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Still P0401 after cleaning egr !! should we drive it?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by ozmatt, Mar 27, 2021.

  1. ozmatt

    ozmatt Active Member

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    I will double check everything today but can not hear a leak, I figure that would be audible? all gaskets are on properly sealed and tight, I'm pretty pedantic lol :) unless it's the eBay catch can? I am almost certain the cans not leaking but could that potentially be an issue or would it be a different code?

    my thoughts keep going back to my original findings of the gasket between cooler and exhaust manifold only fit via one stud and as a result restricting the path of flow around 50%, I guess the car was like this for 3 years since engine was installed by previous owner, could this possibly cause the exhaust manifold pipe to block up? (although I could not see any blockage in there from up top) there is a couple tight turns and elbows in that pipe

    Been thinking, why would my exhaust pipe block when lots of people get completely blocked coolers and it never seems to go any further, the only thing I come up with is plugged coolers generally start from the intake manifold and find it's way down to eventually plug the cooler, however this potential exhaust manifold blockage started near the misfit gasket at exhaust manifold pipe on an otherwise clear system.. thats the only difference I can think of?

    I don't know what to try next but have been contemplating what's the easiest way to check the damn exhaust manifold, remove exhaust manifold completely or just pull the cooler again and disconnect exhaust pipe from the flange (as to not push any crud through to cat)

    I don't want it to be the exhaust manifold tbh I really cbf doing this job lol but unsure where to go from here

    Thanks again, please post an easy fix that will take me 3 minutes to do :)

    Posted via the PriusChat mobile app.
     
    #21 ozmatt, Mar 29, 2021
    Last edited: Mar 29, 2021
  2. wheezyglider

    wheezyglider Active Member

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    I'm trying to think this through and it's too late here to have another coffee... We're trying to explain the active valve-step test data, which shows normal vacuum (4psi absolute reported) but zero change in MAP for valve steps 0-24 (!!), and then suddenly chokes the car out (8psi absolute) within the next few steps, right?

    If there were a gasket leak between exhaust and valve it would only explain the sudden drop in vacuum at the (intake) manifold if it happened as soon as the valve (actually) opened.

    But the reported pressure isn't changing for valve steps 0-24. Hmmmm....

    (For myself I'm ruling out a faulty MAP because the active valve step test data trumps.)

    As far as the crud falling into the cat -- the cat eats that stuff for lunch. Raw gasoline or solvents would be a threat for it, but not EGR crud.
     
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  3. ozmatt

    ozmatt Active Member

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    Hey Wheezyglider .. mate its never too late for coffee!

    yeah its strange, trouble is i do not know how a faulty valve might look on techstream, we can see the MAP doing its thing once the valve is ramped up past step 24 so im with your thoughts on the MAP being okay but i do not know what a "lazy" stepper motor looks like, basically i think its down to two things either bad/lazy egr valve /motor/magnet or its still blocked, which points towards the manifold

    The misfit gasket was found prior to cleaning, its not like that now! basically a couple weeks ago i got P0401 one hot day driving up hill with a loaded car and when i took it apart to clean everything i found the gasket between exhaust manifold and cooler was not correctly fit and restricting flow around 50%, didn't think too much of it at the time i just took off all egr bits cleaned everything and reinstalled with a fresh gasket and catch can, i am no stranger to spanners and its my own car so made a conscious effort to get everything neat tidy sealed and proper!. Nothing was really that "blocked" to begin with .. and FAIL. stil P0401

    Pretty sure i am down to either still blocked somewhere which seems the most likely as i have similar test results to what people get BEFORE they clean the entire system, or a faulty valve which i do not know enough about to really guess if its the problem

    The only solid thing i have to go off is the fact my system was never blocked to begin with, yeah it was a little dirty but not blocked enough to cause P0401 so its been something else from the start!

    just wish i could source another stepper motor magnet to try, its so much easier to try than removing cleaning the manifold

    im hearing you about the cat eating carbon for lunch however it still wouldn't be great to send through 100,000km worth of crud in one big black package lol, its going to have trouble dealing with that much crud in one hit and will almost certainly cause a big black nasty patch on the entry mesh

    closing note! .. the car has been driven for 3 years /100,000km with the egr 50% restricted where the cooler meets the exhaust manifold, i guess that junk has to go somewhere!
     
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  4. ChapmanF

    ChapmanF Senior Member

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    The good news is stepper motors are such simple things, I'm not thinking of a way for one to 'go bad' in such a way that 24 steps don't actually happen and then the next one does. Each time you switch polarity of one winding, the rotor twists by one step. If it's mechanically overloaded and can't twist a step this time, it misses the step, and it'll likely miss the next one too. It's not as if a bunch of consecutive missed steps somehow keep adding up until it goes sproinnnggg.

