S3C WONT START
Discussion
HI all i went to start her up today and no go, turns over fine and nothing just wont fire up,checked for a spark at the plug end and nothing ht lead of dizzy cap and still nothing,i put the meter on the coil and i have 6 volts with ignition on and stays at 6 volts when engine is turned over is this right or should it rise is it the coil gone nige.
You should have 12 volts plus, with ignition on, 9 volts or so minimum when cranking. What's the battery voltage? Do the headlights light up normally? Do the wipers and indicators work normally?
Anybody see where I'm going here?
(ETA and no, I don't think it's the coil)
Anybody see where I'm going here?
(ETA and no, I don't think it's the coil)
Edited by tvrgit on Monday 6th June 20:10
Looks like u guys were right i replaced the coil today with a intermotor 11330 same problem still got 6.6 volts at the coil, but if i remove the wires from the coil and test them straight to the meter i get 12 volts ? if u see what i mean,not to sure were to check next maybe ignition amp i think i need some help on this one guys nige.
Forgive me if I have got this wrong, but it sounds to me as if you are measuring the voltage across the two coil terminals (and then the two wires disconnected from those terminals)?
If so, you're not getting a reliable reading - the "supply" side of the coil should be more or less steady at battery voltage, but the "trigger" side will fluctuate (that's what makes the coil spark!) and I suspect that, if you are connecting the meter as above, the reading you are getting is an average of the highs and lows as the engine turns, because the meter can't react quickly enough.
What you need to do is connect the "earth" side of the meter to a known earth, and then test the voltage reaching the supply side of the coil, both with ignition on, and then cranking.
You also need to make sure that the body or bracket of the coil is earthed - you don't say if it's mounted on the engine or the body, but if it's on the fibreglass body, it needs an earth or it won't trigger properly. Then no sparky!
AFAIK, you can't really test the "trigger" side of the coil with an ordinary voltmeter - you need an oscilloscope or something that can measure wave forms to check the high and low of that trigger voltage.
If the coil is getting a good supply, and is earthed, and since the one you are using is new, this would suggest that if there is still no spark, it's the trigger side - either the hall sensor, the ignition amp or the signal between those and the ECU.
If so, you're not getting a reliable reading - the "supply" side of the coil should be more or less steady at battery voltage, but the "trigger" side will fluctuate (that's what makes the coil spark!) and I suspect that, if you are connecting the meter as above, the reading you are getting is an average of the highs and lows as the engine turns, because the meter can't react quickly enough.
What you need to do is connect the "earth" side of the meter to a known earth, and then test the voltage reaching the supply side of the coil, both with ignition on, and then cranking.
You also need to make sure that the body or bracket of the coil is earthed - you don't say if it's mounted on the engine or the body, but if it's on the fibreglass body, it needs an earth or it won't trigger properly. Then no sparky!
AFAIK, you can't really test the "trigger" side of the coil with an ordinary voltmeter - you need an oscilloscope or something that can measure wave forms to check the high and low of that trigger voltage.
If the coil is getting a good supply, and is earthed, and since the one you are using is new, this would suggest that if there is still no spark, it's the trigger side - either the hall sensor, the ignition amp or the signal between those and the ECU.
tvrgit said:
You also need to make sure that the body or bracket of the coil is earthed - you don't say if it's mounted on the engine or the body, but if it's on the fibreglass body, it needs an earth or it won't trigger properly. Then no sparky!
I dont understand this bit Andrew... why does the coil bracket need to be earthed ? mines on the fibreglass body and not earthed and it works ok (so far anyway 
)I'm not contradicting you, I honestly dont know why it is needed... maybe I should make an earth before something goes wrong ?
K
tvrgit said:
Forgive me if I have got this wrong, but it sounds to me as if you are measuring the voltage across the two coil terminals (and then the two wires disconnected from those terminals)?
If so, you're not getting a reliable reading - the "supply" side of the coil should be more or less steady at battery voltage, but the "trigger" side will fluctuate (that's what makes the coil spark!) and I suspect that, if you are connecting the meter as above, the reading you are getting is an average of the highs and lows as the engine turns, because the meter can't react quickly enough.
What you need to do is connect the "earth" side of the meter to a known earth, and then test the voltage reaching the supply side of the coil, both with ignition on, and then cranking.
You also need to make sure that the body or bracket of the coil is earthed - you don't say if it's mounted on the engine or the body, but if it's on the fibreglass body, it needs an earth or it won't trigger properly. Then no sparky!
AFAIK, you can't really test the "trigger" side of the coil with an ordinary voltmeter - you need an oscilloscope or something that can measure wave forms to check the high and low of that trigger voltage.
If the coil is getting a good supply, and is earthed, and since the one you are using is new, this would suggest that if there is still no spark, it's the trigger side - either the hall sensor, the ignition amp or the signal between those and the ECU.
ok yes that is how i measured it first of all across the two terminals on the coil and got 6.6 volts i have done as above and ran a seperate earth to the meter and i have 9.8 volts and about 9 volts when cranking ? still got 12.56 at the battery what to do next nige. If so, you're not getting a reliable reading - the "supply" side of the coil should be more or less steady at battery voltage, but the "trigger" side will fluctuate (that's what makes the coil spark!) and I suspect that, if you are connecting the meter as above, the reading you are getting is an average of the highs and lows as the engine turns, because the meter can't react quickly enough.
