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

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  1. #1
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    3A90 Intake valves stuck open, carbonized, full of gunk and car won't start

    I'm asking if anyone else has experienced such problems with the 3A90 (1.0 L) engine. Please report!

    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. The engine is 1L, 3A90, no AS&G and consequently no EGR. Remember, this is a non direct fuelinjection engine, fuel is injected before the combustion chambers and not into them.
    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.

    After telling the dealer about the problem, he said it would take 3 or four days in the workshop, but perhaps longer, and
    Mitsubishi would see the bill taken care of. After all, the car is under waranty and there is a mobility garantee.

    I asked him how he could tell without having even seen the car. He replied he'd already seen numerous with that problem in his tiny workshop...

    On the following day using a mini endoscope camera, the dealer confirmed the problem. The intake valves were not closed because of massive "gunk" or carbon deposits all over the intake valves.The massive buildup did not allow the valves to close, and without closed valves no compression, no starting. He reported the problem to Mitsubishi, asked for permission to perform the waranty repairs, and ordered the parts Mitsubishi allowed him to replace.
    The next day the cylinder head was removed, valves removed and cleaned manually. The removed carbon deposits were "hard as rock". The original valves were to be put back in and grinded in the late afternoon or next day, which is tomorrow.

    I will keep you posted on this matter, but am travelling throughout Europe and don't always have Internet.



    Update:immmediatly after repair:
    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 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...


    UPDATE, March 12 2016

    1) The dealer briefly showed me a picture of badly fouled exhaust valves, but did not let me take either the photo with me or to photograph or copy it. He said:"The picture (supposedly of my car's valves) is Mitsubishi property and may not be disclosed, copied or given away!"
    2) Since the repair, I have noticed higher fuel consumption and lower top speed. Driving to work the bult-in display showed around 4.3 to 4.5 L/100km before repair, and now afterward always more than 5L/100km, usually about 5.2L/100km. The top speed on a flat autobahn with no wind was displayed at around 172-175kmh according to the car's speedo. Now it reaches around 160kmh under the same conditions.

    After visiting the dealer about this, I was told new software was flashed into the ECU.

    I hope to find out more, or get the situation resolved.
    I will post updates.




    UPDATE September 2019

    Valves look just as clean as ever. Perfectly clean, just as inside combustion chambers.

    Ever since the car was "repaired" and carbon removed, the compression has been much lower at around 9bar (about 130 psi) on all cylinders, and fuel consumption is consequently about 10% or so higher than before. This car has a compression ratio of 11.5 : 1 and therefore compression should be much better.

    Does anybody have the official figures for compression of the 3A90? I do have the figures for the 3A92, but they don't apply.
    Last edited by foama; 09-07-2019 at 08:01 AM.

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    Interesting. You're the first I've heard of this on the 1.0 or 1.2L engines.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

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    The carbon is a symptom, not the problem.

    regards
    mech

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        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)


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    Thanks for the report, foama. Please keep us updated.

    I'm sure the garage has a theory about what caused the build-up.

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    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

        __________________________________________

        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)


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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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    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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    Quote Originally Posted by BRagland View Post
    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.
    Answer:

    1) This car has no EGR.

    2) Old Mechanic's assumption the fuel being no good sounds logical and makes sense, but:
    a):I filled up last at a well-known Shell brand station in Luxemburg a few hundred km away.
    b) The local company using a half a dozen similar 3A90 Space Star/Mirages has suffered the same problem with each vehicle at least once, and they had much less milage at each occurence than my long-distance driven car, and I don't buy from "their" same gas station. After filling up last time, I immediately drove a few hundred km, so nobody could have done anything to the tank.

    3) I don't really believe it is a software problem either, but I have to give them a chance to fix it. Then if they claim to have fixed it, I would have to wait to see how long their fix lasts...
    Last edited by foama; 01-06-2016 at 06:09 PM.

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    Quote Originally Posted by foama View Post
    Answer:

    1) This car has no EGR.

    2) Old Mechanic's assumption the fuel being no good sounds logical and makes sense, but:
    a):I filled up last at a well-known Shell brand station in Luxemburg a few hundred km away.
    b) The local company using a half a dozen similar 3A90 Space Star/Mirages has suffered the same problem with each vehicle at least once, and they had much less milage at each occurence than my long-distance driven car, and I don't buy from "their" same gas station. After filling up last time, I immediately drove a few hundred km, so nobody could have done anything to the tank.

    3) I don't really believe it is a software problem either, but I have to give them a chance to fix it. Then if they claim to have fixed it, I would have to wait to see how long their fix lasts...
    Thanks for the reply.

    There is a common problem in the US where the dealers regularly put 4-5 quarts of oil into the engines, when it requires much less. This could be causing excess aeration / foaming which could be either going through the now over-saturated PCV valve, or through some kind of a seal leak due to the oil overfill (or just bad seals from the start) or even both. That excess oil could easily causes carbon build-up problems.

    This could have been the cause for that fleet, maybe you as well, but I'm not sure if you changed your own oil.

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        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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    Interesting, lack of cleaning chemicals in the fuel an issue in Europe? I normally run some Marvel Mystery Oil in my fuel on occassion but maybe I'll add some Seafoam next tank

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        click to view fuel log View my fuel log 2015 Mirage ES 1.2 automatic: 40.5 mpg (US) ... 17.2 km/L ... 5.8 L/100 km ... 48.6 mpg (Imp)


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