More troubleshooting

Posted by Bob E. On 2019/8/29 11:32:42
Still working through a troubleshooting process on the miss at idle and at elevated RPM and documenting what I am doing so I can recall later in time if this happens again:

Tested all the spark plug wires for continuity; nothing interesting there.

Listening to the exhaust pipes, the right (passenger) side is noticeably more 'forceful' than the driver side. I know the exhaust manifold riser valve can restrict this to some degree, but I have the spring removed so it is mostly open. (note, i manually close it when starting the car until it is warmed up). Have some muffler holes that were patched with tape so maybe there is some leakage on the driver's side

The miss is audible from the right exhaust pipe along with a low frequency "whoom" sound at the sound of the miss (and reduction of rpm).

I think this is telling me that my problem is not a generic fuel/carb problem or primary side ignition problem.

Pulled the even cylinder plugs and 2,6,8 look normal. #4 looks too clean to be right; the insulator core is very clean. Started engine with #4 plug removed and touching block. Seems like a proper spark visually so I would assume it is firing in the cylinder.

I also have lowish vacuum (oscillates between ~16"-~17")so maybe there is a vacuum leak in #4 air path that is causing a very lean condition.


More to come, just wanted to write down what i did recently so I didnt forget.

Next steps: pull right valve cover to see if anything weird going on with #4 intake valve. Also maybe use a spark tester to see if any difference between the plugs.

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