How do rev counters work?

[NickW]

Nigel,

 

 

Errrrr, sorry about the highjack!!

 

Have you looked at the link for the CA tacho that Chris sent, if you have one of these then there are 2 setting for different types of feed from an ECU source. Might be worth experimenting with the switch settings.

 

 

Nick.

[NickW]

Chris,

 

From what I can see then 1&4 are connected to the same coil and 2&3 are connected to another coil, so when coil A fires you get a spark on plugs 1&4 and then coil B fires you get a spark on 2&3, so for any one spark there is only one coil firing.

 

I can understand a double quantity of kickback pulses in a system with individual coil packs for each plug, but from what I can see of the diagrams of the coil pack there are only 2 coils.

 

Am I getting things very wrong here 🤔

 

 

 

Nick.

[Chris W]

Nick

 

The shiftlight system I designed for the 7 has to take into account wasted spark being twice as many pulses. You can see it clearly on a scope.

 

The reason is that each coil pack has to fire twice per revolution; once for example on plugs 1&4 when 1 is on the power stroke (and 4 is on the exhaust stroke) and once for the opposite situation ie: 4 on power stroke and 1 on exhaust stroke.

 

So any tapping from a coil with wasted spark will produce twice as many pulses as normal.

 

Chris

 

2003 1.8K SV 140hp see it here

 

 

Edited by - Chris W on 22 Jul 2004 23:28:11

[NickW]

Chris,

 

I've admitted defeat for the time being. The Ford EDIS module has a tacho out signal which appears to drive the tacho OK, so I'm using this at the moment. The main reason for contining to try and get a usable signal out of the coil pack and not trying the EDIS before was so that I can connect my Omex rev limiter as well.

 

Tried connecting the Omex lead that normally goes to -ve on the coil to the tacho output from the EDIS along with the tacho and this causes the tacho to die at about 2000rpm, so it looks like the signal from the EDIS is not strong enough to drive the tacho and the Omex.

 

I'm assuming that the -ve connection to the Omex is just to sense the rpm and then the Omex grounds the 12v feed to the coil to limit the rev's???

 

If so then maybe if the Megajolt tacho output might drive the Omex and the EDIS can continue to drive the tacho??

 

Have to wait till I get my Megajolt from Bill!!!

 

 

Thanks for all you help, very much appreciated.

 

 

Nick.

 

 

BTW, I checked the pulse frequency between the old system and the new and they are the same, so I'm definetly not getting double the pulses needed.