Follow up on "A very annoying problem"

Does the distributor look like it's got a fair bit of oil accumulated in it when you take off the rotor and dust cover to look inside? There is an o-ring seal around the base of the distributor where it fits into the cylinder head cover, but the distributor shaft would wear over time and oil could get in around the shaft itself.

Have you tried a new distributor cap? If the cap has hairline cracks they can become conductive and short the ~40 KV pulses from the coil away from where they're supposed to be going, but unless it stopped all the spark plugs from getting their HV pulses, the engine wouldn't just stop.

I agree that the problem seems to be electrical in nature. I own a 1983 and a 1985 C900, and both of those have been giving various electrical issues recently. They're 20 year old cars though so the electrical wiring is bound to give problems at that age.

When the car 'dies' what does it do when you (or your daughter) try to start it again? Does anything at all happen? Or nothing? What happens to the dash lighting, etc. if you turn the ignition key all the way to off, then back around to 'run' without trying to start the engine? I would have a look at the ignition switch itself and see if the electrical portion of the switch has a fault, or the wiring to it is faulty.

Also check the ignition lock relay in the fuse/relay panel above the left-front wheel to make sure that isn't faulty. While you're at it, make sure the fuel-pump relay works too. If you can hear relays clicking and the fuel-pump running after moving the key back to off then around to 'run' again if the car dies mid-flight for no reason, I'd say the problem is going to be in the wiring or components of the ignition system.

Can you get the engine to turn over (even if it doesn't fire again) after the car dies mid-flight? If yes, that proves that the starter is ok and that some of the wiring from the ignition switch is not damaged.

Regards,

Craig.

PS. Your email address is Australian - I'm in the Sutherland Shire part of Sydney. Let me know if you're local and we can arrange to meet up.

Hi Pete

The distributor cap has a piece of carbon (with a spring behind it) which presses onto the distributor arm. The carbon brush wears and you get the sooty material.

You said (in your previous message) you replaced the plug leads you should replace the cap and the rotor arm. Whilst you are at it, when were the conventional points replaced. I seem to remember me replacing them (the points) every couple of years. For the work that was involved it was not worth reseting the old ones ... which always got pitted and thus could not be set accurately.

I think you should replace all 3 components. They are cheap enough.

Regards Charles

Agreed. Something I noticed the other day when I replaced the cylinder head cover in my 8V NA car was that the mechanical advance in the distributor (1983 900S - no hall-effect in our C900's until 1985 apparently) doesn't do anything. The Bentley manual says something like 'turn the rotor 1/8 of a turn and it should spring back'. Good in theory, but nothing like that happened. I didn't try to test the vacuum advance as I don't have a vacuum pump, but the whole distributor is going soon when I convert the car from points ignition to hall-effect. I've got a new hall-effect distributor coming, and already have everything else I need.

Craig.

You do not need a pump, just disconnect the hose at the manifold and suck on it! If the vacuum unit is ok, you should see the mounting plate move.

Thanks guys, all good advice. Craig...yes there is certainly a small pool of oil resting inside the lip of the metal body of the distributor when I take the cap off. Maybe the seal needs replacing. It was night time when I finally had the car fault whilst I was driving it so it was hard to tell what the "moist feel" was inside the cap, mixed with the sooty material (I agree with Charles that this is probably the carbon brush). I guess the oil could be affecting the spark, but then why does it always happen a few minutes after starting on a damp day! My service guy has suggested some work on the distributor....points, cap, rotor, etc. But suggests I have a few more "incidents" first and see if cleaning the cap fixes it evrey time to get a better diagnosis. I've given my daughter good instructions on how to do it Craig, regarding how it "dies". It first loses power, splutters and you are forced to pull over. It then idles but splutters when you throttle it. Then often it stalls. The starter motor turns the engine over well and all dashboard lights are normal. Sometimes it will restart and continue to run rough, sometimes it won't restart. Leave it for 20-60 minutes and it starts again and runs normally.

Pete

Charles C. wrote:

Because as the engine warms up the distributor, the trapped moisture can turn to water vapour which is the actual cause of the problem.

Graham

Ah didn't realise that would move it - dunno what 'quantity' of vacuum pressure is needed but will give it a go tomorrow.

Craig.

Ah well that makes electrical problems less likely then. How is the fuel pressure all this time? Check the central carbon contact in the distributor cap to be sure that isn't the cause, though if the starter is ok and the interior electrics behave as they should, and the engine doesn't just 'die' totally, it sounds like electricals aren't the cause IMHO at least.

If you have a good Saab tech available near you, get them to check out the fuel system, specifically the fuel distributor, etc. just in case something is going wrong with the airflow sensor unit. It's a longshot and I'm not a guru with K-jetronic, but checking things out from other angles can't hurt.

Craig.