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Old 09-29-2020, 09:31 AM   #14
Licensed to kill
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Join Date: Aug 2016
Location: Alberta
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Default Re: Mystery missfire .

Originally Posted by john charlton View Post
No resolution as yet I have done the trick of holding no 4 lead off to induce a hotter spark but no change.........
But did you have spark?. if the spark jumped from the lead and you have swapped the plugs around and the problem persists at #4 then the problem is not an ignition one. As you stated, #3 and #4 share the same intake runners so it can't be a fuel problem with #3 firing fine so that only leaves valves/rings. One thing you can try is remove the vacuum line from the intake manifold and add a fitting with a hose with a small funnel. Ideally you would put a ball valve in the line somewhere so you can stop a vacuum leak while you start the car. Then, with the engine running on high idle, pour MMO in the funnel and open the valve. You can use the ball valve to regulate the flow so you don't stall the engine but with that small of a line it likely wont. That will be sure to free up any sticky valve and, like most things on a car you only need three hands to achieve this ( one holding the funnel, one pouring the MMO and one to work the valve). Also do NOT do this inside as in very short order you will not be able to see through the smoke in a garage.
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