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Thread: MAP sensor showing spike during throttle tip-in.

  1. #1

    Default MAP sensor showing spike during throttle tip-in.

    I have a 5.3L that I'm dealing with some throttle tip-in issues. A few times at a stop sign, I have went to give it throttle to pull away and engine would just die. It acted flooded for a few seconds restarting. I was able to reproduce the issue and grab a datalog, and screen captured what I saw, but I don't know why it's doing it. It appears if I repeatedly stab the throttle, very quick blips, every so often the MAP value will spike. On the bubble on the (ONLINE, LIVE) VE table I saw it jump to 170 kPa once, did not get a log on that one, when that happens engine dies right way. I was able to grab datalog when it spiked to 127 kPa, and engine bogged for a moment & recovered.

    It's a 5.3L turbo with 3 bar GM sensor. I don't see how it would build any boost at idle, so it really seems to be some sort of issue in the controller? Screen shot and datalog attached.

  2. #2
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    Default

    It's not at idle there, it's at 1653 RPM. What's the MAP kPa value at key-on/engine-off?
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    I'm not real familiar with turbos, but could the blow-off valve be sticking?

  4. #4

    Default

    Backfire through the intake maybe?

  5. #5

    Default

    Quote Originally Posted by Danny Cabral View Post
    It's not at idle there, it's at 1653 RPM. What's the MAP kPa value at key-on/engine-off?
    Default. The issue happens during quick blip of the throttle. The 1653 RPM you see is from when I quickly pressed & released the throttle, from idle speed.

    Quote Originally Posted by 81 TransAm View Post
    I'm not real familiar with turbos, but could the blow-off valve be sticking?
    Blow-off valve appears to be functioning properly, it's barely closed at idle. I've adjusted the spring to make it open just below idle vacuum. (Engine idles 54 kPa, BOV starts to open around 45 kPa.)

    Quote Originally Posted by squarles67 View Post
    Backfire through the intake maybe?
    Had not thought about that. I will investigate this some more. I have a weird uneasiness to the engine at 1400-1700 very light load. Especially noticeable with torque converter locked, feels like a misfire maybe, but completely smooth with no issues under a load. I've got a new direction to check, thanks.

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