Electrical/ignition fault?

[Aussie John]

After a 6 hour drive back from Scotland the car died for maybe 1/2 second a few times, I noticed the tacho dropped then the car picked up and ran fine. A faulty coil or ignition amp maybe? Any way of testing these?
Maybe heating the coil and seeing if the resistance changes? Any help gratefully received, cheers, John.

[TVR Stef]

I had a similar issue where it was like the ignition has been briefly turned off. But when running, ran fine. For me it was the ECU relays, changed them and the problem disappeared.

[Sir Paolo]

Any chance that damp has gotten somewhere it shouldn’t?

We’ve had/having quite a bit of rain lately and standing water is everywhere!

[Aussie John]

I have a spare relay for the ecu, maybe try that, I don't think it's a water problem as it was dry for the last 5 hours back, thanks for the suggestions guys.

[Belle427]

I’m sure it’s been discussed before that if the misfire is accompanied by the tacho dropping then it’s a coil or module problem.
Worth checking the wiring at the coil and module first.

[2 sMoKiN bArReLs]

Or the big fuse is loose?

(that's what happened to me)

[jr6yam]

Aussie John said:

After a 6 hour drive back from Scotland the car died for maybe 1/2 second a few times, I noticed the tacho dropped then the car picked up and ran fine. A faulty coil or ignition amp maybe? Any way of testing these?
Maybe heating the coil and seeing if the resistance changes? Any help gratefully received, cheers, John.

Coil and amp defo worth checking
I had the same problem when I first had my Chim; turned out to be the distributor...

[Steve_D]

The sudden drop of the tacho along with the engine dying will be ignition related. The ECU or pump relays will have nothing to do with it.
However, the ignition supply does come from the loopback connector in the loom close to the relays so disturbing the loom in that area may have given an impression that changing the relay solved a problem.

Steve

[Aussie John]

Is there any way of testing the coil or amp other than changing them? I hate not proving a part is faulty.

[Loubaruch]

John,

It does not sound to me like a coil problem as in my experience once a faulty one gets hot it stays faulty until it cools down.

It does seem as Steve says more like an intermittent connection and there are plenty of possibilities in the passenger footwell and or behind the dash to cause problems.

[Steve_D]

Loubaruch said:

...... intermittent connection and there are plenty of possibilities in the passenger footwell and or behind the dash to cause problems.

I doubt it will be behind the dash as most of the engine loom bits are just in the footwell. Prime contender there is the loopback connector (blue plastic jobbie).
Far more likely is the wiring up around the coil as it has been getting quite hot for 20 years or so and will be rather crusty.

In answer to the other question no there are not many tests you can carry out on the amp or the coil which is why I have built us a test rig for our workshop so I can prove a faulty part. Coils normally just die. (or worse still we had one dead straight out of the box).

Steve

[blitzracing]

If you loose the tacho, you have lost the trigger to the coil primary. The only way a coil would cause this if it failed in such a way to loose the spike it produces as the primary switches off that the tacho picks up. Amp most likely culprit.