Cutting out when hot - Advice on where to go next

[gizzardio]

Hi All

Just hoping for a bit of advice on where you would go next to solve a cut out problem. A few weeks ago my (almost completely reliable in my 9 years ownership..) cut out suddenly just a few miles from home. It re-started after a while cooling down whilst I looked under bonnet for anything obviously. Anyway, I've since started up and noticed that it will cut out when hot. This isn't a splutter and cough, but a total on/off switch die. I have managed to work out that it's the ignition failing using an inline spark tester and have checked wiring and inside dizzy etc and can't see anything obvious. I've also had all wiring loom down in footwell and tried looking for loose wires, waggling, etc and nothing down there will cut it out. Tried the yellow connector in steering column and it seems OK.

So after some reading I think it's time to swap out coil and/or ignition amp, and for about £80 for the pair I'm happy do this. But the question is, is there anything else to reliably check before I do this? I have read about the Hall effect sensor on dizzy also causing these symptoms but think it'd rather try coil & amp first before taking that to bits. Maybe I'm wrong about that?

I followed this video which was pretty helpful but as the guy says, it's more for complete non-starters rather than cut out. https://www.youtube.com/watch?v=RWIH4WS6RAw&li... I think it'd be pretty tricky waiting for cut out and then diving to set this up before it cooled down to the point its all working again.

Thanks for any suggestions

[phillpot]

I'd start with coil, cheap and easy to swap. even if its not that a spare is always handy

[gizzardio]

Hi

thanks for replying. I think it's logical to replace coil at this point too and if it happens again, I know (at least assuming new part works 100%) what I can eliminate.

Cheers

[MisterTee]

I’d definitely go with the coil.

The same happened with mine not long after I bought it. The previous owner had changed almost everything (except the coil) in an attempt to fix it. His rationale for not changing the coil was that he had never had one fail in over 40 years of motoring!

I went for one of these as a direct replacement for the wet coil.

[gizzardio]

Thanks, I've already ordered a coil though from TVR Parts so can't switch now.

Take it you had exact same symptoms then? I really hope it's the coil (or amp if not). Apart from failing loom wiring I can't see there's much left in the ignition system to cause total loss of spark seemingly caused by heat or perhaps duration of use.

[MisterTee]

Yeah, the same symptoms. I bought the car in the February and it was cold with rain and sleet, so it drove the 150 miles home without a hitch. The next time out - much warmer weather and sat in traffic it was horrendous - cutting out and misfiring as if switched off and back on again. A few hundred yards up the road and with a bonnet full of fresh air it calmed down enough to get me home.

Given that I had receipts for almost everything else that came with the car, the obvious starting place for me was the coil.

Hope you get it sorted.

[gizzardio]

Ha ha, yes the one remaining part does seem the likely culprit in your case!

I'll see how I get on with this new coil

[cabs]

If the new coil does not cure the hot cutting out, it may be worth trying cleaning and applying some Heat transfer paste underneath the amplifier.

[aka_kerrly]

Also worth checking any relays for the ECU & fuel pump as these can suffer from dried out/fractured connections which cause similar symptoms to ignition component failure by only becoming a problem once everything is warm.

[gizzardio]

Thanks but I've already replaced these 2 relays before I traced the fault to be an ignition one. Of course it could be both but I definitely had an ignition failure at the point of cut out as shown on the spark tester.

[lordofthewings]

As you've tried everything else, have you checked (replaced) the main earth lead from the battery to the chassis ? I had similar problems to you, and after wasting money on coil/distributor/plugs/TPS, "the man from the AA" sorted it with a new heavy-duty earth lead.

[Penelope Stopit]

gizzardio said:

Hi All
Just hoping for a bit of advice on where you would go next to solve a cut out problem

Just now viewed the video you linked to, here @ 1min 37 secs https://youtu.be/RWIH4WS6RAw?t=97, the chap doing the testing shows the world that he hasn't got a clue how to check the coil supply voltage, proving yet again that the internet is full of..........

