Convert diesel rev counter to work with a petrol engine

[mike1978]

Hi,

I was wondering if its possible to convert the standard rev counter in a turbo diesel t25 to accept the signal from a petrol engine.

I`ve just fitted a subaru engine in my van and i`d like to get the stock rev counter to work with the subaru engine. I believe the diesel rev counters work from a signal gained from the alternator whereas the petrol engine rev counters work off the ignition coil.

Thanks,
Mike

[Grun]

mike1978,

Why not try running it off the alternator on the Subaru. It is unlikely that the crankshaft pulley to alternator pulley ratio will be the same, there may not be that much difference, but what about the red line for the diesel against the Subaru?
(I am just thinking aloud). Probably better to search for a petrol replacement.

Mike (1937 )

[mike1978]

hi mike,

i`m not sure how i would take the take the signal from the alternator - i can easily take a signal from the subaru wiring.

I was just hoping to keep the dash looking stock and use the orignal tacho if possible. It seems a shame to have a dash mounted one when i`ve got one sitting in the dash!

cheers,
mike

[steve8090]

The tacho feed is usually the blue / silver wire from the Subaru ECU and the diesel type rev counter (DIS type) is correct

[mike1978]

i know the blue wire you mean. So if i connect that wire to the signal input on the back of the rev counter it should work?

[Grun]

mike1978,

steve8090 knows his stuff and, (I am told) is a very nice man

I have no diesel or Subaru, just the old wasserboxer (no rev counter!!) it is just that I hate to see a query go unanswered if I can post a thought or two.

Welcome to the madhouse by the way, and if you need more help, have you tried the alternative engine forum? Lots of Subaru stuff there.

Mike

[mike1978]

thanks - i`ll give that a go tonight when i get home from work.

and .. hello! i`ve been posting mostly on www.vwkd.co.uk but i own an 1992 LLE multivan - i`ve just fitted an EJ20 subaru motor to replace the old smokey 1.6TD that was fitted. Just got it going now

[Grun]

mike1978,

My thoughts were..... if it ran off the alternator on the diesel, it should run off the alternator on the Subaru, but when it comes down to which wire........ I expect the loom has been changed more than just a wee bit but I have no experience to draw on.
Wasserboxer is green wire from terminal 1 on the coil.
Diesel (I would think) is blue wire from D+ on the alternator.
Someone will have the answer.

Mike

[mike1978]

well i tried connecting the blue wire from the ecu that controls the tacho - i tested the voltage it was giving at idle and it was giving 6.5V. obviously i can`t see the pulses as they`re very high voltage.

i tried connecting this to the tacho but no luck i`m afraid. If i can`t get this to work, i think i`ll be on the look out for a 2nd rev counter to mount on the dash.

[steve8090]

Thats a shame, the blue wire with the silver dots is the correct one, mind you last tacho I fitted was an off the shelf programmable one, you could configer it to run from a coil pulse or from the output of the ecu or alternator

[mike1978]

ah well - nevermind!

thanks for the advice anyway.

cheers,
mike

[billy739]

if you havent blown your rev couter up, i have a petrol one i can swap with you.
you will find the alternator dosent have a w terminal by choice.

use the -(neg) coil wire on the new engine and just join it to the w signal wire from your vw engine loom. once you have changed the tacho

[mike1978]

that sounds like a plan - i`m pretty sure the rev counter isn`t blown , but i can`t say for absolute certain as i`ve no way of testing it. i`ll email you some of my details.

cheers,
mike

[steve8090]

Billy won't work, the coil on ther Subaru is a generated spark, the only take off for the tacho is the blue/silver wire, Andy at TSR Drag Racing has some nice Tacho's in stock that they use on the Subaru motor

[mike1978]

but as part of my wiring, i had an extra circuit added to work with the petrol tacho which has worked fine on another van with a petrol rev counter, so it might work. it combines the signal from the 2 coils with some diodes and eliminates the blue wire completely.