Topic: Diagnose engine miss

[Tiny]

My 66 289 Coupe has an issue which I need some help.  Whenever the car is cold I start the engine (Fires Straight away) but is missing on 1 cylinder.  It does this for about 1 minute then it comes good.  I'm thinking a faulty lifter which bleeds out overt time then once the engine starts it becomes pressurised again.  But there is no typical tapping sound during this one minute period.  I thought if it was a lifter that bled out then it should create a knocking/tappet sound until it builds pressure again.

Any ideas?

[bgp429]

Check the vacuum, if unsteady possible valve train issue. Also check for a vacuum leak. How about water in the cylinder? Will cause a misfire until it is burnt out.

[69cobrajetrugae2]

Check the cap and rotor and choke and all the basics first.

A combustion leak by bgp429 is the most likely.  Pull the plugs cold and if one has a green look to it break out the wrenches.

A Chinese aftermarket intakes are known leakers.  Heat expansion might seal it but it could ruin the engine by flooding the crankcase with coolant.  If plugs look good then apply 140PSIG to each cylinder on it's compression stroke and look for air bubbles at radiator or a hissing noise.

If the preload on a lifter is excessive then it would be possible for the valve to hang open on start up when the oil is cold.  Once the lifter has been cycled a few hundred times under full oil pressure and full compression strokes and spring pressure the lifter plunger might close enough to stop the majority of the misfire, but it would still be likely leaking.  A cylinder balance power test would lead you in that direction.