bennygoodman Posted August 17, 2014 Share Posted August 17, 2014 Hello all, I wonder if anyone has had a fault like this, on my MK3 GT6 I have some kind of earth fault.When I get in the car and it is cold it starts as it should, I.E. the starter motor spins the engine over freely.Then if I stop the car after a few miles when the engine is hot and try to restart it a few minutes later it is as if the battery is flat, sometimes it will barely turn the engine over, other times it will turn it over very slowly.Then if I leave it for 20 or 30 minutes it starts up as if nothing was ever wrong.When I took it for my MOT the mechanic put his meter on the battery and said it is charging correctly at around 14v, the battery is brand new by the way.He then asked me to turn the engine off and put his tester on I pressume the battery positive lead and an earth and said it has dropped down to around 7v while trying to start the engine intimating an earth fault, any ideas anyone? Quote Link to comment Share on other sites More sharing options...
JohnD Posted August 17, 2014 Share Posted August 17, 2014 Benny,Remember that the battery puts an enormous current into the starter, at least 100Amps, which is why the cable is so hefty.But a current must return to the battery, or it won't flow at all.How does it do so?Triumph fitted a manky little length of wire braid from the engine to the chassis, that often either rots away or is forgotten after a rebuild. Without that, the current has to find its way from the engine block (rubber mounted) though the gear box (rubber mounted) along the transmission to the differential (Rubber mounted) and the rear axle (rubber mounted). meanhwile the body is monted on the chassi - on rubber! The least resistance pathway for the earth return is probably the hand brake cable! Make sure that the starter, bolted to the engine block has as good an earth return as it has a supply. A length of starter cable, bolted to the engine block and earthed to the same earth point as the battery avoids the convoluted pathway above and will cure any starter earth problems for very little. Ensure that the connections are made to metal that are scraped bright and clean of paint or corrosion. A little copperease grease will maintain the conduction and stop more corrosion. JOhn Quote Link to comment Share on other sites More sharing options...
piman Posted August 17, 2014 Share Posted August 17, 2014 Hello Benny, as the voltage is dropping so low, it seems that there is a heavy current draw so the earth return is probably OK. Was the starter turning very slowly when this measurement was taken, if so that is where the problem is. A starter motor is virtually a dead short across the battery when first operated and it's rotation makes it generate which opposes the current draw (I.e. a spinning starter takes less power from the battery than one that is barely turning). Either the battery is defective (not so likely if it cranks OK cold) or the starter motor is getting tired? I'd take the starter off and have a look inside as the first step.Alec Quote Link to comment Share on other sites More sharing options...
Spider Posted August 17, 2014 Share Posted August 17, 2014 JohnD wrote: The least resistance pathway for the earth return is probably the hand brake cable! Or the throttle cable. I got a nice surprise when I felt how hot the cable was after I saw the outer cover melting :B Quote Link to comment Share on other sites More sharing options...
bennygoodman Posted August 17, 2014 Author Share Posted August 17, 2014 piman wrote:Hello Benny, as the voltage is dropping so low, it seems that there is a heavy current draw so the earth return is probably OK. Was the starter turning very slowly when this measurement was taken, if so that is where the problem is. A starter motor is virtually a dead short across the battery when first operated and it's rotation makes it generate which opposes the current draw (I.e. a spinning starter takes less power from the battery than one that is barely turning). Either the battery is defective (not so likely if it cranks OK cold) or the starter motor is getting tired? I'd take the starter off and have a look inside as the first step.AlecNo when the measure was taken it was turning quite fast but not quite as fast as when first starting from cold. Quote Link to comment Share on other sites More sharing options...
cappowon Posted August 17, 2014 Share Posted August 17, 2014 Mine was earthing through the clutch hydraulic pipe where it touched the bulkhead, saw it sparking. Quote Link to comment Share on other sites More sharing options...
piman Posted August 18, 2014 Share Posted August 18, 2014 Hello Benny,I assume the battery is large enough for the car? I still think that a check on the starter motor is worth while, if only to eliminate it from the equation. Brushes a good length and free in the brush boxes and the commutator clean, even and smooth, also check the bearings.Alec Quote Link to comment Share on other sites More sharing options...
RedRooster Posted August 18, 2014 Share Posted August 18, 2014 If you have a set of jump leads use one half of them for an earth wire, it will rule that one out, then it's probably the starter or solenoid. Quote Link to comment Share on other sites More sharing options...
bennygoodman Posted August 19, 2014 Author Share Posted August 19, 2014 I've not had chance to look yet but from memory I recall and earth lead from the engine to the battery earth point.I'll look as soon as the weather improves enough to get the car out of the garage. Quote Link to comment Share on other sites More sharing options...
savvy2500 Posted August 19, 2014 Share Posted August 19, 2014 You may want to have a look at my post from a couple of months back entitled: "one of those annoying niggles that can't be found". Exactly the same issue that you are experiencing.Mine was resolved by replacing the solenoid, fitting a new earth strap and replacing the battery and starter motor leads.Hope that helps! Quote Link to comment Share on other sites More sharing options...
bennygoodman Posted August 19, 2014 Author Share Posted August 19, 2014 Cheers savvy2500.I took the car out of the garage tonight because it was a nice evening to have a look around.Firstly it is a brand new battery of the recommended type, secondly and I had forgotten this, i don't why because it was only a few weeks ago, it has a new (refurbished from Paddocks) starter motor and a new solonoid, what I did find was the screw in the starter motor that the lead from the solonoid goes to was loose, I have tightened it up and will when the weather permits take it out for a run and see if it has solved the problem. Quote Link to comment Share on other sites More sharing options...
savvy2500 Posted August 19, 2014 Share Posted August 19, 2014 Hi Benny,First of all, my post may have confused things... I didn't replace the battery just the battery leads and starter leads.My solenoid came from Canleys and was getting VERY hot. I fitted a brand new braided earth strap from the battery to the chassis as opposed to the bolt on the bell housing where the standard one is.Your issue definitely sounds like the same as mine which caused many a frustrated night. In the end I bought a NOS Lucas solenoid and that seemed to be part of the solution. Remember that all the ignition wiring goes through that splendid so any heat will cause resistance until it cools down.Hope you get it solved - wouldn't want you to have the worry I did.Terry Quote Link to comment Share on other sites More sharing options...
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