Just curious if you guys would have any idea. I have a 1992 cabriolet with a 2bbl holley carb swapped on. Anyways making a long story short, 4th cylinder has 150 compression and spark but will not fire. I m guessing a major vacuum leak either from the brake booster or the silicone and penny injector hole. What do you think?
Just curious if you guys would have any idea. I have a 1992 cabriolet with a 2bbl holley carb swapped on. Anyways making a long story short, 4th cylinder has 150 compression and spark but will not fire. I m guessing a major vacuum leak either from the brake booster or the silicone and penny injector hole. What do you think?
If compression is good then I'd be focusing on the ignition system personally. Pretty hard to have a fuel delivery issue to just one cylinder on a carbureted engine.
What troubleshooting have you done on the ign side?
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Easiest thing to do is to plug the hose to the brake booster and see what it does.
A common check for vacuum leaks is to spray a flammable material onto the area of the suspected leak, and see if the engine surges due to the entrance of fuel into the intake. You can use something like starting fluid or propane because they dissipate quickly, but still be careful doing this- use safety glasses, have a fire extinguisher, do it in an open, well ventilated area. Spray it around possible sources of leaks, like the intake manifold gaskets without letting the fuel get into the carburetor air intake.
Figured it out. One of the extra block off caps on the brake booster had fallen off. It was causing a MAJOR vaccum leak for the one cylinder. My hypothesis is that there was not enough vacuum to pull the right amount of fuel/air to cause a combustion. Idles and revs perfect now.
I think it's that the vacuum leak resulted in more un-enriched air entering that cylinder, causing the ratio of gasoline vapor to fall below the lower flammability limit. Flammable vapors are only ignitable under certain conditions. Too much air in the mixture, or even too little air, and it won't ignite.
Exhaust is "depleted air."
