MK2 1.6L carb (EZ) History: engine started to develop misfire on cylinder #4, after going through some diagnosis steps like swapping plug wires and plugs misfire stayed with the same cylinder, checked cylinder pressure and the missing cylinder was the lowest one @8.0 bars with a diff to near by cylinder of 3 bars. Then I used a borescope to check in cylinder if I have a burnt valve or something obvious and all was good, then I removed the carb and I used borescope in the intake runners and cylinder head and to my surprise it was way worse than a direct injection cylinder. it was full of rock solid oil sludge stuck to the walls and the back of the valve. Removed the intake manifold and tried to clean it to my best while the cylinder was still on, it was a bit cleaner but still needed loads of cleaning still, after assembling everything back the car ran great for 2000 km, then developed the same misfire. So I decide to go through cleaning the whole head, I removed the head and completely stripped it down, cleaned it thoroughly, changed valve stem seals and even lapped all the valves, after assembling everything back the car still have the misfire any thoughts what might be the cause?
I presume you fitted a new headgasket? What does a compression test show now? Check the brake servo vacuum hose and any connected pipes for leaks. I think an air leak into that point on the manifold will selectively affect cylinder 4 more than the others. You could maybe clamp that hose while car is stationary and see if the misfire goes away?
yes new gasket all around intake, exhaust and head. compression is now 2 bar better all over and cylinder #4 is only showing 1.5 difference from #3. will have a look on all hoses for leaks, thanks
@EZ_Pete rubber hose between the intake manifold offtake (@runner #4) and the one way valve (for brake booster vacuum) had a crack, replaced and every back went to normal again Appreciate it, thanks
