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Venturing into the Gen 3 world with a Gen 4 engine swap

Discussion in 'Gen 3 Prius Technical Discussion' started by techguy802, Jun 4, 2022.

  1. techguy802

    techguy802 Junior Member

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    Over the past few years I've bought a couple Gen 2 Prii that weren't running- one needed a new engine and one needed a new transaxle.

    I've been itching to get my hands dirty on a 3rd gen and found one for a great deal that had a blown engine. After doing some research it looks like the way to go is swapping in the 4th gen engine. I already pulled the existing engine last night and am just waiting for my replacement 4th gen from LKQ to arrive.

    I thought the swap looked pretty straightforward from the guides I have seen, but now it looks like the EGR repin isn't a thing anymore, and maybe the 4th gen EGR isn't compatible after all? Is the 3rd gen EGR able to be cleaned and reused for a better result? Will this still be problematic like it was on the 3rd gen or was that more the result of them burning oil with the faulty piston rings?

    IMG_3557.jpg IMG_3561.jpg

    Thanks for any insights and look forward to getting another dead Prius up and running!
     
  2. ChapmanF

    ChapmanF Senior Member

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    The EGR systems are electrically the same and mechanically pretty much the same, only the Gen 4 EGR components are all upsized, because they are fed with lower-pressure exhaust gas in a Gen 4, and need to be bigger to have the same flow.

    The trouble people run into when they use the Gen 4 EGR components with a Gen 3 exhaust is now the gas is at the higher Gen 3 pressure, and the upsized EGR components flow too much of it.

    There's at least one thread here where somebody experimented with ways to restrict the flow "just enough". But it's easier, when you've got the Gen 3 exhaust pressure, to use the Gen 3 EGR components that were designed for it.
     
  3. techguy802

    techguy802 Junior Member

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    Thanks for the explanation. That's what I was leaning towards from reading your older post. Will I still need to clean the Gen 3 EGR on the Gen 4 engine or do you think the clogging problem is eliminated with it running off a Gen 4?
     
  4. ChapmanF

    ChapmanF Senior Member

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    You'll still have to watch the EGR flow (you can get the test results with any scan tool that reports Mode 6 test values) and clean if it gets low. First vehicle with EGR that I ever encountered was a 1979, and it needed reaming yearly or more, and I've never met one that didn't need some attention.

    The newer OBD systems where you can just ask for a test result and see the number are a great step forward from the old world.

    Still also good to check the four small passages in the intake manifold now and then, because if they get differently plugged up, the single overall EGR flow test doesn't catch that.
     
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  5. Mendel Leisk

    Mendel Leisk Senior Member

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    Using the 3rd gen EGR is the prudent approach. It's cleanable, and that's best done at the time of the swap, then say every 50K miles thereafter. EGR cleaning info in my signature.
     
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  6. techguy802

    techguy802 Junior Member

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    Just to update: got the swap done and it was a success! I followed @Ragingfit 's guide and it went without a hitch. I used the Gen 3 exhaust and intake manifolds, EGR, oil dipstick tube, and engine mount. I probably wasted the most time confused on the coolant pipe routing because the Gen 4 engine still had a rigid metal pipe attached above the flywheel that attached to a rubber hose to the thermostat housing. This doesn't line up right with the Gen 3 EGR. I swapped the longer all rubber hose from the Gen 3 engine over and then routing was easy. I no longer had any "extra" pipes and it was exactly the same setup as the Gen 3 engine except for where the T is added for the throttle body.

    Oh, and pro tip: make sure that the dowel/alignment pins for the engine and transmission aren't doubled up. I didn't notice that the donor engine had a dowel in the same space that my transmission did. One of them must have corroded into place and stayed behind when it was pulled. Let's just say that much wresting and cursing was done trying to mate the engine and transmission together before having to lift the engine out again and figuring that one out.

    All in all totally worth it and very pleased with the results.

    IMG_3741.jpg IMG_3761.jpg IMG_3809.jpg
     
  7. bisco

    bisco cookie crumbler

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    congrats, well done!(y)