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Thread: Bosch 49 sticks at 15-15.3 AFR.

  1. #1

    Default Bosch 49 sticks at 15-15.3 AFR.

    WBO.zip
    Super Sniper 800
    HyperSpark unit
    SBC 383
    Weiand 142
    Forgot cam specs, only pulls 12 or so inHg at idle, it has some overlap.

    Running HBX-1 bung extender. Sensor is installed on the L/H header nine inches after the collector and at near 12 o'clock position. No evidence of leakage around the WBO2 sensor bung or the heater merge pipe joint. I put a fresh coat of paint on everything to help see if I have an exhaust leak. No leaks from the header to H-pipe & muffler.

    Installed new header seals. Just installed new Iridium plugs gapped at .030" to replace NGK V-Power plugs gapped at .028" to rule out plugs. Installed new 8.8mm MSD wires. No change in symptoms. Plugs do not show anything abnormal occurring in the cylinders. All eight look the same and all eight show engine running rich.

    Previously installed new header seals, running a second smaller battery inline with Sniper power leads, installed ferrite rings, ran ground leads to everything, including the air cleaner. No signs of EMI.

    Problem:
    AFR ratios stick at 15-15.3. CL Comp rises to keep adding fuel, eventually sensor reads normal again and CL Comp pulls fuel.

    Troubleshooting steps:
    I thought an intermittent spark was the culprit. Replaced plugs. No change. I though an exhaust leak might be the cause, no leaks. Jamming the throttle, speeding up the airflow through the exhaust system doesn't have any effect either.

    When the sensor sticks, it's pretty much stuck there until it decides to start reading correctly again. MAP sensor readings pretty much unaffected until actual A/F ratio becomes increasingly rich and eventually too rich to run right. Everything in the datalog seems like it's simply trying to solve a lean condition as reported by the WBO2 sensor. This would be third sensor now and same problem lead to replacing two previous sensors. This sensor has roughly 4500 miles on it.

    The issue is intermittent, but has gotten consistent enough for me to grab the datalog attached.

    Reversion and cam overlap might be the culprit, but if that's the case, how can I keep from killing sensors? Even if I disable sensor readings at specific RPM ranges, As noted in the datalog, I hit 3500 RPM and sensor was still stuck at 15-15.3, so something is causing the sensor to stick at 15-15.3.

    In the datalog, the AFR ratio was sitting static at 15.3. When I started the engine, it acted normally for a moment and then stuck for a while at 15-15.3. I hit the gas a few times seeing if I could snap it back to normal, it didn't work, it stayed at 15-15.3. Bosch 4.9 sensor is supposed to be a 100,000 mile sensor. What am I not seeing here?

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
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    26,999

    Default

    Quote Originally Posted by Gen2Van View Post
    This would be third sensor now and same problem lead to replacing two previous sensors.
    Contact Holley Tech Service (LINK).

  3. #3

    Default

    Just for my own education, is it normal to run 30° timing at idle in this type of application?

  4. #4
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    26,999

    Default

    Blower (supercharged) engines require more initial timing and less total timing than naturally aspirated engines. They also like a short, yet quick ignition advance curve and retarded timing while cranking to start.

  5. #5

    Default

    Thanks! I hadn't seen a table like that before. Makes a lot more sense.

  6. #6
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    26,999

    Default

    I haven't seen his Base Timing Table, so I'm not affirming or discrediting it.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  7. #7

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    I've had this problem as well. My unit "locks in" right around 15.0. Mine has progressed to going full lean after about 30 minutes of running to now it only goes for about 3 minutes before it's dead lean and pig rich. I have swapped the WBO2 sensor, checked fuel pressure, exhaust leaks, added grounds, rerun wires and am currently waiting patiently for Holley to respond to my support requests. I've also seen this happen on a Sniper with a known bad ECU (that car had the Sniper controlling timing and it would die due to intermittent firing signal). Sorry I don't have better news. Oh, and my Sniper ran well for over two years before this started.

  8. #8

    Default

    I recommend checking injector spray pattern. Only time I seen one stuck at 15 AFR, one injector wasn't firing.

  9. #9

    Default

    Chris85, was there any noticeable driveability issues? When the problem occurs on my setup, the engine still runs fine and the symptom that tells me there's a problem is when the engine runs rich from the Closed Loop Compensation kicking in. Hence why I have it set so low.

  10. #10

    Default

    Silver7, did you need to replace your Sniper EFI system? Was there a fix?

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