roomer

Hi y'all, I have a 72 cutlass 350. Can anybody point me the right direction? I have a dead miss on number 3, I'm getting good spark.

J-(Chicago)

Disconnect the 12v source to the coil/distributor, and run a compression test on that cylinder. You should inspect for a vacuum leak, or you could possibly have an obstruction such as a dead mouse in that intake runner.

oldcutlass

Did you make sure your spark plug is firing, or just the wire to it?

tru-blue 442

I would pull the valve cover, crank the engine
over with the coil wire off, and see if both valves
are operating properly. You would need someone
to crank it over so you could see.

roomer

Yes, I made sure the plug was actually firing. I guess the valve cover is next. Do you think broken spring might be the culprit? Thanks for the input!

Rickman48

I broke a valve spring at about 100 MPH while racing a BB El Camino on the tollway. ['69 442 w/3:42's]
Dead miss - yes.
But the MAW's got me - new springs, shims,seals, rockers and stands.
Ran great from then on!

roomer

I know this has stretched out awhile, but here is the latest. I've been running the car with this miss. The cylinder has 150# per comp tester. Good spark from plug. I pulled the valve cover and had a friend turn over the motor with power off to dist. Everything looked good. Hooked up the distributor and cranked motor. With the motor running, the exhaust for #3 cylinder is not opening as much as the others. If you put your finger on top of the rocker the motion is weaker feeling. My question now is, would you expect a bad lifter, or bad cam lobe? Also, how can you tell which?

oldcutlass

It could be both and/ or a bent pushrod. The only way to tell is to pull the intake and take a look.

seansolds

Give us some history.. Did you purchase the car with the cylinder miss or did it just pop it's ugly head for no real reason? someone do a rebuilt? Or all stock low or high mileage..another question how do you drive it?

roomer

I bought the car 3 years ago and drove it 500 miles home. Original 72 Supreme convertible. 99000 miles now, about 91000 when I bought it. The motor was running about like it does now, the roughness I blamed on the carb originally. Further checking showed the miss in #3 only. Decided to look further, I do need to replace the accelerator pump in the carb. Can't find any vacuum leaks or gasket leaks around carb body. I was hoping for a broken spring, lol, not looking forward to wrestling that cast iron manifold. How frequently do you only have 1 lobe wash out? All the other valves are doing their thing just like they should. Really hoping for bent push rod or collapsed lifter at this point. Will pull the push rod tomorrow and check.

oldcutlass

Normally there is valve train noise associated with what you describe. Yes, you can wipe out 1 lobe of the cam.

roomer

The lack of valve train noise is one reason it's taken me this long to get this far. No tapping or rattling at start up or when warmed up. With the valve cover off I can detect a slightly quieter click when the valve in question open/closes. I'll pull the push rod this afternoon. Have physical therapy this morning. Getting over a broken knee, picked up in a motorcycle wreck in May.

jpc647

Wait a minute, you've driven 9000 miles with a miss? How bad is it? Is it bad like when you unplug a plug wire bad?

This would have to be a cam lobe, right guys? I mean a bent push rod or lifter would make noise, certainly after 9000 miles. But wiping out a cam lobe, damn you'd really notice that. Like it would be a pretty big miss...

Roomer, make sure to take pictures and post them up when you take the intake off. And when you put a new gasket one the intake to put it back together, don't use the end seals!!! Use Permatex's The Right Stuff. I had to do 3 intake gaskets last summer before I got it right. No fun. And that was with an aluminum intake, the Iron was in 25lbs heavier.

roomer

Thanks for the tip on the seals. I will try to post pics. It's an odd situation. On the road the car seems to run fine. No noise, I pushed it up to 110 once just see you know. It had the same miss at idle then. Yes, at idle you can pull off the #3 wire and nothing changes. Pull any of the other wires and it gets worse. Is it possible that the miss lessens at rpm' s above idle? I've tried to test this in my shop by increasing the revs and pulling wires. Results were inconclusive.

jpc647

Do you have a digital camera or a decent smart phone? Maybe post a video of the car idling, and slowly brings the revs up. It's a shot in the dark but it might allow us to better help.

If I unplug one plug wire on my car the thing runs like dogshi*. Happened to me yesterday morning. I removed one to make room and forgot to put it back. It was idling in the driveway, sounded a little funny, and it was burning hella rich. Could smell it in the house. Got 40 feet down the road and it was like dub dub dub dub dub. No way it would have gone 30mph, nevermind 110.

roomer

Sorry it's taken me longer than I thought to get back. House full of grandkids taking up time. Still haven't pulled intake. Ran up the idle a few minutes ago, cylinder is firing at driving speed, obvious change when wire is pulled. I guess this explains why it runs so well while driving. Miss goes away above idle. Didn't check to see at what rpm this happens, maybe this afternoon. Oh yeah, did pull pushrods, they are straight, rockers look good. Might just wind up raising idle a bit and running it.

rjohnson442

Have you checked the distributor cap/rotor for wear on the #3? And switch a plug wire for another one and see if it moves before taking the intake off.
ya beat me to it...

roomer

Yes, did all the ignition stuff first. Replaced the plug, cap, rotor, switched wires, no difference. Down to valve train now. Like I said earlier, only runs a little rough idling, runs down the road great. Still thinking cam or lifter, not sure if I want to pull it down to find out. Maybe a winter project. Maybe just rebuild carb. and replace accelerator pump to fix the bog on heavy acceleration. Just to recap, if it's a collapsed lifter it should be making noise, and not so for a rounded lobe?

MDchanic

Buddy of mine drove a '67 Chrysler Newport with a 440 from New York to California towing a heavy trailer, found one spark plug wire was off when he got to Cali., never noticed it on the road.



I'm thinking lifter or cam lobe.
He's got a perceptible difference in one rocker's movement. This could cause enough of a flow restriction to cause the cylinder to make almost no power at idle, but still make enough not to be noticed at higher RPMs.

- Eric

tcarroll

You took the valve cover off, did you take 5 minutes to take off the rocker and inspect it? Take out the push rod and roll it on a piece of glass? This will help tremendously before deciding if this is a lifter or lobe issue. Between you and me I would personally change the plug and wire from a different cylinder and see if the miss changes cylinders. These are easy inexpensive trouble shooting I would do first to eliminate the obvious.

Best Todd