Where to start if your CF is misbehaving and you're not sure where the problem may be.

Re: Starting problems

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Post by Phil Bradshaw » Club admin » Sat Aug 04, 2018 3:30 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3733
Wikis are fine for an intro but keep in mind that opinions may vary, just like on forums... :)

One thing that puzzles me is the capacitor on the coil positive terminal: it's not listed in the GM catalogue for CF2 models so I assumed it isn't needed (like on contact breaker systems but for different reasons). However ...

Back in the 1980s (Lucas HEI on BL models I worked on then - same system basically) modules could be sensitive enough to drop some of their balls if ripple frequencies coming in once an engine is running began to interfere with the front end (or back end or both - ripple ain't fussy what it interferes with).

It shouldn't make any difference at cranking speed though: module has bigger things to contend with due to supply voltage drop and low reluctor output at low rpm; just getting sparks out at all will be a success.
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Starting problems

Post by flipflop » Sat Aug 11, 2018 8:24 am
Joined: Sun Nov 12, 2017 5:55 pm
Posts: 21
I'll leave the capacitor disconnected for now and see how it goes. The multimeter finally arrived (broken) so I've sucked it up and bought one from Argos. Primary resistance is 1.5 and secondary is 5700 so can I assume the coil is OK? Got really lucky and found a German seller with a distribution cap so I've ordered that just so I can cross it off my list of suspects. Also ordered a beast of a battery with 800 CCA as I'm not convinced the current one's up to the task. Having said that, the bloke who had it before me was running it off a leisure battery.

Were/are you a mechanic Phil? Thanks again for the help here. Your karma points must be through the roof.

Re: Starting problems

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Post by Phil Bradshaw » Club admin » Sat Aug 11, 2018 12:37 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3733
Coil primary and secondary winding resistances appear to be good.

I've been doing some digging: looks like the capacitor is needed on the coil positive terminal because there isn't one large enough in the module to kick off oscillations needed for spark sustain, as for contact breaker ignition when the points open.

(Capacitor and coil together form what's known as a resonant LCR circuit, L being the reactance of the winding, C the capacitance and R the resistance which mostly is that of the primary winding, resistance due to the capacitor being very low in comparison.)

Now I've reminded myself about so much that I'd forgotten :oops: here be a rough and ready test procedure for narrowing down the possibilities.

Capacitor checks

With the capacitor wire connected to the coil positive and all other wires disconnected there should be a spark from the HT lead to ground every time the coil positive and negative terminals are flashed with 12V from the battery (spark occurs on disconnection).

If no sparks then try a new capacitor. Any capacitor for ballasted contact breaker systems (about 0.1µF for 1.5Ω coil primary) with integral support bracket should do if the wire is long enough. E.g. Intermotor 33450 or equivalent for BL, Peugeot/Renault/Talbot (swap bullet for spade terminal).

If a new capacitor makes a lot of difference then you may have found the problem: throw everything back together and try starting the engine.

If no difference then suspect faulty coil (e.g. internal HT short to ground). Bog standard 1.5Ω for ballasted contact breaker ignition should do at a pinch, e.g Intermotor 11070 or equivalent.

Reluctor checks

With your shiny new multimeter the reluctor winding resistance can be checked: go for the two wires connected to the module but disconnected from the module for a resistance check.

Resistance should be about 1kΩ or a bit more. Fail is open circuit (lots of kΩ to infinity depending on meter) or short circuit (much less than 1kΩ for only some windings shorting, zero for all shorted).

Digital meter switched to AC low Volt scale may register reluctor output at cranking speed (depends on meter screen refresh rate) but a cheap'n'cheerful analogue meter will do it better -

Image

Usually under £5 from cheap shops ('DC/AC 1000V analog' on eBay). Battery (1 x AA) can be a tight squeeze but it will go in!

On AC low Volt scale the pointer should kick every time a reluctor pole (pointy bit) passes the permanent magnet at cranking speed; with the spark plugs removed for the starter to spin the engine faster the meter may indicate a steady reading.

If reluctor winding resistance is ok and there is any output and the coil sparks when tested then suspect faulty module.
Were/are you a mechanic Phil?
I've been mending Bedfords for nearly 50 year: part of the ship, part of the crew. :)
I've been messing with electronics for a bit longer...
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Starting problems

Post by flipflop » Sat Aug 18, 2018 8:08 am
Joined: Sun Nov 12, 2017 5:55 pm
Posts: 21
Phil, thanks as ever for the epic advice. I'm sure you've saved me a small fortune in garage fees. It's unusual to get this level of help in a forum.

To the issue... The lightest of touches and this happened

Image

So off I went and ordered a new one. I went for the intermotor 33450. New battery also arrived, went for a 920 CCA in the end. I hooked it all up yesterday and gave it a blast... To no avail. I added my spark plug tester (flashing light thing) which showed me there was no spark from the coil to dizzy at all. Hmm very odd. Just for testings sake I then removed the capacitor and lo and behold, a spark!

The beast even fired up! Although died instantly... (With no capacitor, is this the spark sustain issue you mentioned?)

So I'm about to do the capacitor and reluctor checks you've very generously given in detail and will let you know how it goes!

Edit: Before trying the checks I rewired the capacitor with a ring terminal - I must have done it wrong initially because it started instantly! Caught me completely off guard. Trading at a busy station today so I'll wait for the next trains to go and try again

Re: Starting problems

Post by flipflop » Sat Aug 18, 2018 9:38 am
Joined: Sun Nov 12, 2017 5:55 pm
Posts: 21

Re: Starting problems

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Post by Phil Bradshaw » Club admin » Sat Aug 18, 2018 3:05 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3733
Excellent news.

I've been burrowing under the lid of modules for Bosch and Lucas EFI: same architecture and NO output capacitor on board. Lucas EFI has a capacitor stuffed in with the module so the capacitor on your coil must be essential, as you've found out. :)

Which just about sews it up I think: fault was a duff capacitor which you've fixed with a new one.

A bit cheaper than a new engine ... :lol:
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Starting problems

Post by flipflop » Mon Aug 20, 2018 6:41 am
Joined: Sun Nov 12, 2017 5:55 pm
Posts: 21
Absolutely! It took a while to narrow it down but going through and testing things logically with your advice has given me a better understanding of how the ignition system works in general which can't be a bad thing!

Thank you for your patience, I'd still be staring at it scratching my head without the help.

Having been buried in amongst it all I'm now sick of the grease, especially on the wiring and the cables/lines that don't go anywhere get on my nerves. I think I might have caught a mechanical bug that I can't shake - time to tinker forth into the unkown

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