Quick update: Ran the timing light on the broken 99 Honda again. I’d checked cyl #1 and #2 before, this time I did all 4. #1-3 were absolutely fine; on #4 I saw 3 times just the briefest of interruptions over about about a 1 min period, but so brief I’m not sure. I watched another minute and everything was normal.
So last night was either an aberration with the gun, possibly i didn’t connect it securely to the battery, OR perhaps the engine was more clogged up…I put some gumout in the cylinders today.
It’s been a few days but I’ve just now had time to mess with the car again. And I have interesting data!
Removed the upstream O2 sensor. Started the car, it ran fine! Shifted into gear, drove it back and forth a bit, it was smooth. Let it idle for 35 min before shutting it off…longest it’s gone since it broke down.
Hooked my vacuum gauge up to the O2 port. The gauge has a 0-10 psi scale. At idle, barely any pressure, less than .5psi. Same at 2000RPM. At 4000RPM…well, the car wouldn’t hold at 4000RPM. It behaved erratically again, revving and dying. Pressure bounced wildly from 0-5psi, and a few times up past 10psi.
Unhooked the vacuum gauge, left the O2 port open, and revved the engine again. Revving was smooth, and it held 4000RPM easily.
I’m suspecting a clogged exhaust somewhere. The cat-back on this car is aftermarket, and at least 6 years old, maybe 8. I took a temp reading fore and aft of the cat and came back with 250F in front and 185F behind. Seems like a malfunctioning converter.
If a bad converter could cause enough carbon build-up to clog the rest of my engine…then this could be it!