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Fast XFI 2.0 erratic 02 reading

Discussion in 'FAST Support Forum' started by Blownnova72, Aug 24, 2017.

  1. Blownnova72

    Blownnova72 New Member

    Joined:
    Jun 3, 2016
    Hey everyone,
    I had an issue this past weekend at the track on my last two passes with the AFR readings bouncing back and forth between overly rich and lean throughout the entire pass according to the data logs(see attached picture). I have the tune very close so it only corrects 1% max in a few spots, but I keep it in closed loop just in case something happens the computer may be able to compensate and add or take away fuel.

    -I made several passes all on the same tune and the afr's were all dead steady until these last two passes. The car slowed down a tenth on the last two passes, however I believe that only happened because of the o2 correction swings. Car sounded fine, nothing to lead me to believe there was a misfire ect.

    -I switched to another o2 sensor i had in between the two passes(it was used but had it in my spare parts box, so I am not positive it was 100% good). The afr swings looked the same in both logs with the two different sensors.

    -I believe if there was an o2 malfunction it will switch over to open loop, however based on the log it was correcting the entire pass which leads me to believe the ecu never got an o2 error.

    -I tried last night in the garage to get it to repeat the issue but was unable, brought it up in rpm, put it on the brake ect. I did move the wideband harness away from some of the spark plug wires(they were very close.) Do you think it could have been getting interference? I checked ground and it was still good and tight.

    -Battery voltage was steady the entire time. Its a 14v system and was at 15.6v going down track, so no weird voltage spikes.

    -The afr's were also bouncing back forth on the decel and return road at a very similar frequency as the pass(so may not be RPM related)

    Anybody have any ideas? Thanks
     

    Attached Files:

  2. Fastmanefi

    Fastmanefi Active Member

    Joined:
    Jun 4, 2011
    Location:
    Sonora, CA
    Email me the tune from the ECU, the version # (2.01, 2.05 ...), and the log. I'll look it over for you.
    rich@fastmanefi.com
     
  3. Blownnova72

    Blownnova72 New Member

    Joined:
    Jun 3, 2016
    Thank you, I am at work right now. As soon as I get home I will send all of that over to you. I believe it is version 2.05.
     
  4. Fastnofast

    Fastnofast Member

    Joined:
    May 16, 2017
    Hi. Your o2 sensor is reading one side of your exhaust system ? Right ?
    So 4 cylinders ?
     
  5. Blownnova72

    Blownnova72 New Member

    Joined:
    Jun 3, 2016
    Yes its only reading the passenger side bank. Cylinders 2,4,6 and 8.
     
  6. Fastnofast

    Fastnofast Member

    Joined:
    May 16, 2017
    Are you sure it is not a misfire problem ? As if AFR fluctuate , you can have a false lean or rich condition ?
     
  7. Blownnova72

    Blownnova72 New Member

    Joined:
    Jun 3, 2016
    I am not 100% sure its not, I just didn't think it was because the car only fell off a 1/10th and attributed that to the correction swings. I will check plugs, wire and distributor.
     
  8. Fastnofast

    Fastnofast Member

    Joined:
    May 16, 2017
    I remember i had the same problem on a race and one wire was bad. At 6000rpm it is not easy to locate the faulty component
     
  9. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Blownnova72, listen to Fatstmanefi. Otherwise, you'll be working in needless directions. Richard will be able to spot the problem from your data. For instance, from the file you posted above, I could say take a look at your valve spring pressures.
     
  10. Fastmanefi

    Fastmanefi Active Member

    Joined:
    Jun 4, 2011
    Location:
    Sonora, CA
    I wasn't much help. The AF ratio was all over the map. I guessed either an ignition issue or a hardware intermittent with the wideband.
     
  11. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Both good places to start. It could be something as simple as an O2 sensor harness. If he has been racing this some time he may want to check his valvetrain and spring rates. I don't know what type of racing he does, but this was something I kept up with when I was. Springs weaken and parts wear, even a pushrod can flex. Plugs and wires are standard enough, but an ignition box would also be something to check. Heat of operation can do some strange things to CD boxes as they age.

    A leaking passenger side header gasket would be easy to check - an intake gasket could be somewhat more difficult.

    Could also be blower related. He has a lot to check, including injectors.
     
    Last edited: Aug 24, 2017
  12. Blownnova72

    Blownnova72 New Member

    Joined:
    Jun 3, 2016
    Thanks for the replies guys. The car runs 8.50 index. I am going to pull off distributor cap and look at everything, check the ohms of the plug wires. I will check all the spring pressures too. I got a new o2 sensor and put that in even though i dont think it was that.
    Do you think an exhaust leak would cause the afr's to act like that at a higher rpm? I would only think that may effect it at lower rpm when you could draw in air between cylinder pulses. I may be wrong though.
     
  13. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Yes, a header leak can affect high RPM AF - actually pulling air into a free flowing exhaust with a scavenging effect.

    Check the pushrod concentricity also. Blower motors are harder on them.

    If you can't find anything, check for a crack in a head, or the block if you don't run a block filler. Such a crack can be extremely hard to find visibly, so chemical means should be used.
     
    Last edited: Aug 24, 2017
  14. Fastnofast

    Fastnofast Member

    Joined:
    May 16, 2017
    Both good places to start A A :)
    First one i told about. Please
    do not denigrate the solutions proposed by the other members. Thank you AA
     
  15. Fastnofast

    Fastnofast Member

    Joined:
    May 16, 2017
    Bang bang you win AA
    You watched too more westerns :D

    @BlownNova. Hope this help.
     
  16. Blownnova72

    Blownnova72 New Member

    Joined:
    Jun 3, 2016
    Well i pulled off the distributor cap and found this.
     

    Attached Files:

  17. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Great! You just saved yourself a lot of time and trouble. From the look of the rotor, the cap and button is also shot. Be sure to check the phasing. I would check and replace all the sparkplugs as well. This is what ruined your fuel maps.
     
  18. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    If that is an MSD running a locked advance, you should be running the MSD phasing rotor.
     
  19. Blownnova72

    Blownnova72 New Member

    Joined:
    Jun 3, 2016
    I am going to replace the cap as well. I just put new plugs in it and checked the ohms of the wires, they were all fine. Rotor phase looks to be fine as well. Not sure why it started melting the rotor, maybe the gap was too large between rotor and button or excessive moisture in the cap
     
  20. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    From what you've found, it was just the rotor spring to the cap button. If the spring is raised too high, it will wear the button away and create a gap. If too lightly seated, and/or it has a gap, it will burn up just like yours did. You want to be sure the spring is adjusted for light contact with the button. Put a tiny dab of dielectric grease on the button, install the cap and then remove it. You will want to see the dielectric grease transferred from the button to the spring contact.
     

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