Clonking noises on ICE at low speeds

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by 1980s_john, Jan 4, 2019.

  1. 1980s_john

    1980s_john Junior Member

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    A bit of a hard one for an internet forum to advise on, as there are all sorts of noises and possible causes of such but here goes.

    Had several moderately loud clonks from the engine department a few days ago on my 2009 Prius (3rd gen). These occurred for about 2 seconds when accelerating between around 10mph to 30mph with the ICE running. Seems to only occur once the car has warmed up (it is about 3C to 10C here at the moment) eg after 15 minutes of driving or so. At cruising speed (40mph and up) no noises noted, and no problems when slowing down or accelerating to 30mph in EV mode. Started 3 days ago after a short hard acceleration, last two days seems to be not so bad (driving more gently!)

    Vehicle history: 158k miles, fully Toyota service history, eg oil changes every 10k, engine coolant 100k & 150k, inverter coolant 150k. No changes to transmission fluid, no cleaning of EGR valve/tubes etc. Had brake disks (rotors) replaced a year or two ago, original suspension / exhaust.

    I've checked fluids / engine oil level and both are fine.

    My thoughts are engine mounts maybe?

    I have the car booked in to Toyota on the 14th for an ECU recall (to fix the stall in limp home mode issue), so will ask for any fault codes to be checked before they re-programme it.

    Regards,
    John
     
    #1 1980s_john, Jan 4, 2019
    Last edited: Jan 4, 2019
  2. JC91006

    JC91006 Senior Member

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    1. How do you have the time to accelerate to 30mph on ev?

    2. Have you changed the spark plugs?

    3. You should change transaxle fluid and clean EGR circuit
     
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  3. m.wynn

    m.wynn Senior Member

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    You describe one of the most typical symptoms of EGR circuit blockage, providing the "clonk" is actually engine knock and on the assumption that you're actually accelerating engine on. If you really mean accelerating to 30mph on EV, disregard this entire post.

    The service history is great in general, but does nothing to reduce likelihood of EGR circuit clogging. The EGR valve and tube you mention are typically the least involved parts of the 4-part circuit, although cleaning both is necessary. The EGR cooler and EGR ports within the intake manifold usually contain the complete, or nearly complete blockage. Based on your symptoms, you will find this to be the case. If you're not already aware, there is tons of info and how-to's on this forum.

    Maybe. But bad engine mounts at your mileage, or any mileage with regard to Prii, is basically unheard of, imo. Engine mounts shouldn't be suspect if you're really accelerating in EV mode.

    Well and good, I spose, but this issue can and does manifest to a pretty non-ideal climax with no advance warning lights or code history until late stage misfire, P030x coding. At this stage the knocking will have become much more concerning, and is often the time when head gasket failure is confirmed.

    Of course I'd love nothing more than to be proven completely wrong with this internet diagnosis. Best of luck with diagnosis and resolution.
     
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  4. 1980s_john

    1980s_john Junior Member

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    1. No problem around town. Press EV button in ECO model and don't exceed threshold (maximum white bar on display - 'Hybrid System Indicator'?)
    2.Yes sparkplugs have been changed at normal service intervals (every 60k from memory).
    3. Well one day, will ask independent garage to do so.

    Regards,
    John
     
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  5. 1980s_john

    1980s_john Junior Member

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    Yes the ICE has to be on for this noise to occur. I will contact my independent garage and arrange EGR clean ASAP.

    Thanks all for the quick replies!
    Regards,
    John
     
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  6. m.wynn

    m.wynn Senior Member

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    Exercise diligence, here. It can be tricky to find a mechanic who can understand the objective, and who will actually take the time to perform this tedious service satisfactorily. Expect a labor charge of at least 6 hours to be able to assume the work was well done.
     
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  7. JC91006

    JC91006 Senior Member

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    The correct Iridium spark plugs are good for 100k+ miles. No need to get them done at 60k unless you the window cowling removed for another repair.
     
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  8. 1980s_john

    1980s_john Junior Member

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    Update - I had the EGR valve cleaned (2 hours labour) in January, and also switched from 95% of refills of cheap supermarket petrol to 100% BP/Shell/Esso. At the recall session for the ECU update (in January) dealer said they would not read the codes for free. Later in March had 160k mile dealer service with no issues raised. Problem has 99% gone away, occasionally hear the odd single pop, no more clonking or loud rattling.

    Not sure how the EGR cooler looks, if problem comes back I will buy a second hand one, clean it, then swap it in.

    In the UK Toyota services include new plugs every 60k miles (so am on my 3rd set).

    Lastly no change from new of the AT fluid. Services just check the level every 40k miles, this seems a bit pointless to me as surely you need to check a sample.

    Regards,
    John
     
  9. Raidin

    Raidin Active Member

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    I have the same problem as you, John, just worse. Started at 375k miles (I only use Shell gas so maybe that helped increase how much time it took for the EGR system and intake manifold to clog up) and has been going on till now (460k miles). It has gotten to where you can hear it "clonking" at 60 MPH while on cruise control, even though it normally only happens when driving at low speeds or when the battery is low and the engine is charging it. I also got misfire (P0304 for cylinder #4 and P219A only recently).

    Car's at the shop awaiting intake manifold and EGR cleaning, and if not, replacement of the manifold per a TSB from Toyota. Have heard multiple stories of people disconnecting the EGR system to test, and the car ran without any unusual noise (TSB says this happens when the EGR system is active).

    Glad to hear your car is doing better. Can't wait to get mine back without any more noise and codes. Then I will have a perfectly-running CT 200h nearing 500,000 miles (that is, after I blew a head gasket back at 375k).
     
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  10. Raidin

    Raidin Active Member

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