Prius III engine knocking at high torque low RPM (solved)

I bought my GenIII prius a few months back and, after a while, I noticed that the motor would start shaking in low RPM - high torque conditions. I went to my Toyota garage, but they cound'nt tell me what was wrong, so I did some investigating of my own:
- All engine mounts seemed OK.
- New sparkplugs --> still same problem.
- Connected ODBII plug --> nothing special.

Then a read a thead about clogged EGR piping that seemed to fit the bill. So I started to take out the intake manifold. Bingo ! The car is running fine now and I decided to put the solution on Prius chat together with some photos that show what is going on.


Firstly: This is the EGR piping. It runs from the exhaust to the intake on the right-hand side of the engine. It makes the engine more environmently friendly in that it reduces N2 emissions by making the engine run cooler than normal. As a bonus fuel economy increases as well...


I took of the air intake, airfilter (screws are inside!) and intake manifold, and this is what I found. Yuck!!!


Before you take off the intake manifold open the intake valve (just rotate 90 deg) and check for any excess oil inside. If there is a puddle of oil use some toilet paper to soak it up. Take care when removing the two coolant hoses. I used a clamp to make sure no coolant leaked out before removing the two hoses. All the other hoses connected to the intake manifold just contain air.


So, what happens when the EGR channels inside the intake manifold get clogged ? Well, in my opinion the 'cold' intake manifold makes the carbon and oil vapour in the exhaust gasses 'condense' inside the intake manifold. The clogging advances from left to right (seen from the front of the car). Above picture shows the intake of the leftmost cilinder. It is clean because no exhaust gasses could reach this cilinder because of the clogging.


The rightmost cilinder however did get more than it's fair share of exhaust gasses. Normally every cilinder would get an equal amount of exhaust gasses, but now the rightmost cilinder gets all, causing the 'misfire' behaviour.


I took the manifold to the workbench and cleaned all channels with a toothbrush with a piece of rubber tubing attached (don't forget to clean the small holes leading to the engine !). I used "wasbenzine" (Dutch. EN: benzene ?) but I am sure normal gasolene would do the trick a well.

After I put back the whole thing I noticed a strange "gasket" stuck between two flanges:

It turned out that someone (I suspect the Toyota dealer !) had put a piece of metal inside to reduce the amount of exhaust gases flowing to the engine (with little success):


Notice the strange shape of the hole. It almost looks like the exhaust gasses punched a hole through the plate !?

I would love to hear what other people have to say about this. I think that every Prius with reasonably high milage will, sooner or later, suffer from this problem. So please, if you had similar problems put your reaction below. Thanks !

 

I think they did it because the previous owner had similar problems as I did and the dealer decided the card did'nt need EGR anymore. If that's the case I would say i'ts a pretty bad habbit ! Did anyone else find a similar 'workaround' onder the hood of his/her Prius ?

 

Bill: I think it may bee too early to tell since I finished the yob only yesterday, but I got a 2,5l/km readout on my 5min MPG indicator today (about half of the average milage). As far as I know that never happened before ! I'll try to give you an update on fuel consumpion the coming weeks...

 

Well... the car has always been serviced by a Toyota dealer... Can't be sure though...
Since this problem should occur in any Toyota Pruis with High milage (?) I am curious to see what other people had done to their Prius to prevent or solve this clogging problem.

 

Bill: "Also, could you tell if there was the 'oilyness' on the EGR valve side of that block off plate?"
The block-off plate was not oily on either side. The oilyness started just at the end of the stainless steel EGR tube leading to the intake manifold. I think that some sort of "condensation" of smoke-particles is taking place in the intake manifold (?).

B.t.w. I found several web sites that sell these "EGR block off plates". It seems to be a common "solution" to EGR problems...

 

I live in the Netherlands.
I did about 200km now with the EGR fix.
It looks like the car uses about .2 liters per 100km less than before.
I asked a collegue of mine if I could have a look under the hood of his 2010 Prius. I could find no evidence of a blockoff plate in his car. His car did about 140,000km.
I am stil puzzled by this. I hope to hear some more about people's experience with high milage gen 3 Priuses and their EGR's.

In the mean while I read the thread about P0304 misfire. Somewhere in the end someone suggested worn piston rings as the underlying problem. Doe anyone have an idea how to check for this ?

 

It's not the misfires I was wondering about. It's the oil puddle in the intake manifold and the clogging of the EGR channels. I think they may be caused by faulty piston rings...

 

Ok, my idea was that somehow excessive amounts of oil get into the exhaust gasses and cause the EGR clogging. The only way they can get there is excessive pcv blowby or worn piston rings (oil scraping rings)... Or am I mistaking ?