It was mentioned that the coil voltage should be very close to battery voltage, obviously this is expected when testing 12 volt coil ignition circuits (not 9 or 6 volt circuits that have a ballast resistor in series with the ignition supply to the coil)

What wasn't mentioned was that all cables connected to the negative side of the coil need to be disconnected and the the coil negative terminal connected to the battery negative or known good engine earth with a thinnish jump lead capable of carrying a minimum of 10 amps (10 amps or higher rated cable avoids creating a volt drop during testing)

It isn't possible to measure a coil supply unless the coil is drawing current through the circuit, the load of the coil needs to be on the circuit when the voltage is measured

The ignition amplifier doesn't earth the ignition coil when the distributor is stationary

---

Suggest you measure the coil supply voltage using the above method, don't leave the ignition on for too long as the coil will begin to overheat, 15 seconds isn't a problem

If your cars ignition coil is 12 volts there shouldn't be a ballast resistor wired in series with the ignition supply to it

A 21 watt bulb can be connected to the ignition coil +ive supply at the coil and earth, the bulb can be placed inside the vehicle in a place visible to the driver, (make sure the bulb can't burn the carpet or trim, place it on a wooden block or hang it off something)

With the above test bulb wired the car can now be driven, next time the engine cuts out the driver will know if the ignition supply to the coil is breaking down by seeing if the bulb is fully illuminated or not

Above test is for a standard 12 volt ignition circuit

Edited by Penelope Stopit on Wednesday 30th September 23:01

[gizzardio]

Hi Stopit

That's some good advice right there. Well at this stage I've already ordered the new coil before your post so I'll just fit that anyway. If problems persist I'll definitely rig up that test. If the bulb does go out does that indicate a bad earth or bad +ve feed or either/both?

[gizzardio]

Hi Lord - I will hopefully be trying the earth(s) next if I still have problems after fitting new coil. If all seems OK then I move to ignition amplifier.

[Penelope Stopit]

gizzardio said:

Hi Stopit

That's some good advice right there. Well at this stage I've already ordered the new coil before your post so I'll just fit that anyway. If problems persist I'll definitely rig up that test. If the bulb does go out does that indicate a bad earth or bad +ve feed or either/both?

Connect one of the 21 watt test bulb cables to battery negative, then you will know that the earth side of the bulb is good

Connect the other 21 watt test bulb cable to the coil positive terminal

If the bulb dims or goes out it's informing you that the ignition coil positive supply is breaking down somewhere

[MisterTee]

Did the new coil fix your issue?

Just curious

[gizzardio]

Hi

I fitted my new coil last weekend and still cut out. Boo.

So I am about to try the method described by Mr Stopit above but since my car cuts out just sitting on drive idling after 10 mins or so and then won't start for about 20mins or so, do I need to connect a bulb? This is just for a visual whilst driving I guess, but if I can test the +ve coil supply right away when it cuts out, could I just stick a multimeter on it and turn the car over so the dizzy is spinning and observe the supply that way?

[v8s4me]

Some coils require an earth (mine does) so if that's the case with yours, how is it earthed? If it does need an earth, could heat be affecting it?

[gizzardio]

I'm really not sure about the earth situation there. I can't trace the wiring so well as a lot of it is combined with other wiring in heat shrink. Any ideas where I'd start looking for the earth for this amplifier module?

I did try this time again with my spark detector installed on the king lead and when it cut out after 10mins there was no spark there so I think I can rule out the dizzy itself. When there was no spark, I checked the power supply on the +ve and -ve coil connections and both were 12.8V dropping down to about 9V during the time when it was turning over which I guess is just down to the load being pulled during turnover on starter motor etc?

So no spark from coil but power supply seemingly there to both +ve and -ve so does that point to amplifier module now? Either the module itself or the earth connection to it?

[GreenV8S]

gizzardio said:

So no spark from coil but power supply seemingly there to both +ve and -ve so does that point to amplifier module now? Either the module itself or the earth connection to it?

Yes, exactly. The problem must be in the ignition pickup, ignition module or wiring. Worth doing a continuity check between the plug on the dizzy and the coil just to rule that out, but most likely IMO you have a failed ignition module.