Super cold (around 15 degrees) start this morning, engine started very rough

Sad thing about that video: all the goop in the intake is going to run down to a storm drain, into nearby streams.

I did all this about a week back, used and collected about a 1/2 cup of brake cleaner. Poured it over about a cup of kitty litter in a tray, left outside the back door to vaporize. Just bagged up the kitty litter, disposed in trash.



for the cooler, oxi clean solution (a mildly caustic cleaner soaks, in laundry sink: drain into sanitary sewer.

 

The most "super cold" condition in which I ever started my Prius was at about 8°F. It was not a rough start. The most alarmingly rough starts, as best I can recall, were in humid weather with temperatures in the 40s or 50s°F. The worst time involved the following sequence:
1) 400+ mile all-day trip;
2) left car parked through the following rainy night;
3) next morning, seemingly normal start to move the car only a very short distance;
4) shut engine off after only a couple of seconds;
5) about one day later, the very rough start.

That's an example of a phenomenon others have also observed, but nobody has clearly explained, to my knowledge, i.e., that too-brief engine run time somehow causes the NEXT start to be rough, a day or more later.

 

If you turn off the car while the ICE is running…

The engine shuts off immediately. The injected fuel stays trapped by the fuel vapor trap. How this causes a rough start maybe you’d know better than me, but I suspect this travels to cylinders it shouldn’t because of the Atkinson design and intake valves left open longer than straight Otto cycle.

When the car shuts off the engine to run on EV it does so by cutting off fuel supply, to avoid this. That is why it doesn’t feel as smooth as when you force a shut down by pressing the start button…

 

I stand corrected.
I'm used to dealing in absolute pressure measurements. I should have thought this through better.

There is the situation where Full throttle (or close) manifold pressure is less than the small amount of Exhaust back pressure. In that case the EGR is pushed into the intake instead of being sucked in.

 

Pressing the power button to turn the car off isn't anything like throwing a kill switch. The button is an input to the power management control ECU, which then says to itself "oh, the driver would like to power down" and follows its programmed sequence of shutdown steps. For example, if the driver has not shifted to Park yet, it will make sure to do that first.

The idea that the power management control ECU sends any different kind of shutdown command to the ECM in the one situation compared to the other sounds like one I'd want to see some clear evidence for. Has someone got that?

Exhaust will flow through a passage whenever the pressure at one end is above the pressure at the other. That's always the case as it flows through the EGR system. During engine operation, the pressure in the intake will always be at least a little below atmospheric, and the pressure in the exhaust always at least a little above. By transitivity, the intake pressure is below the exhaust pressure, which is all that matters for the gas to flow. The same thing is happening whether we call it pushed or sucked.

 

I'd be skeptical that the vapor recovery system is involved. It mainly deals with fuel vapor from the tank.
Whether, previously injected fuel is somehow involved in rough starts, I'm doubtful, but not sure. There's a thing in the air cleaner housing that's supposed to absorb fuel vapor to prevent it from escaping via that route to the great outdoors from the manifold (and possibly from a cylinder with an open intake valve?).

 

Nicekonbass: You presuppose that I'm saying something inappropriate to Mendel when I'm allowed to have an intellectual debate with him. Your presupposition serves your purposes as it allows you to sculpt out inappropriate diagnoses which are not founded on testing. I'll have a debate with you too but we are trying to do is scotch my opinion by proclaiming that I've treated somebody else inappropriately which I have not. I do not appreciate this attempt to make me quiet. You're wrong for not doing a diagnostic workup and trying to make me look bad is not going to make me quiet about your failure to do the hard work which is necessary to make appropriate diagnoses. I do not appreciate you trying to make me look bad in your pursuits. You've crossed the line from intellectual debate to manipulation. When you seek to squelch someone else by ulterior means that is the definition of manipulation. I'm not tolerant of that. And for that I do not respect you. I also do not respect you for not doing the hard work of diagnostics. So please do not attempt again to make me look bad by ulterior means. It is clearly your avoidance of the hard work of diagnosing your problems. I wish you luck as you seek a cheaper way to solve your issues. Good luck my friend.

And with that I am done with this thread.

 

As a "ASE certified mechanic-Hybrid Repair Certified" can you describe some of the steps he, as a simple Prius owner, could have done with this intermittent issue?

I, as a simple Prius owner, assume that an oil/water emulsion that was pooled in the intake manifold got sucked into combustion chambers at start up and that was that?
Shake, rattle and roll. Not good for the engine, correct?

What can be done once that pool has been digested?

I can't imagine a 'Trouble Tree' to get to the bottom of this intermittent issue.
Is there one that you would follow?
What is this 'Hard Work' you mention?
Do you have a step by step idea of what you would do?

Me? I'd hang an oil catch can with each hose having a downhill slope to the can.
I'd install it while doing a complete EGR cleaning service and engine coolant change.

And then I'd still worry that the head gasket will fail within the next 50-100K miles.

 

It's been my experience to find that little pool down below the throttle body in every Prius, all the time (unless someone has just gotten done sopping it out).

