HA coil and resistortrouble

[Bob perry]

Evening all. I've been chasing my tail with a non starting viva for some time now,as many of you will know!

Originally a blocked fuel line,which I cleared.Then a full clean out of the carb. Engine fired up and stopped almost immediately.
Timing checked. Valve clearances checked and set. Still the same.
So on to the electrics.
Spark, but a bit weak!. Points checked and set. New plugs fitted. New condensor fitted.
Same problem, full throttle and die off immediately.
Cleaned coil terminals and refit.
Engine actually ran for about five minutes!!, but very lumpy, with massive back fires and sounded a bit choked.

Then I noticed that the resistor on the coil was red hot!!

Now my vehicle is a late one with Negative earth, and I've only found one copy of a wiring loom for negative earth. Every manual I read talks about Positive earth, even the Genuine Vauxhall manuals.

I am wiring the white wire to the resistor and positive terminal on the coil, plus the white/blue wire to the positive terminal also.
The black and white wire is from distributor to negative terminal on the coil.
All as per the negative earth wiring diagram.

Am I doing right?, and has anyone else experienced a similar problem? Will a new coil and resistor cure the problem?

Al help appreciated.

[thomas]

I can only offer a picture (and on an HB, but no difference).



The white wire connects to one of usually two lucar/spade terminals present on the resistor and thus through the resistor, the white/blue connects under the resistor, bypassing it and connecting directly to the coil (the original differently sized spade connectors make error here unlikely). The resistor should only get over-hot if ignition is left on and engine is not turning (points not opening and closing). In my experience the resistor when overheated fails closed, its resistance drops to near zero, subjecting the coil to increased primary voltages at all times, in turn potentially causing the coil (and condenser) to fail eventually, as well as burning out the points more quickly.

I think that part of the rationale for this setup (and it wasn't unique to Vauxhalls) was that batteries then were poor, low-spec, and couldn't supply a decent voltage to the coil when the starter was cranking, a situation not helped by dire dynamos that couldn't keep even a good battery well-charged; nowadays stone cold well below freezing with correct (thickish 20w50) oil, these engines spin over well with healthy sparks. If, as I suppose -you have a decent battery and can replace the dynamo with an alternator, then all reasons, other than originality, for retaining this ballast setup are void. One other advantage of the ballast setup was that arcing at the points was reduced with the lower voltage, a constant 12V coil would reintroduce this problem, wearing/burning out points more quickly even with a good condenser. There is one obvious solution to all these issues noted, and many others such as variable/inconsistent points gap from one distributor cam lobe to another ...

I cannot recommend highly enough replacing the coil/ballast setup with a coil designed for constant 12V operation, eliminating the ballast resistor, and at the same time eliminating the points and condenser by fitting one of the electronic kits that fit entirely inside the distributor itself. Faultless and fuss-free, easy to fit, huge juicy sparks, starts in all conditions.

Substituting components, the coil, ballast resistor, condenser is one way of fault-finding, never to be sneezed at, but any outlay could be not much less than the magic wand of a new 12V coil and electronic-ignition kit.

These are just examples, many alternatives are available:

http://www.simonbbc.com/ignition-coils/ ... ition-coil

http://www.simonbbc.com/electronic-igni ... -kit-delco

[Bob perry]

Great response Thomas and thank you. Can't wait to get home tonight now and get stuck in!
One question though, does it matter that my vehicle is negative earth? and would it affect which way the wires are attached to the coil + and -?

[thomas]

As you describe it in your own post, the white live feed goes to the +ve terminal of the coil (sometimes called SW on wiring diagrams, from ignition SWitch) and the short wire from the distributor, whatever colour goes to the -ve terminal on the coil (sometimes called CB, Contact Breaker). This is absolutely correct and as it should be with negative earth. The electronic ignition kits are designed solely for negative earth, positive earth vehicles being a special case and kits for these would be difficult if not impossible to find.

Very lumpy running, popping and backfiring could also be valves not fully closing due to tappet clearances being out, one or more being too tight and a valve not closing properly, possibly causing unburnt fuel to enter the exhaust system. As an outside chance, the firing sequence is wrong, trace each individual spark plug lead back to the distributor cap, the firing order is 1-3-4-2 and looking down at the distributor, it turns anti-clockwise. 4-cylinder engines with the plug leads mixed up rarely ever run at all though as two out of four cylinders at a minimum would be wrong. It might help too look at the running engine in the dark, to see if any HT lead is failing, burned or chafed, and the spark being lost, jumping from the lead to any adjacent metal that is earthed

Can't think of anything else at the moment that would help and have to run.

[Bob perry]

Brilliant Thomas. Lots to work with and thanks for your help. I will get back when we have lift off!!