NEW!!! Service Bulletin for Engine Knocking at Startup T-SB 0012-10

Hi there bc9,

Hope the one that got totalled was the "bad" one!

What you say is very interesting, especially that it can happen right after a long drive. Have you tried the "when knocking happens, hit the gas pedal" trick to try to bring it out of this?

How long did you stop for after the 2 1/2 hr trip, and what was the outside temperature at the time?

Even more interesting. I wonder why Toyota is so fixated on the IM...? Presumably, it IS condensation that's getting in to it, do you know?

Of course, that's mechanic's hyperbole for "There was much more water than I'd have expected!" or "... more water than I've ever seen in an IM before!" They can't have meant filled, literally...

There can only have been a "small amount" - I'd guess no more than an eggcup full, if that. If you tried to start the engine with a manifold that was, literally, filled with water, a huge slug of water would get pulled into the first cylinder to have its intake valve open, and if the volume of water was more than 35cc's (35mls, just over 1 US Fluid oz, which is about the volume of the combustion chamber) the engine would get almost to the top of the compression stroke, and would "hydraulic"! It would stop dead, because water cannot be compressed, and something major would probably end up bent or broken. You might bend or break a conrod, break the piston, blow the head gasket or possibly even break the crankshaft or crack the head, depending on how fast it was turning when the piston hit the "solid" lump of water, and which part is the weakest link.

That's not a good explanation by the Service Agent or whoever, unless the water in the manifold happened to be a solid block of ice at the time! What apparently happens is that a small amount (a few mls or less) gets sucked into the cylinder along with the normal air-fuel mixture, and the water splashes all over the spark plug.

Spark plugs don't tend to work when drenched with a few drops of water - they "short out" and don't spark, so that cylinder doesn't fire for a while, causing the engine to run roughly on 3 cylinders. That causes irregular rotation of the engine crankshaft which causes severe blacklash in the power train between the engine and MG1. It's the "lashing back and forth" of all the components (gears etc) that makes the noise.

I suspect this issue is greatly enhanced by the HSD system itself, which is why I want someone to try putting the car into Neutral when the banging noise is happening. (I have a G2 and live in a warm climate so can't try it myself, but the problem fascinates me...)

 

Hi again Guys,

The mind grapples with this new info... Another couple of brief questions, if I may?

I guess it gets pretty cold in WI? Was it very cold out at the time?

sm: I don't think I need to ask if it gets cold in Alaska!

To both,

Can you remember, after the fully warmed up drive and short stop before the knocking incidents, was it windy that day? Could it be that you parked the car with the rear facing into the wind?

I'm still chasing the wet exhaust system, open EGR valve theory, and if it was a cold day with a tail wind when parked, that would potentially blow a lot of water vapour backwards through the IM. If it was that cold, the plastic IM would likely have cooled down pretty quickly, particularly as it is (I think) on the grille side of the engine, creating the perfect scenario for a fast dump of water into the intake manifold.

 

It was in Oct. so I am guessing it was probably in the 40F range. Can't remember any other details about the day.

 

Hi again bc9!

Many thanks for your detailed and very helpful responses!

Yeah, bad luck! Too bad. But if no one was hurt, I guess one can't complain too much.

Sorry - I'm confused here. Is that 0 Celcius or Fahrenheit? If it's F, man, that's cold! Canadian cold air, right? Down that sweep past the Lakes. Spent a few days near there in winter many years back. That was cold!

Yeah, I bet! It's probably no consolation, but I believe having to cope with Ice Ages in our ancient past sharpened the intellect of those forced to live in the Northern regions, real quick! There's always a bright(er) side...

Ok! More vital information. Many thanks.

That completely eliminates the "wind up the bum" theory!

So, I have to come up with a new scenario, but coincidentally, another piece of the puzzle falls into place. This now explains (I think) why Toyota has been so fixated on the Intake Manifold itself. Obviously, they think that's where the problem is. Seems to me, they are not (yet?) considering the condensation as possibly coming from the exhaust system. They designed it, so they should know whether the EGR valve is a possible route. Maybe, in fact, there's a malfunction in some of them (your good car may have had a good one), and maybe they need to start looking at that too, because I'm still 100% positive that this is the most rational explanation for the knocking following a cold soak following one or more interrupted ICE warmups.

Anyway, I was pretty much joking when I suggested the water in the manifold could have been a block of ice. But as the great man said: "Many a true word is spoken in jest." (Whether by accident or intention...)

Carburetor icing has been a problem since the ICE was invented. That's why ICE'd aeroplanes have a carb heat control, and why cars had / have hot coolant manifold heating. (Back in the day, manifold heating was first achieved by bolting the IM on top of the EM beneath the carby, with a "heat riser" plate to stop too much heat getting to the carb after engine shutdown. Back in the day when a bit of fuel evaporation was no concern. It's a wonder more of them didn't catch fire.)

Fuel injected engines are a bit different, as most of the cooling effect (that caused carb icing) was due to the vaporization of the fuel, with some also due to the pressure drop across the throttle valve. Reduced air pressure means colder air, so at low throttle settings, more cooling was due to the increased pressure drop, while at high throttle settings, more was due to the increased fuel flow, so they kind of balanced out. Now, it's all changed.

Now, the throttle body has replaced the carburetor, and the fuel is injected at the other end of the manifold, so these heat and cold problems are quite different, and in different places.

And maybe the guys who Steve1945 quoted were more or less quite right. Maybe the real issue with the plastic manifold isn't that it cools down too quickly (as it isn't going to get hot anyway, being plastic, and sitting out front in the cold air stream, carrying cold intake air to the engine). Maybe the real problem, in extremely cold climates, is that the plastic manifold doesn't conduct quite enough heat from the hot engine head, down the individual arms of the manifold, to stop ice forming inside it during long trips through freezing conditions. AFAIK, this problem has never been reported in the Gen2, which has an aluminium IM. Maybe this metal IM conducts enough heat down the arms to keep any condensation that formed while running, in the liquid state. This small amount of condensation would simply be sucked into the cylinders along with the normal fuel-air mix, and provide a form of "water-injected" combustion, FWIW...

