Delete egr - yes or no?

I thought it was a no no to mess with emission related components. As in modify, disable detete.

 

While some have asserted that an EGR can't logically cause a blown head gasket, both problems seem to happen at the same time quite often. What's more Toyota Stealerships seem to act like there's no maintenance work is needed with a system that was poorly designed in Gen3. As you mentioned, it seems like a perfect design for clogging that they didn't have in Gen2 and got rid of in Gen4.

As for eliminating it from the system, I submit that the vehicle is so precisely tuned for maximum MPG and minimal air pollution, you'll compromise the benefits of both in doing so.

Also, isn't just ignoring it and letting it clog up the same thing as bypassing it, but without the work?

 

Which half are you in?

 

The prius is designed to regurgitate and choke on its own puke throughout its life see that motorized contraption right behind the EGR cooler or ahead of it depending upon how you want to look at it i believe that thing is constantly adjusting to flow the most EGR gas is into the system that possibly can go without causing it to shut down in a nutshell i believe that's what goes on in this system so when you delete it what are you going to do where is it going to go to atmosphere you going to pump it all into the engine all the time full tilt don't think the car will run

 

A partially clogged EGR passageway absolutely can cause a blown head gasket.

While it may seem counterintuitive, EGR lowers combustion temperatures. Automakers began using EGR systems to lower NOx emissions. Emissions of these various oxides of nitrogen increase with higher combustion temperatures. At the same time, automakers wanted to increase fuel efficiency and lower hydrocarbon and carbon monoxide emissions. These emissions decrease as you run leaner air/fuel ratios. Unfortunately, leaner air/fuel ratios are hotter so a very fuel efficient car might have high NOx emissions. Enter EGR (and catalytic converters).

For us, the problem begins if you manage to restrict the egr port to one chamber more than the others because that chamber will run hotter. Aside from increasing NOX emissions, this will also increase cylinder pressures which can cause pre-ignition. Toyota's ECU can quickly adjust the tuning after it detects a knock, but the knock already occurred. Over time, these minor knocks & misfires will occasionally reoccurr which can eventually blow the head gasket (the weakest link).

If you completely disable EGR this isn't a problem because Toyota's computer will revert to a different air/fuel map. This also happens of Toyota's computer senses insufficient airflow for the entire EGR system. The problem comes with the system is only a little clogged - especially when the restriction affects one cylinder more than the others. #1 clogs first and #1 blows its head gasket first.

Servicing it is best. You could just unplug the electrical connection to disable EGR, but aside from a check engine light & higher emissions you would also lose some fuel efficiency. "What?" "How?" I'm sure you ask...

Pumping efficiency. Toyota uses the EGR rather aggressively in the Prius so it can open the electronic throttle body more while still delivering modest power. The hot rods you built in the 80s had mechanical linkages going to their throttle bodies to the accelerator pedal. The more you opened the throttle, the more power you got. Toyota opens the throttle electronically based on how much power it thinks you need based on your accelerator pedal. The difference is that it can open the throttle wide while also opening EGR wide to reduce the amount of fresh air and lower power as if the throttle were closed more.

If you did a lot of compression tests in the 80s you probably noticed you got higher compression numbers if you held the throttle open because the engine could breath better. You got even higher numbers if you pulled all of the other spark plugs out so the engine could really spin freely. That is pumping efficiency - and toyota uses the egr to make its engine pump more efficiently.

 

Likely in the 1/2 known as denial & dismissiveness and definitely not in the 1/2 known as inquisitiveness & learning more. I keep looking for the first 1/2 but for some reason I can't see it...

 

It is interesting that Toyota and their Master Mechanics don't see the correlation between egr clogging and head gasket failures. There is little doubt that egr systems reduce emissions and reduced pollution is their stated purpose. Reports from those who have disabled the gen3 egr seem to indicate mpg is not impacted. Clearly bypassing the system will throw a code, potentially masking a subsequent issue.

Certainly most Toyota engines including non hybrid 1.8L versions have egrs without head gasket issues. It is also interesting the gen4 1.8L engine still has an egr without hg problems. The massive reengineering of gen4 is significant and would seem to reflect flaws that have been corrected. Moving the egr intake and improved cylinder cooling seems relevant. Finally we see owners losing gen3 head gaskets even though they clean the egr every 40k-50k miles.

Personally I think the gen3 issue is excessive blowby creating carbon in the cylinders thanks to the egr and pcv systems. Aggravated by Toyota's decision to go with 10k mile oil changes and low tension rings. Toyota offered free pistons and rings for gen3 oil burners through the powertrain warranty. Regardless of cause, the gen3 head gasket and brake booster flaws are certainly factors impacting Toyota's reputation. I suspect used buyers are being hurt the most.

 

I'm not as ready to assume every advancement from one generation to the next should be called "correction" of a "flaw" from the previous generation. The EGR intake was moved because "catalyzed EGR" was an industry-wide research topic during the years of Gen 2 and Gen 3 and the researchers learned how to manage its benefits and drawbacks for a net positive in time for Gen 4. We've got armchair PriusChat experts here saying the prior state of the art was an obvious "flaw" that their toddlers could have explained with crayons, but talk is cheap.

To a degree it comes down to how you want to spin it. The first Prius corrected the flaw in earlier cars that they didn't come with electric motors and batteries. Or maybe they were the state of the art of their time and the Prius advanced it.

That does suggest that the story linking the two might not be as cut and dried as some make it sound.

