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Thread: 3A90 Intake valves stuck open, carbonized, full of gunk and car won't start

  1. #11
    Moderator inuvik's Avatar
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    Quote Originally Posted by ahausheer View Post
    You would need a serious amount of blowby on a port injected engine to create such a problem at 20,000 km (12,500 miles!!). At such low mileage and seemingly mild driving I would suspect something else is at play. I would be curious as to the condition of the EGR and the PCV valve. Perhaps you can pull the rubber hose off the PCV valve and let us know if it has lots of oil in it and/or any other problems reported by the dealer. Thanks for reporting.
    I agree, very unusual problem. Oil starvation wouldn't create this condition or would it due to overheating. Somehow a ton of oil is being introduced into the intake.


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        click to view fuel log View my fuel log 2015 Mirage ES 1.2 automatic: 40.4 mpg (US) ... 17.2 km/L ... 5.8 L/100 km ... 48.5 mpg (Imp)


  2. #12
    Senior Member ahausheer's Avatar
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    Quote Originally Posted by old mechanic View Post
    Get rid of whatever is in the fuel tank, if they just clean up the residue. Reminds me of what happens when someone puts sugar in your gas. Had it happen to a customer in the Navy. .........

    regards
    mech

    This makes sense. Badly contaminated fuel (station tank with some bio-diesel mixed in for example) or purposefully contaminated fuel fits with the description of no reported issues (codes, idle issues, drive-ability issues etc) the day before despite the ''massive'' carbon build up that was ''hard as a rock'' on a basically new port-injected engine. If that much carbon buildup occurred over time you would expect a previous code or drive-ability issue or at least significant and noticeable oil loss in the days/weeks/months prior. Seeing ''numerous'' similar issues in a tiny workshop in a country that hasn't sold a huge amount or these cars, and the fact that rest of the global community is not reporting this as a known issue points to a local gas station with severely contaminated gas or local Mirage-hating-sugar-stealing-kids with gas tank access.
    Last edited by ahausheer; 01-06-2016 at 05:41 AM.

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  4. #13
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    What gasoline were you using? Is there an equivalent of Top Tier gas in your country?

    What grade/type of the oil have you used? Synthetic? Conventional? Any indication of oil burning?

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        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 46.4 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.7 mpg (Imp)


  5. #14
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    Quote Originally Posted by inuvik View Post
    We have a lot of members with way more mileage than this without a issue. My best guest would be overfilling the crankcase at oil changes, resulting aeration of a lot of oil. Causing a bunch of oil to pass through the PCV which of course would cause carbonization.
    It is a possibility if oil foams at high speed.

    OP is a special case as I don't think anyone in NA runs at autobahn speeds for prolonged periods of time.

    Another possibility is valve seals.

    Maybe it is time for PCV oil catcher..
    https://m.youtube.com/watch?v=SWhsMsRmYzs
    Last edited by cyclopathic; 01-06-2016 at 07:02 AM.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 46.4 mpg (US) ... 19.7 km/L ... 5.1 L/100 km ... 55.7 mpg (Imp)


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    Moderator Eggman's Avatar
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    Quote Originally Posted by ahausheer View Post
    You would need a serious amount of blowby on a port injected engine to create such a problem at 20,000 km (12,500 miles!!).
    Are Autobahn speeds too much for these engines?

    Quote Originally Posted by foama View Post
    My car has about 20 000 km on it, and is only used for long-distance driving. It had no history of any problems at all.
    Coming home after a 300km drive on the autobahn, driving at 100 - 130kmh, the car was parked in the garage. Next morning it refused to start, but cranked normally and began smelling like fuel.
    Emphasis added.

    I wonder if fuel usage was affected by this condition as it developed.

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        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 48.8 mpg (US) ... 20.7 km/L ... 4.8 L/100 km ... 58.6 mpg (Imp)


  7. #16
    Senior Member Cobrajet's Avatar
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    Sounds like bad fuel to me. With the mpg these cars get, it doesn't make sense to put in cheap gas. I only run top tier.

  8. #17
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    Quote Originally Posted by old mechanic View Post
    No other symptoms of increasing restriction to intake flow, even at 130 kph on the last drive?

    Then the next day there is not enough compression for it to start?

    Doesn't sound right to me. Did it idle right when you got home from the trip? Other symptoms?

    regards
    mech
    A: It ran just as always, no idling problems at all. Perfect rythm and no Valve sounds. Next morning it would not start.


    Q: I wonder if fuel usage was affected by this condition as it developed?

    A: I did notice a slow gradual increase to about 5% higher fuel consumption than in the very beginning.
    The fuel in Europe is generally very good, maybe with the exception of a certain supermarket-brand in the UK. In Germany frequent and regular checks are undertaken, and a failed fuel-quality check would badly hurt any brand. Also applies to supermarket brands. Dirty combustion chambers or valves are quite uncommon here.
    I usually buy at a well-known brand fuel-station, but not always the same one.


    Q: Are Autobahn speeds too much for these engines?

    A: The car was well under its max speed/load. I was quite swift, but not pushing it. To give you an idea, my autobahn fuel consumption was always well under 5L/100km, usually averaging around 4.3L.


    Q: You would need a serious amount of blowby on a port injected engine..? Oil overfilled..? Foaming..?

