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Thread: Running rich

  1. #41
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    Don't drill & tap one size up - get a set of helicoils to give you a replacement thread of the correct size.
    Do all of them while you're at it, you only want to do the job once!

  2. #42
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    Quote Originally Posted by Confused View Post
    Don't drill & tap one size up - get a set of helicoils to give you a replacement thread of the correct size.
    Do all of them while you're at it, you only want to do the job once!
    Knew someone would have another suggestion so ask garage to do that

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    Quote Originally Posted by galantnight View Post
    Knew someone would have another suggestion so ask garage to do that
    I had to Heli coil one of my plenum to inlet manifold connection.
    It is very easy to do, you just have to be careful with what you are doing especially when you snap off the screw in tang.

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    The heli coil was an awesome suggestion. They are not available where I live. I'll probably order them and wait.

    I used a thin depth measure tool and found that the 2 long bolts (rear) had room to fit longer bolts. I used bolts that were 6mm more in length and for now they have been tightened.

    The hiss if there was is also gone. But the AFR oscillation is still there. I even tried disconnecting O2 sensor.

    The only 2 things that I can think of now are exhaust leak and bad ground.

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    Am I right in saying that the AFR oscillating is correct ?
    I sure Gary said that’s how it is finding the correct AFR or have I forgot what you mean about it oscillating

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    The narrow band sensor output is interpreted by the ECU as either rich, stoic or lean. It can't tell by how rich or lean. A Stoic of 1 is the perfect burn for any fuel.
    If you were to try and watch it's output it would be constantly moving between the 3 states as the ECU tries to maintain a Stoic of 1.
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    a narrow band will constantly switch from rich to lean about the stoic point when the car is running normally.

    if you artificially create a vacuum leak at idle the narrow band will show lean constantly and the long term and short term fuel trims will come into play and gradually add more and more fuel to bring the AFR back to stoic even with the leek. as the fuel trims do there thing and adjust the fueling the narrow band out will show you the output going from constant max lean back towards the stoic value in a gradual change (it will not flip rich/lean) and then if the fuel trims can cope with the size of the leak you have created the narrow band output will go back to the rich and lean flipping state about the stoic value.

    when you plug the leek again. it will all start again but in the opposite direction because now the ecu will see a rich signal from the narrow band as the fuel trims are still adding loads more fuel to cope with the vacuum leak you created. this will gradually go back to normal as the long and short fuel trim reduce the amount of fuel that is being added until it is back in the state where the narrow band out is flipping rich lean constantly.

    the long and short trim fuel trims should sit at zero & zero if everything is working perfectly but what you will probably find is the short term fuel trim will sit at zero and the long term fuel trim will be at a small positive of negative figure.

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    I get the point that ecu in trying to adjust the AFR constantly. But the variance is not to my liking before all of this began I had the AFR vary by 0.2 for a specific scenario. Since this issue began in both the situations idling or cruising. the variation in AFR is almost 1.

  9. #49
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    While you're there, replace the plenum gasket the final time you do up the bolts after helicoiling. Over the years of this being taken off and put back on, this gasket has likely been crushed, especially if someone has tried tightening up the plenum bolts so much that they've stripped the threads.

    Once you've sorted this air leak, disconnect the battery to reset the long term fuel trims, then see what happens again. You should find the oscillation on the narrowband between 0.1v (lean) and 0.9v (rich) as usual, and Long Term Fuel Trim closer to 0.

    You need to go over every single thing that's been touched since it was last running correctly - it's unusual that things just start going wrong, it's usually because something has been touched!

    Exhaust leak will definitely affect AFR reading, and ground offsets can cause variation between what a controller is wanting to say, and what the listening device hears.

  10. #50
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    I wouldn't worry about the AFR cycling at this point, main thing is to get the intake and exhaust air-tight.

    When I pressure test, I go to around 30psi, using the flexible pipe on the top of the engine to the left (just after turbo outlets where it merges into 1 pipe) and then fill from there. At 30psi I find there are lots of things that can come out of the woodwork.
    I have had hose clamps on the pipes and throttle body, throttle body to plenum, plenum to engine, injector seals, BOV, PCV valve etc.

    Once you get that sorted, you should get much better afr readings. Keep an eye on the short term fuel trims, if they max out then something is still wrong.

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    As some have pointed it’s not safe to pressure test our engines. How can I pressure test the intake manifold and plenum only?. If I open the oil cap won’t It be releasing all the pressure form there ?

    Some valves will always be open. So I will be sending all the pressure to the exhaust or past the pistons. That won’t let me build the pressure correct ?
    Last edited by iftekhar.frt; Today at 08:04 AM.

  12. #52
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    Personally, I figure that the peak cylinder pressure is upwards of 1000psi at high load, so 30psi probably won't do much harm.
    I never had any trouble as a result. However you make your own decision on that, as you have to live with the outcome.

  13. #53
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    Definitely do a pressure test in my opinion! Major issues will show themselves before you reach any kind of significant pressure. Without doing this, you'll not know if you're chasing your tail looking at other symptoms.

    Stick your bung into the rubber hose coming from the Y piece to the intercooler. Most common leaks are intercooler, plastic intake elbow, recirculating blow off valve, throttle body, intake plenum, and injector seals.

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