2001 Prius misfire cyls 1&2

Discussion in 'Generation 1 Prius Discussion' started by M0GXB, Apr 28, 2022.

  1. M0GXB

    M0GXB New Member

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    We have been plagued by misfires on 1 and 2 (codes P0301 P0302 with P0300) under rather specific conditions, something that we diagnosed and understood or so it seemed. But now the problem is back solidly.
    The back-story here is that we kept getting misfires always 1&2 in a very specific way:
    1) From cold, drive a short way and stop for about half an hour
    2) On switching back on we only run on 2 cyls!
    3) Switch off and leave it a long time (days) and it was back working.
    The reason: condensation water was pooling on the engine, covering plug-coil #1 and sometimes #2 which have little vents(!). The short drive warms the engine but the water doesn't fall off. On cooling it sucks water down the coil hole. Wait long enough and it dries out. For a couple of years we had this and so long as we dried the engine before cold-starting it was fine. We also demoed the failure by flooding it deliberately. It was easily and consistently reproduced.

    *BUT* we recently got the same effect (cyls 1&2 failing) after driving 120 miles. It cleared after opening up the coils. 300 miles later and it came up almost solid. Now, once warm it soldily fails the same way, same codes.

    It could be coindidence - but we always wondered why it was that for 20 years we never had the above problem and then it started. (Very little water can be sucked down the coil). Nothing obviously changed.

    With the solid fault I changed plugs and coils - no effect.
    Checked compression (convinced myself it must be head gasket failure between 1 and 2) - all came up as 95psi.

    The thing is that it ALWAYS says it is cyls 1 and 2 together - never seen just 1 or 2 or any other number reported.

    The problem seems to start fairly suddenly when it starts, and now it doesn't stop until cold.
    Any ideas what to check next?
     
  2. Josey

    Josey Member

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    I could use a little more clarity on the part quoted above. Got the same effect after driving 120 miles - meaning you're driving along and it started misfiring? Or you drove 120 mi, stopped and it misfired on restart? What does "opening up the coils mean? Drying them out? And then 300 miles later...? What...exactly happened? And it now only happens warm?

    It is all weird, of course. I agree w/ you there. When you checked compression did you do it with all plugs out? If you did have a compression leak between 1 & 2, e.g., and check #1 with the #2 plug in you won't see it and vice versa. 95 psi is also pretty low, although if it was the same/close across all 4 cylinders, I'd chalk it up to the gauge.

    Anyway, since the problem did change "format" I'd go back to compression check again. Do it warm/hot. That can be dicey with alum heads, so loosen the plugs while cold, snug them back down with a light touch, hook it all up, run the car til warm/hot and then pull them out - without burning yourself, of course.

    Carefully check the electrical connectors and wires to the coils. That past moisture thing - for whatever weird reason it occurred - may have helped along some corrosion. What does that have to do with the warm/cold thing? Increased wire heat = increased electrical resistance.

    Consider moving on to fuel. Check the injector wiring harness for signs of issues. I haven't needed to mess with the injectors on my '03, so I don't know how hard it is (often easy), but try swapping the 1/2 fuel injectors to 3/4 and see if the problem follows.
     
    #2 Josey, Apr 28, 2022
    Last edited: Apr 28, 2022
  3. JahT

    JahT Member

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    It could be fuel injectors needing to be replaced. I had an intermittent misfire and CEL codes on 1 and 3, I never noticed it driving, but at idle it would shake quite a bit, but not every time and if it shook once I started driving it went away. I tried plugs and coils first, and fuel cleaner, but a set of $40 for 4 refurbished injectors fixed my problem.
     
  4. M0GXB

    M0GXB New Member

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    To clarify:
    Got the same effect after driving 120 miles - meaning you're driving along and it started misfiring? yes, 120 miles fast driving OK and on nearing journey end it suddenly started misfiring (unlike the water problem).
    What does "opening up the coils mean? lifted them out of the head Drying them out? In effect
    And then 300 miles later...? What...exactly happened? Exactly the same - it fairly suddenly started misfiring about 40 miles from journey start on fast road - and this is now 100% when hot.

    And it now only happens warm? yes. It comes on at idle in about twice the time it takes for the blue "cold" indicator to go out.
    NEW RESULT: I scanned the fault codes just as it started to misfire, on warming up. This time, first time ever, I got just a single code of P0301 (misfire #1). The manual is vague but given how these codes are done; I wonder if the number is a bit approximate? I think #2 is the cylinder that fires before #1 so I wonder if at higher or varying speed it struggles to be exactly correct since this seems to be based on the ECU measuring the exact instanteous rotation rate to spot small variations due to misfires. It takes it minutes to figure it out.

    FYI The workshop manual gives cylinder head pressure test results as 77-106 so 95 is pretty good I would say for an old engine, and my results were almost exactly the same each cylinder - so I guess the head must be OK (do heads ever give intermittent faults?)

    I am now thinking that this must be an injector fault after all so will investigate that (awaiting a new one).
    BTW I had thought the MPG figures were unusually good in the last couple of years, maybe sign of slightly weak injection?
    New theory: dirt got in injector(s) and so it under-injects making mixture weak in #1. When cold it over injects so it fires up OK but when hot the problems are now bad enough to kill it. The water problem could be that there is not enough sucked in to kill the spark - just makes it weak. With weak enough mixture due to bad injector it could then misfire? The whole thing could have been creeping up over a couple of years?

