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Thread: Misfire under accel, right bank rich - left is lean

  1. #21

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    Quote Originally Posted by Gaz64 View Post
    With only a single sensor on one bank, the fueling will based on that average.
    If you have higher oxygen from intermittent misfire, incomplete combustion etc, further investigation is necessary.

    Have you thought about fitting the O2 to the suspect bank?

    Your engine sounds rough as you are accelerating on your video.
    I thought of it but would have to buy some connectors and make an extension for the O2 sensor to make it reach the other header. The engine does stumble on throttle tip in since this issue started. The side with the O2 for the EFI system could be running rich which would make the drivers side lean and the problem is on the passenger side, or the drivers side is the issue and the EFI system doesn't see it because of the single O2 sensor and keeps the fuel trims normal.

  2. #22

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    Quote Originally Posted by alberta_joe View Post
    It is the same fuel pump with both EFI systems. Fuel is supplied by one line to the bottom of the firewall, then splits and feeds each fuel rail separately, the outlet of each rail then goes to the regulator and ties into it with their own ports (the regulator has two inlets and one outlet). Don't worry about the questions, any ideas are welcome as I don't want to pull the heads off yet.
    Just a thought, have you tried feeding it to the one side and then a cross over to the other side? I know some other guys have setup your way with no problems, but I set mine up like I said with the single feed and crossover. I'm not sure it would change anything but I do believe that there is only one fuel pressure sensor so if there was an issue with one bank you wouldn't see what the pressure is there but only on the bank with the sensor. I feed the pass side and cross over in front of the engine and out the driver side into my reg. It also has 2 ports but one is plugged.

  3. #23

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    Figured I would give an update as to what I have found so far. I pulled the heads off the car a few weeks ago and checked them out myself then dropped them off at the shop to get fixed. Visually inspecting them I found one valve that appeared to be bent, when it was turned in the head you could see it spinning off center. Over half of the valves had excessive play in the valve guides, only 2 were good in my mind. These heads were rebuilt at the same time as the block was and they only have about 3500 kms on it, but they only replaced one valve guide back then. We did a vacuum test on one head and the valve that was bent didn't pass the test (not sure how it pasted the compression test or leakdown other then the valve spring was in place then and not during the vacuum test).

    Here is a video of what I believe is excessive play. From talking to the GM dealer mechanics they said the valves should have almost no play in the guides, it shouldn't be this visible.


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