 

When I originally caught on I thought it was because the knock sensors don't detect the knock well enough. My car was clearly knocking, not audible, or rod knocking, so understand what I mean by the term when I say I could feel the knock, and the knock sensors never caught it and I never had a check engine light. I imagine if you waited long enough to get a check engine light it would've been too late. For me when it did knock it was between 1500-1900 rpms so I would go above and below that for a couple weeks until I decided to stress myself out and read priuschat. Viewing the gasket master's EGR clog diagnosis video I unplugged the EGR connector and the knock went away immediately so I knew I was somewhat on track.
I am inferring that the uneven flow of partially clogged EGR passageways is what was causing the knock/misfire etc... I'm not sure if that is the only thing damaging the head gaskets on these cars but it seems like knocking for 10k miles would be a good way to weaken a head gasket.
When I cleaned the EGR circuit I will just say it was clogged because it was blocked as far as i could see. Maybe the car was able to still push some EGR through it has better lungs than I. Also, a lot of people could still be losing head gaskets due to uneven flow. I see a lot of people still do a poor job cleaning the intake EGR passageways and end up still getting an imbalance in flow.
I actually made mine worse the first time I did it. Didn't clean it well enough and got a clear misfire from 1200-2500 and still no check engine light! (which was scary)
This is probably the reason why Toyota says they have a strict rule against cleaning parts and only replace parts when they do TSBs (in fear of wasting time messing up the job)

15k miles now on the EGR delete by unplugging the EGR connector. The car runs smooth. (205k)
Load stays at 92% like it always had so for the majority of the time the car is on the throttle body is still basically wide open (unchanged in case people wonder). Still, 50+ mpg like it was.
Don't get me wrong though i still feel unsure about the car. It could still blow up soon.

I'm not doing this to "prove anyone wrong" I am just noting my experience with the gen 3 Prius. We are all just inferring here. At the end of the discussion it could always be weak head bolts or improperly manufactured head gaskets in some way.

 

That's not a clean test though, because when you unplug the EGR connector the ECM can immediately tell you've done it (P0403, single-trip detection), and the ECM makes fail-safe adjustments like retarding the ignition timing in order to protect the engine, and those adjustments by themselves can make the changes you notice in how the engine runs.

Now, there was a thread with folks putting Gen 4 engines into Gen 3s, and somebody came up with a clever electrical sabotage to make the valve not work but the ECM think it still did. That would be more along the lines of what you were trying to test here. (It could also be too clever by half, breaking the EGR system while preventing the ECM taking the engine-protective measures it normally would.)

 

I would suppose that disabling the egr on a gen 3 would cause higher cylinder pressure and possibly cause a head gasket failure at some point...so that's why I cleaned the intake manifold and exhaust gas cooler at about 120000 miles...
our gen 4 Prius v obtains exhaust gas for the egr system after the cat converter instead of at the exhaust manifold...cleaner exhaust?
so egr cooler needs servicing at higher mileage than gen3...

 

Yikes I would think an engine map that uses egr and then making it think the mixture is getting egr when in fact it isn't would be the worst way to go. That sounds as bad as before where the car was getting less egr than expected. That thread where the guy pulled his valve apart to take the magnets out and spoof the valve was a mess if I remember correctly. He was wondering why his mod wasn't working.
Do you have a link to the thread with the gen 4 swaps you are talking about?
I need to find the thread where a guy was talking about gen 3's in his country came without egr since they didn't have emissions regulations.

Yup code is p0403. I have incorrectly stated p0401 before.

 

Concur.

You can start with this post and this one, and they contain links to earlier ones with more details.

One detail that had slipped my mind was that Toyota happened to change a few wire colors between Gen 3 and Gen 4, and that might have been what misled Sandog53 originally into thinking the pins should be swapped.

So it might not have been a case of deliberately looking for a way to disable the valve without the ECM noticing. It might just have started with "hmm, I don't like how the engine is running, hey look, these colors changed, maybe that means I need to swap these wires, now I am happier with how it runs, so that must be the answer!" but was never followed up with "maybe I should look up the details and figure out what I just did".

 

By the way i wanted to come back and update. I was wrong. The car swaps to a different operating strategy when you do the egr delete. Before I'm assuming (dangerous i know lol) it used the egr flow to fill the intake manifold at differing rpms with egr gas so that it can float the intake butterfly ~90% open at pretty much at all times to avoid the pumping loss associated with the valve and still only get the amount of fresh air it needs to operate at that RPM. After you do the EGR connector unplug its load goes between like 50-75% during the operating range and up to like 90% at WOT (maybe like 80ish% at 2000 rpm) so it probably has an operating strategy more akin to a Corolla at that point. Also, toyotas never read 100% load as 100% so im not sure if those numbers mean the exact percentage of open throttle body. My ls400 and sequoia throttle bodys are 100% open at 80% load so its weird
I haven't been driving my car as much lately as I work from home and have too many vehicles but still running great besides being an oil burner. (2010...) Still getting 50s.
I have been dabbling in sequoias and ls400s lately and I've figured out a great cleaner for the intake valves, piston rings, manifold etc... last week while cleaning out the fuel system and oil system on an ls400 last week that had sat for 13 years without running. So I will be doing that on my Prius today and it will be really cool to see if it makes a difference. Its almost magic. And yes 13 year old gas and oil is the stickiest shit ive ever seen. Liquid gasoline won't even dissolve them.

 

secret sauce? ;-)

 

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