tacho difference

[metcap]

I'm on MSII V3 board with 2.34code, MS is running a single fire coil and I've another tacho hooked off the negative terminal of the coil. My problem is that this external tacho reads about 400rpms lower than whats on the Megatune screen. Anyone got any ideas what to check for to solve this? Thanx.

tkm

[metcap]

could anyone please give me some pointers where to start troubleshooting? is it a setup problem or hardware problem?

tkm

[grippo]

If the second tacho is a tachometer then I am not surprised at all that it is 400 rpm off. I have seen a difference of at least 200 rpm on my car and I have an expensive (not a good) tach. To me this is a disgrace. Any ECU counts pulses and has a very accurate timer so you can count on the rpm you see coming out of the ECU as long as the times are taken from the internal computer clock and there are no missed pulses which would show up as erratic rpms. If at steady idle your ECU reads a steady rpm I would trust it over a meter any day.

[metcap]

If the second tacho is a tachometer then I am not surprised at all that it is 400 rpm off.

yeah it's my car's stock tacho, analog needle thing thats at least 20 years old well so I guess there's nothing much to do but live with this.

If at steady idle your ECU reads a steady rpm I would trust it over a meter any day.

what accounts for a steady idle? my engine running individual throttles currently idle at about 850rpm plus minus about 30 rpm.

tkm [/quote]

[grippo]

That's normal for that kind of setup. You don't have a plenum to smooth out the pulsing. I have a plenum but a very large cam and it fluctuates like that.

[metcap]

it's good to know I dun have anything serious to worry about with my set up, thanx for your time. Take care.

tkm