Exhaust System 6k rpm misfire

Discussion in '7th Generation (2003-2008) [Acura TSX]' started by MGrimes, Thursday 7th Mar, 2019.

  1. MGrimes Junior Member ☆ ☆ ☆ ☆ ☆

    United Kingdom Martin G Worcester
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    Hi guys, just bought myself a 2003 2.4 accord with 120k lpg fitted.
    Today I had an engine light come on which is p0171(i assume it's down to the crack on the flexi pipe of the exhaust drawing air? Therefore the downstream o2 is not reading correctly) and I will assess that ASAP.
    I noticed also today that giving the car a good thrashing that during acceleration reaching 6krpm when I can hear the v-tec exactly at around 6k it misfires/lags massively for a second as if it cuts out and carries on after with what I can only describe is reduced power. Any pointers before i start stripping parts on my day off would be very much appreciated! Thanks
     
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  2. SpeedyGee Club Manager Club Staff

    England Speedy Birmingham
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    Could be but more likely its the LPG system not tuned properly

    Does it only do this on LPG or does it do the same on petrol?

    Also have you checked the oil level recently? VTEC system relies on good oil pressure, so you need to have the right amount of oil in the engine.
     
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  3. Matt at H-Tune Service Team H-Tune Staff

    The P0171 code on an OBDII Honda will often be thrown if the fuel injection system is not operating properly. Typically the code will be triggered by a lean condition in the engine.

    This suggests to me that the LPG system fitted needs it's map adjusting or needs attention. But, this could also (as you say) be caused by excess oxygen getting into the system between the MAP sensor and lambda sensors through any means (such as a vacuum leak, leaking manifold/throttle body gasket or cracked manifold(s)) - keep us posted, I'm keen to see what's causing this.
     
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  4. honda_saj Club Veteran ★ ★ ★ ★ ★

    United Kingdom saj east london
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    Could also be caused by crack in air supply pipe, i had hariline crack on air box intake causing this used some electrical pvc tape to create seal while replacement fitted.
     
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  5. MGrimes Junior Member ☆ ☆ ☆ ☆ ☆

    United Kingdom Martin G Worcester
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    7
    Thanks for the input

    Monitoring my stft and ltft lately has given me alot to think about during my time away, have not been driving the car much at all however in the time that I did I found out that my STFT on lpg reaches as high as 40% during a spirited drive and 20% at a steady idle and the LTFT goes up and sits at a 20%, much similarly to when it's running on petrol however stft on petrol is usually 30%+ on idle. Have not done anything yet in terms of checking for vacuum leaks as not had the time but I will update this topic when I investigate it thoroughly
    - - - Updated - - -
    Thanks, the pipe looks a little bit degraded in one of the flexes in it however it doesn't look like the crack is all the way through but maybe it could still potentially be drawing some air
     
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  6. SpeedyGee Club Manager Club Staff

    England Speedy Birmingham
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    Drop me a PM if you need any help checking out the LPG system, I'm due to go down to Worcester next Saturday morning.
     
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  7. DrSam Club Moderator Club Staff

    United Kingdom Sam Birmingham
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  8. MGrimes Junior Member ☆ ☆ ☆ ☆ ☆

    United Kingdom Martin G Worcester
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    7
    Just an update guys, visited SpeedyGee yesterday after a thorough investigation the flexi pipe is cracked between upstream and downstream o2 sensors, that could be a reason for the vacuum leaks --- thanks brother!

    Today stripping a few parts myself have noticed that the engine mount holds no vacuum at all, so whilst the new one has been ordered I plugged the vacuum pipe so it isn't sucking air for nothing, the stft improved slightly but still high 30s on idle but drops significantly upon opening the throttle under heavy load so once the flexipipe is sorted perhaps we will see a change(drastic I shall hope)!

    To top it off the PCV valve is blocked, new one ordered to change...bought a nice car right there lol.

    Thanks for the help guys will keep this topic updated as things get done

    @DrSam will do that ASAP, thank you for the welcome
     
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  9. SpeedyGee Club Manager Club Staff

    England Speedy Birmingham
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    Was nice to meet you. Sorry I only had limited time free.
     
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  10. MGrimes Junior Member ☆ ☆ ☆ ☆ ☆

    United Kingdom Martin G Worcester
    5
    7
    Why guys, thought I would update this topic.

    Continuing the mission of trying to diagnose the issue hit a dead end, almost.

    Things so far that myself and speedygee have come up with and done:

    Checked every single vacuum point - fine
    Swapped o2 sensor for a good one
    Compression test - perfect
    Leak down test - nothing unusual
    Checked every single sensor and AFR - all appears fine
    VTEC solenoid signal and operation - fine

    One last thing before I rip my hair out is to check the LPG map and adjust it to increase the injection and run it primarily on LPG to see if it runs correctly - that would tell me more about the condition of the petrol system components - hopefully.

    Will keep this posted if the problem gets resolved, perhaps help someone on the same boat as me!
     
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  11. SpeedyGee Club Manager Club Staff

    England Speedy Birmingham
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    As I said yesterday that's not possible as the LPG system is a piggyback off the Petrol system it will always copy what the Petrol system "would have done" because the cars ECU still thinks its running on Petrol.
     
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  12. MGrimes Junior Member ☆ ☆ ☆ ☆ ☆

    United Kingdom Martin G Worcester
    5
    7
    Hey guys, I guess this is the final update to this thread

    After much head scratching I finally managed to get to the bottom of the so called "misfire", plugged an lpg interface into a laptop and much to my surprise the previous owner had set the lpg to switch to petrol at 6k RPM, which was far from optimal and I will tell you for why... having checked literally everything to do with vacuum on the car I have found nothing extra terrestrial except for the engine mount leaking vacuum straight through which I disabled straight away I had no luck with the car still driving like a potato on wheels...wheels being smaller potatoes. So, something I should have done in the first place along with a simple vacuum check is ...check the fuel pressure which turned out to be...wait for it.....27psi . Long story short, the previous owner was a moron - and I'll tell you for why with a photo, basically what you're looking at is the white housing which at the bottom holds the pressure regulator in place with the white tab, the PO snapped the white tag and still decided to put the unit back inside, so the pressure regulators gasket shat out into the tank and the regulator itself went abit...loopy.

    Special thanks to @SpeedyGee for the help!
     

    Attached Files:

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  13. honda_saj Club Veteran ★ ★ ★ ★ ★

    United Kingdom saj east london
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    Nice find glad you finally found out:clap:, there are many bad examples of screwed up lpg installs.
     
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