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Misfiring mystery

Discussion in 'Generation 1 Prius Discussion' started by mo_, Apr 24, 2015.

  1. mo_

    mo_ New Member

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    Hello,

    New to the forum so not sure if I'm proceeding correctly with this question (please let me know if not).

    I recently bought a 2001 Prius (~175000 km; 108000 miles). The previous owner told me there were evap codes on the car but it was running fine (I have his records on the specific issue and will dig them up). My apologies for the long story...

    Recently, it began shaking (I think on acceleration only initially) and the check engine began to flash. I'm new to hybrids and don't know a hybrid-savvy mechanic, so took it to the Toyota dealership.

    I will type out the notes verbatim below, but this is how the situation unfolded. The dealership took a look at it and told me 3 of the 4 ignition coils were gone, the plugs were bad, and the MAF sensor was dead. They suggested replacing all the coils on the logic that the 4th coil would go soon too. They also wanted to do a throttle body and injector cleaning (not bench cleaning the injectors but I think adding cleaner to the fuel rail). Perhaps foolishly, I told them to go ahead with the coil, plug, and MAF replacement but not to do the cleaning. I also declined to have the evap system diagnosed for now. Also foolishly, I didn't ask for the old parts back.

    I got the car back (after a hefty bill) and within 2 days, it displayed exactly the same symptoms. I took it back and asked Wth? Surprisingly, they weren't fazed by this at all and suggested a vague computer problem as a possible cause. I asked if they bench tested the coils and was told that, "that's not something that's really possible" and that the mechanic looks at the computer and examines the coils. Unless coils have changed a lot, I didn't think bench testing was that difficult (just a multimeter to read resistance on each winding, right?). After I mentioned that testing the coils should be straightforward, he began back pedalling and said he'd have to check with the mechanic. My feeling was that they had misdiagnosed entirely as the symptoms were exactly the same, but they disagreed and said it was entirely plausible that two different problems were causing the same symptoms.

    They offered to take another look (at no charge) so I took them up on it. Now, they are telling me that cylinder 4 has low compression (40 psi, I guess they didn't check that first time around). First, they told me it was probably the head gasket. I mentioned that I haven't noticed any coolant loss or white smoke. After another day of tinkering, they are telling me it's likely a piston ring and I need a new engine. I mentioned that I don't have oil loss, nor do I notice the telltale oil burning exhaust colour. They said that wouldn't happen with a ring failure.

    I asked if they did a leakdown (no), checked for oil in the exhaust pipe (no), if they scoped the cylinder (answer was no and insisted not worthwhile). On their first examination they noted that the system was running lean. I asked if it could be a clogged injector. They told me the tech moved the injector to another cylinder and it was ok (at this point I'm not sure if I believe what they have/haven't done). I asked why, if on their initial diagnosis, they noted cylinders 1,3, and 4 were misfiring, why they are now sure the problem is a ring on piston 4? I can't remember the answer other than it felt evasive. At any turn, they just kept insisting that I need a new engine.

    I've taken the car back (the condition is much worse now and it shakes at idle). I have a feeling that they aren't doing enough to diagnose- their approach is just keep replacing stuff until the issue goes away (even if that means the entire ICE). From reading on this forum, perhaps the evap codes are related to the problem? My spouse noticed (for the first time), that there was a faint odour of gasoline right after she filled the car. The symptoms first started after a rainfall- perhaps water is getting into the tank or into the engine, or there is a bad cable (there is no note that they checked any cables).

    Below are the notes from both visits- the second are very brief- they have promised to send me detailed notes when the mechanic returns (I would think these would be done right after he does the work but apparently no). If you stuck around this long, thank you! Any advice appreciated. My next step is to get a code reader and ask around for a competent mechanic (we're in a new city).

