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Intermittent miss??

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  • #1

    Intermittent miss??

    Not sure how to completely describe this...

    Drove the mustang to work the other day, and on the way home, the temps were a little high for my comfort (around 230F). Then all of a sudden, the A/F gauge showed lean while under slow acceleration. If I gave it more gas, it'd richen up, but still lacked power and ran like shit. The car sounds like a cylinder isn't firing... I pulled over, let it cool down, but it still did the same thing. Then all of a sudden while I was sitting at a red light, it went away. Car richened up, and was smooth again. I chalked it up to a fluke.

    Then, today took it out to run to Starbucks, and got on it on the service road headed home. Once I got out of it, same issue as above (except temps were normal).

    Where do I start? I checked the plug wires, checked the injector plugs....

    I'm running the autolite 24's gapped at .030 (per Andy @ Prime-Tuning) if that matters.

    Car runs great 90% of the time... but when it gets in this "mood", it sucks.
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  • #2
    It may be a long shot but check the injector harness for bad spots in the wire. I chased an intermittent dead miss on my s-10 for a LONG time. Every shop I took it to said it was a blown head gasket. Finally found someone willing to spend some time diagnosing it properly. It turned out to be a bad spot in the harness.

    Sometimes it would run just fine, others, it would not fire on cylinder 3 AT ALL. Bumps or hard acceleration would cause the wire to either make or lose contact/continuity.

    Is it throwing a code so you can see which cylinder or if it is s random cylinder misfire?

    Sent from my SAMSUNG-SGH-I727 using Tapatalk 2
    Originally posted by Leah
    Best balls I've had in my mouth in a while.

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    • #3
      Fuel pump ?

      320rwhp. 7.67 @ 90mph 1.7 60'

      DD: 2004 GMC Sierra VHO 6.0 LQ9 324whp 350wtrq

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      • #4
        Describe rich/lean condition also.

        My car also tuned my Andy, will idle at 14.5-15:1 afr. and drives at 13-14:1, wot is 12.6-12.8:1. On decel in gear it can spike to 16:1 but that's normal.

        320rwhp. 7.67 @ 90mph 1.7 60'

        DD: 2004 GMC Sierra VHO 6.0 LQ9 324whp 350wtrq

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        • #5
          Afr is the same as when it was stock with a wide band. Except it idles better now, new IAT.

          320rwhp. 7.67 @ 90mph 1.7 60'

          DD: 2004 GMC Sierra VHO 6.0 LQ9 324whp 350wtrq

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          • #6
            Originally posted by black2002ls View Post
            It may be a long shot but check the injector harness for bad spots in the wire. I chased an intermittent dead miss on my s-10 for a LONG time. Every shop I took it to said it was a blown head gasket. Finally found someone willing to spend some time diagnosing it properly. It turned out to be a bad spot in the harness.

            Sometimes it would run just fine, others, it would not fire on cylinder 3 AT ALL. Bumps or hard acceleration would cause the wire to either make or lose contact/continuity.

            Is it throwing a code so you can see which cylinder or if it is s random cylinder misfire?

            Sent from my SAMSUNG-SGH-I727 using Tapatalk 2

            I'll check. I don't have a CEL, so its a pain in the ass on these cars. Counting blinks and shit... how gay.

            I will say the injectors were bought used. Of course everyone says they have low miles, so who knows. They are the Bosch "Mean Green" 42lb ers.

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            • #7
              Originally posted by 91CoupeMike View Post
              Describe rich/lean condition also.

              My car also tuned my Andy, will idle at 14.5-15:1 afr. and drives at 13-14:1, wot is 12.6-12.8:1. On decel in gear it can spike to 16:1 but that's normal.
              Idle is around 18, crusing is around 14 - 15, smooth acceleration is around 15 - 16, WOT is 11.4 - 11.8.

              When the issue is going on, my smooth acceleration value is around 20 - 22.

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              • #8
                Originally posted by 91CoupeMike View Post
                Fuel pump ?
                It's a new Walbro 255.

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                • #9
                  Which bank is your wide band on?

                  Sounds like the lean is just picking up the misfire, mine pegged my gauge at 18 when I melted a plug and had a dead hole.

                  Best way to find which one is dead is to see which header primary is colder than the rest., or hotter if its a lean miss.

                  320rwhp. 7.67 @ 90mph 1.7 60'

                  DD: 2004 GMC Sierra VHO 6.0 LQ9 324whp 350wtrq

                  Comment

                  • #10
                    Originally posted by 91CoupeMike View Post
                    Which bank is your wide band on?

                    Sounds like the lean is just picking up the misfire, mine pegged my gauge at 18 when I melted a plug and had a dead hole.

                    Best way to find which one is dead is to see which header primary is colder than the rest., or hotter if its a lean miss.
                    Its in the drivers side of the H pipe before the "H", and after the O2 sensor. I'll have to track down an infrared thermometer to determine which one is cooler / hotter. Think my dad has one so we shall see.

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                    • #11
                      Ran the KOEO and KOER test today...

                      KOEO: 15, 31, 84, 95
                      KOER: 12, 31

                      Havent ran the cylinder balance test yet... it got too late.

                      Looked up the codes, but I'm not 100% solid on what exactly they mean, or if any of them would cause my symptoms.

                      Thoughts?
                      Last edited by danielhv; 05-17-2013, 10:47 PM.

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                      • #12
                        Not Found
                        https://Www.canobd2.com

                        320rwhp. 7.67 @ 90mph 1.7 60'

                        DD: 2004 GMC Sierra VHO 6.0 LQ9 324whp 350wtrq

                        Comment

                        • #13
                          Originally posted by 91CoupeMike View Post
                          Www.canobd2.com
                          15 = EEC (PCM) Read Only Memory (ROM) test failed
                          31 = (Cars ONLY): EVP or PFE circuit below minimum voltage
                          84 = (Cars ONLY): EGR vacuum regulator circuit failure
                          95 = Fuel pump secondary circuit fault

                          12 = RPM at idle out of range/high
                          31 = (Cars ONLY): EVP or PFE circuit below minimum voltage

                          The only one that I would suspect would cause my symptoms is 95... but I dunno wtf it means. Fuel pump is running fine as far as I can tell...

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                          • #14
                            95 could be from my kill switch. It is tied into the fuel pump power wire...

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                            • #15
                              Check your grounds.
                              sigpic
                              1987 Mustang LX Coupe, yes it's slow
                              1985 Mustang LX Coupe, not slow

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