    SImilarly, the valve is mechanically simple. The pintle moves in and out, it has threads, and the rotor rotates on the threads. Each step of rotation is going to move the pintle, according to the thread pitch.

    Now, the rotor's on a couple of bearings, and those should be clamped securely in the housing and not leaving the rotor much end play. If the end play is excessive, I could see the first several steps being wasted as the rotor 'climbs' up the pintle until the top of the housing stops it, and only then starts pushing the pintle open. When the ECM tells it to close, the final several steps would be the rotor 'climbing' back down.

    Having the stator/cap not quite cinched down all the way on the valve would result in excessive end play like that. I'm not sure what else would.

    I've seen somebody post that "the motors go bad" but without details, and I'm skeptical about a permanent magnet stepper motor "going bad". If the story is that the rotor loses its magnetic strength, that's an interesting story, but I'd kind of want to see somebody actually compare the field strength of a new one and a "bad" one before I would get it all lodged in my belief system.
     
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  5. ozmatt

    ozmatt Active Member

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    Hi Chapman, firstly thanks again!

    This all makes sense and I agree its not likely to skip multiple steps then just come true at 24, would be nice to know what sort of behaviour to expect from a failed motor/ magnet, maybe they get lazy or do they just completely stop stepping all together, if anyone knows please chime in!

    Can I ask, are you suspicious of my exhaust manifold being plugged?

    Posted via the PriusChat mobile app.
     
  6. ChapmanF

    ChapmanF Senior Member

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    I've got a spare valve here and I'm kind of tempted to play with it, but maybe not tonight. Doesn't take more than a pair of SPDT pushbuttons, a 12 volt battery, and maybe a dial indicator. You might also be interested in checking yours.

    The valve has two rows of three pins. Bring +12 to the middle pin of each row. Arrange two SPDT pushbuttons so their common terminals go back to the battery − and the other two go to the end-of-row pins on the valve. Make sure each button is connected to pins of the same row of three on the valve, you don't have them connected across rows. I'm too lazy right now to open a drawing program and draw it.

    Now you can step it by pressing and releasing your two buttons, call them A and B. The order you play them in determines the direction. If press-A, press-B, release-A, release-B, repeat, moves it one way, then press-B, press-A, release-B, release-A, repeat will move it the other way.

    What I would do with a dial indicator is just set it on the end of the valve with the tip on the valve pintle, and just note down how far the pintle moves on each step, and how many steps of 'slop' there are at full-closed and full-open.

    I don't know what to think about the manifold being plugged. The readings you're getting make me think of something being plugged.
     
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  7. ozmatt

    ozmatt Active Member

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    It would be an interesting test however I would need to strip the valve back off the car to do it as can't see the valve position in situ, and count on the fact the bench test is relevant to real world use, my luck it would test fine on the bench just to throw me off! Wish I could find a rotor aka magnet to try on car that would take 5 minutes and pretty much cancel out the valve /motor from the equation however unfortunately I can not find a good used valve locally and a new valve in Australia is literally half the value of my car! a decent outlay considering it's not overly likely to be the problem.

    The egr cooler, piping and valve are definitely clean, so .. guess I should cancel out the manifold (lots of swearing & moaning)

    Wonder if I disconnect the cooler from exhaust manifold can I wiggle it out enough to access the exhaust manifold pipe without actually removing the cooler (or manifold) and disconnect the cat under car.. and clear the pipe with exhaust manifold still in situ

    Posted via the PriusChat mobile app.
     
    #27 ozmatt, Mar 30, 2021
    Last edited: Mar 30, 2021
  8. ChapmanF

    ChapmanF Senior Member

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    I'm pretty sure the construction of the valve is just plain too mechanically simple for it to harbor the level of malice you seem to be ascribing to it.

    Even if you found a rotor and did that swap, and you liked how your car ran better afterward, you could be in danger of jumping to conclusions about what that told you. It would be more useful if you took the time with both rotors out to compare them, such as by measuring them next to a known magnet. There could be other possible confounders, like, in taking the stator off again to do the swap and putting it back on again, is it possible a bearing was a little cockeyed the first time and not the second?

    It would be great to learn more about what's going on, and best to really learn it. The usual tendency is to overestimate what some hurriedly-thought-out experiment has taught.
     
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  9. Rocky Mountain Priusman

    Rocky Mountain Priusman Active Member

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    Reading this thread is fascinating and educational. Excited to see if you ever reach any conclusions!
     
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  10. ozmatt

    ozmatt Active Member

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    Will compare them if ever lucky enough to get the two next to each other however im having issues finding a good used valve, this one "wrecking yard" quoted me $660 for a used valve lol what a bunch of jokers hey! bloody ripoff merchants, I can get one cheaper brand new through the local dealer..

