EGR delete or disabling through software

Not to dispute, just to understand: How does a plugged EGR passage cause a misfire (say, cylinder 1)?

 

The same way that forcing too much EGR via the Techstream active test for the EGR valve causes misfires in all the cylinders, only here they are concentrated in the cylinder that is blocked the least. You get too high a percentage of EGR and your precious air/fuel ratio is no longer perfect for combustion.

 

@ChapmanF

Well now you know it helps with the warm up cycle.


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Do I? The part where you were going to argue that it does is missing from your posts.

As is the part where you acknowledge that this was false:

 

Just to elaborate on this a little: the ECM does get feedback information on how much EGR is flowing; there is a manifold absolute pressure sensor. But there's only one for the whole manifold, so it doesn't know if the right amount is flowing from all four ports, or just too little from some and too much from others, coming out to the right overall amount.

If that's happening, the cylinders getting too little face detonation risk, and the ones getting too much face misfire risk.

 

The whole EGR system, and the EGR passages in the intake manifold, can clog, royally. A further foible of the 3rd gen system: the intake EGR capillary passages, tend to prone progressively, becoming completely clogged first at cylinder #1 end (passenger side, aka right side).

As the combustion chambers are denied exhaust gas they get hotter. As they get hotter they accelerate deterioration of the head gasket seal, coolant starts getting into the combustion chamber, and so on.

when the car rolls out of the factory the EGR is all shiny clean. After 125~150k miles, the guts look like this:

 

insanity! There’s no way that the head gasket would ever blow due to that!!!

 

This is another oft-repeated part of the story that we don't really have evidence for; the effect of EGR on combustion is to change the shape of the heat-release-over-time curve, not the area under that curve (total amount of heat released), and whether it has much of any macro effect on the temperature of the water-jacketed aluminum for that cylinder compared to its neighbors is a question without evidence presented on PriusChat to date.

What is supported in published literature is that a cylinder getting too little EGR faces detonation risk, and detonation certainly stresses everything in sight including the head gasket.

 

I gather that misfires themselves are also considered dangerous to engines.
(Could that be why Toyota has those warnings in the EGR valve active test instructions?)

 

I don't think misfires stress the combustion chamber to the same extent detonation does. But they do send unburned fuel down into the catalytic converter, which can melt the honeycomb there and make a bad situation. (Ever seen misfiring where the check-engine light flashes? The ECM decides whether to flash the light by calculating how much unburned fuel is getting to the cat, and whether it's in danger of getting melted.)

In a Prius, misfiring also bounces around the tranny input shaft and the springs in the torque damper pretty well, sometimes leaving bits of those springs in the bottom of the bellhousing where you can scoop them out through the little hand hole.

 

@wheezyglider , @ChapmanF , and @Mendel Leisk : Thank you.

 

At the risk to the near-kumbaya detente in this thread , it's interesting that in the Gen 4 teardown article they show Toyota moving heaven and earth to manage temperature at that location (not just waiting around for the thermostat to just average everything out).

 

That is interesting. I'm not sure how much it bears on the issues in this thread, though.

When we talk about the way EGR changes the shape of the heat release curve, we're talking about a curve that is measured in mere degrees of crank angle. A pattern repeating itself 25 times every second in every cylinder at 3000 rpm.



There isn't any hint there of "waiting for the thermostat to just average everything out" (a much, much, much slower proposition).

The issue is more: given the mass of aluminum involved (and the fact that aluminum has a crazy high specific heat, higher than concrete), what do we think happens to it whether the same amount of heat inside the cylinder is released to it over 20° or 80° of crank angle?

 

In the right chart, the rise in NOx levels “looks” alarming, is it significantl?

Any 3rd gen with 150k (miles) and no cleaning done; it’s maybe out of compliance for NOx? Or by 200k?

 

Yep, it's always been a good idea to dump raw exhaust into a clean intake charge.

EGR systems are about smog control folks...not engine efficiency, mpg or anything else. The side bars are BS arguments.

The problem with the Prius egr system is it was designed worse than what VW used on the TDI. Clean it, replace it or delete it...if they ever come out with delete s/w.

 

Yes this EGR system is poorly designed. Yes you (and many others) don't like have to deal with the problems it causes. But there's never going to be any legal delete for it because that would be federal emissions tampering. You might not have local emissions inspections or enforcement but any company that offered anything like that would get charged by the feds.

Posted via the PriusChat mobile app.

 

Well, again, it's a closed loop feedback-controlled system; it has the MAP sensor to tell it how far to open the valve to get the flow it wants, as long as it can at all.

Again, the shape of the curves on the right is plotted with degrees of crank angle as the x axis; the steep rise in the graph is showing you how essentially all of the NOx that's going to be produced, in one power stroke, gets produced in the first 20 or 30 degrees of rotation following the spark (the first 1/600 of a second or so, at 3,000 rpm).

The heights of the different curves are showing how extremely effective the EGR at 20% is for cutting down the NOx.

Umm, sure, you already showed us that's what you think.

Anybody can come to a subject not understanding it well, but it takes a special kind of dedication to stay that way when accurate information is published and easy to find.

What you're saying is pretty much true for diesels; they get a smog benefit from EGR, but it costs them MPG. At least that was still true for diesels as of the write-ups I've seen. (People have a pesky way of improving technology while I'm not looking.)

It's not at all true for spark-ignited gasoline engines; they get the smog benefit and an MPG benefit, rather large one too.

Why? Besides the effect of pumping loss across the throttle ... take a moment to remind yourself what pre-EGR gasoline engines did to keep combustion temps down at high load. (Hint: the Journal of Engine Research article linked to back in post #12 gave result data "with the largest improvement occurring in the typical enrichment region." What the "enrichment region" means is something you can look up.)

 

I am very familiar with these systems old, new, diesel and gas. Deriving any benefit from the federal mandated systems is a side bar because we are stuck with it. Work with what you have...so to speak. I won't get into save the planet conversations on PC due the nature of the forum, but EGR and PCV are smog systems and bad for engines. There are much better ways to find thermal and fuel efficiency. Needless to say...it is the law...so there it is. As a reminder, I've been a wrench for over 45 years and take care of systems far more complicated and expensive than anything that will ever be discussed with any intelligence here.

 

The pumping loss improvement has been presented here for at least as long as I've been on this forum. Atkinson cycle is the biggest pumping loss improvement, but this adds in too.

 

In England, too: see “Modifying your vehicle’s emissions: the legal, safety and health implications,” DfT, 2018. Even if the car is unlikely to be inspected in a way that would detect emissions tampering, I’d suggest that it would be better to find and fix the root cause of the trouble.

To answer one of the original questions: I don’t know of a practical way to change the EGR-related behavior of the engine control module (ECM), nor to suppress diagnostic trouble codes.