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Thread: Idle AFR all over with RPM spikes.

  1. #1

    Default Idle AFR all over with RPM spikes.

    Car has been running great! Had it sitting in the driveway idling getting ready to go for a cruise. Had my wife get in and give it a rev, so I could hear the exhaust (sounded great if I must say). Immediately following, the idle was dropping down to about 400 RPM, then spiking up to about 1,500 RPM, then back to target at 750 for about four seconds, then repeating the process continually. I was watching the AFR, and started a datalog, AFR was sitting at about 9.9, RPM would drop, AFR would shoot to 32.5 and RPM would run up, then AFR would drop back to 9.6, RPM would follow, and so on. On my datalog, the AFR numbers are creating a flat line at the mins & max values, not a smooth curve. Once I start driving, everything settles out perfectly. Even if I bog the engine in 3rd gear at 1,000 RPM, it's fine. If I take the unit out of closed loop and put it into open loop, the problem goes away. I have inspected thoroughly for air leaks at, around, before, and everything in between on the exhaust with no finds. WBO2 sensor wiring is not damaged in any way. Holley told me that a failed WBO2 sensor would show 30 something all the time, it does show that before I crank the car up. Any thoughts anyone?

  2. #2

    Default

    Sounds like the WBO2. Use a shop vacuum and some duct tape on the end of the exhaust pipe to check for leaks. Spray all joints with a spray bottle with a dish soap mixture.

  3. #3
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    19,283

    Default

    Read the 4th paragraph under "Wideband O2 Sensor Notes": http://forums.holley.com/showthread....ension-Harness (WBO2 Sensor Information)
    WBO2 sensor testing procedure at end of "Wideband O2 Sensor Notes": http://forums.holley.com/showthread....ension-Harness (WBO2 Sensor Information)

    Is the Sniper EFI Learning? Is the ignition timing synchronized? Is the fuel pressure 58-60 psi (LINK)? IAC Position
    of about 5% at hot idle? Check for ignition misfires/RPM signal problems, exhaust leak upstream of WBO2 sensor,
    or if the WBO2 sensor (or other sensor) has failed and corrupted the Learn Table. Look at the Data Monitor/Gauges.
    Also, the Holley Sniper EFI will inhibit Closed Loop if the AE vs TPS/MAP RoC Blanking values are set too low.
    http://documents.holley.com/techlibrary_199r11259.pdf (Holley Sniper EFI Help File)
    http://documents.holley.com/199r11369.pdf (Holley Sniper EFI Troubleshooting Guide)
    https://forums.holley.com/showthread...8356#post88356 (Holley Sniper EFI Fuel Pressure Tester/Gauge)
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  4. #4

    Default

    Thanks for all the info. I did another inspection, didn't find anything. Put an air hose with a regulator to it, didn't find anything. I went with the idea from "BITE_ME", and boom! Leaking like crazy around WBO2 sensor. I have to say though, I'm using the crappy clamp-on setup right now until I can get to a welder, so go figure, it's leaking. Thanks for all the help, waiting for the high temp sealant to cure overnight and I'll post the outcome. Danny, thanks for the links. Also, Danny, so far you have replied to both my posts and you're a wealth of info, so thank you for that!

  5. #5
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
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    Default

    You're welcome, and thanks for the compliment. BITE_ME, good call on the exhaust leak.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  6. #6

    Default

    Quote Originally Posted by 68camro View Post
    ...waiting for the high temp sealant to cure overnight and I'll post the outcome.
    Make sure it's oxygen sensor safe.

  7. #7
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
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    Default

    All the quality (reputable brands) RTV sealants are nowadays.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  8. #8

    Default

    You really need to read the sealant packages now. Due to them being O2 sensor safe now, and safe for humans.
    1. Says to wait 10 minutes for it to "skin over" before assembly.
    2. Says to use on both parts while "still wet". Then "lightly tighten bolts". Wait one hour. Then torque the bolts down.
    3. Both say you can't use the part for 24 hours.

  9. #9
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    19,283

    Default

    Quote Originally Posted by BITE_ME View Post
    1. Says to wait 10 minutes for it to "skin over" before assembly.
    I disagree with this (LINK).

    2. Says to use on both parts while "still wet". Then "lightly tighten bolts". Wait 1 hour. Then torque the bolts down.
    3. Both say you can't use the part for 24 hours.
    I agree with this.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  10. #10

    Default

    VersaChem makes multiple formulas of Gasket/Adhesives Silicone.
    Example: Use their "Mega" on polished aluminum. Their regular line will tarnish shiny parts.
    Their instructions have very good tips for its use.
    Regular: http://www.itwconsumer.com/userfiles...7039%20TDS.pdf
    Mega: http://www.itwconsumer.com/userfiles...9839%20TDS.pdf
    Most Permatex formulas (#29132 needs a minute of air time for both parts) use the "still wet" technique.

    My point is. Read the instructions. Most tubes just have the warnings on them now. Only the package has the instructions.
    And know what your using. Remember: Aluminum "was" an exotic metal. So the manufacturers of sealant "had" to make it both compatible for Steel & Aluminum.
    The chemicals that "etch" into steel, are generally too strong for aluminum.

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