The V8 Owners Forum -

Anyone running a MegaJolt on a flapper RV8? If so, how did you derive the tach signal from the MJ to the Lucas ECU?

Isn't it just a bunch of zener diodes? Will see if I can find a diagram

Isn't it just a bunch of zener diodes? Will see if I can find a diagram

That's the usual way (diodes) to derive the tachometer signal off the EDIS coils, but I was wondering about the signal to the injection ECU. The MegaJolt has a tach output which should be ideal for this. But I can't find any info about it. The same signal might be fine for both, of course. But the one from the MJ is likely to be 'cleaner'.

I sell a Tacho Adaptor, this generates a spike that the EFI system needs, its designed to fit to the MS ECU tacho out to run Rev counters which were originally fed from the coil -ve.

This should work fine
Phil

I know about the adaptor for driving the rev counter off EDIS coils. Needed for a rev counter originally fed from the coil. However, it doesn't always work perfectly with all rev counters. As you'll know by the variety of alternate circuits on the MS site.

The flapper ECU has an inline resistor when connected to the original coil. Without that, I wondered if driving it from the MJ tach output was a better way - as that is a pure square wave.

It's not my car, and MJ doesn't seem to provide much info about this, so I'm just basically curious.

daxtojeiro wrote:I sell a Tacho Adaptor, this generates a spike that the EFI system needs, its designed to fit to the MS ECU tacho out to run Rev counters which were originally fed from the coil -ve.

This should work fine
Phil

Sorry to hijack you thread but have you a link to this adapter

Mick

texpis wrote:

daxtojeiro wrote:I sell a Tacho Adaptor, this generates a spike that the EFI system needs, its designed to fit to the MS ECU tacho out to run Rev counters which were originally fed from the coil -ve.

This should work fine
Phil

Sorry to hijack you thread but have you a link to this adapter

Mick

If you can make simple electronics, it's likely similar to the circuit here on the right. The relay coil is just a normal car 30 amp type - not critical.

I think you need a flyback or snubber diode across the relay coil on the right hand side circuit otherwise your transistor will fail.
http://en.wikipedia.org/wiki/Flyback_diode

Chris.

Hi,
Im afraid the diode version doesnt work well on most rev counters or on the Lucas ECUs. The other one would laast about an hour befroe the 2N2222 transistor would fail,
thanks
Phil

texpis wrote:

daxtojeiro wrote:I sell a Tacho Adaptor, this generates a spike that the EFI system needs, its designed to fit to the MS ECU tacho out to run Rev counters which were originally fed from the coil -ve.

This should work fine
Phil

Sorry to hijack you thread but have you a link to this adapter

Mick

http://www.ms2tuning.com/products.html

If you email Shaun directly he will give you a discount if your a member on here
Phil

ChrisJC wrote:I think you need a flyback or snubber diode across the relay coil on the right hand side circuit otherwise your transistor will fail.
http://en.wikipedia.org/wiki/Flyback_diode

Chris.

That's precisely what's not needed, as it's the flyback pulse you're after.

The transistor should be a higher voltage type like a 2N5551, though. But if you have a 2N2222 lying around, it will work for long enough to prove if the circuit is what you need. I used that exact one on my SD1 as a trial. But the rev counter cut out at approx 5000 rpm. I ended up changing the electronics inside the unit for something more modern.

Hi
I ordered 50X2n5551s off ebay wednesday night, 100X1k resistors and 5X 100 uH chokes to make up this adaptor, then I bought a ready done adaptor off Phil yesterday to save me a lot of grief. . . If any one wants resistors or 2n5551s let me know and you can 2 of the trannys and 4 resistors for 60p the chokes will be £3 each, I only have 5, (I have no real idea if they are the right size, I guessed! but I think they should work) all including postage. If you buy the choke I will throw in 2 trannys and 4 resistors for free (they should all be here in about a week)
personally I think the best plan is to buy a ready made one off Phil!
Best regards
Mike

This is the circuit from the MS Extra site:-

100uH should be fine - the SPDT ones on my SD1 measure 106 uH. Which is what I used, as I have lots of spares.

You're absolutely right that it will be easier to simply buy a ready made one.
Unless you already have the bits lying around and like playing.