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EGR clogged Intake Manifold

Discussion in 'Gen 3 Prius Technical Discussion' started by donzoh1, Dec 15, 2022.

  1. donzoh1

    donzoh1 Active Member

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    I'm fixing a Gen 3 Prius that I will likely use personally, possibly for Uber or similar tasks. I am replacing the input damper plate which has broken springs which I believe were caused by misfire and there were misfire codes in three cylinders. The small ports at each intake manifold opening show various levels of obstruction with one appearing totally clogged.

    I believe the Toyota TSB on this suggests replacement of the manifold but I'm wondering whether cleaning the ports will work. I'd rather avoid the $200 expense of a new one. I'm planning to clean the EGR cooler and associated parts. I don't know yet whether the TSB computer update has been done.
     
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    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?
     
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  3. donzoh1

    donzoh1 Active Member

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    This particular car has already been down the bent piston road so if there's a head gasket issue, I will definitely be checking that. Would the coolant get in through the broken gasket or can it get in through the EGR cooler? This car had a broken gasket and then the bent piston rod. I am planning a leakdown test after I get the engine out of the car and I'm guessing that will show any problem with the head gasket. It doesn't make white smoke, doesn't have oil/coolant mixing, and doesn't lose coolant. But, I think it did overheat because it has some coolant spray remnants between the coolant reservoir and radiator. I didn't see any coolant in the intake manifold at least.

    I was hoping the misfire codes were from EGR fouling of intake manifold ports.
     
  4. donzoh1

    donzoh1 Active Member

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    1. The car has 180K but the engine has around 120K.
     
  5. donzoh1

    donzoh1 Active Member

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    It also had the P261b code for coolant pump which I think went along with the overheating. I don't mind doing the head gasket but a bent piston rod might bring me to engine replacement.
     
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  6. Mendel Leisk

    Mendel Leisk Senior Member

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    Yes.

    my take, it’s a cascade: EGR clogs, head gasket then fails, coolant leaks into cylinder, piston arms bend and/or damper breaks.
     
    #6 Mendel Leisk, Dec 15, 2022
    Last edited: Dec 16, 2022
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  7. Raphael Muscarelle

    Raphael Muscarelle Active Member

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    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. IMG20221216060418.jpeg IMG20221216060450.jpeg IMG20221216061337.jpeg

    Posted via the PriusChat mobile app.
     
    #7 Raphael Muscarelle, Dec 16, 2022
    Last edited: Dec 16, 2022
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  8. Tombukt2

    Tombukt2 Senior Member

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    Will bring you to replacement or stop all of it ..
     
  9. donzoh1

    donzoh1 Active Member

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    I saw an engine on LKQ with 60K for $750 shipped. I would also consider a rebuilt but I'm guessing that would be quite a bit more.
    I'd definitely agree that the problems now are likely way worse than when things started. The prior owner had a habit of driving well beyond the first signs of trouble until severe failure. (In this case, it was the awful banging of the broken damper/springs that caused him to seek help.) I am still curious as to why EGR caused broken head gasket.

    The prior time when he broke the car, there was a bent piston rod from the coolant injected past the broken head gasket, although then there was white smoke and hard starting. Opposing sides of one cylinder had also been nicely polished by the offset piston.
     
  10. ChapmanF

    ChapmanF Senior Member

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    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).
     
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  11. Mendel Leisk

    Mendel Leisk Senior Member

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    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.
     
  12. ChapmanF

    ChapmanF Senior Member

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    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.
     
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  13. Mendel Leisk

    Mendel Leisk Senior Member

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    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.
     
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  14. Tombukt2

    Tombukt2 Senior Member

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    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
     
  15. Mendel Leisk

    Mendel Leisk Senior Member

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    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.
     
  16. donzoh1

    donzoh1 Active Member

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    If I recall correctly, when I worked on this car several years back, it had the head gasket failure in cylinder 1 or between 1 and 2. At the time, I knew nothing about the EGR problem. Of course, this motor is a different one and it brought its original EGR setup to the party.
     
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  17. donzoh1

    donzoh1 Active Member

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    This cars first ICE was repeatedly hydrolocked with the result that the number 1 piston rod bent and eventually broke. In the recent trouble with this replacement motor, there was at least one overheat but no white smoke and I don't believe any hydrolocking. There was initially a code relating to the water pump and for cylinder misfires in 1, 2, and 3 although I think the owner had also cleared some codes so there could have been more. I see clogging in several intake ports.
     
  18. donzoh1

    donzoh1 Active Member

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    I haven't even looked in the EGR cooler yet where I'm guessing there's clogging but there for sure is clogging in the small intake manifold ports.
     
  19. donzoh1

    donzoh1 Active Member

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    Interestingly, the damper springs in the first power train were not damaged by the hydrolocking or by the catastrophic engine failure.
     
  20. ChapmanF

    ChapmanF Senior Member

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    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....