Advice on gen 4 engine into gen 3

Revert it to 3rd gen EGR? Hopefully wouldn’t stress the exhaust manifold connector pipe too much.

 

Right. The P0403 code is detected when the ECM sees that its electrical connection to the valve is open or shorted. The code does not wait for a second trip to confirm; it is reported right away.

Right again. When "re-pinned", you have not opened or shorted the ECM's electrical connection to the valve. You have just rearranged it so that none of the ECM's signals will ever move the valve, and done that in a way the ECM can't directly detect. (There is no movement or position sensor on the valve to give the ECM that information.)

When the ECM knows of an EGR problem (that is, when it has reported a P0401 or P0403 code and the CEL is showing), the ECM then makes fail-safe adjustments to engine parameters like ignition timing in order to mechanically protect the engine. You can find this information in the "fail-safe chart" in the "SFI system" section of the repair manual.

The other EGR-related code that can be set is the P0401. That is detected by a self test monitor that the ECM occasionally runs. Some time during normal driving, when the engine is warm and you happen to be decelerating with the fuel cut, the ECM will sneak the test in, which is to open the valve some and watch the manifold absolute pressure sensor to see the reading increase. Because that's a real test for actual flow, your re-pinning will not fool it. But that code will not be set until the right conditions have occurred for the ECM to run the test, and it has to have run the test in two different trips and failed both before it will set the code. (And of course if you clear the code, then all of that has to happen again before it will come back.)

So you don't see that one right away, and in the meantime, the ECM does not know the EGR isn't working, and does not make the engine-protecting adjustments.

 

The reasoning is sound as far as it goes, but I am not sure it won't run into difficulties with the math.

The right amount of EGR to be let into the engine is something calculated by the ECM for different conditions of speed and load, according to a curve programmed into it at the factory. It's possible that with the ECM's existing programmed curve combined with some size of hole in a plate, you could come somewhere close to the right EGR flow over the whole range of driving conditions.

But it's also possible that doesn't work out, and it turns out that the math governing flow through a hole in a plate just isn't a good-enough match for the math giving the right amount of EGR over the operating range.

I am not enough of a fluid dynamics geek to know the answers myself. I can only reiterate what I said above, that I've been watching threads about this for a while, and I still haven't seen one that ends with "and now I'm happy how the engine runs."

 

What happened to your old Gen 3 EGR parts? Off to the scrap heap?

 

I believe its more than the amount of gas, the composition is different as well since the gen3 intakes prior to the catalytic converter.

 

Right, the papers on "catalyzed EGR" (the system adopted for Gen 4) also talk about some different combustion chemistry effects because the source is after the catalyst and the ingredients have changed.

But the upsizing of the Gen 4 components to account for the lower pressure is obvious enough that people notice just by looking (and then it's surprising how many will say something like "oh, obviously Gen 3 had a design defect and was too small, and they fixed it by making Gen 4's plumbing bigger").

In any event, once you have a Gen 4 to Gen 3 swap, and the exhaust is coming from ahead of the cat from the normal Gen 3 place, the chemical composition is the same as what the Gen 3 ECM expects. Now if you could just get the volume flow to match what the Gen 3 ECM expects—everywhere on the curve—you could probably call it a day.

 

An unbent exhaust manifold would be less than $180 at toyotapartsdeal, maybe well under $100 at a recycler.

Or with the cowl out of the way and some shielding draped around, re-bending the one you've got in place might not be as big a deal as it sounds.

 

Neat!

For your next experiment, you might pull your EGR flow numbers after a bit and see what it's saying.

The number is actually a "pressure" number; the test is, the car measures how much the manifold pressure goes up when the EGR valve is opened some during deceleration.

We haven't got definitive knowledge about how good or bad a particular range of numbers might be, but mine has been around 21 kPa since I cleaned it in the summer. (It was around ten point something before cleaning.)

There is another test that is more hands-on (the ECM's pressure test is all automatic, all you do is ask it what the most recent result was).

The hands-on version is where you have the engine idling and use Techstream to command the valve open by steps. The valve has about 110 steps to full open. At idle, stock and unclogged, it seems typical you don't get beyond the 14th step or so before the engine is noticeably rough, and only a few steps past that it's about to stall. Systems with too much restriction, you can open the valve further steps than that.

There's some more information about that technique in this post and thereabouts.

 

Instead of aluminum foil, may I suggest using some aluminum flashing?

They sell them in rolls, but since you don't need a large amount, something like these will do nicely.
https://www.lowes.com/pd/Union-Corrugating-3-in-x-4-in-Aluminum-Step-Flashing/3499756

Posted via the PriusChat mobile app.

 

I think aluminum foil would eventually oxidize and fall apart. Try a steel sheet metal gasket?

moto g power ?

 

Plenty of people using non-Techstream options to pull up the automated test results ... anything that can do a "mode 6" monitor results query. Lots of the usual-suspect phone apps etc.

 

Anybody notice the following modifications done to the gen 4 engine by this shop (Hybrid 911 in the two part YouTube video series):

- Replaced the 4th gen goose neck coolant outlet with a straight pipe outlet - same as gen 3.
- Installed the temp sensor on the gen 4 head in the same location as the gen 3 head. Did they drill and tap a new hole for this?
- Installed a straight pipe on the gen 4 head in the same location as the gen 3 head. This is for the coolant hose that goes to the bottom (inlet) port of the heater core. Did they drill a new hole here?

Has anyone done this when swapping gen 4 engine to gen 3 Prius? @RightOnTime Do you do this as well at your shop? I understand it makes it plug and play for the gen 3 but how reliable are these modifications?

@Ragingfit Did you consider these modifications when performing your swap?

 

I looked at the systems, how they would change and what I needed to do to restore them to functional.
I wanted my old "car" to see it's old engine, so the old stuff had to go on the new engine.
Specifically, Intake, MAP and throttle body, EGR and EGR cooler, Exhaust - manifold, cat, and all, and to hook up the new sensors, knock, cam position, oil pressure, coolant temp all compatible.
Easy work. Very few modifications and almost no issues.
Put the 3rd gen stuff on the 4th gen engine.
On the video, I'm not sure how they accomplished the re-plumbing of the head. They are clearly using 4th gen engine and had to cut the mount for the EGR cooler.
Too much work for me. I used an 8" long 1" pipe from home depot and added a pex T.

- Fix That Prius !!!

 

Quick question: can anyone suggest if there are ANY Gen4 Hoses from the Gen 4 Engine that can be brought over, and likely fit better in the Gen 3 engine compartment ? I have an G4 engine with alot of cut Gen 4 hoses. I thought I remember reading that one or two of the Gen4 hoses should be kept and fit better in the Gen 3 engine compartment . Any insight? I’m planning on staying with the G3 EGR valve and “cooler”.

 

Have you watched the @Ragingfit video series (pinned in Prius v Accessories forum)? He utilizes some left over hoses, has good strategy I think. It's his second time 'round.