    Update !!! .. i took the time to pull the exhaust manifold today aaaaaannd....... its perfectly clear! .. minimal contamination

    Definitely didn't miss any part of the system when cleaning, i am known for my pedantic nature when it comes to these things, i wasted two cans of oven cleaner, 2 cans of brake cleaner, two cups of oxi cleaner, two brushes and about 10 hours of my life cleaning that stuff, like three times! its clean ..
     
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  11. ChapmanF

    ChapmanF Senior Member

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    Seems like getting the exh manifold off would position you pretty well to bring the EGR valve to the workbench without a lot more effort?
     
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  12. AW82

    AW82 Member

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    $660? Jeez. Seems like you could overnight a brand new one from the US for a lot less than that.
     
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  13. wheezyglider

    wheezyglider Active Member

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    Hey since you have that spare valve, can I nudge you to make a video on bench testing it? Like with the NutzAboutBolts videos, we're all more confident when we see that someone else has pulled it off. You already found a bunch of reference information on how it works, it would be awesome to see it in action!
     
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  14. ChapmanF

    ChapmanF Senior Member

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    Collecting the data for a valve does seem worth doing and posting, and I'm totally willing to do it; there's just the question of finding some tuits and how many of them are round.

    Video, maybe. The last PriusChatty experiment I did was the water pump business, and I did try to write that up fairly completely, but didn't make a video. That's just another level of preparation and editing/postproduction and yeah. I did one for the Gen 1 center cluster finish panel but that was kind of a case in point; finally uploaded in November after shooting in August. It's just not something I do a lot of. On one hand, picture may be worth 1,000 words; on the other, in the time to make a video one might help a lot of people with some text posts and stills.

    Anyway, I think I put complete enough instructions above in case somebody else gets around to it before I do. Then if I do later, we'll have multiple results to compare.
     
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  15. ozmatt

    ozmatt Active Member

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    anyone have a spare valve they would like to sell? :) :) With postage to Australia

    I took the exhaust manifold off from under the car as I really didn't want to take the cooler off again if I didn't have to, couldn't get the manifold out past the drive shaft so visually inspected the pipe from both ends, punched some compressed air through it and put it back on

    I am keen to bench test the valve but even more keen to just find a stepper and magnet to try, have been piddling around with this thing for too long im running out of mojo with it

    From memory it's near impossible to get the nuts between valve and cooler off without removing the complete cooler, although I did not have any trouble getting the cooler to exhaust nuts undone from up top yesterday, definitely no need to remove wiper cowl for those two nuts, please remind me what is the reason for removing the wiper cowl? I removed it when doing the job because the video told me to

    So how about it who wants to send me a valve lol :) I will settle for just a magnet and motor :))



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  16. Mendel Leisk

    Mendel Leisk Senior Member

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    I did have the cowl removed, and yeah the video was part of the reason. It does really open thing up.

    IIRC @Raytheeagle (whose done more Exhaust Gas Recirculation cleanings than he has fingers) omitted the cowl removal one time, and swore never again.

    OTOH, maybe helps if you leave one or more of the hold-down nuts/bolts, for next time?

    @Ragingfit’s 4th gen engine transplants use 3rd gen EGR components that free-span from exhaust to intake, no intermediate support.
     
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  17. ozmatt

    ozmatt Active Member

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    Please send me that spare egr valve you don't need it.

    Hi Mendel :) .. yeah it opens things up I guess, I have only undone the two cooler to exhaust nuts with cowl on which took perhaps two minutes however I can not comment on what the rest of the job might be like with cowl on, its probably just easier all round to remove it I guess

    I did leave the bottom cooler bolt out because it's a pita, not sure about free spanning the whole egr only support being manifold to manifold, I mean it's probably okay but my ocd would insist on fabricating some sort of simple bracket system in the middle somewhere, mostly because I'm annoyingly pedantic

    egr valve on 4th gen looks similar to 3rd gen just with an extra cooler line, wonder is the stepper motor and rotor/magnet part the same





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  18. Mendel Leisk

    Mendel Leisk Senior Member

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    Apart from that lower nut, the rest are pretty easy. It maybe helps to remove the lower bracket stud as well, might negate the need to remove the studs on the rearmost connection??
     
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  19. AW82

    AW82 Member

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    Yeah, when I was watching the video I was wondering why the back studs needed to be removed if you removed the ones on the side of the engine.

    My neighbor who has a 2015 swears he can change spark plugs without removing the wiper cowl. He's promised to show me how.
     
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  20. Mendel Leisk

    Mendel Leisk Senior Member

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    Right hand drive models have a cowl that’s just a leetle bit higher, enough that you can snake plugs out.
     
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