    Cheers
    Mo

    First visit:
    Condition:

    Cause: C/S: check engine light is on. Found cylinders 1,3,4 misfire. Also P0171. System too lean bank 1. Found faulty mass air flow sensor. Vehicle has multiple evap related codes. Guest only wants misfire fixed. Replaced 4 spark plugs, 4 coils and mass air flow sensor. Vehicle runs good. Has excessive fuel in cylinders. Recomend EFI and throttle. Declined at this time.

    Correction: Engine light will come back on. Misfire issue is corrected

    Second visit:
    Original customer request:
    1. C/S engine light is on and vehicle is misfiring and there is lack of power. Engine light blinks

    Additional recommendations:
    misfire cyl #4 low compression (engine)
     
  2. ChapmanF

    ChapmanF Senior Member

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    Regrettably I don't have much to contribute about the whole overall story (I'll be reading with interest, and hoping the dealer gets their act together), but as to the coils, yeah, they've changed a lot. There's a whole transistor ignitor circuit built into each of those, so no, the terminals you can access in the wiring socket are not connected to a simple coil you could measure the resistance of.

    I'm not sure that means nobody could build a bench test circuit for them, but I don't know that there is such a thing.

    -Chap
     
  3. mo_

    mo_ New Member

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    Thanks for the info about the coils. Maybe it isn't so easy. However, the guy I talked to really didn't know one way or the other- I assume he's an auto technician but maybe not.
    mo
     
  4. The Electric Me

    The Electric Me Go Speed Go!

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    Is it at all possible for you to take the vehicle to a different dealer?
    Because the message I take most primarily from the post is that you've lost confidence in your dealership service department.

    Sounds that what you really want, and probably need, is a second opinion and diagnosis.
     
  5. mo_

    mo_ New Member

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    I can find another dealer... kind of. I actually went to this dealership (which is a little out of the way) because the one that is closer to me really gave me a bad feeling. I can look up their ratings and such. Since the problem doesn't seem to be hybrid-related, I was hoping to take it to a 'regular' auto tech
     
  6. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Please read the sticky about who should buy this Prius.

    We are patient people who will help you as much as Internet postings can IF you are a willing partner. But to afford our model Prius, you have to be willing to become the expert. We like it because it is a wonderful puzzle but if you just want a ride, there are choices.

    We'll help but you have to value your time.

    Bob Wilson
     
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  7. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. How long have you owned the car?
    2. How many trouble-free miles did you log, prior to the engine demonstrating misfire symptoms?
    3. When you got the car back from the dealer, did it work OK for the first day? How many miles did you drive after getting the car back, before it started to show problems again?
     
  8. mo_

    mo_ New Member

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    Hi Patrick,

    Thanks for your questions.

    1) I've had the car about 6 months (~15000 km). Largely highway driving (but through rush hour commutes). If it's of any value, when the weather was warmer, I was averaging around 4.9 L/100 km (48 mpg), though this dropped to 5.3 L/100 km (44 mpg) in winter (snow tires and much colder).
    2) it ran largely trouble free until this incident. Probably unrelated but just for completeness- one other issue that occurred was the fuse to the running lights blew. I isolated this to the front driver side marker light having somehow shorted and melted into the socket. Replacing the socket and the bulb (and the fuse, of course), resolved that. It did leave me wondering how water got in there- I wasn't able to find an obvious point of entry for water in the wheel well.
    3) The car ran ok for 1/2 day before the symptoms came back. Keep in mind the symptoms were intermittent from the start. When they first happened, it was only briefly on the highway. I was essentially on the way past the dealership, so I drove it there as the shaking stopped soon after starting. When they recurred after being at the dealership, it was also only a brief episode.

    Hope that helps. Let me know if there's any other info I can provide.

    Cheers
    Mo
     
  9. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Since the condition is intermittent I doubt that the mechanical condition of the engine (i.e., low compression) is the problem. You also mentioned your fuel economy is excellent, which also would point towards good mechanical condition of the engine.

    I agree that the dealer service department is not doing a good job for you.

