. That may mean a bad connection or wire in that general area. Can you try to verify which wire makes the Tach work? Also the OVP has a fuse in it, some have two, you can make sure they are good and that the connections are clean too. Whoops, I see you already did that. I took my OVP apart once and it is a simple device. There is a relay inside that I suppose you could clean the contacts on. A few solid state devices which are not user serviceable iirc. I had a dead Tach problem that took quite awhile to diagnose and fix, the path I took to do so does not yet apply to this thread I think. Keep at it, you will find the problem soon I bet. If not, you can check the signal to the tach at the instrument cluster connection. I can help you with that later if you need it.
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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 http://www.fuelly.com/sig-us/40601.png |
#6
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Thank for the input OLDWOLF!
My next door neighbor is a mechanic and he said we will get the car in his shop and try to find the trouble. Glad to know it is not the device on the flywheel as I looked at it yesterday and don't know how to replace, and I can't even find one on the internet. We will find out what wire is causing the problem and let you know. And as you say it may be in the ovpr. Thanks: L L L |
#7
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BTY OLDWOLF!
I noticed you are averaging 32.5 mpg on fuel. Do you dirive much in town or mostly on the road? I drove to Texas and Ok. last week from Al. and got up to 36 mpg+ but in town and around here all I can get is about 25 mpg. The 36 mpg was strickly road miles on the interstate. However I am pleased with the mpg I get because the car I am driving is heavy and very comfortable. L L L |
#8
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I would estimate my driving is 80% hiway and 20% city. I have hit 36 mpg also when traveling.
__________________
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 |
#9
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I think the problem is in the OVPR as I took it off and removed the fuse and sprayed
contact cleaner in it. After replacing the OVPR the tach works! If it quits again I may invest in a new OVPR. I think I can get one for around $50.00 shipped to me. Thanks for the help: L L L |
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