Tachometer shorting out at 6000rpm

[Richard Gibson]

I have just installed an MSD ignition system which provides a Tachometer send. Which I hooked up to. I replaced the Lucas System. My car is an 85 Caterham Super Sprint.

 

This is what happens. When I accelerate and reach somewhere in the vicinity of 6000RPM the tach needle drops back down to ZERO. When I lift off, the tach springs back into action.

 

Any ideas? Another source on where to hook the Tach send?

 

I must mention that I have a SureShift2 Sequential Shift light system which works fine. www.sureshift.com I have completely disconnected unit and it makes no difference to my problem.

 

My problem started with the MSD 6AL ignition system.

 

Any help would be very welcome!

 

Richard Gibson

Washington DC USA

[AMMO]

Richard

 

What a coincidence. I've recently fitted a MBE ignition system to my Zetec engined Supersprint and it does exactly the same thing. My tacho is a VDO one which reads to 7,000. I tried earthing the casing of the tacho last night. That didn't work.

 

Will try making a new earth strap to the tacho's negative terminal today to see if that helps.

 

The tach worked perfectly with the previous X-flow engine and Pirahna/Newtronics optical ignition.

 

Any ideas anyone?

 

AMMO

[philwaters]

I think Steve Foster had this when he fitter Weber Alpha to his VX car... I can't remember how he fixed it - or if he had to get the map sorted out to suit the gauge. I have sent him the link to this thread.

 

Phil Waters

2000 Zetec is in, waiting to start it up wink.gif

[The Stig]

Indeed the Weber Alpha unit for VXC's had the very same problem

at 6000 rpm. Don't these guys do any testing?!

In fairness it did work in on the simulator they had but not on the live test plant. I had fun burning up and down near Webcon testing anyhow!

 

It was a bug in the firmware and required the Italian SW designers to fix it. This they did pretty quickly and it is now fine....

 

Handy having Webcon only up the road....

[Geoff Johnson]

VX & Weber Alpha & guess what, mine does the same thing. Keep your foot down until the tacho drops off, leave it a bit & then change gear? I do agree though, does piss me off. If anybody comes up with a cure then I am keen to hear.

 

 

 

Geoff

[AMMO]

Tried the car with earth from tacho wired directly to the same point as the ECU earth. Problem still there.

 

After further investigation it seems that the signal from the ECU is a different wave form and voltage to what the tacho is expecting to see. The ECU has a low voltage square wave form and the tacho is expecting a high voltage spiky type (I think?). Apparently there are resistors in the tacho to reduce the voltage.

 

The solution with the MBE is to swop the tacho for a later type Elliot or Stack that is designed to work with the ECU. However I quite like my VDO and will investigate the possibility of having the tacho altered to suit the ECU.

 

I'll report any findings.

 

AMMO

[EFA]

I had this when I converted to MBE injection in 1995. Elliot tacho was required anyway as the VDO unit was only good for 7200rpm. Not much use in what was then an 8500rpm engine.

 

 

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

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[AMMO]

Spoke to a guy last night who has done tacho repairs and mods for me in the past. He reckons that he cannot guarantee the tacho conversion would work.

 

So it looks like a new Elliot or Stack is the solution to the problem.

 

AMMO