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Retardation and rough acceleration

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  • Retardation and rough acceleration

    Well the old rig has held up well for years now, but just lately I can't figure out whats up with it.
    New spark plugs 40K ago.

    Starts nice and no issues idling.
    No change in fuel economy
    No strange noises


    An Issue has come on pretty suddenly.
    If I don't let it warm up for 5 mins its pretty hard to drive it. Even smooth slight acceleration has it retarding and jumping around as it tries to pull forward. Almost like it was missing as you try to accelerate away. This has sometimes been the case previously (And i couldn't figure that out either) but after it gets warmer a minute down the road things got back to normal.
    But now, this is persisting. Its pretty bad when cold, jerking and jumping trying to accelerate. When warm, its now a bit jumpy all the time when trying to accelerate.
    Give it a boot full when warm, and it will be jerky / notchy acceleration until finally in the upper revs band it smooths out and pulls pretty well.

    Normally I would say spark plugs, but they are pretty new (not that i should rule those out given the circumstances).
    Also wondering if there is some temperature sensor issue. No indication of anything. But i seem to remember threads here which may have indicated this type of thing can be temp sensor related.. Can't see any faults on the Scan gauge.

    Have checked the mass airflow wire on the intake. Always keep that clean.
    Final thoughts are coil packs..?
    Oxygen sensors - from memory theres several of these but would have thought bad economy to be the result of this failure?

    BTW its duel fuel still. Petrol and Gas Injection (yep, still seems to be going fine after all these years.... until now). Doesn't seem to matter if on fuel or gas. Problem persists so likely whatever it is, its a common element not related to the fuel system and more central.

    Thankful for any suggestions / Thoughts. 220K on the clock (It only gets out on weekends now days)

  • #2
    Might pay to inspect those spark plugs.
    Had similar diagnosis after replacing plugs, several had cracks in the porcelain.


    • #3
      Replace plugs (Gap them correctly)
      Check coil packs.
      Change fuel filter.
      Change air cleaner.
      Clean MAF.

      Worst case: Replace all 4 x o2 Sensors.


      • #4
        Have you got a decent scanner to check the error codes as a starting point


        • #5
          Originally posted by KRH View Post
          Have you got a decent scanner to check the error codes as a starting point
          He doesn't mention any ECU light, so likely error codes are not present.


          • #6
            Same problem started on mine, about 2,000km after new spark plugs


            • #7
              *** Solved... It was a bad MAF (IAT) ***

              It's been a while and tried a few things and now seems like we might have success, So posting up where we are at currently.

              I do have a code scanner, but no engine lights and no codes present. Which was the main challenge with this.

              In the following order, I replaced:

              Spark Plugs
              O2 Sensors - all 4
              Coil Packs - all 6 (replaced after checking, but its hard to really check these so I just bit the bullet and got new Denso ones)
              MAF Sensor - See below.

              I also went to 2 Mechanics, One that is a good local and I trust and has a better computer scanner. But no codes seen.

              In addition, Went back to the place that fitted the Injected Gas system. They are very good and did a real in depth analysis of everything. The Injected Gas system was perfect after many years of running - which is amazing as when I first put it on, I expected I would have to do something at some stage. It has always been extremely reliable with zero issues to date.
              They did find a fault code pending, related to the MAF - PO113 Which I believe is "Air intake temp Current High Output". This was pointing to the MAF which I believe also contains the IAT sensor, so at this stage I replaced the MAF.

              Since then... I have not had the issue return as of yet. Its been around 4 weeks now with the new MAF. Everything is back to being super smooth.

              I've always checked and kept the MAF clean with electrical contact cleaner, as we all know how dirty they can get.
              The bad MAF was also registering resistances all normal and within OEM speck with the multi-meter.

              So now I have 6 spare coil packs and a set of Spare O2 Sensors. lol. Still, not the worst outcome. An easy fix is a good fix.


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