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Fitting an after market rev counter.


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My Mercedes Sprinter 214 registered September 1999, VIN WDB9020622P938127 was never fitted with a rev counter.

Can anyone help me with the following questions:

1) where is the best place to pick up an input signal, on one of the twin coils, on the ecu or on the diagnostic socket?

2) will a tach adaptor be required on any of these options?

3) what division ratio will the rev counter need to be set to?

4) where can I source a circuit wiring diagram for this base vehicle to enable pin connections and wire identification?

Any information would be greatly appreciated as I have not had any experience of twin coil, wasted spark ignition.

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  • 4 weeks later...

As you mention wasted spark ignition, I presume you're talking about a petrol-engined vehicle. Which is good, as fitting a rev-counter to a diesel engine is far trickier.


You can do this in two ways:


1. Splice into the low-tension wiring leading to the coil packs. They normally have three wires going into them and you'll have to experiment which is the trigger wire.

2. Wrap a trigger wire around one of the HT leads.


Most aftermarket rev counters allow you to do one of the above methods (and they all usually come with full instructions).


I'd suggest you go for an electronic rev-counter as these often allow you to input different correction values to allow for different ignition systems.


You don't need a circuit wiring diagram of your vehicle and I'd avoid going anywhere near the ECU or diagnostic socket.


Hope this helps


Peter R

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Peter, thanks very much for your advice and sorry about the delay in responding but we have just returned from a holiday in the motorhome.

Unfortunately the 2 coil packs , plugs and wiring are all tucked away within an aluminium enclosure which is part of the camshaft housing and to get at them means removing the MAF and lots of other bits and bobs. Never the less in view of you advice I shall press ahead with picking up the trigger pulse as you suggest - after all no pain no gain I suppose. Best regards. James

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