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Odd intermittent electrical fault

The last couple of times I have gone out in my Triumph 2000 it has died on me, but has restarted after half a dozen goes at the starter.

The first time I was driving along, and about a mile from the initial cold start, when the temperature gauge had started to climb off the cold mark, and the engine just cut out. I had enough momentum to get to the side of the road, and after it restarted, I had no more trouble.

The second time, I had parked in the supermarket car park, had done a fair amount of shopping, during which time the car had cooled down. It started first time, but just as I was going to drive away the engine died. It restarted eventually, and I drove home with no further trouble.

This morning, the car was covered in frost. It started OK and started warming up. I had pushed the choke into the fast idle position once the temperature gauge got off its stop, and was happily (?) scraping the ice off the side windows when the engine suddenly died. This time, I noticed that the rev counter went up as I tried to start it, but as soon as it sounded as though the engine was firing, I let the key return to the ignition on position the rev counter immediately dropped to 0. If I held on to the key in the Start position, I got the revs up to 2500, but as soon as I let go the counter dropped straight to 0 again.

The rev counter has a feed, an earth and a count wire. The feed and count wires are connected directly to the coil terminals, so if it drops suddenly to 0 then either the feed has gone dead or the dizzy points have shorted or gone open circuit. Which leads me to assume that the coil itself is OK, and the problem is going to be either the ignition switch itself or the distributor or the dropper resistor. Or a bad connection in the wires feeding these circuits.

But why do I only get a problem when the engine is lukewarm? I can't see why any of these components should be temperature sensitive and cure themselves once the 6 to 8 goes of restarting have taken place.

Any ideas?

Jim

Reply to
Jim Warren
Loading thread data ...

hiya,

think I'd go for the dropper resistor or the points condenser.

m
Reply to
pottsy

If anyone is interested in the outcome of this, I did some tests at the weekend. I ran the engine from cold at a fast idle until the engine cut out. This happened just as the thermostat opened and hot water flowing into the radiator gave the fan warm air to blow back over the engine. The car exhibited the same symptoms as before, of apparently firing while the starter was being operated, and not when the key was let go. A temporary link wire from the coil SW to the battery plus allowed the engine to start first try. Then when the battery connection was disconnected, the engine started to die, but it caught again when the temporary battery link was reconnected. Clearly then it was not the points condenser and it had to be the ballast resistor.

According to the manual, the resistor is held by the coil mounting bolt, but mine was held by the alternator mounting bolt for some reason. I got a new resistor today. The new one, checked on a digital meter was 1.2 ohms (and according to the manual it should be 1.2 to 1.4 ohms). The old one read

14.4 ohms. I mounted the new one on the coil mounting bolt and connected it up and all my problems went away.

Mounted as it was on the alternator bolt, the old resistor was in the draught of the fan. I assume then that it got wet when driving through heavy rain. The electrical connections that the spade connectors went on were riveted. So I suppose a combination of corrosion and thermal expansion of the rivet gave some strange and varying resistances, and that eventually I let go of the key while the points were closed and the inductance in the coil created enough of an arc across the bad connection in the resistor to clean off the corrosion for a bit and let the engine run normally.

An interesting diagnostic exercise, but I don't want too many like that.

Jim

Reply to
Jim Warren

"Jim Warren" realised it was Tue, 07 Dec 2004 17:32:52 GMT and decided it was time to write:

Indeed. Thanks for posting this.

Reply to
Yippee

Thanks for all of that Jim - may help me get to the bottom of a similar (but not identical problem) on my PI.

Reply to
DocDelete

Want to give details Ken? It might throw up some ideas you haven't thought of.

Jim

Reply to
Jim Warren

Sure. It doesn't *seem* to be related to a cold engine but my problem does only usually occur within the first ten minutes. Sometimes it's all okay, if I can get by that first ten then generally all will be well thereafter.

The engine momentarily wants to die, if I'm prepared I can hold the revs up and avoid it for the most part (like pulling away from lights). BTW it only happens from idle. From experience it feels sudden and transient enough to be electrical.

I do have a slightly faulty tachometer, sometimes it goes dead. I've traced this to the +ve feed connector being dodgy at the back of the unit. You may know that if you disconnect this, the ignition also dies. I wonder if this could cause the problem? Surely this would happen at any engine load / time though?

Your comments about the ballast resistor will lead me to check that. It's a pre-face lift model, so the resistor is separate.

Reply to
DocDelete

I had something similar on my PI, which I never did find the exact cause of. But it went away when I fitted a new set of plug leads and plugs. The distributor is very close to the underside of the bonnet, and the torque of the engine twists it on its mountings, any loops of HT lead can hit the bonnet and flex the lead. Make sure the coil to distributor lead is a 30cm length (which is a tight stretch, but it does reach and work OK. The tendency is to fit a 40cm lead, and this does hit the bonnet and doesn't last very long. Also check that the leads from distributor to plugs are a snug fit in the distributor cap, and route them so that there are no tall loops.

The ignition wiring circuit has the ignition live side routed through the tacho to the ballast resistor and then on to the coil. In other words, the tacho, resistor and coil are all in series, though not when you are operating the starter, when the tacho and resistor are both bypassed. A fault in any one of the series components, or a bad connection on the way would interrupt the ignition circuit. So your dodgy connection sounds like a prime suspect - particularly when you consider that that particular connection is carrying around 5 amps each time the points close. An occasional momentary interruption at reasonable revs would be a little misfire, with enough engine momentum to carry it over until the sparks came back. But at idle, it might last long enough for the engine to die - particularly when you are suddenly adding a big charge of petrol/air to a cylinder, requiring the plug to give a fatter spark to fire it. As a simple expedient to make the car more driveable until you cure it, you could increase the idle revs (BTDT!).

They are not horribly expensive (change out of a tenner even when you pay for postage and packing - and certainly a lot cheaper than new HT leads). You might like to consider changing it anyway, to eliminate that as a source of the fault.

Good luck

Jim

Reply to
Jim Warren

Thanks for that Jim - it really helps to confirm these odd unformed suspicions. None of the actions are expensive to fix, and the car is due a few winter tweaks anyway. I'm sending the PI meter off to be recalibrated soon too, so a few electrical remedies won't break the bank.

That tacho circuit really is a B isn't it? Is it true that the later tachos (2500s) are in parallel? I think SixAppeal ran an article once on rewiring to fit this.

It's a shame that the later tacho's face style doesn't match the older gauges - I feel a delicate dismantling / parts swapping exercise coming on....

Cheers, Ken.

Reply to
DocDelete

If that is the case, then it can only be the very late ones. Up to 1977, the tacho wiring is like you have at the moment - white wire from the ignition switch, white/grey to the ballast resistor and green to instruments, heater and wipers. So to remove the tacho, connect these three together and all the circuits continue to work. The tacho I fitted in the

2000 is in place of the (non-working as usual) clock. It is an after-market addition, so has to be parallel wired.

I tried this once on a replacement Imp speedo I got from a scrappie. It is not as easy as it looks to put the hand back in the right position for accurate readings, and I hope you have got steadier hands than I have :-)

Jim

Reply to
Jim Warren

after-market

Interesting - I may be getting confused with the difference between voltage-sensing and current-sensing. I'll dig the article out later, and maybe stick a JPG on the net for you to see.

LOL I doubt that!

Cheers Jim!

Reply to
DocDelete

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