Hi,
Well now that’s a rather common problem. (:-)

I don’t remember seeing you say if you have new ignition components but soapy surfactants make water become a better solvent by breaking down surface tension.
Combine with dirt that may have some salts in it, then you have a prime conductor for high voltage leakage. The Wattage to heat the plugs drops off so the spark is weaker.
High voltages are surprisingly agile and jump easily unseen as they are tiny paths.


Be suspicious of the main ignition wire off the coil to the distributor.
The reason I say this is because in lots of cases you buy a wire set it does not come with that wire included.
Especially if the people before you shopped by price only. No telling how old it can be and it does four times the duty of only one at a time.

You might want to do an under the hood nightfall test with a spray bottle of a tap water mist.

Was the engine warm when you washed it?
Some engine cleaners want that environment to remove warmer oil. It’s advertised to call it to be like steaming cleaning without high pressure.
Sounds nice but then now, that will make vapors. They love that travel to a cooler place as that’s what the exceeds energy does.
More Importantly it can drift up under a distributor cap that looked to stay dry or protected but not from below.

Phil