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Tachometer 190d 2.5; Unusual fault?
Topic Started: Sun Jan 7, 2018 7:16 pm (201 Views)
LonghamRob
Newbie
[ * ]
Hi,
I have a 1989(G) 190d 2.5 manual, 135k, no air con, with a problem i cannot seem to fix.
When i bought the car 6 months ago the rev counter did not work.
Not long afterwards i changed the relay 005 545 ???? with a s/h unit (Cant remember the last 4 digits and i am away at the moment) which is located on the bulkhead shelf to the left of the battery.
The rev counter worked and i thought that was that.
The trouble is that after a few miles it stops working for a while then works fine again and it keeps repeating this cycle over & over.
I acquired another 2 relays but it does exactly the same.
I have checked with my local Mercedes dealer and the number on the relay is definitely the correct part. A new one is £120+ but i am reluctant to buy as i cannot believe i have 3 faulty ones.
There is a weird thing that might give a clue to what is wrong...
With the relay in place, if you blip the engine in neutral it misfires on 1 cylinder although you would not notice this when driving. With the relay removed (and no rev counter working) it does not misfire.
Can anyone explain this?
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Oil burner
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Volvo owner
[ *  *  * ]
Your engine misfire is nothing to do with any electrical issues because itís mechanical fuel pump.there is a gauze filter inside the fuel tank which can block up with filth. It can be removed easily from under the car.if that is clean it will be a worn delivery valve in the fuel pump or a worn injector.the relay you have replaced only causes issues with abs brakes if fitted and some electrical issues e.g wiper and radio on diesel models, but petrol models are completely different.
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LonghamRob
Newbie
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Thank you for that quick response. Perhaps I should not have mentioned the misfire as I dont want the topic to come to a dead end without solving the tachometer issue. Have any diesel owners out there suffered from similar tacho problems? My 190d 2.5 does not have ABS brakes so i assume the relay I have only additionally serves the anti jerk syetem.
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optimusprime
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Part of things
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Faulty rev counter will make problems within the ecu ..Remove the rev counter wire and see if the miss goes away..
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Oil burner
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Volvo owner
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LonghamRob
Mon Jan 8, 2018 10:30 am
Thank you for that quick response. Perhaps I should not have mentioned the misfire as I dont want the topic to come to a dead end without solving the tachometer issue. Have any diesel owners out there suffered from similar tacho problems? My 190d 2.5 does not have ABS brakes so i assume the relay I have only additionally serves the anti jerk syetem.
Above the starter motor is the feed for the Rev counter, you will have to remove the complete airbox to access it. Remove it and clean the contact as they usually attract metal fillings off the flywheel. Unless your car is a import it wonít have the anti jerk system.
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Bradders
More than part of things
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Start with the basics. Almost every electrical problem with my 190D has been solved by either wiggling or replacing a fuse.
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Oil burner
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Volvo owner
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Bradders
Mon Jan 8, 2018 8:36 pm
Start with the basics. Almost every electrical problem with my 190D has been solved by either wiggling or replacing a fuse.
Replacing all the fuses is a good option and cleaning the connections as the 190 is getting old now and do benefit from clean fresh fuses.
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LonghamRob
Newbie
[ * ]
Thanks for the many responses. I ought to add that with diesel variants the tachometer is fed by a pulse from the crankshaft position sensor. I replaced this as the part was only £25 direct from Mercedes.
It was an easy job other than squeezing under the car to loosen the single bolt.
You can follow the wiring from this right up to the relay mounting so the fault is certainly between there onward and the back of the tacho which is probably only 2 foot away but impossible to check without dismantling half of the dash,wiper motor, heater motor and so on.
I note 'Badders' has a 2.5d who i hope may have access to a multimeter. Just an idea but is it possible for you pull out the relay, switch the ignition on and take the voltage or resistance readings at the relevant pins. This may take 5-10 mins of your time but would likely show up any differences between mine. There is no hurry to do this as i am currently in Tenerife where incidentally i fell back in love with the 190 as there are absolutely hundreds & hundreds of them here. The taxi drivers also prefer the older Mercs here too.
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