    A: The engine is otherwise perfectly clean, no buildup elsewhere. Oil fillercap 100% clean inside, cam area on top of cylinder head under the cover also perfectly clean. Dealer used Mitsubishi's own brand oil. The oil was still transparent when I put it into the garage for regular yearly service. Oil consumption is practically zero. Less than one cup consumed when it returned for regular service.







    Update:
    It seems this issue is not uncommon in 3A90 engines.
    A local service-provider with five or six SpaceStar's has seen the same problem at least once with each one, albeit at maybe half the milage. Their Space Star (Mirage) are used for short-distance customer to customer hauls, and are equipped with AS&G. The A390 with AS&G supposedly have EGR, the non-AS&G (mine) don't.

    The dealer said, there will come a new software for these engines sometime in the unspecified future, which should address and hopefully remedy this problem. Currently no new software is available for this car yet...

    I am trying to get some pix of the problem and post them here.
    Last edited by foama; 01-09-2016 at 04:02 PM.

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    Lets ASS-UME their diagnosis is correct. With an engine running perfectly, the only rational explanation of which I know is the contamination accumulated on the intake valve stems and the engine cooled overnight that same accumulation cooled and congealed into a kind of plastic type of material that would not allow the valves to close completely when you tried to restart the car next morning.

    This makes sense, but there would be one piece of evidence. The engine would crank over faster than normal, just like an engine will when you remove the spark plugs and there is no compression.

    If the repair shop is familiar with these symptoms then there must be a lot of bad gas sold at stations near that shop. Never heard of it happening in the US, from personal experience, with a single exception posted previously.

    Based on the belief that you're description of the problem is perfectly accurate.

    I know of no other possible cause. That's after over 30 years working on cars, with a single example of virtually identical symptoms.

    How could the engine run perfectly then loose compression on every cylinder?

    I'll follow this thread carefully, maybe learn something new.

    UNDER NO CIRCUMSTANCES DRIVE THE CAR ON THE "FUEL" IN THE TANK OR YOU RISK HAVING THE EXACT SAME THING HAPPEN AGAIN AND I DOUBT SERIOUSLY WORK WOULD BE DONE AGAIN UNDER WARRANTY.

    regards
    mech

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage de 1.2 manual: 55.7 mpg (US) ... 23.7 km/L ... 4.2 L/100 km ... 66.9 mpg (Imp)


  11. #19
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    The issue, if related to fuel quality would be apparent in any engine. Assuming there is a contamination in the fuel sprayed at the head of the intake valve stem when the valve is opened, the hot valve will keep the contamination in a liquid form, also diluted by the fuel spray itself. Like cooking caramel to a certain heat level there is a "stasis" in the accumulation. Once shut down, the engine heat soaks and the temperature increases in all areas around the combustion chamber, which allows the accumulation to solidify in the area between the valve stem and the valve guide.

    The camshaft forces the valve to open or something breaks, but the closing of the valve is only due to spring tension, which is not strong enough to overcome the resistance provided by the foreign substance.

    Sadly the whole sequence is hard to pinpoint as to where the contamination was introduced into the fuel tank, but the last fill would be highly suspect.

    With the worldwide glut of gasoline, the advent of "stale" fuel will increase greatly and the incentive to do something with that stale fuel is very powerful financially.

    I though of a single additional instance of similar damage. A friend had an old work truck that he filled with gas that he got for free from salvage yards and stored in tanks on his property. That fuel eventually destroyed his engine but he was spending $30-40 daily for fuel and the truck was a cheap patchwork of salvage parts. The state came after him for not paying the gas tax, which I told him was absolutely ludicrous since the tax was paid when the tank was filled before the car was wrecked and the case was quickly dismissed.

    I would see to it that the fuel from the last station where you filled the tank was tested to possibly help someone else to avoid a similar scenario.

    regards
    mech

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage de 1.2 manual: 55.7 mpg (US) ... 23.7 km/L ... 4.2 L/100 km ... 66.9 mpg (Imp)


  12. #20
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    Quote Originally Posted by foama View Post
    A: It ran just as always, no idling problems at all. Perfect rythm and no Valve sounds. Next morning it would not start.

    Update:
    It seems this issue is not uncommon in 3A90 engines.
    A local service-provider with five or six SpaceStar's has seen the same problem at least once with each one, albeit at maybe half the milage. Their Space Star (Mirage) are used for short-distance customer to customer hauls, and are equipped with AS&G. The A390 with AS&G supposedly have EGR, the non-AS&G (mine) don't.

    The dealer said, there will come a new software for these engines sometime in the unspecified future, which should address and hopefully remedy this problem. Currently no new software is available for this car yet...

    I am trying to get some pix of the problem and post them here.
    I hate to burst your bubble, but I highly doubt the software has anything to do with this problem. The EGR system is not as dirty as people make it out to be. Ironically, the highest contaminate in combustion gasses is water (other than CO2). Yes, there is some soot in those EGR gasses, but it's very-minimal in such a small engine, and the spray pattern from the fuel injectors would take care of it without a hitch.

    If the fuel is dirty, than perhaps the EGR gasses would be too (sticky substance in, sticky goo out). But that cannot be remedy by software. The only remedy, would be to put clean fuel in the tank.


        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 automatic: 51.7 mpg (US) ... 22.0 km/L ... 4.6 L/100 km ... 62.0 mpg (Imp)


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