Maybe the notion that it has been slurped a foot upward, by the slow-moving starting/idle airflow in the large bores of the manifold, could be checked by taking a quick look afterward to see if it has disappeared?

 

That is the “HC” trap that I am referring to. It’s been on the air filter housings from at least (our 2004 Sienna). Putting in an aftermarket intake removes this, and since aftermarket have not incorporated one, all have failed to get CARB EO#s from CARB.

I believe the engine shuts of instantly when the power button is pressed. (Gonna have to do some research to check my theory it is different when running and it is shut off due to EV mode…). I could see Toyota sued if there were some sort of delay between pressing the button and engine stopping…

 

I doubt a human would be able to notice the delay between when the power management control ECU sends the ECM an engine stop command while driving and when the engine stops, either.

 

I stand corrected. I have never removed a prius throttle body.
It still seems strange to always have that sloshing around down there.
What limits its quantity?
What if you get air at a crest of a hill at full throttle and that pool gets airborne also?

What do you believe causes the cold start clatter/knocking ?

 

Often it's more comfortable to me to just say I don't know, rather than to not know and say something else anyway.

One time you can definitely get cold start clatter/knocking is when a head gasket leak is letting some coolant into a cylinder while the engine is stopped. But that can't be the story every time, because there do seem to be cold-start clatters and knocks that aren't head-gasket failures. And there is that pattern where they seem to crop up when the engine has cold-soaked after running only briefly, not up to operating temp.

There was some talk a decade ago, when T-SB-0010-12 first came out, of some redesign to the intake manifold to make it harder to aspirate water that has condensed in the EGR passages (which would also cause a clatter, naturally). I don't think the TSB itself came right out and said that (it just said "we've got this spiffy new manifold, put that on").

It was just somebody here, in this post. And, as so very often, that poster didn't say a word about where that information came from, or why it should be believed. And it seems not to be remembered as much, these days, in discussions that come up about what's going on.

But there do seem to be some things making it plausible. The EGR passages in the manifold did get changed, less of a straight shot in the new one. Exhaust is largely water, which can condense in there, in cool weather. When I have taken my EGR pipe off, I have poured some clear condensed water out of it.

And the idea of slurping some water out of the EGR passages on startup is a lot easier to picture than slurping some goop from a foot below that level down at the throttle body. The EGR passages are of small diameter and located just barely below the intake ports.

The EGR valve should be closed at startup. But if those passages contain some water and some air at atmospheric pressure, and then the engine cranks and the whole area drops to 20 inHg vacuum, the sudden expansion of the air in those skinny passages could easily spray the water out. That, I could see happening.

The remaining question would be: is there something about running the engine briefly, shutting it off before warm, that might leave more water vapor to condense in the EGR passages than there would normally be if it had warmed up?

That's a part of the picture I don't think I have a clear story for. The EGR valve would have to have opened some, for any moisture-bearing exhaust to have arrived there. I don't expect it to open at idle. But perhaps if the car is driven a little distance, like down the driveway, the valve might have opened briefly, some water or water vapor could end up in those passages, and then the car is turned off without fully warming up.

So, again, I haven't seen enough details in that story to hang my hat on it. But it's got, at least, some elements less hard to believe than some of the other explanations going around.

It doesn't have to be the only explanation for super-cold-start rattles, either. Maybe it mostly explains the ones that happen after partial warmup. (Or maybe it doesn't. )

Beyond that, engines just haven't ever been very easy to start in super cold. They're balky and run poorly for a few seconds. And a Prius powertrain running poorly will pretty much always sound awful.

 

There are actually two (or three) T-SBs, one for the updated intake manifold and one for a redesigned EGR valve. (I believe I saw a third but I’ve misplaced them now, found back towards the end of 2020 when I last subscribed to TIS).

It’s $20 for two days, and really worth it if you figure/understand how to use it.

In really cold weather per Toyota, and not so cold weather (I have experienced) cold start knock/rattle. Toyota says a stuck EGR valve can cause it and has a redesigned one. I believe the manifold caused a no start in extreme cold, hence the updated manifold. Both have the same ECU flash from what I could tell.

My car has the flash but old EGR, and likely the old manifold. It never gets that cold here and I haven’t had a no start….

 

Thanks for this informative and very plausible explanation!
And the link to the new intake explanation.

This brings back the idea of insulating that stainless steel pipe from the EGR valve to the plastic manifold to keep the gasses hot so there is less condensation settling out onto the pipe.
(I got this idea from a friends diesel. Its pipe is about 2ft long and has a factory insulated sleeve.)

And then why not insulate the top area of the intake manifold where the EGR passages are?
(spray foam covered with saranwrap, and molded gently into place. Peal off the plastic wrap, trim excess, and some spray paint...)

Dang, it's winter again. I'm thinking in terms of cold.
Need to install the block heater, put the pipe foam tubes over the lower grill, what else?

 

You’re doing that? There’s some install tips in my signature.

 

Clean egr, install red bullet solenoid, custco chassis braces, and short ram air in take!!!