EGR clogged Intake Manifold

Cleaning the intake manifold is relatively easy; the cooler will be most difficult. The first couple of links in my signature have tips.

that said, there’s a reason the damper has broken springs. The “misfires” usually are due to coolant collecting in the cylinders, typically starting with cyl 1 or 2, due in turn to long clogged EGR circuit.

Piston comes up but meets resistance due to (incompressible) coolant, conflict ensues, damper takes the brunt of it.

simplest way to determine head gasket integrity seems to be pressurizing coolant system and checking for coolant leaking into cylinder, with a boroscope. Leak down test is also good.

what’s the miles on it? It sounds like you have failing head gasket and broken gasket. Maybe bent piston arm too. If that’s the case, swap in a rebuilt engine?

 

Yes.

my take, it’s a cascade: EGR clogs, head gasket then fails, coolant leaks into cylinder, piston arms bend and/or damper breaks.

 

Last time I cleaned out my EGR cooler I made a cooler cleaning tool.
I bent the rod to hand twist and cut an angle and hand drilled through the carbon. Worked pretty well. Just have to keep track of which holes are done. Can use the second rod down a hole as a reference to where you're at. Then I soaked it in B12 and a rinse.
Can't get at all the holes from either side so do what you can from one side then switch to the other side. Was a pain and can probably use a cordless drill but my pos broke.
I did like using these rods because they are very stiff so I could put some pressure on them without them bending.

Posted via the PriusChat mobile app.

 

Will bring you to replacement or stop all of it ..

 

While that sequence could certainly lead to damage to the damper, it is not the only way damage to the damper can occur. Ordinary misfiring—actual literal simple misfiring, where the piston comes up, compresses a fully compressible mixture, and the stuff just doesn't ignite—can also do it.

It's well established that misfiring in a Prius creates loud banging noises and serious mechanical stresses in the powertrain, because it foils the ECU's attempts to keep the massive MG rotors synchronized with the engine. An early, well-documented example was this one, where an owner let a Prius go for scrap price over what turned out to be one bad spark plug.

It is not helpful to go around putting air quotes on "misfires" and conflating them with hydrolock on incompressible liquid. Misfires and hydrolock are both real things that can happen in engines, but they are drastically different things.

Misfires are individually small events with damaging effects that add up over time if the misfiring isn't corrected. Besides the awful noise, their effects can grow to fatigue failure of the damper springs (which then makes the mechanical stresses much worse, and can eventually break the input shaft off the tranny), and to melting the honeycomb inside the catalytic converter.

Hydrolock puts all the powertrain's rotating mass into compressing an incompressible liquid in a cylinder, a major event that will have left something broken or bent if it happened even once (unless it happened at low enough power to just stop everything cold, and maybe still even then).

 

EGR system introduces exhaust gasses to combustion chamber; the amount and timing controlled by computer. When functioning properly, it definitely changes the temperature pulse with each combustion. @ChapmanF has some graphs. IIRC it spreads out and flattens the peak temperature.

When EGR gasses are stopped the temp spikes higher a shorter duration. If the computers are aware of this they can and do retard timing to protect the engine, but this is a stop gap I think, and the computers can be slow to react. One reason: the clogging can be uneven: overall not bad, but cyl’s one and two (in particular) virtually starved.

and that’s where the head gaskets are commonly failing.

 

When the ECM retards the timing in response to EGR malfunctioning, it does so to reduce the risk of detonation, a very specific, extremely high pressure condition that is mentioned in the literature about EGR as a risk for mechanical damage.

While the graphs showing rate of heat release per degree crank angle are surely part of the story in gauging detonation risk, it is probably a mistake to speak of the heat as being what damages the gasket.

 

Whatever the precise mechanism, I see a cause and effect and opt to thwart it. Specifically: maintain a carbon-clear EGR system, see how that goes.

4th gen EGR appears to do that without intervention, and I don’t recall a single confirmed head gasket failure.

 

Yep exhaust gas recirc cools combustion temps . In the electric EGR valve is capable of variable flow of the puke from the exhaust to the intake by some computer demand and sensors. So that's what you get here You're getting the flow of the puke being regurgitated constantly

 

I'd say the PCV is much more capable of puke. Hence the Oil Catch Cans are employed.

What's coming through the EGR is oxygen depleted air. With enough dry soot to clog itself over the miles though.

 

The damper springs are probably more vulnerable to different hazards, like sustained misfiring.

Springs are springy. Some whacks, even big ones, probably aren't the route to fatigue failure. On the other hand, if an engine is routinely misfiring, not nearly such big whacks, but is driven that way for a long time without fixing the misfiring....