    Huge worry: maybe a sign of rusting inside fuel system?
     
  5. Josey

    Josey Member

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    It's hard to follow you much of the time. No offense intended.

    You can avoid the expense of buying new injectors (and just "throwing parts" at it) by first swapping them to see if the misfires follow the injectors.

    On the question of setting codes and whether or not something is "approximate" - I wasn't sure of the reference, but I do know that codes aren't set just because one or two glitchy / out of spec readings come in. (In the case of misfires, yes, it's typically triggered by little hiccups in crank speed). There's always a "rule" programmed in that has to do with number of times glitchy reading comes in given whatever amount of time or drive cycles. All ICEs misfire from time to time even if all is well. So the programmer/engineer question is basically how many misfires in what amount of time is "abnormal." I wouldn't dwell on it too much. You could clear the codes and next time it would hit the threshold on #2 first rather than #1 just by random sh**. And in the end it's clear that your issue is 1 & 2.

    Thanks for clarifying on the compression re: the manual. 77-106 is just oddly low. But I never bothered to look. Rule of thumb in my mind has always been min of 100 for reliable compression/ignition, and the average auto in good health us like 150 or better. But I never did look it up for the Prius. I guess its just a low compression engine.
     
  6. M0GXB

    M0GXB New Member

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    I am going by the official service manual that I came with the car when new. The snag is that it expects you to have the diagnostic kit and also it isn't the worlds best example of translation from the original Japanese!
    It does give some detail, so the misfire detection is based on analysing the rotation rate for some minutes (depends on speed) but given the instantaneous variations will be small there is a lot of scope for getting the wrong cylinder - and it kind of admits as much in the manual. I think all the standard ODBC fault codes work on the basis of 2 strikes and it flags the error so it takes a few minutes to get the fault light on. But while the misfires are happening, if the ECU is sure it flashes the engine fault light which is documented as meaning that there are enough misfires happening that the catalyst could overheat.

    I was not keen to try swapping the injectors about given their great age and the warning in the manual about always changing the o-rings (which I do not have). So I will get the garage to change one injector and then we will see what difference it makes and examine the old one. The snag with garages seems to be that these days they want to charge hundreds of pounds just to tell you what is actually wrong!
     
  7. Josey

    Josey Member

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    I'd say the real snag is that they charge you whether they can tell what's wrong or not. And that half the time (or more) they tell you what they think is wrong, but they're wrong. This is one of the largest reasons I just started working on my own darned cars.

    In any case, if you get ambitious, fuel injector o-rings are very inexpensive and not hard to get. I'm not sure what you mean by inspecting the old injector, but it's highly unlikely that there's anything about one that you'll be able to identify visually. They have to get hooked up to test equipment in order to be evaluated for flow. It would also be weird to just replace one. Most of the work is in removing the fuel rail - once that's off, if the parts are there you'd just replace them all.

    Best of luck with it.
     
  8. M0GXB

    M0GXB New Member

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    OH! The manual made it look fairly simple, but the manual skips a huge lot of detail at times.
    The idea of replacing just one was to see the difference, and also if it does make a difference then there will be a question of whether dirt is getting into the fuel lines. It may all need cleaning before doing the rest. Well that was my logic - in the absence of pricing info.

    I really hate the way modern garages dump the responsibility for it all on the owner. I hear stories of garages just replacing things to fix a fault only for these actions to be futile. But they don't reverse out the changes and say "our mistake".

    Since all modern cars have flashy VDU screens there is no excuse for ALL the diagnostic data not to be available on the screen. All it would take is for a few governments to make that a part of type-approval. Ugh.
     
  9. M0GXB

    M0GXB New Member

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    UPDATE
    It turned out that injector #1 was faulty. It was going open circuit on heating up.
    So an open-and-shut case once it exhibited the open-circuit. It is always nice to finally get a definitive test result!

    So interesting that the ECU misfire detector was flagging misfire on #1 and #2 when actually it was only #1 that was faulty. I had always thought that the misfire detection was likely to be a bit approximate and this is now confirmed.

    The question in the air is whether there was a connection to the water-down-coil issue.
    Before the injector went totally open circuit when hot it seems likely that it might have been going a bit high resistance so maybe was chronically under injecting. So it may be the resultant weak mixture that failed to ignite when the spark was reduced by water getting sucked in. We will do some tests on this to see if that was the case. But at least it drives ok now!
     
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  10. JahT

    JahT Member

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    I had misfire codes on 1 and 3, I just replaced all 4 injectors with refurbs to expedite the repair but it sounds like there is a good chance I only had one bad injector too, maybe #1. I kept my old injectors in order, so is there a way to test them off the car?
     
  11. Josey

    Josey Member

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    Sort of, but not really. (you can figure out how to do just about anything on youtube, so have a look). It's not that expensive to send them out to one of any number of injector testing/refurbishing companies. If you're interested look into it. They can give you a report back on existing injector conditions and likely send all 4 of your back refurbished/cleaned/tested, and ready to go.
     
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  12. M0GXB

    M0GXB New Member

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    > I kept my old injectors in order, so is there a way to test them off the car?
    The one that failed for me could be trivially tested by measuring its electrical resistance while heating it with a heat gun. The resistance went up and then to open circuit when really hot.

    The manual describes a way of testing them but you need to have them being fed from the high pressure petrol supply.
     
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