Maybe a dumb question

Discussion in 'Performance & Fuel' started by rileyjr16, Aug 20, 2013.

  1. rileyjr16

    rileyjr16 New Member

    But can my knock sensors being bad rob me of fuel efficiency or make my O2 sensors read faults?

    Dont want to have to dig into the truck too much as that stuff costs money. But so does gas.
  2. dobey

    dobey Member

    Yes. The knock sensors are an important part of the ignition system, and their proper functioning helps the computer to adjust spark timing, so that a more complete burn of the fuel can happen. With bad knock sensors, you could not be completely burning the fuel, which can damage the O2 sensors, and then cause them to fault, making the gas mileage even worse.
  3. rileyjr16

    rileyjr16 New Member

    Exactly the news I was looking for... New project for the week. [MENTION=44531]Sierraowner5.3[/MENTION]?
  4. McClintoc

    McClintoc Super Moderator

    Dumb question follow-up: how long do knock sensors usually last or what is a good interval to change them?
  5. rileyjr16

    rileyjr16 New Member

    I always thought when they throw codes. Water likes to get under the intake. Come to think of it I gotta change the head gaskets anyway so...
  6. Sierraowner5.3

    Sierraowner5.3 New Member

    im more or less one armed right now, but i will help with what i can.

  7. dedmon27

    dedmon27 New Member

    Mine went about two years ago, but it was completely my fault. I was out of town for work for about two weeks. Knowing when I got back I had to change the oil and stuff. So when I returned and started to add the oil I noticed a nice mouse nest under the intake. So I took my pressure washer and sprayed the heck out of it. Needless to say about a day later Check Engine light on. Scanned and sure enough Knock sensor. So I replaced them both, yep under water. So I used silicone to seal the ports when I replaced the covers. Anyway anytime your check engine light (CEL) is on you lose fuel economy. After your vehicle reaches operating temps it goes into "closed loop" meaning the computer reads all the sensors and adjusts the way your engine runs. CEL on means your vehicle stays in "open loop" and runs off pre set perameters in the computer, hense lower MPG's.
  8. rileyjr16

    rileyjr16 New Member

    Well i now have some water dropping out of my exhaust pipes so... Gotta change those head gaskets anyway.
  9. dedmon27

    dedmon27 New Member

    Are you losing coolant? Your exhaust will always drip moisture because of the heat cycles it goes thru. Condensation forms when it goes thru that cycle. If your not losing coolant or oil and you did a compression test I don't know that I would change head gaskets.
  10. dobey

    dobey Member

    Also, water vapor is one of the things that modern catalytic converters end up producing during the chemical catalyst process. It condenses as it exits the system, which results in small amounts of water coming out the tailpipe.
  11. rileyjr16

    rileyjr16 New Member

    Yeah that's true. Didn't really think that through. Making the knock sensor change now. Pain in the asthma right now.
  12. a.graham52

    a.graham52 New Member

    depends on what code sets or what sensor fails. if maf or o2 sensor (etc) fails then yes its stuck in open loop because it NEEDS those sensors to be in closed loop. if its just an evap code setting the light then close loop is still going to function.

    good rule of thumb... for every gallon of gas burned, a gallon of water is produced.

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