Packard Forum Index » Post-War (1946-54)

could plugs be not firing while installed?they fire strong grounded to block..

Rather than just casting about with speculation, I'd suggest some diagnostics. It only takes 3 minutes, recheck the compression on #'s 1 & 2 to make sure changing the head gasket solved that problem. If low or no compression, pull the valve cover and make sure the lifters for both valves in #1 and #2 have some clearance and the valves are indeed opening and closing. Then with the engine running at idle, measure the intake manifold vacuum.

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It is possible. For a plug to reliably fire under compression the spark needs to be considerably stronger than it does in open air. If the spark is marginal or the plugs fouled or moist then the spark could fail.

Make sure you have a good solid voltage at the coil. Engine off it should be battery voltage or maybe a tenth or so lower. Engine running it should be a bit higher depending on what the generator is doing. When cranking, ideally the voltage should not fall below 5.5v but as long as it stays above 5v it is usually adequate to start the engine if the plugs, wires, dist etc are in good condition.

Plugs work best -- particularly when hot -- when the spark starts at the center electrode and jumps toward the side electrode. To ensure that path and for the most efficient spark, If the battery ground is positive, make sure the + or positive terminal on the coil is connected to the distributor. Also make sure the distributor has a good ground. If grease, corrosion or looseness at the mount or oxidation has built up on the points the coil may not get a good solid ground so the resulting spark would be weaker. The gap and dwell spec is also important to ensure the points stay closed as long as possible to get the best coil saturation for the strongest spark.

thanks!ill check all that...rest of cylinders firing fine

Hi

If you have black walnut trees nearby, squirrels like to store those away in places you can't imagine. Exhaust systems are a favorite.

Steve

Ok did compression test..all cylinders close to 120 but #1...it was 95...car runs good and smooths out nice with plenty of power...still no change in rpm when pulling 1 and 2 wires at idle..I'm just gonna rest on it a while..it needs an oil change anyway

If the engine runs well at speed but has no fire on an adjacent pair at idle there is probably a vacuum leak on the runner feeding those cylinders. Squirt some oil around where the runner meets the block and see if it doesn't pick up. Also, if this is a 23d series, plug the vacuum line that is tapped off the forward end of the intake runner. You might have a leak in the vacuum booster pump that will lean the mixture on the front pair to where they will not fire at idle. At higher speeds a minor dilution of the mixture hardly matters, but at idle it is critical.

Ok..I'll check that out...thanks...vaccum gauge shows 21 inches but is bouncing some...I'll for sure check for the vaccum leak...appreciate it!

Ok Ross...it looks like u hit the jackpot on this!!sprayed area with carb cleaner and engine responded...guess I'll get new gaskets now...I've never had an intake leak bad enough to stop a cylinder from firing..thanks alot for everybody's suggestions..I continue on...this old car is telling me what's going on..I need to listen to it!!all of yall have a great day!!