67 429 Eng. Question need advice

[cadillacproject]

I am restoring a very nice 67 Eldorado.  In going through the engine I found one cylinder (#4) which is providing now power.  That is removing the spark plug wire while the engine is running has no effect on the idle RPMs.  All other cylinders give a 40 RPM drop when their plug wires are removed while the motor is running.  The compression is great on this "dead" cylinder and right in spec.  The spark is good too.  I am thinking either the lifter is not pushing open the intake valve or there is carbon build up somehow blocking the intake for that cylinder. 

I was going to watch the valve rockers while cranking the engine a bit with the valve cover off to see if the valves move on #4.  I guess if the intake valve does not move the lifter may need to be replaced?  Any other ideas.  The engine has good power but idles a little rough.

[TJ Hopland]

Have you swapped the plug to be sure? Tried a timing light on that wire to be sure its firing while in the cylinder?  My next thought would be bent push rod from a stuck valve which can be fairly common for engines that sit.   It should be obvious with the covers off.

[cadillacproject]

I will check with the timing light to make sure it firing in the cylinder.  It probably is because if I pull the plug at the distributor I see good sparking from the wire to the distributor.  It sounds like watching the valve with the cover off will show if a rod is bent or a lifter is bad.  Reading the shop manual if that is the case replacing the rod does not sound too bad.  Take off the manifold and rocker parts etc.  I have never done it before but I have replaced intake manifolds before.

[TJ Hopland]

I believe the 67's have the 't' pedestal rocker setup like the 472's so they are in pairs.  That will make it a bit easier if its just a pushrod because you will only have to take apart that one pair. 

[cadillacproject]

Yes that would be good news.  Why would a push rod get bent in the first place?  Should I replace the lifter in any case too?

[TJ Hopland]

When engines sit sometimes the valves get sticky or even stuck.  When they get turned over something has to give, most of the time its whats sticking but sometimes its the rod, sometimes its the rocker.

[cadillacproject]

Makes sense. If I don't have to change the lifter I can leave the manifold in place.  Replacing the rod should be pretty easy I guess?  This engine willl run great once I have this cylinder firing. 

[35-709]

From reading the posts above it does not sound like the spark plug itself has been taken out and checked --- which is the first thing I would do.

[Dave Shepherd]

Agreed, the plug could be bad or a piece of carbon stuck in the electrode, if all is ok go right to a compression or leak down test.

[cadillacproject]

Thanks for the advice.  I pulled the spark plugs and it looks great.  It is also sparking fine via. the timing light test.  I also did a compression test on this cylinder and all the others and its great 180 PSI for this one.  So my next step is to pull the valve cover and see if the valves go up and down for this one.  Either the intake valve is not moving or the intake manifold has a clog right?

[TJ Hopland]

It would be unlikely that only one would be clogged from something like carbon.  Most likely for a single clog would be critters.  Who knows maybe that one had a leaky valve seal from the factory and it looks like this:



Im still thinking you will see something when you get the cover off.

[cadillacproject]

Ok I need more help.  I pulled the valve cover and everthing moves up and down just like it should.  From the valve cover side everthing looks great.  Earlier I said it was cyliner 4 that had no power but it is really #2.  To restate the problem the idle is rougher than I like.  If I pull the spark wire for #2 there is no change in the idle speed.  All other cylinders see a drop of 30 RPM at idle of about 900 RPM when disconnected.

If I leave the plug for #2 in and pull the #1 wire the idle smooths out. This I suppose is because we now have a balance of powr.

So The spark is great ( I have a Pertronic and MSD6  and high voltage coil).  The compression for all cylinders is good upto 180 PSI.  The valves move up and down just great. 

One more clue at about 1500 RPM the motor smooths out very nicely.  I have trippled checked for vacuum leaks of course.  So is the next thing to do to pull the manifold and look for a clogged intake passage?

I read a post on this forum last night about someone who had a rough idel unil 1500 RPM he pulled the maifold and found poor sealing of the gaskets and lots of carbon build up preventing good seal(?).  That is my next step unless you all have a better idea!

["Cadillac Kid" Greg Surfas 15364]

I trust you have checked the firing order and the timing.  Try and replace the plug wire on "#2" cylinder and see if that does anything.
Greg

[cadillacproject]

Hi, It would be great if a plug wire fixed it up.  I will try that.  I had kind of ruled it out because I see the timing light fire on that cylinder with no problem and the wires are only a few months old.  But it will be far better to try that rather than take off the manifold if I don't need to.  I have checked the firing order and in fact a few weeks ago I verified the order in great detail.  Ill do it again just in case. 

Its is interesting how much smoother the engine runs if I shut down the oposing cylinder or I guess any cylinder that would be firing at the same time.  One I get this cylinder fiiring the thing wiill be super.  The compression tests good ( 180 psi) which I guess means that at least on the compression cycle the valves are working well. The intake valve moves very nicely when cranked.  I sure hope its the wire!

[Glen]

Swap the #2 plug with and other one.  See if the problem follows the plug or stays with the cylinder.  I once fought a similar problem and found the spark plug would fire OK out of the cylinder but would not fire under compression.  It might not be the problem but it is sure easier than pulling the intake manifold.        

[cadillacproject]

That is a great idea.  If that does not do it I am going to change the rotor just in case.  It looks good and was replaced a while ago along with the distributor -  but just in case. 

[Guidematic]

I would have to agree. If the plug is indeed firing, the valve moving as they should, then it may be only a case of a couple of mixed wires.

But, did you do a compression check on all of the cylinders? That would be a check I would have done just as soon as I found the spark is good and all valves move. Also, check for a vacuum leak. A leak in the area of #2 could lean out the cylinder enough at an idle to cause a miss.

Mike

[Dave Shepherd]

Nice trick here to eliminate a vacuum leaks as asource of the problem is to get a hand held propane torch, put a hose on the pipe and feed some propane around the intake to head area on that cylinder, see if the idle changes, that confirms a vacuum leak.

[TJ Hopland]

Is the 67 429 an 'air gap' intake?

[cadillacproject]

Hi All,  OK I switched plug wires and the problem is still in #2.  I also put in a new rotor with no change.  I retested the compression and it looks good.  I also have done the propane test and no leaks. 

I should have added a while back that I believe that the engine has been rebuilt in its past.  When I got the car it was owned by a guy who new absolutely nothing about cars really. He purchased it on a whim from a stranger.  Well  the car ran pretty well when I got it considering the carb was a total mess and the previous owner was using it with the PVC hose disconnected and several other vacuum leaks.  Anyway got those all fixed and put on a Pony Carbs rebult original correct Rochester. It improved so much I did not notice the idle miss until recently. 

Anyway the block was painted orange when I got the car indicating to me it has been rebuilt ( is the correct engine 429 eldorado).  So I wonder if the rebuilder put a manifold gasket in wrong or otherwise clogged it up and never noticed the miss?

Pull the manifold?