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Joe_Pinehill
05-08-2008, 12:10 PM
When I drive the Spitfire (78), I sometimes get a very quick intermittent flicker when driving. Even at 40 - 50 mph.

Tach goes to zero for an instant, and then comes back up.

I was going to pick up a new coil ( I have no idea how old the coil is, and they dont cost that much, terminals look corroded, and I cleaned as best as I could), and change the spade connectors on the wires going to the coil to know I have good connections.

Any other suggestions on where to look?

eejay56
05-08-2008, 01:48 PM
Check the ignition switch. Mine would cut out and if I jiggled the key it would come back on. Before I replaced it, it got progressively worse until I had to hold the key to keep it running

TR4
05-08-2008, 01:48 PM
Failure to remember to use the clamps on the distributor cap will cause a similar result. Yes, I did that once.

Joe_Pinehill
05-08-2008, 02:07 PM
Ill check the ignition switch, though its just a slight intermittant, less than the time to snap your fingers.

guzzul
05-08-2008, 02:45 PM
I would carefully check the ignition switch, particularly terminal 3, the white wire circuit to the ignition. The tach could cut out because of no signal from the (-) side of the coil, or it could cut out because the green-wire circuit is shutting down. Both of these could be due to a faulty ignition switch.

If you lose power on terminal 3, you will lose power on both the white-wire (ignition) circuit and the fused green-wire (gauge) circuit. If its a very short loss, you might not notice it on other components of the green circuit.

If the ignition switch checks out ok, then a bad coil could also cause the symptoms you're getting. You might also check the connectors to and from the distributor drive resistor, and that 4-wire white plug that connects at the distributor, to make sure they are not somehow jiggling loose.

I'm assuming power is ok to other circuits (e.g. dash lights, etc) when this happens?

Joe_Pinehill
05-08-2008, 02:58 PM
Ill check the ignition switch.

My car doesnt use the four wire connector on my distributor. The PO installed a Beck Arnley breakerless system, and two leads from the sensor go directly to the coil.

I'm not sure I have a drive resistor either with the after market set up.

Again, for around $25 a new coil cant hurt.

eejay56
05-08-2008, 05:34 PM
That's how mine started out too, just a real quick cutout and the tach would drop to zero. It's hard to diagnose when it's so intermittent. Try jiggling the key to see if that makes it happen or hotwire across the switch and if it never happens then, that's it. It's an expensive switch. I think I paid around 100$.

Joe_Pinehill
05-08-2008, 07:28 PM
I put a new coil in tonight. Still the same symptoms..It was a Lucas coil, maybe original, replaced with a NAPA coil

I do notice it happens more when I accelerate or shift.

Also it sat most of the winter without a lot of driving. And recently sat 8 weeks without being started, I was away.

It idles perfectly, and without a load, I can push the accelerator down and no hint of hessitation.

foxtrapper
05-08-2008, 07:44 PM
Any other suggestions on where to look?
All the wiring from the firewall to the distributor. With the engine running, wiggle the wires. I suspect you're going to induce a stumble doing this, and may even kill it. When you do, there's the intermittent open.

guzzul
05-08-2008, 08:20 PM
If the tach is cutting out it definitely sounds electrical (i.e. not carbs or something). As foxtrapper suggests maybe wiggling the wires and checking all connections in the white-wire circuit if you have definitely ruled out the ignition switch. I would also check the connections at the top fuse and make sure they're good.

It would be interesting to see if you still have power to anything else on the green circuit when the tach quits. Could be the tach is just not getting any signal from the distributor (via the White/Slate wire). If the entire green circuit fails at the same time as ignition quits, it would argue for a problem with the ignition switch. If only the tach fails, it would suggest a problem with the dizzy (or wiring thereof) and not the ignition switch, since a switch failure should affect both circuits.

With the problem so intermittent its hard to isolate. Maybe you could try turning the wipers on and see if they quit at the same time as the tach, or the heater motor, which is also on green. The turn signals are also on green, you could try turning them on and see if the indicator light quits when the tach quits or if it keeps running. If other stuff on green keeps running, then I would be looking for an ignition problem and not a switch problem.

Joe_Pinehill
05-08-2008, 09:55 PM
It idles fine, but Ill try the jiggling tomorow

I have a Beck Arnley sender unit, could that be going bad?

Joe_Pinehill
05-09-2008, 06:26 AM
Do the ingnition modules have intermittant failures ? or do they tend to have hard failures when they go?

The engine idles fine, and pushing the accellerator in the garage, I cant repeat the intermittant.

Its only when driving. Which Im guessing means something is jiggling around getting a less than good connection

guzzul
05-09-2008, 10:10 AM
I had a Lucas electronic ignition module in a '75 Spit that would work fine until I parked the car warm. After about 5-10 minutes, the heat from the engine somehow affected the distributor electronics and the car would not start no matter what. If I left it for another 20 minutes (i.e. let it cool down again past it's peak), it would start fine. Changed it for a pertronix and all was well.

So electronic ignitions do go intermittent, but usually when they fail they fail hard.

Your problem sounds more like something shaking loose, or a corroded connector or ground somewhere, though. It could be something very simple. But you need to isolate whether it is ignition only or whether there are other circuits involved.

If it is strictly ignition circuits, then there are only so many components and wires in that circuit. You've already tried the coil. Start working through every wire and connector and every ground from the battery through to the dizzy. Has to be there somewhere.

Joe_Pinehill
05-10-2008, 04:18 PM
I replaced the coil, put new lugs on the leads coming from the ignition sending unit going to the coil, sanded all the lugs and terminal on the other coil wires, and the low voltage side of the solenoid.

I moved/jiggled the harness, from the coil back, and the ignition switch, couldnt get it to repeat.

Fresh tank of gas, and added a can of Sea Foam.

The car seems to be running back to normal, and the problem didnt repeat on my afternoon drive today! Hopefully one of the above curred the problem.

A square of sand paper is more important than a wrench in the boot tool pouch.

thanks for feed back

guzzul
05-10-2008, 05:39 PM
That's great Joe. Sounds like success. If the tach was quitting, then it would not be a fuel problem, since the ignition would keep sparking even if fuel was bad. But Sea Foam can't hurt.

Hopefully it was a connector. Cheers.