Weird non starting problem GT6

[rulloyd]

12 hours ago, Mark B said:

Don't know if you a are using an original live lead from the battery to the solinoid, seen two types one clearly a larger diameter than the other. Only after occassional problems spinning over, I paired back the insulation on four original leads, and found they all had badly corroded along the length, covered in green corrosion. Replacd with new cable, problem solved.

I have problems starting my Gt6 from cold, if unused for a couple of weeks, everything replaced and adjusted I've put it down to a tired worn engine. A little squirt of easy start always works, and saves caning the battery. Maybe worth carrying a can for emergencies.

 

Hi Mark,  my engine normally fires immediately.  Cables are good 👍

[rulloyd]

8 hours ago, PeteH said:

Ford, ran a start system, which basically used a 6volt coil on 12volt systems, protection for the coil during running was by a Ballast resister, by passed by feeding the coil 12v via the starter during cranking. This meant at the point of lowest voltage during starting the spark was not deteriorated. Later they changed the resister for a resistive wire, which was often incorporated in the loom. (and which led some to assume it was a 12v Coil) The wire from the start solenoid was not separately switched, as normally only live when cranking. If said, solenoid, wire failed as little as 4volts could be getting to the coil which would result in a massively degraded spark and difficult (to say the least) ability to start!. A battery which was already low would exacerbate this phenomenon. Food for thought?.

Pete

Thanks Pete,  I’m still thinking!

[PeteH]

Back in the 70`s, We had a Cortina. Weird issue, kept cutting out. Would run until it got a bit warm under the Bonnet and then splutter and die. After a lot of searching, the cause was found to be the HT lead from the coil to the distributor as it warmed up was moving closer to a bulkhead bolt and arcing from a "radio suppressor" fitted in the lead, killing the engine. Spotted on the first occasion it happened at night when the spark/arc was visible. Of course every time someone had checked the ignition, the lead was moved away from the bolt and the engine would then run again.

Pete

[NonMember]

1 hour ago, PeteH said:

Of course every time someone had checked the ignition, the lead was moved away from the bolt and the engine would then run again.

I had a long and persistent fault on a VW Passat that would just cut out suddenly. Every time I took it to the garage they replaced a different component of the ignition system, and declared it fixed, only for me to find the problem just as bad or worse. Eventually I replaced the car (with a 1973 Toledo for the extra reliability) but in the two weeks between buying said Toledo and going to pick it up, I discovered the real cause of the Passat's woes. The engine earth strap was rubbing on the main engine harness and had worn through the insulation so that, intermittently, it shorted out the distributor pickup. As you say, every time somebody fiddled with it they moved the harness or the earth strap just a little.

[Pete Lewis]

the other intermittent is the actual ignition switch if the sweep contact has worn  you may not be getting the ballast supply when cranking stops 

so this can give a i want to start but wont, 

does it crank ok  when its died  

simple test add a small pea bulb to the coil ign feed make sure its on all the time when you try to start , if its dead theres a fault in the feed 

Pete

[NonMember]

1 hour ago, Pete Lewis said:

you may not be getting the ballast supply when cranking stops

Oh yes, had that on the Stag. Would fire up perfectly - enthusiastically even - then stall immediately I released the key from the starter position. Fairly easy to diagnose when the symptoms were so clear.

[dougbgt6]

4 hours ago, Pete Lewis said:

the other intermittent is the actual ignition switch if the sweep contact has worn  you may not be getting the ballast supply when cranking stops 

Is there an echo in here?

"Last year I had to replace my ignition switch because it wouldn't connect the 6v on start up." 

Nobody listens to me! 

Doug

[Pete Lewis]

wot   sorry   need new batteries   

Pete

[Stratton Jimmer]

When a starter motor commences to spin, it takes a huge amount of current as it is effectively a short circuit - copper windings with very low resistance. As it speeds up, a back electromotive force (back emf) is generated which resists the flow of current else the motor would accelerate indefinitely. At some point, the back emf is sufficient to allow current from the battery (and generator) to flow elsewhere and power up the ignition circuit. If all is in order, this happens very quickly but if there's a problem anywhere e.g. a poorly charged battery or a sluggish starter motor then there will be less charge available for the ignition system.

What may happen with sluggishly turning starter motors is that they may hesitate with their commutator in such a postion that momentarily, the short circuit they are creating is switched off. This is sometimes sufficient time for the ignition system to generate a spark and start the four stroke cycle. That will also initially accelerate the starter motor before the starter dog drops out and enhance the back emf and thus current available for the ignition circuit.

[NonMember]

50 minutes ago, Stratton Jimmer said:

When a starter motor commences to spin, it takes a huge amount of current as it is effectively a short circuit - copper windings with very low resistance. As it speeds up, a back electromotive force (back emf) is generated which resists the flow of current else the motor would accelerate indefinitely. At some point, the back emf is sufficient to allow current from the battery (and generator) to flow elsewhere and power up the ignition circuit.

Err... no. Yes, the inrush current is huge, but it's being supplied by a car battery with a massive CCA rating. The voltage does not drop "briefly" (or even instantaneously) to zero as your description implies. Indeed, if the battery is so weak as to allow that to happen, the starter just stops. Current does not "choose the shortest path" exclusively, as some pub "experts" might tell - it follows all paths simultaneously in proportion to their conductance. Further, the coil is not sensitive to the instantaneous voltage but rather to the integrated voltage over the period it's turned on, clamped by its internal resistance towards the end of that period, which is approaching TDC with the engine rotating, and hence after the starter motor has spun up.

