Need a diagnosis UPDATE

CJim7

OK, best guess from whoever wants to take a shot at this.

I have an intermitant dead cylinder. It fires probably every 2nd or 3rd cycle.
I swapped plugs and wires around (and then wires and plugs), and it's only showing up on the same cylinder....every time.

Everytime i pull a plug on that cylinder it has fresh oil on it, the rest look great.

I havent done a compression test on it yet, but can someone give me an "educated guess" as to whether this is most likely a bad set of rings or a valve issue (keeping in mind the intermitant miss and the oil) The fact it's not missing every time tells me i probably dont have a burnt valve or a hole in the piston...but that's as far as im willing to guess.

the miss started up rather randomly, and only occasionally, but now it's all the time.

Will a compression test diagnose the difference between bad valves and bad rings?

dbesade

This is probably a longshot.. but my friends old waggy had a cylinder like that and it ended up being the distributor cap had worn out the contact on the bottom side of the cap. Sounds like and ingition issue.

82Waggy

Possibly a bad valve seal or a leaking intake gasket.. Do the compression test though. A valve that is not seating will probaby show little to no compression compared to a bad ring. Look into the intake manifold runner to that cylinder. If there is oil, you have a leaking intake gasket allowing oil to be sucked in from the valley and then deposited into the cylinder. If no oil in the intake, check the valve seal.

CJim7

dbesade wrote
This is probably a longshot.. but my friends old waggy had a cylinder like that and it ended up being the distributor cap had worn out the contact on the bottom side of the cap.

Sounds like and ingition issue.

I checked that after ascertaining the plugs and wires were ok. pulled the dis cap and checked the contact. They all looked uniform, and the suspect contact looked fine. I also got zapped pretty good removeing and replaceing that wire on the dizzy as it was running :mrgreen:
Thought it was the wire, swapped wires, same result.

CJim7

82Waggy wrote
Possibly a bad valve seal or a leaking intake gasket..

Do the compression test though. A valve that is not seating will probaby show little to no compression compared to a bad ring.

Look into the intake manifold runner to that cylinder. If there is oil, you have a leaking intake gasket allowing oil to be sucked in from the valley and then deposited into the cylinder. If no oil in the intake, check the valve seal.

Thanks. i'll check all that. Need to borrow a compression tester from my neighbor.

CJim7

OK, did a compression test. Dry, i couldnt even get the needle to move. The leakdown gave me 90psi immediately. So....bad rings i suppose. :-|

82Waggy

CJim7 wrote
OK, did a compression test. Dry, i couldnt even get the needle to move.
The leakdown gave me 90psi immediately.
So....bad rings i suppose. :-|

Do the other cylinders show higher?

I take it you found no oil in the intake runner?

Might be time to pull the head and take a look inside.

CJim7

82Waggy wrote
CJim7 wrote
OK, did a compression test. Dry, i couldnt even get the needle to move.
The leakdown gave me 90psi immediately.
So....bad rings i suppose. :-|

Do the other cylinders show higher?

I take it you found no oil in the intake runner?

Might be time to pull the head and take a look inside.

I havent pulled the intake yet. Wanted to do a quick comp test first to see if it was oil killing the spark or not enough compression to create a burn....i got my answer real quick. :roll:

All the other cylinders showed between 120 and 125 dry.

So now i guess i'll be makeing a shopping list and starting a teardown.