HOWEVER, with the plastic manifold which would conduct very little heat, under those rare conditions very like those which form ice on the wings of aeroplanes, ice probably forms inside the intake manifold when running at higher speeds through very cold, damp air. While you are running, this ice is probably not going to present much of a problem. It probably just forms a thin layer on the inside of the manifold - maybe 1 or 2mm thick. This won't restrict the airflow very much, and given that very cold air increases engine efficiency anyway, and you probably wouldn't notice any difference. Unless you ran for a whole day non-stop, maybe.

BUT, get to where you are going and stop the car... As soon as the car stops the cold airflow also stops, and thanks to a little heat from the warm engine, the ice inside the manifold is gonna melt, and run down to form a puddle in the bottom, pretty much right below the throttle valve plate. If you had say 1mm of ice over the entire inside surface of the plastic manifold, that would create quite a puddle. If, say (guessing, looking at my G2 manifold), the inside surface area is equivalent to a pipe 400mm long x 30mm diameter, and you have 1mm of ice evenly coating the entire surface (of course, you won't), that works out to be 30 x pi x 400 / 1000 ~= 38mls of water!!!

That's a scary amount of water to be sitting inside the IM. No wonder the mechanics were describing this as FILLED! But is it all starting to make sense, and the pieces are starting to fit together.

Of course, when starting the engine with this much water in the manifold, it's going to seriously misfire, for quite a while. It's lucky it runs at all!

Incidentally, the volume of water I calculated (38mls) which was based on a pure guess, works out to be just a little more than the combustion volume of one cylinder in the 1.8 litre Prius engine.

BUT DON'T WORRY. It wouldn't be possible to get all of this water to flow uphill, aided by air flow, into just one cylinder, to cause hydraulic-ing. But now I see why the Japanese have been messing with the IM design.

So, many thanks to all who have contributed their valuable observations.

I'm not 100% sure, but looking at my G2 intake manifold, it appears to be coolant heated, perhaps through the hoses running to the throttle body, and I imagine this is necessary to prevent manifold icing. I have no idea what happens with the G3 plastic manifold, but I can see there could be major differences, and particular issues, particularly with heat transfer through the plastic. I guess this is partly why the revised manifolds don't seem to work in all cases.

Or, it may be entirely because, in fact, there are two problems, one of which they haven't yet recognised. If that is the case, then maybe the manifold changes DO fix manifold icing, but don't address an open EGR valve during cold soak, which is entirely a different problem.

To analyse that, we'd need to now who has the latest manifold but still gets bad starting right after a long trip. If that happens, the manifold fix has not worked, but I haven't tried that analysis yet...

 

Of course, other ways to prevent this and give your engine an easier life as well, is to fit a winter curtain over part of your radiator.

But that must be pretty scary to do in a vehicle with no temperature gauges!

 

This is to benefit the new folks looking for ideas.
Please comment if you have found another option. Details on each one can be found with a search in PC.
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Current site Suggestions/Ideas to help minimize engine knocking issue

1.) At the start up, press gas pedal down method before ICE starts.
2.) Move from the recommended 87 octane to the higher 93 octane with Heet gas treatment.
3.) Also try to just put it in gear right away
4.) On short car movements(ie. in driveway), wait for initial warm-up to finish before shutdown.

Of course YMMV.

 

Got it back and will monitor for knocking. It is smoother with the new mount. Funny thing I asked they reprogram the door handles so that when you grab the drivers door they all unlock. They charged me $20 for that and it does not work. Tech plugged in the pc again and I watched him go to smart key then unlock and change from driver to all. Still does not work? Any ideas? And they kept the $20!


iPhone ?

 

Got it back and will monitor for knocking. It is smoother with the new mount. Funny thing I asked they reprogram the door handles so that when you grab the drivers door they all unlock. They charged me $20 for that and it does not work. Tech plugged in the pc again and I watched him go to smart key then unlock and change from driver to all. Still does not work? Any ideas? And they kept the $20!


iPhone ?

 

And now it works! Let it sit for 20 min and went out again and this time it works! Go figure. All doors unlock with one touch of drivers handle. I'm happy.


iPhone ?

 

The procedure wasn't in your owner's manual?

 

It requires the pc odbc plug in.


iPhone ?

 

I jinxed. Now the brake Pedal goes to floor and the skid control light comes on. Geez. What a joke. Car goes in for 7 days and they jack up the repair.


iPhone ?

 

On mine, you can change the driver's door handle function back and forth by holding the transmitter lock button down and then pressing the unlock button down for about 5 seconds, with the power switch off. It'll cycle to driver's door only or to all doors. It's under the opening, closing and locking the doors section of the owner's manual.

 

Yep I checked my manual and it says you need the dealer. And it seems so because as I said, I watched him do it. Is yours a 2010?


iPhone ?

 

I thought if seen it all, but the Prius still surprises me. I think I'm just activating the hill start assist by pumping the brakes to the floor. Maybe it is ok. Does everybody have a relatively soft brake pedal that goes to the floor? Also, I hear the accumulator / booster run with a couple if pumps? Normal?


iPhone ?

 

When I had the 2010 III, the pedal would not go to the floor without a LOT of pressure. It shouldn't feel soft. How much mileage does your car have on it? Not sure but maybe it needs the brake accumulator fix.

 

They must have changed it for 2011 and 2012 then, for both could be changed through the remote.