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Intermittent Stutter, Fuel Injectors, MAF, and 272 Cam

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    Intermittent Stutter, Fuel Injectors, MAF, and 272 Cam

    This first part is for knowledge in case anyone else is having a similar problem.
    So I have been trying to diagnose an intermittent stutter for the last 2 months. It only occurs when the engine is warm, or warming up after about 5 minutes of driving. It's been painful. I replaced the coil, plugs, intake gaskets, cleaned the contacts on the c191 connector, temp sensor, all body grounds. I have a new cap and rotor and plug wires.
    I also have a Miller MAF so I cleaned that with MAF cleaner.
    I decided to adjust the valves thinking that they could possibly be too tight and and once it was hot the CTE's causing an issue... A long shot, i know. All of these things did absolutely nothing for the problem.
    Finally I thought O2 sensor but I didn't see any CEL so I couldn't diagnose it with the stomp test.
    I disconnected the battery and shorted the positive and negative leads (not the battery terminals!) to hopefully clear the ECU of any memory which I'm not sure it even stores.
    Then I disconnected the O2 sensor from the harness. The O2 sensor is relatively new, about 4 years old. But the plug on the harness is original and the pins were quite corroded. I cleaned them up and and plugged it back in, and reconnected the battery. The car ran differently, not correctly, but differently. Idle was much higher - about 1100 when warm. While traveling on a flat road at constant RPM, and engine up to operating temps the CEL came on. When I gave it gas, it went off. Same thing while idling at a stop light. I got home and let it idle to get the CEL to come on then shut down the car to hold the code. Stomp test revealed a 1222 code. Excessively lean or rich. high idle suggests rich and probing the sense wires on the O2 leads revealed .85V which translates into rich running.
    So, I can throw out low fuel supply problems as I have an excess of fuel.

    My next step is to replace the injectors.
    So here are my specs:
    Miller MAF
    IE headers, full custom mandrel bent exhaust
    Bimmerheads 272 Billet cam

    I've been reading that the M50b25 injectors are a good replacement option. Does anybody feel strongly about a certain design over another?

    I'm not saying that this is definitely the problem. I will update this thread once I replace the injectors.

    This has probably been covered ad nauseam but I couldn't find anything really conclusive, especially when considering modified internal engine components.

    Thanks,
    Pete

    #2
    I ended up buying injectors off of ebay that did not solve the problem.

    here is a list of everything I changed:
    injectors
    fuel pump
    fuel filter
    fuel pressure regulator
    O2 sensor
    CPS
    cleaned MAF
    vacuum hose from FPR to manifold

    In the end it ended up being the distributor cap. This was the last thing I changed, obviously, but it was relatively new at just a year old.
    It was not an OEM cap, though. It was a duralast cap from autozone. I replaced it with a bosch unit and the problem is gone.

    Pete

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