Maybe a rocker on that cyl is too tight holding the valve off the seat?

 

I had a lifter that acted normally, let the cylinder make compression for a compression test, but when the engine ran, it pumped up and held the valve open. To find the problem I backed the rockers for that cylinder off until I had about a quarter turn slack in the valve train, fired it back up, and the cylinder came back. It turned out that the lifter for one of the valves had internal check valve issues that allowed it to pump up when the oil pressure was up, as in engine running, but acted OK when no oil pressure was present. I found out it was made in Bolivia, sold as a "rebuilder's set" not a brand name set of lifters like they were supposed to be. I replaced all the lifters with a set of new brand name lifters, and all was well.

Regards,

Milton

 

But if the valve wasnt seating how would I have the same compression as other cylinders ? Confused ??


Ok I reread the last statement and I guess it could pump up ? I will try that and back off the rockers before I tear anything apart.

 

That spark plug is most likely fouled!....Change it out for a good one and you'll be OK!

 

Wish it was that easy but I have installed 2 new plugs and same result. Even switched plugs and wires from other cylinders still no fire on #1. Will back off the rockers tomorrow and see what happens. Thanks for the help. Chad

 

Ok, dug a little deeper. The rockers are not it, back them off until they ticked while running and still dead. The cylinder is only dead at idle, when I rev the eng. #1 cylinder hits fine. I am getting smoke out the tail pipe which I assume is just unburnt fuel once that cylinder ignites ? So it seems I am not getting fuel to #1 at idle any ideas ?

 

Also its a 650 double pump carb I just rebuilt because I originally thought it was a carb problem. I dont know much about idle circuits but can a carb on a dual plane intake really cause 1 cylinder to not get fuel ??

 

No can't be the carb...
The 2 primary barrels supply fuel and air for all 8 cylinders at idle and part throttle and there is no way that it could stop fuel from getting to one cylinder at idle.

Do you have any vacuum connections on the runner for that cylinder? You could try plugging them off.

 

Yep, sounds like vacuum, but I would re-torque your intake manifold. A vacuum leak there is compatible with each of your symptoms.

 

I just replaced the intake gaskets , but I guess I will do it again ?? The vaccum leak is about all I can think of at this point ? I did spray around the intake with no notice of a leak but dont know what else to do and its driving me crazy. Thanks for all the help.

 

Did something maybe fall into the intake and get sucked into the #1 runner? I imagine it would have gone part way into the cylinder by now though.... worth a look.

 

Bump. Anything new Chad?

 

I guess when i get time I will pull the intake and replace gaskets again. May be a few days as I am very busy with work and a newborn baby. Thanks for the help.

 

You said the spark was there. Was it yellow or blue? It should be blue, if not, bad dizzie tower? Or, (I know this is a stretch) bad lobe on the dizzie cam affecting the dwell/timing on that one hole?

alan

 

New born baby!? Didn't you hear of the Mexico City earthquake back in the '80's? The maternity hospital collapsed. It took two weeks for rescuers to dig their way into the babies. ALL OF THEM were fine! We learned that human bodies, at that age, shut down to survive. Of course there's no way anybody but a Nazi would know that. We probably evolved that way because when we were cave men and a rival tribe would attack, parents would stash their kids and come back later. The kids who could survive the longest passed on their genes. Cool product of evolution, huh?
How does that relate to Camaro's? Easy. Don't sweat your kid screaming. The suspension on your car can be massaged with no harm to Jr.:yes:

 

HuH ?? Ill have 3 of what you have ????????

 

I would double check for a bad cam lobe. Low mileage maybe wiped out a lobe with the junk oil we have nowdays.

 

X2

Is there a funny ticking/rattling sound coming from 'inside' the engine?

Mark

 

Only problem with that Andy is his compression is good across the board.

 

Good cranking compression should indicate the engine is mechanically sound. Fuel issues are gennerally not going to cause one cylinder to miss on an engine with a carburetor. It seems strange to have a vacuum leak on one cylinder. Seems like it has to be electrical. Bad plug wire? Either shorting (should cause missfire, though), or have too much resistance. Check resistance compared to one of the others.

 

No noises except when I backed off the rockers but then readjusted. I doubt a cam lobe issue as rockers move fine and I did swap 2 plug wires and plugs to eliminate that as well as new cap and rotor. Its a areally anoying problem as these engines are very simple but this is a pain and I guess it will come down to pulling the intake again and resealing all that and hoping for the best. That cylinder comes alive when I rev the engine and then the exhause starts to smoke a good amount but I also was spraying carb cleaner around to search for a vaccum leak. Just wish there was something simple I overlooked but no such luck thus far. thanks again for all help and ideas.

 

Sheeze Chad. Sounds like you found the cause. Spraying carb cleaner and looking for smoke is the method used to find a vacuum leak. That, or oil at the seal.

What's the history of your intake manifold? Has it been machined to match up to a set of surfaced heads? Have the heads been surfaced and not the manifold? There's not much wiggle room. They gotta be close. Oh, a mismatch will in all likelihood be under the manifold. When you pull the manifold, look VERY CLOSELY at the bottom half of the intake gasket. You're looking for proper alignment and squish. Here's mine after 25 years. I don't know why it didn't act like yours, except Karma, of course.

 

Ok, pulled the intake and the intake valve to #1 cylinder had a small puddle of oil in it.
I am going to assume this is whats causing the problem but why ? Valve stem seal ? This stuff is all new and just seems very strange to have a major issue with less than 500 miles on the motor. What do you guys think ??

 

I know someone will say use a leak down gauge but i dont own one. If there is another answer let me know.

 

Might be able to borrow one from a auto parts store. They usually loan them for free.

 

I guess leaking Intake gasket could cause this problem, if leaking up into the cylinder ??