2 Cylinders Not Firing Update

DScott

DScott

Junior Member
I removed the plugs from the two cylinders that are getting voltage from the distributer, but not firing. The front cylinder has enough pressure on the up stroke to move your thumb off the plug port. Feels like significant pressure, the number 2 cylinder has some pressure, but not as strong as cylinder 1.


It has been suggested that it is a head gasket between cylinder 1 & 2. If it were a head gasket problem there, would I have high pressure in 1 but not 2 ?


If it is a stuck valve, why would spark plug 1 not be firing ? I am getting a good spark to it, but when I remove the copper strip from the distributer, I hear no noticeable change in the engine idle.


In fact, I get no change when I remove 1 or 2 . I swapped the plugs from 1 & 2, with 3 & 4. The back two cylinders are still firing, the front two are still not. That should rule out a plug issue.


Any suggestions ? Despite the issues. I love this old car.
 
A humble suggestion...You might take a look at the condition of the distributor cam and see if it still has four pronounced lobes on it. Also there should be .025 thousands between the four studs in the distributor body and the end of the rotor. Check to see if the distance is as it should be. You could have a warped distributor body or one that has a short in it. Check to see if you have continuity between the interior stud and the one on top where the little brass clip connects. My mentor years ago, Howard Dennis of Newport Beach Marine Engine always said 'Check the simple stuff first'. Ernie in Arizona
 
Thanks for the reply Ernie. I went ahead and ordered a new distributer cap, rotor, condenser and new copper strips to run from the cap to the plugs. I have e new set of points already, so I will replace all that stuff and see what happens. That would not explain the low pressure in two, that is looking more like a stuck valve. I could actually have two separate problems, independent of each other. I will get it figured out, but again, thanks for the reply and suggestion.:)




Ernie Vitucci said:
A humble suggestion...You might take a look at the condition of the distributor cam and see if it still has four pronounced lobes on it. Also there should be .025 thousands between the four studs in the distributor body and the end of the rotor. Check to see if the distance is as it should be. You could have a warped distributor body or one that has a short in it. Check to see if you have continuity between the interior stud and the one on top where the little brass clip connects. My mentor years ago, Howard Dennis of Newport Beach Marine Engine always said 'Check the simple stuff first'. Ernie in Arizona
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It is good that you realize; there can be more than one problem. That is usually the case with machinery this old. That is the reason a compression test and later a cylinder leak down test are important, They provide numerical values that can be compared for evaluation. Same goes for using a vacuum gauge. Testing is a matter of verifying data on compression, valve and ignition timing, carburation - absence of vacuum leaks & incorrect mixture. So far a thumb test. The wet test indicates rings. and NOT valve leakage.
 
You are very correct. Ordered a bushing adaptor that I can use for compression check on both cylinders. Out of curiosity what is the wet test ?
BTW, thanks for responding.




100IH said:
It is good that you realize; there can be more than one problem. That is usually the case with machinery this old. That is the reason a compression test and later a cylinder leak down test are important, They provide numerical values that can be compared for evaluation. Same goes for using a vacuum gauge. Testing is a matter of verifying data on compression, valve and ignition timing, carburation - absence of vacuum leaks & incorrect mixture. So far a thumb test. The wet test indicates rings. and NOT valve leakage.
Click to expand...
 
I would assume what he is talking about is putting some oil into the cylinder prior to a compression test. That oil helps the rings to seal better, so if you have poor compression without the oil, but good compression with the oil, it is a good indication your rings are worn out. However, if there is not a lot of change, then it might be a valve seating issue.
 
If it will run, you may want to try a little WD 40 around the intake manifold gasket near the front two cylinders. If you have a intake gasket leaking you may not have adequate fuel to the cylinder that is not firing.
 
Has your bushing adapter come in yet? In the meantime, do a vacuum test. any auto parts store or even wallmart. Don't be replacing parts untill you have diagnosed. Remember what you said - could be two things wrong. You might be adding a third issue. When you find an issue by organized testing, by all means fix it. then continue testing to verify a fix. Corley is correct on the wet test. Google engine vacuum test in the meantime so you understand how to make sense of the readings.
 
Thanks, for the very sound advice.:)








100IH said:
Has your bushing adapter come in yet? In the meantime, do a vacuum test. any auto parts store or even wallmart. Don't be replacing parts untill you have diagnosed. Remember what you said - could be two things wrong. You might be adding a third issue. When you find an issue by organized testing, by all means fix it. then continue testing to verify a fix. Corley is correct on the wet test. Google engine vacuum test in the meantime so you understand how to make sense of the readings.
Click to expand...
 
Another update. Finally got bushing for compression test. Cylinders 1,3 & 4 show a little over 50 lbs. Cylinder # 2, shows nothing. I took out plugs 1 and 2 and poured some marvel mystery oil into the cylinder, let it sit ran it, did the same process again, and it is cylinder 1 is now firing, and cylinder 2 is firing on and off. Thinking now it is an exhaust valve sticking or not shutting. I watched down inside the cylinders and the intake valves are opening and closing, so either exhaust valve or rings ? I plan on running a vac. check tonight.
 
An intake valve can open and appear to close BUT not seal. Same goes for the exhaust. Next test would be to bring #2 up on compression stroke, exactly at TOP dead center. #3 would be at top but on end of exhaust stroke. Need an air hose with the pressure regulated to 35 psi. Listen for the air loss happening at !.tail pipe, or 2. carb. with the throttle held open with the hand throttle ,3 crankcase breather, or 4 adjacent cylinder. By the way the hose is going to put air in the spark plug hole at #2. if the air pushes the piston down, crank just less than 1 1/2 revolutions and relocate to TDC. Compression testers that use a hose with a threaded adapter are perfect for this leakdown tester, just have to remove schrader check valve in the end of the hose.
 
DScott said:
Another update. Finally got bushing for compression test. Cylinders 1,3 & 4 show a little over 50 lbs. Cylinder # 2, shows nothing. I took out plugs 1 and 2 and poured some marvel mystery oil into the cylinder, let it sit ran it, did the same process again, and it is cylinder 1 is now firing, and cylinder 2 is firing on and off. Thinking now it is an exhaust valve sticking or not shutting. I watched down inside the cylinders and the intake valves are opening and closing, so either exhaust valve or rings ? I plan on running a vac. check tonight.
Click to expand...

MMO is are friend ! Normally 4oz in 10 gals ratio, double or triple that in the gas tank and go for a long drive !
When you/ we are testing for dead cylinders, use a screwdriver and touch the top of a spark plug to engine head nut !
When you remove the plug wire that spark needs to go somewhere! Leaving carbon tracks where we don’t need them.
 
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