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Thread: Backfiring When Warm

  1. #11

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    Where do you have your WBO2 sensor installed? You should probably check to ensure that you haven't developed a leak upstream or downstream from the sensor. Before running much more, you need to get a pressure gauge on it to see what your actual pressure is. I see it go way lean and then the Sniper responds by trying to add more fuel. What we see in the datalogs is what the Sniper is commanding, not what's actually happening when you have bad fuel pressure, for example. The increase in fuel commanded by Closed Loop shows that commanded fuel flow is responding as expected. It's still jumping in & out of Closed Loop a lot. There are a number of conditions in the Sniper program that will cause it to kick out of Closed Loop, and a number of reasons are not published or widely known. Regardless, verify your WBO2 sensor. I don't think it has failed, just may not be reading correctly from leaks, and check the fuel pressure. I'm betting on the fuel pressure, but I've been wrong before. Also, we've seen some of this behavior from clogged pre- or post-pump filters. If this is an older tank you may have churned up enough debris to gum up the filters. Let us know what you find out.

  2. #12
    Join Date
    Jun 2021
    Location
    Nashville, TN
    Posts
    20

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    The WBO2 sensor is installed on the driver's side exhaust. It's probably six inches or so past the manifold on the exhaust pipe. I can definitely hear what sounds like an exhaust leak at the passenger side manifold, so I'm betting there's a leak on the driver's side as well. I'll try to get that corrected as soon as possible to see if that helps out at all. I'll also get a pressure gauge and try to check the fuel pressure. I did a quick look at the fuel filters and didn't see any obvious debris in them.

  3. #13

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    Your system is acting like it has an exhaust leak. The exhaust leak will make the system think it's lean at idle which is why your Sniper is dumping all of that extra fuel into the engine. You'll never be able to tune it until you get rid of the exhaust leak. (An expert could tune it by putting it in Open Loop at idle, but I don't think that's what you want to do.)

  4. #14
    Join Date
    Jun 2021
    Location
    Nashville, TN
    Posts
    20

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    I'm dropping the Scout off at the exhaust shop in the morning to get the necessary repairs done. I'll let everyone know how it drives after I get it back tomorrow evening. Hoping that will correct the majority of my issues.

  5. #15

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    Once you get the exhaust leak fixed, you'll want to Clear the Learn Table and let the system start over Learning new habits.

  6. #16
    Join Date
    Jun 2021
    Location
    Nashville, TN
    Posts
    20

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    So no exhaust leaks on the driver's side manifold to WBO2 sensor or after to where the pipes Y together. The passenger side manifold gasket was blown though. I got the new gas cap and cleared my Learn Table and took it for a drive from the parts store (it was running rich and boggy before). After the new gas cap it drove a lot better, it didn't seem like it was going to stall out at all, however, did have some hesitation from stop signs or complete stops. Throttle response was so much better. I've uploaded the datalog from that drive. Would a blown manifold gasket on the opposite side of the WBO2 sensor cause the Sniper to make it run rich? I was under the impression it was really only upstream from the side that the sensor is on? Regardless, I'm going to replace the manifold gasket this weekend when I get some free time. Does it sound like I have a vapor lock issue? The PO took the stock tank out and replaced it with a Rock Auto generic 33 gallon tank, not sure if he added any ventilation though.
    Attached Files Attached Files

  7. #17

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    Exhaust leaks on the other side of the engine don't matter, only when they are upstream of the WBO2 sensor. Sounds like your problem is the tank vent. If the tank isn't vented then the fuel pump pulls a vacuum and starts to pump less fuel and the Sniper adds fuel to try to make up for it. That situation can be a real mess and can be difficult to figure out.

    I looked at your current datalog and it looks really good when the engine is in Closed Loop. When the engine goes Open Loop then you can see that the Base Fuel Table isn't correct since the engine tends to go lean. But if you drive it a few hours and do a Transfer Learning To Base, you'll be able to start narrowing in on the correct fuel map for your engine.

  8. #18
    Join Date
    Jun 2021
    Location
    Nashville, TN
    Posts
    20

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    I'll try to get a few hours of driving in the next couple days and do a Transfer Learning To Base and see how it responds and let everyone know. I have a wheeling trip planned for Saturday, but might hold off till I know there aren't any other issues that might cause me to be stranded in the middle of nowhere. I really appreciate your and GPatrick's help through all of this and will definitely give an update! Thanks again!

  9. #19
    Join Date
    Jun 2021
    Location
    Nashville, TN
    Posts
    20

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    I've read a few different opinions about Transfer Learning to Base and using the Smooth function. Just wondering if you would suggest using the Smooth function the first few times when Transferring Learning To Base, or should I not use that functionality and attempt manual smoothing?

  10. #20

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    I'm fairly sure if you Transfer Learning To Base that it smooths it once in the transfer. I would not do more than that for now. If you've cleared out the old stuff and it's running well, then you can certainly Transfer Learning To Base. I would not recommend ever Transferring Learning To Base unless it's indeed running well. Has it been as warm as it was when you were having issues?

    When you Transfer Learning To Base with minimal smoothing you can get a sense of where it wants to run versus where the rest of your Base Fuel Table is. If the Learn area is quite a bit higher or lower you can begin to manually raise or lower the surrounding cells so that the are close to the areas where Learning has occurred.

    Pay attention to the sound your fuel pump makes as you drive. It starts to get noticeably louder, you may still be pulling vacuum or have a pump heat problem.

    Glad it's running better and let us know how it does this weekend.

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