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Cold start hesitation

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Old Feb 17th, 2021, 10:30   #11
Clifford Pope
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Update:

Having replaced the plugs, tried swapping in a complete ignition set with cap from the last time I needlessly replaced them, cleaned again unnecessarily fuses 4 and 6, needlessly replaced the fuel pump relay, run injector cleaner through the system, none of which made any difference, I think I finally may have cracked it.

I noticed the radio suppression capacitor on the coil, and tried unplugging it, for want of anything else to do, and the the result was an instant and dramatic improvement to the idle smoothness.
I've never read anything about them, just grown accustomed to odd components being earthed with capacitors. No one else has ever reported any faults, so checking them has never featured on any to do list.
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Old Feb 17th, 2021, 10:38   #12
Laird Scooby
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Quote:
Originally Posted by Clifford Pope View Post
Update:

Having replaced the plugs, tried swapping in a complete ignition set with cap from the last time I needlessly replaced them, cleaned again unnecessarily fuses 4 and 6, needlessly replaced the fuel pump relay, run injector cleaner through the system, none of which made any difference, I think I finally may have cracked it.

I noticed the radio suppression capacitor on the coil, and tried unplugging it, for want of anything else to do, and the the result was an instant and dramatic improvement to the idle smoothness.
I've never read anything about them, just grown accustomed to odd components being earthed with capacitors. No one else has ever reported any faults, so checking them has never featured on any to do list.
Which coil terminal was it connected to?
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Old Feb 17th, 2021, 12:24   #13
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Which coil terminal was it connected to?
Positive
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Old Feb 17th, 2021, 12:32   #14
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Positive
Thanks, i wondered if it had been on the -ve and been causing a partial short to earth across the contact breakers.

However, if the capacitor had goen partially short-circuit, it could have been pulling the primary voltage down via the ballast resistor resulting in a much-reduced output voltage.
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Old Feb 17th, 2021, 13:03   #15
Clifford Pope
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Thanks. I have found a few reports on other internet forums, mainly in US, of suppressor capacitors causing misfiring.
My car is the LH 2.4 system - no contact breaker, no ballast resistor, but presumably the effect would be the same?

It seems odd that the effects have been so specific - cold start, misfires 10 seconds into a journey, corrects itself after a further 10 seconds, then runs perfectly. If I idle the engine for the 10 seconds first, or take my time going down the drive or stop to shut the gate, it doesn't do it.
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Old Feb 17th, 2021, 13:29   #16
Laird Scooby
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Originally Posted by Clifford Pope View Post
Thanks. I have found a few reports on other internet forums, mainly in US, of suppressor capacitors causing misfiring.
My car is the LH 2.4 system - no contact breaker, no ballast resistor, but presumably the effect would be the same?

It seems odd that the effects have been so specific - cold start, misfires 10 seconds into a journey, corrects itself after a further 10 seconds, then runs perfectly. If I idle the engine for the 10 seconds first, or take my time going down the drive or stop to shut the gate, it doesn't do it.
I would assume it would have a similar effect, might be worth cleaning the main LT connections and tightening the spade connectors to be on the safe side.

Given those symptoms, i'd suggest (as above) cleaning the connections as it would appear there is resistance somewhere but also that the capacitor is probably breaking down internally - not completely as yet, just a minor short circuit that gets "cleared" by use, maybe a bit of water ingress into the capacitor that gets burned off. Cold engines need a better spark to fire the mixture consistently so that part fits as well, it could even be the capacitor is continually breaking down but on the warmer engine, it isn't noticeable.

Have to say it's the first time i've come across this, however given that the newest suppression capacitors (assuming OE fitment) will now be approaching 22 years old, highly possible this is beginning to happen.
The change to distributorless ignition around 2000 or so more or less made them redundant as the loom could be designed to reduce interference, also audio units were better insulated from interference and so on so i'd say the answer now would be if you don't experience interference on the stereo then lose the suppression cap and if you do, buy a new replacement. Looking back, they would probably have been OE fit on many cars from ~1980-2000 so this problem is likely to become more obvious with a simple solution.
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Old Apr 29th, 2021, 10:56   #17
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Update

The symptoms returned a few months ago, in exactly the same manner as formerly. 99.99% of the time it runs perfectly, but then it again did it momentarily, on exactly the same stretch of road - 300 yards from the house, slightly uphill, for about 5 seconds.

By experimenting, it only does it when opening the throttle a bit, in second gear. If I don't try and crack on but just take it gently at 1000 rpm it never gives the slightest sign.
5 seconds later it has got over it, and is its usual forgiving self - fast or slow, any gear, it never hesitates.

So basically the problem is cured. But it's very strange that it only happens in this very short time span, and very rarely.
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