Discussion
Hello all,
My Interceptor is usually the most reliable thing in the world, but yesterday after a short trip it span and span eventually fired up - as if it was flooded. All was fine, started first time this morning, took her out for a 10 minute drive, parked up for 5 mins and then the same, span and span as won't start. There is certainly petrol - half full gauge and looking down the carbs when the pedal is pressed it squirts into the barrels - I checked a couple of easy to access plugs and they are bone dry and look normal, battery strong and fully charged, electronic ignition - she's started fist turn of the key faultlessly for as long as I can remember so this is completely unusual behaviour. Recovery chap reckons it's the coil but didn't have a multimeter with him...it's now recovered home but checking myself with the ignition on I'm getting 4.9v across the coil which jumps to about 6.8ish when cranking - should this be cranking at 12v? I really don't understand coils...
Anyway, I put a spare coil I had from my Scimitar on and it still won't start, but not sure if this is a straight swap scenario anyway
Thoughts anyone, or anything else simple I can check?
cheers
Joe
My Interceptor is usually the most reliable thing in the world, but yesterday after a short trip it span and span eventually fired up - as if it was flooded. All was fine, started first time this morning, took her out for a 10 minute drive, parked up for 5 mins and then the same, span and span as won't start. There is certainly petrol - half full gauge and looking down the carbs when the pedal is pressed it squirts into the barrels - I checked a couple of easy to access plugs and they are bone dry and look normal, battery strong and fully charged, electronic ignition - she's started fist turn of the key faultlessly for as long as I can remember so this is completely unusual behaviour. Recovery chap reckons it's the coil but didn't have a multimeter with him...it's now recovered home but checking myself with the ignition on I'm getting 4.9v across the coil which jumps to about 6.8ish when cranking - should this be cranking at 12v? I really don't understand coils...
Anyway, I put a spare coil I had from my Scimitar on and it still won't start, but not sure if this is a straight swap scenario anyway
Thoughts anyone, or anything else simple I can check?
cheers
Joe
Are you using a coil that has been satisfactory in the past or is it a new one?
I presume the Jensen, like many cars of the time, is wired to include a ballast resistor for normal running which is short-circuited when the starter is activated. That's what gives a different voltage at the coil for static and cranking cases, the idea being that the coil is matched with a reduced voltage when running and is given all that's available when starting.
If you fit a coil that is not designed for low-voltage working you won't get much of a spark but I'd have thought there'd be enough to re-start it hot - but that's what you say it didn't do.
Can't remember if the Scimitar had that system, as mine worked without me needing to fiddle with it and it's long ago. If not fitting a coil from a Scimitar won't help
I presume the Jensen, like many cars of the time, is wired to include a ballast resistor for normal running which is short-circuited when the starter is activated. That's what gives a different voltage at the coil for static and cranking cases, the idea being that the coil is matched with a reduced voltage when running and is given all that's available when starting.
If you fit a coil that is not designed for low-voltage working you won't get much of a spark but I'd have thought there'd be enough to re-start it hot - but that's what you say it didn't do.
Can't remember if the Scimitar had that system, as mine worked without me needing to fiddle with it and it's long ago. If not fitting a coil from a Scimitar won't help
Edited by Allan L on Sunday 16th May 16:17
As it's name implies an ignition coil contains coils of insulated wire, like a transformer. If the insulation breaks down your electric current can cheat by only passing through some of the coil, not all of it, and the output will be reduced.
To test a coil you need to know what the resistance of its primary (input) and secondary (output) coils should be and test them with a multimeter. A "bad" coil will either show infinite resistance if the wiring has burnt out or too little resistance if the insulation has broken down. Typically a primary coil might be about 1.5 ohms and a secondary coil about 10,000 ohms.
To test a coil you need to know what the resistance of its primary (input) and secondary (output) coils should be and test them with a multimeter. A "bad" coil will either show infinite resistance if the wiring has burnt out or too little resistance if the insulation has broken down. Typically a primary coil might be about 1.5 ohms and a secondary coil about 10,000 ohms.
thanks guys - as an update I had another fiddle. Apologies to anyone who actually knows about electrics....Anyway the connectors to the ballast resistor looked a bit loose so I bridged them and bypassed the ballast. Then connected a wire directly from the battery to the + of the coil. Turned the key and she started! She's such a good old girl and will do her damnedest to start for me even if electrics are wired up in a Heath Robinson manner. New ballast resistor and coil I think should solve this properly.
Cheers
Joe
Cheers
Joe
As soon as I read the thread I thought ballast resistor and 6V coil.
Back in the 1980's I had a Clan Crusader (Imp based car) and for some reason the factory used a ballast resistor wire and a 6 V coil. Played havoc with any electronic ignition and of course swopping to a "spare" coil in the garage didn't help as it was a 12V coil.
Back in the 1980's I had a Clan Crusader (Imp based car) and for some reason the factory used a ballast resistor wire and a 6 V coil. Played havoc with any electronic ignition and of course swopping to a "spare" coil in the garage didn't help as it was a 12V coil.
hello again all,
So I replaced the ballast resistor and the coil, as well as all the HT leads with new items and cleaned all the plugs. Some of the HT leads had certainly seen better days... Anyway, she starts up now which is great but nowhere near as easily as she used to before she failed. Used to be that she would fire up almost as soon as you touched the key, now she turns over a few times before starting. Rather stupidly I didn't change the rotor arm (just cleaned it) nor distributor cap so I'll do those next. However, still perplexed over what a coil should and shouldn't do - I read the voltage across it and whilst on tickover the voltage fluctuates between around 5.5v and 2.5v, sometimes reading almost 0v - is this normal or is my multimeter not reading quickly enough, ie does the voltage fluctuate between 0 and 6v through the engine firing cycle? Sorry for being a auto-electrical numpty, just trying to understand what should be happening!
Thanks
Joe
So I replaced the ballast resistor and the coil, as well as all the HT leads with new items and cleaned all the plugs. Some of the HT leads had certainly seen better days... Anyway, she starts up now which is great but nowhere near as easily as she used to before she failed. Used to be that she would fire up almost as soon as you touched the key, now she turns over a few times before starting. Rather stupidly I didn't change the rotor arm (just cleaned it) nor distributor cap so I'll do those next. However, still perplexed over what a coil should and shouldn't do - I read the voltage across it and whilst on tickover the voltage fluctuates between around 5.5v and 2.5v, sometimes reading almost 0v - is this normal or is my multimeter not reading quickly enough, ie does the voltage fluctuate between 0 and 6v through the engine firing cycle? Sorry for being a auto-electrical numpty, just trying to understand what should be happening!
Thanks
Joe
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