Any V8 ignition experts kicking about?

[fesuvious]

Hi, I have a wierd problem with my 3.5 V8, Its got a Mallory Distributor being fed from a 6v coil with ballast resistor.

I have no spark. I have confirmed I have 12volts from ignition switch to the ballast resistor BUT, as soon as this cable is connected to the BR it immediately drops to 10volts. There is only 4volts coming out of it.

I could swear that for a split second earlier when I was testing I saw 6volts coming out, but only once.

This problem has been intermmitent, and arose on left hand corners (which was wierd). I put it down to a fuel issue and rebuilt all the lines and fitted a new pump. However, after a test run last night where on a hard left turn she would kangaroo she then just died when ticking over. She had no spark.

Everything I have read suggests that a solid 12volts should go into the BR but then 6V should come out to the coil. As Iv said, I have a 12v feed which then drops to 10v on connection and the BR is only sending 4v to the coil.

A few of the readings from the BR have been erratic during my atempts to find the problem. I suspect I have, and its the BR but is there anyone on here with more knowledge than me that has an idea?

Thanks

[kizz81]

sounds like a short out or a bad connection

[Lucy1978]

can you not just ditch the BR and put a 12v coil on it, or is there some odness with a mallory that requires a 6v coil?

Oh and if I remember correctly there should be 2 suplies to the coil, one that's live when the vehicle is being cranked (12v ballasted by the current drawn by the starter) and one that is live when the vehicle is running, that goes via the ballast resistor (12v in 6 out).

[fesuvious]

Would a 12v coil need the 'boost' from the starter motor feed to provide the spark still?

[Lucy1978]

From what I remember you just, plug both wires on to the +'ve side of the coil, i.e. move the current feed to the BR to the coil +'ve.



Curently you should have a  feed which is live whilst the ignition is in the cranking position this should go direct to the +'ve side of the coil.  There should also be a 12v feed which is live whilst the ignition is in the run position, this will currently go to the ballast resistor and then from the BR to the +'ve side of the coil. 

Both of these are effectively 12v feeds, but the one that is live only whilst the starter is turning is effectively ballasted by the starter motor drawing so much current, (so it doesn't need the BR to stop it blowing a 6v coil)  The other feed is 12v all the time, as once the engine is running (as long as the electrics are working fine) there's no huge current draw to sap the power from this suply, so it needs a BR to stop it blowing the 6v coil.

If you fit a 12v coil, it will cope with running at the reduced power whilst you're cranking the engine, but will also cope fine with the unballasted 12v supply whilst the engine is running.

If I were you I'd have a good check through the wiring and check there's no loose connections anywhere and that all the earths are good too.

Hope this helps and doesn't confuse you further.

[300TDi Disco]

Where abouts in solihull are you??? pm me..

[Range Rover Blues]

If it were me I'd also be checkoing where the 2volts or so is going.  Connect the vloteter between the battery and the 12volt input to the coil, check the reading is almost zero, if not you have a supply problem, ignition switch, relay or winring depending on what's fitted.

Check the ground resistance through the points with the coil disconnected.

Check that the battery is fully charged