What is the benefit of the EGR system and can it be bypassed.

depends on your state inspection. not where they inspect emissions

 

sometimes stupid fits, even with engineers. from what i understand, gen4 is different. some people have to learn the hard way...

 

I didn't really have a clue about EGR till a few years after we got our Prius, Just a couple of glimmers now:

1. It reduces air pollution.
2. It allows engine to run a bit more efficiently, without overheating: the reintroduced exhaust gasses slow combustion, reduce temps. (That's assuming it's in pristine condition.)

I would think it's simpler/smarter to just maintain it (clean it, and the intake manifold, and maybe throw in an Oil Catch Can), then to second-guess the engineers.

The sense I get is that Toyota rushes cars to market, with insufficient long-term testing: there's been a few carbon-clogged horror stories, high mileage 3rd gen cabs.

 

Specifically, it reduces formation of nitrogen oxides by lowering peak temperature during combustion.

 

EGR has historically been use to reduce NOx emissions. I understand it does this by reducing the temperature of combustion. I've been thinking lately on my long commute about the EGR and all the posts about plugged systems and failed head gaskets and such. Are we really certain that restricted to blocked EGR is directly contributing to head gasket failure? I can't imagine this failure mode with engine oil and the cooling system keeping the engine block at functional temperatures. Is it a point overheating issue or insufficient gasket material between cylinders or something like that?

 

Every piston engine gets its power from displacement- the amount of air it can breathe on each cycle. There is a fixed ratio between the amount of air breathed and gasoline burnt- at least over a long average. If some of that air isn't actually oxygen-bearing air, then you will burn less gasoline. You are technically making the engine a little smaller and less powerful. You get the added benefit of lower combustion temperatures. And if you control the EGR flow through a valve, you gain a simple way of controlling quite a lot of the engine's total range. Almost a way to dial-a-size.

Giving it up would create many complications and sacrifice efficiency. You'd potentially gain some real HP though. Maybe not though. A Prius is a rolling computer- it's programmed to expect certain behavior from each system. Changing the behavior of the engine could freak it out.

 

Here is an article on that: Clean and cool: cooled EGR improves fuel economy and emissions in gasoline engines. Technology Today, Southwest Research Institute, Summer 2010, pp. 10–13

That link is to a copy on yumpu, because the hosting site at SwRI seems broken at the moment. Yumpu is one of these annoying document-host sites that will show you page images in-browser but not let you download unless you bend over sign up. But you can read the whole thing in the in-browser view.

I will fling defiance at the copyright gods and paste the conclusion:

Not peanuts.

Turns out there are such codes, P0401 for "EGR flow insufficient detected" (the ECU actively checks for this by opening and closing the EGR valve during times of coasting without fuel injection, to see how much the manifold pressure reading changes) and P0403 for electrical open or short in the EGR valve circuit.

It's worth saying that, as far as I can tell, the connection between the EGR system and head gasket failures has the status still of a PriusChat theory. It has advocates, and they are members I respect, and they have posted explanations of why such a connection could be plausible. I'm not saying I disagree. It's just that, well, the difference between arguing that something is plausible and showing that it really is what's behind the head gasket issues would call for an amount of work and data comparable to getting a research paper published, and that hasn't been part of anything I've seen posted on the subject so far. So in my head, anyway, it is still hovering in the vicinity of something that's been proposed as plausible, but not yet conclusively shown.

 

The EGR system is for smog reduction only...and required by law. There are much easier and better ways to control engine efficiency/power/durablity than dumping raw exhaust into the metered fuel/air intake and combustion chamber. The problem with work-arounds is that the software must be addressed...the mechanicals are easy. This is very common in diesel circles, but the green factor in Prius circles has not created enough demand for our s/w solution to be "made available"...legal or not.

 

Or, it could be there for all of the reasons found in the work quoted in #9.

 

What a maddening link. At least in my version of firefox, if I zoom in one increment to make it legible, the tool bars disappear, and I'm stuck, have to reload the page, back to default scale. It invites plagirism: it's the only way to make it readable, lol.

 

I ended up going fullscreen; that way it was readable without having to wrestle with the zoom controls.

 

Yeah I did that, then did a print-screen, then paste/crop/save as jpeg in Photoshop, then compile to a pdf. Which it was to begin with I suppose.

It's reasonably legible then with fit-by-width, which I set as default.

Interesting stuff too, just skimming so far, might be as far as I can get, lol. Relating to this this thread, I think it reinforces the argument, to just maintain the EGR, keep it close to as-new condition.

That shouldn't have to be, considering how buried it is, but I guess that's the 3rd gen penance.

 

Wait til you feast your eyes on a Gen4 or Prime for egr cooler access .

Makes the Gen3 look like a walk in the park .

When I do our Prime, I’ll probably end up shifting the inverter for access.

Time will tell.

 

They've more-or-less doubled the cross-sectional volume of the EGR too. If access is so difficult, definitely good to just monitor the EGR pipe at first. Are you contemplating an OCC install too?

Judging from the article, the EGR allows significant mpg improvements.

 

I do plan on installing an OCC, but time hasn’t been on my side now that school is out for my kids.

But for your viewing pleasure, here’s our Prime under the hood around the egr cooler:


Pretty tight and that’s the inverter next to it.

All in the name of getting the 12 volt up front.

But I’ll get it sorted eventually .

 

If you haven't, take a look through the throttle body, see if there's a pool accumulating? Who knows, maybe fourth gen PCV is improved?

The pipe at least looks to be reasonably accessible, the "canary".

 

I’ll probably have time in a couple of weekends to take a look.

The pipe is the canary in the coal mine for sure, but isn’t always accurate in its portrayal of the facts.

But getting 150 mpg definitely extends the time of the cleanse in my mind.

But I’m the preventative maintenance type, so you know it’ll get inspected .

 

Rub it in...