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Engine pinging. Fuel trims and more….

Home Forums Stay Dirty Lounge Service and Repair Questions Answered Here Engine pinging. Fuel trims and more….

This topic contains 3 replies, has 2 voices, and was last updated by Billy Billy 11 months, 2 weeks ago.

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  • #894663
    Alberto Wong
    Alberto Wong

    Hello there,

    I am a new member here and a new DIYer. This is going to be a long post so if you have the time to read it, or at least the TLDR section, and give me some input I would appreciate it. My English is not very good so If there’s something I wrote that you have trouble understanding please ask me.


    I have been reading a lot about fuel trims lately but I feel there is a lot of information missing in the articles I am reading. Here are 3 screenshots from my OBD II scanner app.

    Things I noticed:

    – Close to zero, or +/- 3 fuel trims when driving.
    – STFT are high on the negative side, usually – 17 to -25 when I put the car on park and try to hold the rpms at 2500.
    – Fuel trims are both negative when idling on neutral or park.

    If these trim values are bad, why is this happening? What should I do next?

    Read this if you are interested in some background:

    This is a 1998 Saturn SW1 with the 1.9L SOHC engine. I got this wagon for $400, currently has 197k miles. It was in very bad shape but I didn’t mind cuz I needed it to learn to how to work on my own cars.

    When I first got this Saturn it had:

    – High idle, around 900 to 1000+ rpms.
    – Sometimes in neutral the rpms would go up on it’s own all the way to 3,000 rpms.
    – Hard time keeping the rpms steady. The needle will bounce up and down a bit.
    – Crank no start condition.
    – Dying battery.
    – Starter died soon after replacing the battery. Sigh…..

    So the main problem of this wagon was that it was running rich and it had a crank no start condition. If you shut off the engine you had to wait about an hour before attempting to start it. You could try to start it all you want in flood mode but it would not.

    This is what I did to solve the problem:

    – Replaced air filter.
    – I replaced the spark plugs and wires (#4 cylinder plug was fouled). Car came with Denso plugs. Replaced them with NGK BRK4ESA-11.
    – Replaced the #4 injector and all O-Rings. Reason for replacement: Injector was leaking.
    – ECTS and the wires. Reason for replacement: Common problem in all Saturns.
    – Replaced the fuel filter with the recommended WIX 33731 with a fuel pressure regulator inside. Reason for replacement: Higher than specified fuel pressure.
    – Replaced the original thermostat. Reason for replacement: High idle. Never reaches operating temps. Temps sits at 1/4 on the gauge all the time, around 154F, unless you are stuck on traffic or driving during a hot day.

    Previous owner said he replaced the fuel pump but when he showed me the bill I noticed the shop replaced the fuel filter, not the pump. Part No. was 33731. But it looked nothing like the WIX 33731 I got later.

    Other things I have done:

    – Cleaned the throttle body. Replaced the gasket.
    – Cleaned the EGR Valve, started the engine without it to expel some of the carbon. Replaced the gasket.
    – Replaced the PCV valve. There are too many PCV valves out there and I have no idea which one is the correct part number. Currently using CV 2333.
    – New Dexcool.

    More troubles ahead…

    So just by doing all these things the car is quieter, smoother and running way better but there is more….. This engine is pinging intermittently under load, specially when it reaches operating temperature. You can also hear it ping sometimes very lightly when the transmission is shifting gears. I have read about the possible causes and I am trying to solve it ASAP.

    I have done the Seafoam spray treatment twice and it didn’t help. I am currently using 91 octane right now to stop it from pinging but it’s not helping much either. I have also cleaned the EGR valve too like I mentioned above.

    Some people think I have:

    – A bad knock sensor.
    – A clogged or semi clogged catalytic converter.
    – Some Saturn owners have mild pinging under load in this same engine when using other spark plugs other than Densos.

    So in the end, I don’t want to throw parts at the problem. I would like some suggestions, a little guidance on what I should be doing next to properly diagnose all the remaining issues in this car. Any questions please ask. If you have made it this far, thank you!

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  • Author
  • #894665

    I would check MAF voltage against spec for expected airflow at high RPM. Or swap in a known good MAF sensor if available.

    BTW, your English is perfect; not sure what you’re talking about there.

    Alberto Wong
    Alberto Wong

    Thanks for replying relative4. =) Should I check the MAP sensor? This car doesn’t have a MAF sensor. Also, in my OBD scanner you can monitor the “Intake Manifold Absolute Pressure”.


    If it’s pinging at the same time it’s making negative fuel corrections, I would suspect a bad O2 sensor or MAP sensor. You can check the MAP sensor against a vacuum gauge.

Viewing 3 replies - 1 through 3 (of 3 total)

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