    If you are willing to DIY then you should get Mini VCI so that you can do a cylinder compression check yourself. You would need a cylinder compression gauge, and remove all four spark plugs prior to doing the test. Then screw the gauge into each cylinder, one at a time, and use Mini VCI to run the engine at a slower than normal starting speed, similar to the speed that a regular gasoline engine would run at when the starter motor is turning.

    A cylinder leakdown test is similar to a cylinder compression check but I think the compression check is better since it is dynamic - the engine is rotating while this is happening - and the compression spec is well known.

    Mini VCI will also provide you with the current DTC being logged by your car so you can keep up with the current list after all of the work that has already been done.

    My guess is that a wiring harness connection to the engine ECU is bad or that the ECU itself is getting flaky after 14 years. Used ECUs are pretty inexpensive, you can probably buy one for $300 or less on eBay.
     
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  10. mo_

    mo_ New Member

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    Thanks Patrick,

    This is really useful. I have done compression tests, but way back when and not on a hybrid. I did figure it would be different because of the different way that the engine is started in the Prius, so the advice on the Mini VCI is really helpful.

    I should have noted that the symptoms seemed to happen after rainstorms. (though I only have a couple of incidents to go by- could be mere coincidence). Could this support your suspicion of a bad wiring harness connection/bad ECU?

    Thanks again,
    Mo
     
  11. Patrick Wong

    Patrick Wong DIY Enthusiast

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    A possibility associated with rain would be that water is dripping onto the engine valve cover, getting into the spark plug wells, and inducing a misfire. The spark igniters do not have an excellent rubber O-ring seal. I believe that your dealer installed new spark igniters, but that would be something easy to check.
     
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  12. mo_

    mo_ New Member

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    I might have some more useful info. The dealership promised to send more detailed info but I've been unable to extract it so far.

    As a first crack, I've used a very basic reader to pull down the following:

    P0300- Random/Multiple cylinder misfire detected
    P0301- cylinder 1 misfire
    P0302- cylinder 2 misfire
    P0303- cylinder 3 misfire
    P0304- cylinder 4 misfire
    P0440- evap emission control system malfunction
    P0441- evap emission control system incorrect purge flow
    P0446- evap emission control system vent control circuit malfunction
    P1300- Toyota: igniter circuit- malfunction cylinder 1
    P1315- Toyota: igniter circuit- malfunction cylinder 4

    Not sure if this is relevant at all, but I also got the following:
    P1436- Renault: diesel particulate filter blocked

    I gently drove the car around the block. I can feel it idling badly, but nothing like before- no shaking or check engine flashing, as it was previously.

    I'll resist any interpretation of the above right now (but it doesn't feel consistent with a bad piston ring on cylinder 4? It has been dry for a few days and no obvious water in the plug wells. Haven't pulled the plugs to check them yet.

    Thanks
    Mo
     
  13. ChapmanF

    ChapmanF Senior Member

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    Looks like Renault uses P1436 to mean something about a diesel particulate filter. Toyota uses it to mean a malfunction of the hydrocarbon-absorber-and-catalyst (HCAC) bypass valve, which is a valve you can see in your exhaust just ahead of the second catalyst, driven by a big ol' vacuum diaphragm. People have had experience with that thing seizing up.

    It seems your ECM has detected problems in two of your igniters (which would definitely lead to misfiring), and there are several codes about the evaporative emissions system, which involves a lot of valve-controlled vacuum tubing drawing extra air with or without fuel vapor into the intake, and it's not hard imagining misfiring from a malfunction there either. The P03xx's are just telling you that, yes, the other problems mentioned are leading to misfiring as you would expect.

    It probably makes sense to pursue the detected igniter and evap issues first, and see if you could get the misfiring under control that way. The P1436 malfunction of the exhaust bypass valve might wait for later, as it's not likely to be contributing to the misfires you're seeing. (Unless, maybe, the problem with it is that its vacuum hose has come loose or failed, in which case you'd have another source of unmetered air leading to possible misfiring and/or a system too lean code.)

    -Chap
     
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  14. mo_

    mo_ New Member

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    Thanks Chap. More good leads.

