924Board.org

[maybeoneday]

Ok, so I go to investigate spark a little further. I was made aware that this may not be as reliable as I had thought when I was compression testing and noticed that my plug leads were not giving a consistent spark against the rocker cover where they were resting.

Anyway I changed the plug leads as the old ones looked... well old, and a resistance test gave me an open reading on one. So with new plug leads on I decide to check the figures of the rest of the ignition system before I tried to start it again.

I check the resistance of the balast resistor which comes out as 1.5 ohms. Then I check the ignition coil primary and get 1.6-1.9 ohms, and move to the ignition coil secondary where I get 14.7k ohms.

So I go to check this with the haynes manual and the figures are different but so is the ignition setup. Ok no problem maybe the porsche manual has the figures... No, only has them for transistorised ignition setup as well.

What I appear to have is a non transistorised ignition with points, except the distributor has been gutted and I no longer have points but a... well... red thing. Which I assume is an electronic ignition module of some description, that was fitted after someone got sick of changing points. The puzzle gets bigger, again. So while the next step was to do a voltage check at the coil and balast resistor I decided that I needed to get some reference figures first.

So assuming that this red thingy does what it is supposed to do, and removes the points effectively, where can I get some better info about the ignition setup in my car (stuff like voltage and resistance figures of the coil and resistor would be a good start)?, and does anyone know how I can tell if the red thingy is doing what it is supposed to do?. Also my tach does not work and I was hoping to figure out why during this diagnosis of the ignition system except the wiring diagrams are all for the transistorised ignition, will this matter or will I need a new wiring diagram also?

I read somewhere that the 924 is a difficult beast at times, they were not joking.
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1977 924 NA Auto

[Ozzie]

pm sent
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[Muz924]

I have some parts from my 'points' model car, distributor & coil your welcome to use to swap around.

Cheers,
Santo
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1978 924 RoW 5-Speed (Current Project)
1980 924 RoW 5-Speed (Donor Car)
1985 Alfa Romeo Alfetta GTV 2.0 (Previous Project Car)

[maybeoneday]

thanks guys, I may need to take you up on that offer muz.

Advanced a bit from where I was the other day. A little investigation on the net showed that the module in my dizzy is a Hotspark ignition. So from their information I found out that they want a 3ohm primary coil resistance. A balast resistor of 1.5 ohms in series with the coil giving 1.6 ohms, and accounting for internal multimeter resistance and crap in my engine bay we are at about 3 ohms. OK. Voltage test at the coil gives 1.5v on coil ground terminal, 7.5v on coil positive terminal, and between 11.5v and 12v coil supply (just before resistor). These figures all seem ok, coil supply is a little low but this was after it had be cranked a few times and had a few other things run off the batt without a top up charge, so I am happy with it.

A few other things to note, I am getting good consistent spark on wires 1 and 2 but not on 3 and 4 (used and inductive pick up on the bottom of the plug wires to check). 3 and 4 go from firing once every 2 or 3 cycles to not firing at all. When I started to check this they were firing semi consistently now they are hardly ever firing. Thinking that the problem is probably in the hotspark module or its setup. Looking at it, it looks set up right, according to the internet instructions, but things like air gap and pick up height I cant and dont know how to check. I will try a new cap and rotor (I think I did both of them already when I got it but I am not 100% sure and it cant hurt, plus they are not expensive).

I think on the fuel side we are fixed and on the timing side we are good so I hope this is almost the end and it will go soon.
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1977 924 NA Auto