What you need to do is connect the "earth" side of the meter to a known earth, and then test the voltage reaching the supply side of the coil, both with ignition on, and then cranking.
You also need to make sure that the body or bracket of the coil is earthed - you don't say if it's mounted on the engine or the body, but if it's on the fibreglass body, it needs an earth or it won't trigger properly. Then no sparky!
AFAIK, you can't really test the "trigger" side of the coil with an ordinary voltmeter - you need an oscilloscope or something that can measure wave forms to check the high and low of that trigger voltage.
If the coil is getting a good supply, and is earthed, and since the one you are using is new, this would suggest that if there is still no spark, it's the trigger side - either the hall sensor, the ignition amp or the signal between those and the ECU.
nigegas said:
what to do next nige.
My advise is to get an auto electrician to look at it. The symptoms you're describing suggest there is a wiring problem, but I don't think you're familiar enough with electrics for it to be sensible to try to diagnose yourself. That's not a dig, just an honest opinion. 
, coil mounted on fibreglass, no earth , no problems.ketvrin said:
I dont understand this bit Andrew... why does the coil bracket need to be earthed ? mines on the fibreglass body and not earthed and it works ok (so far anyway )
I'm not contradicting you, I honestly dont know why it is needed... maybe I should make an earth before something goes wrong ?
K
Hmmm... when you think about it, neither the primary nor the secondary widings are earthed to the case - yet I can distinctly remember being told in my "learning stage" (which started 42 years ago and is still continuing) that a good earth was essential. Now that I think about it, perhaps that has more to do with radio suppression (ie the coil case then acts as a Faraday cage and contains interference from the build up and colllapse of the magnetic field through the windings) than with the working of the engine... )I'm not contradicting you, I honestly dont know why it is needed... maybe I should make an earth before something goes wrong ?
K
The other possibility is, of course, that I am talking b
ks...GreenV8S said:
nigegas said:
what to do next nige.
My advise is to get an auto electrician to look at it. The symptoms you're describing suggest there is a wiring problem, but I don't think you're familiar enough with electrics for it to be sensible to try to diagnose yourself. That's not a dig, just an honest opinion. What you could try, is running a piece of wire (preferably with an in-line fuse) direct from the battery to the coil positive, and see if the car starts then. Be very careful if you try this, and do it as a diagnostic test only - don't leave the car running like that for more than a few seconds.
That would confirm whether the wiring fault is on the supply side, or the "trigger" side, but doesn't get you any closer than that, to where that fault actually is.
GreenV8S said:
My advise is to get an auto electrician to look at it. The symptoms you're describing suggest there is a wiring problem, but I don't think you're familiar enough with electrics for it to be sensible to try to diagnose yourself. That's not a dig, just an honest opinion.
yes electrics is not my strong point i know just trying to have a go really the only way to learn so to speak,but thanks for the advice as i have only had the car a few months my first tvr s and what a great car it is when its running so all advice welcome nige.Auto-electrician may well be the way to go but before you call them in I would do some extensive visual checks to see if you can spot the problem before you pay someone else to do it for you...
check the condition and connections of each wire in the ignition circuit, look and feel for chaffed, burnt, crushed or just plain knackered wires and insulation,
check the connections for verdi-gris (the grey/green corrosion that builds up on these.
check your fuse box to ensure fuses are clean and a good fit.
check for any unexplained/spurious wires that might be a previous owners attempt at an immobiliser. (mine had wires twisted together beneath the dash and then just hanging...)
check any alarm connections (my car had two knackered alarms fitted)
Yellow connector ?
just common sense stuff before you get someone in to investigate the smoke and mirrors of auto-electrics.
hopefully you will spot something obvious and be on your way again.
good luck
K
check the condition and connections of each wire in the ignition circuit, look and feel for chaffed, burnt, crushed or just plain knackered wires and insulation,
check the connections for verdi-gris (the grey/green corrosion that builds up on these.
check your fuse box to ensure fuses are clean and a good fit.
check for any unexplained/spurious wires that might be a previous owners attempt at an immobiliser. (mine had wires twisted together beneath the dash and then just hanging...)
check any alarm connections (my car had two knackered alarms fitted)
Yellow connector ?
just common sense stuff before you get someone in to investigate the smoke and mirrors of auto-electrics.
hopefully you will spot something obvious and be on your way again.
good luck
K
HAY HAY now up and running again i was looking under the steering column and found a choc connector with 3 wires the earth was hanging by a thread so i sorted the wires out turned the key and she fired up straight away and on the plus side i have a spare coil happy days thanks for all the help guys nige.
nigegas said:
HAY HAY now up and running again i was looking under the steering column and found a choc connector with 3 wires the earth was hanging by a thread so i sorted the wires out turned the key and she fired up straight away...
On monday I said:
You should have 12 volts plus, with ignition on, 9 volts or so minimum when cranking. What's the battery voltage? Do the headlights light up normally? Do the wipers and indicators work normally?
Anybody see where I'm going here?
Where I was going at that point was the yellow ignition connector - but your voltage readings later seemed to contradict that. Anybody see where I'm going here?
Ah well...
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