GQ running fine one minute, cutting out the next, tacho jumping around

[gone bush SA]

hi, our GQ is playing up lately, it can be running lovely then out of the blue it misses, and sometimes just cuts out. then after it dies it usually just starts up again until next time. sometimes when the car is turned off and the ignition is just turned on (not to start the car but to put up the windows) there is like a slight preignition start. it doesn't seem to matter if the motor is hot or cold on gas or petrol. when it is playing up the tacho jumps around like mad and sometimes when the ignition is first turned on the tacho jumps or just goes to the highest mark
it has a electronic ignition, 4.2 carby type , LPG/ petrol.
we have replaced the coil lead, checked all the connections
i'm greatful for any help as to where to look as it's getting quite dangerous to drive
thanks chris

[AB]

Good luck with it mate, hopefully someone can help with a TB42.

My neighbours old TB42 had pretty much the exact problem, I'll ask him tomorrow and see what he came up with.

[Ben-e-boy]

Gday
I would probably check the wiring to the coil first you may have a dodgy earth

[97_gq_lwb]

I would replace the points and condensor with pertronix ignition if not replace them remove the noise suppressor check the ballast resistor .

[gone bush SA]

it already has the pertronix ignition and all the earth wires around the coil have been checked, have checked the ballast resistor., all fuses checked & cleaned (well contact points).
i even wondered if it might have something to do with the ignition barrel etc but don't want to keep just buying things on the off chance, so that's why i'm picking everyones brains.
thanks for help so far

[97_gq_lwb]

Ok sounds like you already have the usual problems resolved try the noise suppressor if not already removed just disconnect it.
Otherwise trace the earth wire from the coil back to the tacho and check for a short sometimes people connected up dodgy kill switches to this as well.
And the switch on the back of the ignition can be a problem.
You could try your own power feed direct to eliminate it i usually fit a relay on the ignition coil myself saves the drain on switches etc.

[Kelvinator]

This is just a wild one but one of the stupidest and trickiest problems i once came across was similar to what you are experiencing, minus the tacho, but i wouldn't rule it out. I had the same trouble you are with a customers car and i was looking everywhere for what it could be and it was in the simplest fix. Took all the crap, rabbits feet, lucky cannon balls, friendship bracelets and the rest off the key chain. As it was driving and vibrating the weight of it all was switching the car on and off as it was driving, sometimes even just idling! Till the point where it had completely worn the barrel and was just killing it straight after idle, yet it still looked like it was switched on. On the off chance that's your problem just thought id bring it up, could save you lookin like the bloke in the supercheap add ;)

[Rosco]

Mine has done this. It was a water logged coil. Have you tried changing the coil yet? Haven't read it anywhere

[gone bush SA]

hi, thanks for the help so far, we have gone over the wires and conections again and touchwood it seems to be behaving it's self, well it's now 3 days without any problems, but it has done this before, so hopefully touchwood it might be resolved (for now anyway)
chris