Suddenly getting misfires on all four cylinders

Were the hydraulic adjusters at the fulcrum end of the arms functional? I don't understand how rocker arms can come off.

 

Were the hydraulic adjusters at the fulcrum end of the arms *present*?

*That* is an easy question to answer, by angling your gaze down at the crankshaft harmonic damper while trying to start.

 

I could imagine a scenario where the valves hit the pistons and the rockers came off. Or whoever machined your head took everything apart and did not label where the individual parts came from. I think you are at pull the head time and with it, the timing chain, no matter what.

I would certainly check the cylinders with a borescope while rotating the engine by hand.

The real question is do you go to that much trouble or just buy and install the Hybrid Pit rebuilt engine? You seem to have already lost the gunfight at the O.K. Corral.

 

Whatever the outcome, it beats the impasse you were at. Good that you’re treading cautiously.

 

Performing a Root Cause / Failure Mode Analysis is always a good idea in an industrial analysis when trying to understand an unexpected failure. In my working experience it sometimes never becomes clear but repeated incidents often present a pattern. I would expect you will find other broken parts. One of them, possibly the rocker installation, will point to a timing fault.

We do know these engines will run with bent connecting rods and slightly off timing chains. Until they further fail. Your case seems to be different variation.

In this video, the suggested hg symptoms seem to include losing significant coolant. That is not always the case in the beginning. Too often a simple hg replacement fails and the results include broken parts and or holes in the block.

 

I believe it was somewhere through model year 2014 the Prius hatchback pistons and rings were changed. With Prius v it's "similar". Specifically, it's per the VIN numbers in attached:

 

New pistons and rings in mid 2014 were standard on all variations. 2015 is the last gen3 for hatchbacks while 2017 was the last gen3 in a v.

Toyota admitted bad rings on the 2010-2014 Prius engines and changed the parts free if high oil consumption occurred during warranty. High consumption was defined as a quart every 1200 miles or worse, which almost never happened during the powertrain warranty. Nevertheless, low tension piston rings were a problem on many Toyota models of the era. One of their issues was excessive blowby whose symptoms include oil in the intake manifold. Excessive oil consumption came later in the engines life. 5k oil changes are now recommended by most Toyota mechanics and other experienced professionals for these engines, especially if started early in the engine's life.

Often the best explanation of a previous generation's faults lies in an examination of the next generation's changes. In other products the improvements are often used in marketing. Not with Toyota, probably due to liability concerns.

Gen4 Cylinder Wall Cooling Improvements

A new large volume gen4 EGR system was designed to pull exhaust gases from downstream of the cat rather than before the cat as used in gen3. New intakes and piston designs were incorporated in gen4.

 

We see far less hg problems on the post ring vins. A v inherently has appeal due to cargo space, a better highway ride with pitch and bounce control and 16" tires. Ideally its a 2015-17 facelift version with improved radio and crash test ratings.

There are cost of ownership advantages buying used even if an engine around 200k becomes necessary. I hate seeing uber and delivery buyers buying one for their livelyhood, especially now in an overpriced market just because they currently look and drive good.

Change the oil at 5k mile intervals like your wallet depends on it.

 

For 3rd gen, Toyota Canada says 8000 kms (roughly 5K miles) OR 6 months, whichever comes first. Accordingly I'm doing the oil every spring and fall. Yearly kms are about 3000...

I'm not so sure the 2015's have a "get out of jail free" card for head gasket issues. Clean dem EGR's.

 

Its kind of like the LBJ killed JFK conspiracy theories, in this case uneven distribution of egr gasses due to egr intake port clogging. Toyota and their Master mechanics say do nothing unless you get an egr code. A symptom, not a cause.

 

Ok, my conspiracy theory:

Exhaust Gas Recirculation was introduced lintroduced in gen 3 to lower emissions. It also has a damping effect on combustion chamber temps, flattening/broadening the temp spike. The engineers are striving for maximum efficiency, use air/fuel ratios, valve timing and all to achieve this, relying on the damping effect of the EGR system, to keep from going too far. Kind of like an interference engine: it works, but only as long as nothing goes awry.

The problem: the 3rd gen EGR system can have overall reduced exhaust gas flow (due to progressive clogging of the cooler/valve assembly, and, local to particular cylinder(s), near-zero flow (due to virtually complete clogging of the EGR capillary passages in the intake manifold, one per intake port). The latter usually clogs progressively starting at cylinder one (passenger side).

End result of an engine with blocked EGR flow is more abrupt and higher temp pulses, with each combustion. My 2 cents, that's what's toasting third gen head gaskets.

Corroboration:

1. The 3rd gen gasket failures are almost without fail at the thin wall between cylinders one and two, the same order as the intake manifold EGR passage clogging sequence.

2. The clogging goes from modest to moderate somewhere between 100~150K miles. And that's when the head gaskets start failing.

3. There's a few members here periodically cleaning the EGR, and AFAIK, have had no head gasket failures.

There are reports where owners have left it, say till around 150k miles or more, begin to get cold-start shakes, and then get into EGR cleaning. Which is closing the barn door after the horses have bolted?

4. 4th gen has essentially the same engine, but a revised EGR, with significant increase in cross-section, inlet moved from exhaust manifold to downstream of the Cat, and likely revised programming.

@jerrymildred (working at Tampa Hybrids) was tasked with cleaning a 4th gen owner's EGR components, and reported it pretty much a wasted effort, it was so clean still. And this was over 300K miles IIRC.

AFAIK there has not been a single instance of head gasket failure in a fourth gen reported here. There has been a rash of exhaust heat recovery failures, that also causes coolant drop, so lots of false alarms.

 

For my money changing the hv battery cells is far easier than replacing an engine or worse yet, changing a head gasket in the car.