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can you figure this one out ?

Discussion in '308/328' started by [email protected], Jul 21, 2010.

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  1. andy2175m4@yahoo.com

    [email protected] Formula Junior

    Dec 7, 2008
    473
    Los Angeles, CA
    Full Name:
    Andy Rein
    #1 [email protected], Jul 21, 2010
    Now that I have converted the 308 to electronic fuel injection, and put on the catalytic converters, It runs clean, and I can't even smell the fuel burning, catalytic converters are amazing, don't leave home without them !

    But, the cat connected to the rear bank of cylinders is running cherry red, so I pulled the plugs to check for mixture. Of the 4 spark plugs on the rear bank, 3 are clearly running very rich (black), 1 is ok, whereas the four plugs on the front bank of cylinders are all a perfect cocoa brown, and that cat runs normally.

    I pulled the injector from the most rich cylinder, and pulled the injector from the most lean cylinder, and did a flow test, the two injectors flowed the same within 5%, so the injectors are OK.

    Now this is a megasquirt so it may be doing something funny with the duty cycle between banks that I am not aware of,
     
  2. st@ven

    st@ven F1 Rookie

    Aug 4, 2008
    3,318
    Germany
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    Steven
    #2 st@ven, Jul 21, 2010
    you're sure your ignition sequence is oke?
     
  3. stratos

    stratos Formula Junior

    Dec 9, 2003
    639
    Switzerland
    #3 stratos, Jul 21, 2010
    or the fire extinguisher/fire brigade truck.
     
  4. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
    Owner Rossa Subscribed

    May 4, 2001
    36,588
    Birmingham, AL
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    Tommy
    #4 Dr Tommy Cosgrove, Jul 21, 2010
    Hyperflow!

    I am a believer now too
     
  5. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
    Owner Rossa Subscribed

    May 4, 2001
    36,588
    Birmingham, AL
    Full Name:
    Tommy
    #5 Dr Tommy Cosgrove, Jul 21, 2010
    I believe in that too
     
  6. wazie7262

    wazie7262 Formula 3

    Feb 13, 2008
    2,357
    Temecula, CA
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    Scott
    #6 wazie7262, Jul 21, 2010
    But, the cat connected to the rear bank of cylinders is running cherry red


    Yes...these cars LOVE cats...
     
  7. flyngti

    flyngti Formula 3

    Jul 16, 2009
    1,256
    Snohomish, WA
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    Eric L
    #7 flyngti, Jul 21, 2010
    If the rear bank is running really rich, unburnt fuel is probably causing the cat to overheat. How does the megasquirt control the a/f mixture? Is there an O2 sensor in each cat?
     
  8. andy2175m4@yahoo.com

    [email protected] Formula Junior

    Dec 7, 2008
    473
    Los Angeles, CA
    Full Name:
    Andy Rein
    #8 [email protected], Jul 21, 2010
    The megasquirt has only one 02 sensor, and it's in the collector of the rear (by bumper) bank, the one with the cat running cherry red.

    The 02 sensor seems to indicate a normal A/F, but I pulled all the plugs, plugs 1, 2 and 3 showed lots of carbon, indcating RICH mixture, consistent with a HOT cat, plug 4 was better, just a tiny touch of brown, but plugs 5,6,7,8 were brown, indcating proper mixture, and the front bank cat was not overheating.

    I would guess that the 02 sensor is no good, since it does not indicate the over-rich condition in that bank of cylinders. I will have to replace it (again).

    So, there is something causing the rear bank to run rich, plugs confirm that. But it's only in cylinders 1,2,3........not even #4.

    Compression is good in all cylinders (>150 psi) ex .cyl #1, which is 110 psi.

    The 02 sensor is on one bank (rear) only, but the ecu can only adust all 8 injectors at the same time, they are all basically in parallel, the exact same pulse goes to all 8 injectors at the same time. It can be set up to alternate between banks (quasi sequential) but the pulse width and duty cycle are always the same for all 8 injectors at all times.

    I bench tested the #2 injector (most rich) vs. #5 injector (most lean) and the cc's per minute was the same. it's not a hardware problem with the injectors, could it be a bad (leaking) intake valve in all 3 cylinders ?
     
  9. flyngti

    flyngti Formula 3

    Jul 16, 2009
    1,256
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    Eric L
    #9 flyngti, Jul 21, 2010
    It sounds like the O2 sensor may be bad, but that seems unlikely if you replaced it recently. Is there a sensor bung in the other cat? Maybe put the sensor on the other bank to see what happens.

    Have you checked that the timing is the same on both banks?
     
  10. CliffBeer

    CliffBeer Formula 3

    Apr 3, 2005
    2,198
    Seattle, Washington
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    Cliff
    #10 CliffBeer, Jul 21, 2010
    Last edited: Jul 21, 2010
    Andy,

    When you say the pulse width and duty cycle is the same for all eight cylinders, I assume you mean that:

    1. it's not possible for different cylinders to have different flow rates related to longer or shorter open flow of the injector, thus all cylinders should (theoretically) be getting the same flow.
    2. the timing of the pulse is static (concurrent) across all cylinders, not in sequential order of a flat crank V8.

    If 2 is an accurate statement, do you think it makes any difference if the pulse occurs when a valve is open or closed, or when the piston is in the downstroke condition v. compression or exhaust? In other words, do you think a static pulse (unrelated to the timing of valves/piston) will affect the AFR and burn rates? Seems to me it would have a meaningful impact. But perhaps not, as the stock CIS system used on injected 3X8 is dumb in this regard. If there's any way to time the pulse to the configuration of a flat crank V8 I would guess that would promote a better/more efficient burn.

    That's a good idea above related to trying to switch the 02 sensor to the other bank and see how that might affect things.

    Good luck!
     
  11. flyngti

    flyngti Formula 3

    Jul 16, 2009
    1,256
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    Eric L
    #11 flyngti, Jul 21, 2010
    In bench testing your injectors, are you testing them using the same sort of trigger pulse as the ECU provides, or just testing overall flow over a certain length of time? Perhaps the injectors on the rich cylinders are not closing fast enough after the trigger pulse, resulting in more fuel per pulse than the others. Have you tried swapping injectors?
     
  12. andy2175m4@yahoo.com

    [email protected] Formula Junior

    Dec 7, 2008
    473
    Los Angeles, CA
    Full Name:
    Andy Rein
    #12 [email protected], Jul 21, 2010
    I just let them spray wide open with a static DC current holding them open for exactly 10 sec, then I measured the fluid, dumped it out, and did it again with the other injector, it was pretty obvious both put out the same amount of fluid.
     
  13. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
    1,606
    Along the Verde , AZ
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    Doug
    #13 AZDoug, Jul 22, 2010
    Many injection systems allow you to tune individual injectors. Dunno if yours does this or not.

    If you have an entire bank running rich, it is most likely a cam timing issue (educated guess).

    Unless your EFI is looking for two O2 signals and only getting one, and going to default rich on the bank without the O2 signal. I am not familiar with the setup on your EFI, so that is a hypothesis. Check your programming.

    Doug
     

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