Results 1 to 7 of 7

Thread: 5.3L misfiring- need help

  1. #1
    Join Date
    May 2007
    Location
    windsor, on.
    Posts
    221
    Time Online: 1 Wk 5 Days 13 Hrs 56 Mins 58 Secs
    Avg. Time Online: 1 Min 2 Secs
    Rep Power
    11

    5.3L misfiring- need help

    Hey Folks, my 2003 5.3l is misfiring like crazy! It's running really rich and stalling. I've tried: Changing fuel filter, spark plugs, checked all plug wires and coil packs. Hooked up the scanner and keep pulling up p0300 generic multiple cylinder misfire, p0101- MAf sensor performance, p0106- MAP sensor performance. I changed the MAF, the MAP, the 2- upstream o2 sensors, reset the computer, checked for intake leaks... uuhmmm i think that it.

    I am at my wits end!! Any ideas before I bring it to the stealership?

    Thanks!

  2. #2
    Join Date
    Jun 2005
    Location
    Burlington
    Posts
    5,009
    Time Online: 1 Mth 3 Wks 5 Days 8 Hrs 29 Mins 23 Secs
    Avg. Time Online: 4 Mins 38 Secs
    Rep Power
    18
    Do you have datastreaming on your scan tool? This will tell you a lot more about what the computer is doing than a code list will (although code list is first step anyway).
    If not, I'd start by unplugging all the oxygen sensors. Let the ECU go back to base maps, and make sure it's not an O2 that's throwing things off.
    Second, I'd check that you have the correct 5volt reference on your sensor feed wire. If that voltage is wrong the MAF will not send the correct signal back to the ECU, and you'll never get it running right. If those O2's are 4 wire, they too depend on a 5v reference, without which they'll feed misinformation too. PM me your application and I'll pull up the diagram at work tomorrow so you're not backprobing blindly.
    You can usually run Chevies with the MAF unplugged. I'd try this too. Yes, all these sensors unplugged is going to throw a mess of codes but when you've got nothing to work with you want to get the computer back to original 'safe' maps and see that you don't have a mechanic problem.

    Did this issue come up all of a sudden, or has it been getting worse?

    Did you check your fuel pressure? I know you replaced the filter, but did you actually put a gauge on it? If your scan tool has data streaming, you can look at the fuel trim levels and it'll show an enrich percentage, indicating a volume or pressure fault.
    ....-Noltz
    '91 Frankenheep Edition. 4.0, 4" BDS, Richmond 8.8, 35" KM2's, Titan 12k, ... gone.
    '95 4Runner SR5. Air-Lift bags, OBA & 8K Winch, DD... gone.

  3. #3
    Join Date
    May 2007
    Location
    windsor, on.
    Posts
    221
    Time Online: 1 Wk 5 Days 13 Hrs 56 Mins 58 Secs
    Avg. Time Online: 1 Min 2 Secs
    Rep Power
    11
    no datastreaming on scan tool... I'll try unplugging the O2's and check they have 5v (and the MAF has 5v) and try running without the MAF.

    Basically, i shut the truck off, went in side. came back out, started it up about an hour later and it was running like shit. Almost seems like its in limp mode.
    2003 gmc sierra

  4. #4
    Join Date
    Dec 2005
    Location
    Beamsville Ont.
    Posts
    184
    Time Online: 1 Wk 4 Days 4 Hrs 28 Mins 7 Secs
    Avg. Time Online: 55 Secs
    Rep Power
    12
    I just had a misfire on my 5.3 after I had to change the fuel pump , I tried wires plugs and a new coil then cleaned the injectors and it went away. I had to pull the injectors out and flush them backwards to make sure they were good and clean .You might try that.
    A married man should forget his mistakes. There's no use in two people remembering the same thing!
    VE3 LFR
    1942 MB
    1946 Willy's / GPW
    1947 CJ2A Willy's

  5. #5
    Join Date
    May 2007
    Location
    windsor, on.
    Posts
    221
    Time Online: 1 Wk 5 Days 13 Hrs 56 Mins 58 Secs
    Avg. Time Online: 1 Min 2 Secs
    Rep Power
    11
    ya might have to try that. Thanks!

  6. #6
    Join Date
    Jun 2005
    Location
    Burlington
    Posts
    5,009
    Time Online: 1 Mth 3 Wks 5 Days 8 Hrs 29 Mins 23 Secs
    Avg. Time Online: 4 Mins 38 Secs
    Rep Power
    18
    Shoot me a PM if you need diagrams.

  7. #7
    Join Date
    May 2007
    Location
    windsor, on.
    Posts
    221
    Time Online: 1 Wk 5 Days 13 Hrs 56 Mins 58 Secs
    Avg. Time Online: 1 Min 2 Secs
    Rep Power
    11
    Well guys- thanks for all your advise. It was a broken exhaust valve spring on the #8 cylinder...fixed and running good now!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •