VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Cadillac engine will not fire on one cylinder

I know this is a Chevy site but maybe someone can help me.. I have a 1949 Cadillac engine in a 1939 Lasalle, we overhauled it, rings, bearings, valve job etc. with a complete tune up. Here is my problem I can not get number 3 to fire, there is spark to the plug, 130 lbs compression but that cylinder is dead all the time no matter what I do. The plug is dry not fouled but when I look into the cylinder the top of the piston looks wet anybody have an idea? Thanks

Restriction in the intake manifold or a huge vavuum leak. Are the valves opening and closing like the rest?

Hello Gene thanks for the come back, I had the valve cover off and the valves are going up and down ok. This car had been setting about 30 years when I got it and I am pretty sure we checked for a restriction in the manifold, as far as a huge vacumn leak would that affect just one cylinder or several? I just put a rebuilt carb on Monday and that did not help, were would you suggest I start to look for a huge leak? Thanks Ross

"engine been sitting for 30 years"---bet a valve serving cylinder #3 isn't closing completly(stuck). pour some marvel mystery oil on both valves and while your buddy is turning the engine over slowly, take a brass headed hammer and tap the valve stems/rockers. repeat this for 10 or 15 minutes and the valve(s), if stuck, may free up . good luck, mike

Possible but he said it had good compression. A mouse may have built a nest in that intake port if its obstructed....or the intake to head gasket may have rotted away causing a massive intake leak. Spraying "something" around the intake to head connection for that cylinder may help find the leak...or a may be necessary to remove the intake for inspection.

Have you removed the plug, grounded it and then cranked the engine? How about switching plugs? I've had plugs that fired when not under pressure but did not when installed in the engine. Never found out why!

With 140 lb pressure the valves are working and sealing. Has to be either spark or fuel if you have compression.

Ross
A small vacuum leak will affect all cylinders slightly but if it is close to 1 cylinder will be more noticeable there. A large leak will affect all to the extent the engine wont idle or not run at all.
I would be swapping spark plugs with a cylinder that is working, if the problem shifts put a new plug in, if the problem stays check plug lead for high resistance and distributor cap for a spark trace to ground from that post (could be inside the cap or inside the bakealight).
Tony

When you say the piston looks 'wet' we assume you mean there's gasoline in it. Could it be coolant? Not likely with 130 pounds of compression but worth a look.
I'm with the guys leaning towards ignition problems. Could be a bad cap or plug wire.

Coach

Hello I have replaced all ignition with new parts, we have checked manifold for restrictions, replaced plug in that cylinder, sprayed starter fluid around manifold and carb but still nothing, unhooked vac advance, unhooked w/s wiper vac. I changed the car to 12 volts and put carbon wires on it, I made a solid one for that cylinder but still dead, checked to see if the wiring was right, it is by the 1949 Cadillac book. I am overlooking something but for the life of me do not know what, can't stand to drive something that does not run right. Thank you all for your help. Ross

Check the timing, not just the distributor but the camshaft to the crankshaft, I think that engine has a timeing chain, (later models did) it could be one notch off. Did you put in a new timing chain?
I once had a Cadillac that ran us ragged, we would reset the ignition timing right on the money and in a hundred miles it would develop a miss on one cylinder, then one morning it wouldn't start for anything. The timing chain had jumped another notch. The Caddy mechanic said the trouble we had with the miss started when the chain had jumped one notch.

Hello I replaced the chain. Thanks Ross

That is good that you replaced the timing chain.

This might sound goofy but, I saw this once. A dude helicoiled his spark plug hole with one that either didn't conduct, or conduct well. Long story short, wouldn't fire. He ended up removing the head and tapping out is 10mm spark plugs for 14mm.
Just something to concider.

I am about to tear the engine back down but I sure hate to, I am going to see a friends mechanic (FORD OUCH) to see if he has any ideas. If I find out anything I will post it. Thanks everyone!!

50 Chev take a look at your distributor cam. You might have a worn lobe that's not giving you enough dwell time on that cylinder.

Ok thanks!!

Looks like you've tried almost everything!
Maybe blocked exhaust manifold?
When cranking does it sound "even" - can you hear each compression stroke?
It might be OK on a compression test, but maybe not when running, for example, a sticking valve will often give full compression at cranking speed ,but be too slow to allow full sealing at running speed.
Similarly, what about valve lifters? (I don't know if Caddies had hydraulic lifters then). If it does have hydraulic lifters, are they staying pumped up for cylinder number 3, so leaving the valve/s open?
Is it not firing at all, or just down on power/missing? (I asume you know which cylinder is not firing by shorting each plug to ground and feeling/hearing the difference).
Hope this helps.

They did have hydraulic lifters.

Hello have tried about everything, has about 55 lbs compression on each cylinder running, checking one at a time. Put on a new 45,000 volt coil from speedway, changed wires around, took off exhaust manifold it was not obstructed. Had valve cover off and looked at valve action rolling it over, seems ok but did not have dial indicator. Was told if lobs or heal of cam are worn to excess it changes the valve timing and it may not hit correctly so I have a new cam and lifters coming and hope that does it. If not I will buy another engine and try that. My late father was a mechanic and would not drive a car that runs like this thing does. Give me a 6 cylinder Chev any day this has been a pain in the you know what.

I just read all the post on this strange problem. have you tried to use a spark tester on this on plug ? this would tell you if you have proper spark getting there. I will ask my father in law when he gets home about this. at 75 and a retired Cadillac GM mechanic I hope he can shed some light on this. better than buying another engine.

Have new wires, 2 sets new plugs, new cap, new points, new cond, new coil, had car running with new plug attached, has fire. I have new cam and lifters coming am going to try that. Thanks Ross

This car starts better than any car I have cold or hot, I have put in a new chain and both gears and am sure they are on the mark but when I start to replace the cam I will give it another look first. I am sure I have missed something but will try to get to the bottom of it. Thanks Ross

If you are suspecting that you have lost a lobe, that can be checked without disassembly. Use a dial gage and measure the lift on the intake and exhaust valves on the suspect cylinder. You can check your reading by gaging another pair on another cylinder. You should be able to identify any valve problems by your compression check and a visual of the cylinder while running.

Just for fun(?) I would run another compression check with a different gage.

Hello I want to thank everyone who gave me suggestions about fixing my 1949 Cadillac engine. After trying about everything including watching the valve action running and not running and thinking it was ok I decided to purchase a new cam. After taking it apart and looking at it I found several lobes about half gone as well and several lifters concaved on the bottom, in other words it was shot. After the installation it now runs and sounds strong like it should, I guess we live and learn as I have not had any experiance with Cadillacs but this thing has been giving me fits. Thanks again Ross

Hello I want to thank everyone who gave me suggestions about fixing my 1949 Cadillac engine. After trying about everything including watching the valve action running and not running and thinking it was ok I decided to purchase a new cam. After taking it apart and looking at it I found several lobes about half gone as well and several lifters concaved on the bottom, in other words it was shot. After the installation it now runs and sounds strong like it should, I guess we live and learn as I have not had any experiance with Cadillacs but this thing has been giving me fits. Thanks again Ross