rpm pulse and mf2 question

[gixxa]

wired up my mf2 today and took a crank rpm feed from the crank sensor but this causes the mf2 to read 9k at idle.

is the right place to pick the feed up.

[luthor1]

Does it say use the crank sensor feed?

I'd bet it would take its RPM signal from the tacho output?

Andy

[gixxa]

well it says to use he coil negative or "This cable can also be used to pick up
any RPM pulses generated by any ancillary device,
ie alternator, crank sensor etc. if coil
negative is not available."

[steviet]

are you not supposed to adjust it to suit the car?

[gixxa]

are you not supposed to adjust it to suit the car?
yeah you set it to how ever many cylinders the car has, so this is set 4

[boz]

you have the manual for it?

i never messed about with min, but i still have the manual. if you dont have yours and need any info out of it.

if not, give john at gmc a call, im sure he will be able to assist you ;)

[gixxa]

think ill try the reading from the rpm feed for the tacho on a multi meter and compare it with what it was from the crank sensor.

[steviet]

i mind when i had mines. never fitted it like but i did read the instructions. am sure it says there`s a screw setting you adjust. so when the car is reving at 3000rev`s you see the LED`s light up on the mf2. no1 led = 1000rev`s upto no8 LED = 8000rev`s. so you adjust the screw so it light`s up the 3rd LED so that would be 3000rev`s like the car.

[gd16]

Mine was taken off of the tacho feed. Wire 426 according to the Haynes.

Wire goes from the ECU, splits off behind the dash and one goes to the diagnostic connector and another to the clocks.


If you've set the cylinder selection up correctly - then changes are you'll need to change the feed from the crank signal to the tacho signal.



Also - don't worry if the lights on the MF2 don't light up exactly at 1k,2k,3k etc revs - as long as they light up every 1k rpm - so 1250rpm,2250rpm,3250rpm for example.

[gd16]

Stevie - the wee screw you adjust adjusts the fuelling for the point at which the light is on. Only thing that changes when the lights come on is the rpm feed and the cylinder selection (unless of course its fucked - but i'd guess nothing would work if thats the case)

[gixxa]

does any one know what sort of signal the tacho feed should read

[luthor1]

The crank sensor will be a "sort of" sine wave with a negative zero crossing point. The negative zero crossing point is the only valid area of the signal since it stays the correct distance away from TDC relative to engine revs.

The peaks, troughs and positive zero crossing point all move closer to TDC with revs and hence cannot be used as a rev signal.

Now, the CRANK signal can vary from 0.7 volts at tickover to 70 volts at 6,500rpm so I doubt there will be an appropriate circuit to read that in your device.

The negative coil signal is digital and doesn't change in amplitude with revs, as with a tacho output signal, so use this :)

Kind regards
Andy H

[gixxa]

just had a quick look and manged to pick up the feed from the diog port, tried this the other day but the pin it was meant to be wasnt there, must have set the autodata to wrong year or something