Very rich at Idle and lean when the vacuum decrease

Discussion in 'URGENT - Help Quick!' started by ranausaurus, Oct 10, 2019.

  1. ranausaurus

    ranausaurus Member

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    Hi all,
    I have the Honda accord from 2000 with the F20B6 VTEC engine and

    after the engine overheated and killed the distributor,
    the engine can't stay at idle when the engine reach the normal temperature 70-80°C when any load was on the engine(A/C,steering wheel) and can't be start when hot without WOT it.
    and when I start the car Cold,warm or hot the mixture is very very rich(it smells gasoline at the exhaust)

    So, when I remove a vacuum pipe caps to let the air come in the engine can manage the Idle and load but always too rich.

    I cleaned the throttle body and the IAC(3 times) and always the same issue but with an improvement.

    I checked the Fuel regulator, there isn't leak and when I disconnect it the STFT goes to negative trim so It works like it should.

    And during acceleration or changing gear there is a huge power loss and the engine lost some power at WOT

    Moreover, the last symptom when I checked the STFT and LTFT Is the LTFT stay in negative between -5% to -7% but the STFT when the MAP sensor stay under 0.4 bar(1.0 bar is atmospheric pressure) change between -1O% to 15% but when the vacuum is less than this value the STFT increase a lot and change between 0% to 10% !!!



    In conclusion this engine is running too rich under vacuum, and became lean under load and low vacuum.
    I conclude it would be the MAP sensor because this is one of the two sensors dependent by the vacuum and the second one works like it should work.
     
    Last edited: Oct 11, 2019
  2. trillobite

    trillobite Active Member

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    I had a very similar problem with a 350 chevy engine about 5 years ago that I bought from craigslist. It turned out that one of the heads wasn't sealing against the block properly. I never determined if the head was actually warped or not, but the head bolts didn't seem to be torqued to the same spec. By the time I dug into the engine, I already had a BF Goodrich crate motor to drop in.

    I suspect your head has warped. In the case of my chevy 350, two cylinders: bank 1 and 3 were passing gasses across each other, and there was a thick layer of soot between the two cylinders. I also had to remove a vacuum port plug off my carburetor to idle. Bank 1 cylinders would run rich, while Bank 2 driver side would go lean.

    Best thing you can do is a leak-down test. There are guides online that will help you determine if gasses are passing into the cooling system, or across to a neighboring cylinder.

    If you cannot do a leak-down test, then the only other idea I have is to remove the head completely, and inspect the gasket. However, only do this after you have exhausted all other possible ways to test. I am sure others on this forum will give you a better check list than I can, but here are a few other things to check first:

    -Look for bubbles in your coolant reservoir coming out of the coolant return hose off the radiator (sign there is exhaust gasses getting into your cooling system).
    -Look for coolant in your oil.
    -Take pictures of all 4 spark plugs, and post it. Look at spark plug charts online, some will even tell you what a spark plug would look like if it's burning coolant.

    There may be other sensors which may have gone bad after an engine has overheated, but I am still not completely familiar with Honda engines yet. However, usually if a sensor goes bad, you should have a check-engine light, or at least a pending code, so look for those.

    One thing I would like to ask is, how did the engine over-heat in the first place?
     
  3. ranausaurus

    ranausaurus Member

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    Hi, I forgot to say that I had change head gasket and intake manifold gasket and the head was rebored and the block didn't move.
    So, I made 800 km with this car and the problem and it doesn't consume any oil and there isn't contamination in any case.

    moreover, I checked all vacuum leak and there isn't any and before I put the head back I check valves,intake and exhaust passages and I didn't see any crack and all the walls are very clean
     
  4. trillobite

    trillobite Active Member

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    I am still trying to think of another reason why your engine may be acting that way. The only other thing I could think of checking is the injector O-rings. If they were removed at any point during any of the repairs, it's recommended to replace the O-rings.

    It still could possibly be a sensor issue, however, it sounds like the engine didn't have this issue BEFORE the over-heat, I can't imagine a sensor failing.

    By the way, what is your STFT and LTFT during idle? (long term and short term fuel trim).
     
  5. ranausaurus

    ranausaurus Member

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    Hi I have already send the information the last symptom when I checked the STFT and LTFT Is the LTFT stay in negative between -5% to -7% but the STFT when the MAP sensor stay under 0.4 bar(1.0 bar is atmospheric pressure) change between -1O% to -15% but when the vacuum is less than this value the STFT increase a lot and change between 0% to 10% !!!

    And no oring leak ;) already checked too
     
  6. ranausaurus

    ranausaurus Member

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    But i will do a New trim read Tomorrow
     

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