    Question- if they replaced all the coils and spark plugs, and the igniter codes weren't in the original problem when I brought it in, could that indicate they could have done something incorrect in the installation of the coils/plugs?

    Also (again- probably a naive question)... do any of these codes suggest a mechanical issue in cylinder 4 specifically (I think you've alluded to the answer but just checking I'm following correctly)?

    I'm not getting the lean codes again- unless I'm not pulling down all the codes (I need to spend some time making sure I'm using the scanner/software correctly).

    Thanks again.
    Mo
     
  15. FL_Prius_Driver

    FL_Prius_Driver Senior Member

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    I have a 2001, so I've been through some of the misfire battles and issues. What is crystal clear is you have a dealership where you have what I would call a "reactionary" technician. They read the code, then spew out what the computer indicates as a problem as what you need to replace. That ends up being everything called out (max $$ solution) and then let you see if the computer answer were right. If you go back to that dealer and get the same technician, expect more of the same....but with more expensive "shot in the dark" guesses.

    So you need to find a "proactive" technician or selectively or pick what you want to change yourself. The smell of fuel is a key clue. It really is.

    In my case, the key fixes ended up being the spark plugs and spark plug wires.
     
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  16. ChapmanF

    ChapmanF Senior Member

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    When you say "spark plug wires" on your 2001, what do you mean exactly? Given that there are no high-voltage spark plug wires as on older cars, do you mean there was a problem with the 12 volt wiring to the igniters? Did that require replacement or repair of the 82121-47030 engine wiring harness? What sort of problem was it? Corrosion? Mice? ...?

    -Chap
     
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  17. mo_

    mo_ New Member

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    That was my feeling- that they are the, "replace stuff until the problem goes away" (or the customer runs out of $$)! I'm definitely not going back to that dealership. Their indifference to not having gotten it right the first time suggested that this is their MO.
     
  18. FL_Prius_Driver

    FL_Prius_Driver Senior Member

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    Great question. It was actually the igniters. I was thinking of what was new and shiny and it was on the "downhill" side of the connectors, not the actual 12V wires. It simply looks like time and Florida heat were the likely culprits.
     
  19. mo_

    mo_ New Member

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    A bit of an update- delayed because of a combination of being away on business and finding a competent auto tech.

    The guy I took it to is a bit stumped too, though what he's finding is clearly not in line with the Toyota dealership.

    He found compression good and even across cylinders. He also said that, after resetting the computer, the car idles fine and doesn't produce codes until he puts a load on it. If I understood him right, that isn't consistent with anything like a vacuum or evap-related problem. It also isn't consistent with a mechanical problem with the engine.

    He tried changing the injectors, which didn't help and checked the wiring to the ECU, which were all fine. His only suspicion at this stage is the ECU is gone, which he'll check next.

    Please let me know if anyone has any other thoughts. He's not a hybrid tech, but is thinking through the issue (and isn't charging an arm and a leg).

    mo
     
  20. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Did the P1300 and P1315 DTC go away after the injectors were replaced or do they remain current?

    May I suggest one more check for your mechanic to make, prior to replacing the engine ECU: have him check the fuel line pressure which should be at least 43 psi when the engine is at idle speed. If the fuel line pressure is not good, check the voltage at the fuel pump and if it is good, then you would need to replace the fuel tank which contains the fuel pump within.

    If the voltage is low, check the circuit opening relay which is in the relay box next to the inverter.

    Since the engine runs OK without a load, maybe inadequate fuel pressure is the root cause of the engine misfiring when under load.

    A failed engine ECU is a reasonable suspicion given all of the other work that has already been done. You can buy used engine ECUs pretty cheaply on eBay. See what the part number on the existing ECU is. It is located behind the glove compartment in the instrument panel.

    IIRC, the latest engine ECU version has a 4 as the last digit in the part number (I believe the suffix is 47054), and that is what you want to buy if you decide you need to replace the ECU.
     
    #20 Patrick Wong, May 22, 2015
    Last edited: May 23, 2015