What happens with a weak battery is that the steady voltage gets pulled down, not by some claimed "short circuit" but by the 80A or so that the starter motor draws in steady state. That doesn't in any way prevent the current flowing through the coil, but it does reduce it, which makes for a weak spark. If the ignition system is in good order, and especially if you have a working ballast bypass system, that may still be enough to start the engine fine.

[Stratton Jimmer]

2 hours ago, NonMember said:

Err... no. Yes, the inrush current is huge, but it's being supplied by a car battery with a massive CCA rating. The voltage does not drop "briefly" (or even instantaneously) to zero as your description implies. Indeed, if the battery is so weak as to allow that to happen, the starter just stops. Current does not "choose the shortest path" exclusively, as some pub "experts" might tell - it follows all paths simultaneously in proportion to their conductance. Further, the coil is not sensitive to the instantaneous voltage but rather to the integrated voltage over the period it's turned on, clamped by its internal resistance towards the end of that period, which is approaching TDC with the engine rotating, and hence after the starter motor has spun up.

What happens with a weak battery is that the steady voltage gets pulled down, not by some claimed "short circuit" but by the 80A or so that the starter motor draws in steady state. That doesn't in any way prevent the current flowing through the coil, but it does reduce it, which makes for a weak spark. If the ignition system is in good order, and especially if you have a working ballast bypass system, that may still be enough to start the engine fine.

That's a better scientific answer Rob. I was trying to keep it simple.

[PeteH]

Looking at the GT6 wiring Diagram(s). It would appear that the 12V supply is via the ign; switch on the Mk1 and 2, and only the Mk3 is direct from the Solenoid, and not via the ignition switch?.

I had forgotten that Haynes lump(ed) the GT6 and Vitesse in the the one W/S manual. I never let go of W/S manuals!. I think I have around 50!.

Pete

[NonMember]

1 hour ago, PeteH said:

It would appear that the 12V supply is via the ign; switch on the Mk1 and 2, and only the Mk3 is direct from the Solenoid

If you're referring to the coil supply, that's because the Mk1 & 2 have a non-ballast, 12V coil where the Mk3 has a ballast resistor - the solenoid connection is the ballast bypass for better starting. The primary coil supply is still from the ignition switch, but via the ballast. Triumph fitted ballast ignition from 1970-ish, which was start of Mk4 Spitfire and Mk3 GT6.

[PeteH]

10 hours ago, NonMember said:

If you're referring to the coil supply, that's because the Mk1 & 2 have a non-ballast, 12V coil where the Mk3 has a ballast resistor - the solenoid connection is the ballast bypass for better starting. The primary coil supply is still from the ignition switch, but via the ballast. Triumph fitted ballast ignition from 1970-ish, which was start of Mk4 Spitfire and Mk3 GT6.

Guessed it`s something along those lines. It was more of a surprise (to me) that the Wiring drawings where in the Haynes Manual. But It was 1986 when we had the Vitesse, so memory can be forgiven!. Ballast systems where a "popular" manufacturer "upgrade". It the attempt to improve reliability?.

Pete

[NonMember]

25 minutes ago, PeteH said:

It the attempt to improve reliability?

No, just to improve cold starting on a weak battery. They give minimal benefit anywhere else (although theoretically some improvement in spark energy at high RPM) and add another possible failure point.

[dougbgt6]

Mine has a resistive wire.

"Lets save money and do away with the ballast resistor, we'll put a resistive wire in the loom" 

"How hot does it get?" 

"It'll be fine! 

db

[Pete Lewis]

and with all this  any mix and not match on a ballasted system can as said many times  >>>>>>>>>>>

if using a 6v ballasted on a 12v coil you get a very weak HT you have halved it

bypass a ballasted feed and put 12v thro a 6v coil and you double the HT and current burns points , blows condensers and dizzy caps and rotors suffer

some 6 v ballasted coils are actually marked 12v as the base ign voltage of the car  ...thats useful ???

12v coils are 3 ohms primary   6v coils are 1.5ohms across the primary  terminals 

so its good the pair of designs are not mixed up 

Pete

[dougbgt6]

6v ones sometimes have 12v printed on them! There is a logical reason for this, but it now escapes me. The only sure way to sort is with an ohm meter.  

Doug

[PeteH]

11 hours ago, NonMember said:

No, just to improve cold starting on a weak battery. They give minimal benefit anywhere else (although theoretically some improvement in spark energy at high RPM) and add another possible failure point.

Your quite right of course. But the "bean counters" would view it as an "enhancement", for the cost of a few feet of cable.😁 How many times do manufacturers do a few quid of "facelift" halfway through a car`s life cycle, and then proceed to call it a "new" model?.

Pete

[Pete Lewis]

the move to these ideas comes about with ongoing emission controls  and the later cars run a bit leaner so assistance on cold starts is all part of the plan

its not a upgrade in isolation 

Pete

[Ian Smith]

I had this problem with a mini, a fair few years back: intermittent starting. A friend traced it back to the wiring on the ignition switch/column lock. Apparently, the live feed was ok, but the ignition feed, and starting feed were reversed. Changing this cured the problem. 

30-odd years ago, mind... I think we've turned decimal since......

Cheers,

Ian.