Had problems starting the old SD1 so decided to take a look. The distributor cap was burnt round the centre electrode - and the carbon brush stuck or worn down to nothing. It's a Mallory Unalite and has only done a few thousand miles. A new cap sorted things. Any guesses what caused this?
Excessive voltages compared to what the cap was designed for. I'd be looking at three things.
1) Non standard ignition system or coil. 2) Excessive plug gaps. 3) Too much clearance between rotor arm and distributor cap contacts caused by worn or incorrect rotor arm.
Or a sticky spring under the electrode.
Well, obviously since it's not a standard distributor. ;-) The Unalite has no points and an electronic driver built in - rather the same as the original unit. I did fit a ballast resistor as advised.
No - quite new and correctly set. Plug leads new and checked out ok as well.
As I said a new complete distributor.
I am using the standard coil, though. The blurb said their (expensive) one would be better. But then they would, wouldn't they? ;-)
You could check out the rotor to cap phasing, especially as you're non standard. It's a common problem on V8s. I've got a scrap cap that I've eaten away with a die grinder so I can run the engine and check rotor phasing with a strobe.
Julian.
6 volt coil with 12 volts running through it? Spark plugs wrong rating or gap? Knackered plug leads?
The distributor is designed for the RV8 by Mallory. Do you mean it might be firing with the rotor between plug contacts? Don't see how it can.
No - the original coil and the car has electronic ignition from new with no cold start system.
No - the same KLGs I've always used.
And pretty new.
Checked those.
I'm thinking the carbon brush must have jammed.
It's certainly possible, cylinder cross firing can be a problem if taken to an extreme. If your dizzy is running more mechanical and vacuum advance than standard and not had the rotor phased correctly then it could be a problem - it's just a thought, probably not too likely. On the Mopar stuff you can buy reluctor (trigger) wheels with off-set keyways to correct the problem.
I see you've have a ballast resistor, are you absolutely sure that the wiring is OK? I Think you should be seeing about 6 to 8 volts to the coil+ when the engine is running at idle.
(As an aside, the FBO system on my Mopar engine has a driver operated switch to short the ballast resistor. It's to get maximum energy sparks for launches at the drag strip etc and limited to a minute every 1/2 hour IIRC....)
Julian.
Yes - I can see that.
As I said it's as supplied.
Right. I will be changing to programmable ignition when the weather gets better - the unit is built and ready to fit, so will be able to optimize the positions. If I don't go the whole hog and fit an EDIS system.
As per the supplied diagram.
In this case it's to limit the current to the electronics in the distributor, than than for cold start. The coil is an ordinary 12 volt one.
If this gives an improvment surely it would be possible to have the higher energy all the time?
Dave Plowman (News) brought next idea :
When that happened to me once, I blamed it on a sticking carbon centre electrode. Make a point of checking the electrode is free to move before you fit it and every time you check/change the points.
It's my guess too. Although considering the cost of the unit a bad show.
No points.
It's really well worth the effort to check, many people have been gobsmacked at how much out rotor phasing can be, even as standard the manufacturer's tolerances are ''ball-park!''
You need an old dizzy cap. Cut a big kidney shaped lump out of the top, between #1 (or any, it doesn't matter) tower and the king tower. Install, connect strobe to appropraite lead and run the engine. You may be amazed at how much the rotor swings away from ideal as the advance kicks in. It isn't really a bother with pissy little 4 pot motors because there's so much space in the cap, but a V8 is cramped as a rule.
Many folks, after correcting poor phasing are delighted with the results, all those odd elusive misfires that you can't quite seem to track down disappear!
Yes, but slip an AVO between Coil+ and earth with engine running - just make sure that the wiring is doing its stuff....
AIUI if you have a ballested ignition system, (and the ballast is bypassed when you crank the starter) then the coil should be an appropriate one too. If you run a 12v coil through a ballast during normal running you'll be getting a poor spark?
AIUI It's mainly to do with heat build up in the electronics and coil, ie running beyond it's rated capacity is short term allowable.
Julian.
Apparently not as that's what Mallory recommend. It's likely a different value from those commonly used for cold start apps. Probably rather lower
- just to limit the maximum current the electronics can take to a safe level.
Then use higher rated components? But I always thought the spark had to work hardest with a lean mixture - so is unlikely to restrict maximum power?
I see, makes sense, it would be interesting to know what its resistance was. Sandard Mopar solution was to use ballast units wound in ceramic insulation, at idle when current through the coil was high the ballest would heat, increase resistance and lower the currect - a crude form of self regulation I suppose.
We're just moving away from engines running stock systems a bit here. This system provides twice the rated output of Mopar's stock system without the boost facility, and will provide solid flawless sparks at almost 9000rpm - take a look here if you want, you'll get the idea:
Julian.
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