Misfires are going to be the death of me

Please. Can anyone help me figure this out? I’ve got a 57 150 with a 327 that seems determined not to run on all cylinders. It will run, but it’s missing hard on 3 at idle and above. I’ve done the following:

Unplugged plug wires to determine what cylinders it is.
Replaced all plugs and wires (they were rough anyway)
Swapped distributor caps (points) for another to see if the problem changed.
Swapped carbs with a known good unit to no success.
Filled the bowls with gas to see if it was the pump not producing enough.
Checked compression and all cylinders are good.
Sprayed ether around vacuum lines to check for vac leaks.

Nothing has produced any difference in behaviour.

My next plan was to start looking at valve train? Maybe a few valves are stuck closed? Or a few wiped cam lobes? There’s no glitter in the oil so I think I’m good but idk. Could something with the points cause an idle misfire on specific cylinders? Or maybe my timing is off somehow? I’m so lost here and have done everything I can think of.


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Yes, check valve train operation. Look for proper valve movement on # 3 cylinder and also check for a broken valve spring. Also you might check for a vacuum leak that would affect only # 3 cylinder (perhaps a damaged intake gasket).

 

Try a different dist maybe the cam lobes in the dist are worn.

 

Which cylinders are missing?
Valves adjusted too tight can make it miss.
On SBC's you can have compression when cranking but not when the lifters pump up full with oil pressure

 

Compression & or leak down test???

 

Valve guides on #3 are so worn the valves don't seat

 

Is this a 'new' problem or has the engine always run this way for you?
History of the engine?

Quick and dirty but works well enough.
Which cylinders did you determine are misfiring?

What type of plugs and what gap are you running on the spark plugs?

Did you swap out the caps, rotor, points, and condenser?
How is the coil?
What brand did you use? Delco, Accel, whatever was at the store?
Verify clean tight connections. Frayed wiring or crusty connections can cause strange issues.

Did you check it hot with the throttle open?
What were your numbers?

Always good idea just to change hoses that are more than five years old.

Pull the plugs, remove the valve covers, and hand crank the engine over.
Verify the mechanical(cam) firing order is correct.

 

Well, good compression...so flat cam/etc...not a factor.

Maybe something simple like plug wire routing?

 

Wouldn't that cylinder still show compression with a flat lobe budge?

 

Would not be like the others, cant get air in, less compression. I'm assuming when OP says "compression good" , OP checked all the holes and compared. But, I've made an ass out of myself with assumptions before

 

I'd think that a worn intake lobe would reduce both degrees of rotation off the valve seat and reduced lift, which could result in impaired cylinder filling and thus less compression. Seem reasonable?

Bob

 

That makes sense, i understand what you're saying now. I've had similar issues with a SBC in the past and it usually turned out to be valve adjustment.

 

Well, you're off to a great start! Most of the basics have been covered. If cylinder 3 has lower compression then I'd start looking at the valve train. If intake doesn't open there wouldn't be a lot of air in the cylinder.
Before everything, check the lobe on the dizzy. Easiest and fastest thing to check. Next, clean the top of your engine and yank the valve cover off. Check spring height and movement. Also, look at the push rod. I've seen ends broken off the hydronic end, sucked into the oil stump, and the rod have little activation.
Albert

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I've had this issue when the bushing in a distributor was worn out. The dist. shaft would wobble causing the points gap to fluctuate.

 

Misfires almost were for Clint Eastwood in Unforgiven as he played William Money....

 

I might be wrong but the way I read the original post it sounds like he has 3 different cylinders that misfire, not just #3.

 

That's how I read it


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Lets start over so we are all on the same page.

Is it a dead miss or an ocassional miss............and is it on cylinder #3 or on 3 different cylinders.

 

had similar problem with SBC,broke a valve spring so replaced all with brand new one,
would not run on 8cyl ,eventually found problem after taking carb/manifold off ,one push rod
had come off cam follower and bent at right angle nearly 3 inches from end,thus rocker arm not working.
motor now runs great

 

I remember a thread, it's been a while, but a fellow was having similar problem with a tri-5 Chevrolet. One side of his carburetor was malfunctioning and due to intake design, only certain cylinders were affected.

 

I'm the guy that checks everything. But had a big block Ford beat the crap out of me. runs good , runs bad , missing and farting around. replaced everything. Finally went out one evening LATE (dark) fired her up and HO look at all the pretty lights. I could have sworn I had all those spark plug wires pushed on good. Probably not your problem but is an easy simple test.