high-pressure hose to wash engine bay. Misfire possible?

Miss-fire
Yes strong possibility. Very prevalent on the Gen1 when rain water ran down the front of the car and collected in the spark plug tubes causing a missfire.
AND a severe rattle coming out of the cush drive between the engine and transmission. Enough to make you think the thing is coming apart (I believe there is a bulletin on this????)

Sufficient cause to remove the plug wires and check--well at least blow out the cavities with compressed air to eliminate the moisture or allow junk to drop in the cylinder if you remove them.
Actros

 

I don't think its anything to do with your son washing then engine comparment. In the old days with distributors, points and unshrouded spark plugs, it was possible to get a brief short and misfire somewhere in the system, but highly unlikely with today's electronics. And a misfire would trigger a code in the computer. No code - no misfire.

 

I listened to your recording and would not call that a misfire. If you want to hear what a misfire sounds like, disconnect the wiring harness connector to a fuel injector or a spark igniter while the engine is running. A Prius engine running on three cylinders is not a pretty sight nor does it make pleasant sounds.

When the Prius is first started after resting overnight, the valve timing is retarded for a brief period to encourage catalytic converter warmup. When the valve timing changes to a normal setting, that will cause the change in engine sound that you observed. If the car performs normally then I would say that you should not worry.

However, I would discourage your son from using high pressure water in the engine compartment in the future, especially on the engine valve cover. It is quite possible for water to enter the spark plug wells, as was previously commented.

A TSB was issued for 2G models because water would tend to drip onto the engine from the center seam of the cowl that runs across the back of the engine compartment. This water can get past the rubber O-ring seals on the igniters, enter the spark plug wells, and cause ignition misfire.

 

I was just reading in Popular Mechanics automotive section that hosing out the engine bay with a pressure washer (or a high pressure hose I suppose) is a bad idea. It can force water under gaskets and seals where it has no business going and can do bad things.

 

I would recommend to use a garden hose with a spray nozzle instead of a high pressure water washer, which may nick or cut the wiring insulation.

 

Why wash at the first place? To promote rust? Wouldn't wiping with a towel sufficient?

 

all,

Just a brief comment here by someone who is not a mechanic. A while back on our 2000 Dodge Caravan (which has since been replaced) we had some very low power issues with its 4 cylinder engine (causing us to use the truck climbing lane on some of the hills on the interstate). We took it to our local mechanic who read a misfire code on his scanner on one of the cylinders. He checked that cylinder & found a small crack in the spark plug's insulator [plugs not too old either (probably 2 yrs or less)]. Apparently it had been arcing/shorting current to the metal of the spark plug well [although there were burns on its plug wire tip too (only about a year old on these)]. So just a new set of plugs & plug wires was all that was needed to restore full power to the Caravan. The individual coils that sit atop each spark plug were fine (thank goodness, as these can be quite expensive as many of you may already know). Nothing had been done under the hood prior to the power loss situation that might have caused the cracked spark plug insulator (& no driving through big, deep puddles or in heavy rain either---so not sure why the insulator cracked).

Ken (in Bolton,Ct)

 

Bear in mind that any water that gets anywhere it shouldn't in or on the engine will evaporate in a matter of minutes when the engine warms up. So, while it could cause a brief problem, it shouldn't cause anything prolonged or permanent. I think your problem lies elsewhere.