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  • Engine Surge Problems

    Hey All,

    I have been having a surging problem with my NL 3.5L, basically the same as in this post,
    http://www2.pajeroclub.com.au/forum/...read.php?t=236, hunts between 500 ? 1800 rpms at idle. I tried cleaning the Idle stepper motor, and followed some multimeter tests, which all seemed to pass, but the problem is still there. It wasn?t till I found another site, that said disconnect the stepper harness, and if the surge is gone, then that?s the problem. For me, disconnecting the idle stepper made no difference to the surging, just idled at around 1800 rpm. So I reconnected the harness, and disconnected the harness that?s connected to the airbox. I think it?s the Mass airflow sensor. With this disconnected, the check light on the dash comes on, but the surging has gone. Does this mean that the MAF sensor is most likely the problem, or is that just coincidence?

    I just don?t want to try and clean it, and break it, when it mightn?t even be the problem.
    Also, the car runs on dual fuel. It doesn?t surge when it is running on LPG, only when on petrol.

    Cheers
    Shane

  • #2
    Although the surging could be caused by a dirty air flow metre, i would imagine the reason the problem disapeared is because when the computer detects that theres no input from the afm, it then reverts to a fix style map for all the outputs, you would have decreased economy, increased emmissions, less power etc. - almost like a limp home mode. I think its fairly inconclusive of your problem.

    First place i would be lookin is your oxy sensor...

    Comment


    • #3
      Mac does the car "hunt" with quick repetitions? I have an NJ 3 litre and at the lights it is fine with the foot brake on but as soon as I let the brake off it hunts quickly. It's almost like a wobbling ... in fact it feels transmissionish (!). Is this the same as yours?

      Comment


      • #4
        Cheers for the Replies,

        I have been searching for a bit of information on the oxygen sensor, but havn't really been able to find anything.

        Is there some way to clean it or can i disconnect it, to see if the hunting at idle still occurs. Or do i have to just replace it?



        The problem is not really how you described it pagerow, its manual, and makes no difference if your foot is on the brake or not.

        What happens is, when you start the car from cold, it will startup, and then rev steadily on about 1800 rpm for about a second, like it used to, but after the second is up, it will drop the rpms down to about 500, then climb up to 1800, then drop down again, and this will repeat untill the engine is warm, then it will just sort of hunt between 500-1100 rpms.

        Cheers
        Shane

        Comment


        • #5
          Hi you mention the vehicle is dual fuel. Have you suffered any dreded backfires like some others here like me Remove the airflow meter from the vehicle and have a look through it check the honey comb piece inside to see if its intact. If this has been damaged in a brutal way it may cause you these problems. If its badly damaged it will thow out the readings that the afm receives in turn the ecu hence your idle going crazy. If its been totally removed it will cause the vehicle to go fully rich on the fuel wont affect the lpg.
          Another thing to look at loose or cracked vacume hoses but this would probably evident on the lpg side too.

          Regards

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          • #6
            Yes i have my 4 pieces of honeycomb somewhere in the garage, lol. They slowly started to deform, then pop out as the car kept backfiring. But the gas installer said they weren't necessary. I cant remember if the problem started after the last bit of honeycomb fell out or not, it backfires all the time.


            My bits of honeycomb are really deformed, so can new honeycomb be brought, or is there some other solution.

            I should probably try and get the backfiring sorted out first but, thats a whole other story

            Cheers
            Shane

            Comment


            • #7
              You need the honey comb to fix the surging. If ur installer said its not requered he is full of it. Mitsu does not sell this part seperatly. A new Afm is expensive just over 700 bucks. Try an efi specialist for the comb or ebay for Afm.

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              • #8
                Is it possible to get the honeycomb from a Magna or some other Mitsubishi engine, or is the problem more likely the whole MAF unit as well will have been damaged by the backfiring. In which case is a Magna MAF unit still an option?

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                • #9
                  Originally posted by Mad Mac View Post
                  Is it possible to get the honeycomb from a Magna or some other Mitsubishi engine, or is the problem more likely the whole MAF unit as well will have been damaged by the backfiring. In which case is a Magna MAF unit still an option?

                  The 3.5 engine in the magna has the same AFM the 3.0 slightly different 2 less pins on the connector from what i remember i believe the honeycomb will be the same in both. You may have a difficult time pulling it out without damaging it so be careful. If you can get a complete MAF from a 3.5 Magna just plug and play. Note you will need to sort out the backfires first otherwise you will blow this one up as well.

                  With mine so far the unit itself hasnt been damaged just the comb all up i have had up to 7 or 8 backfires with the old lpg system.

                  Regards

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                  • #10
                    Have you disconnected the Battery at some time, if you have try this,
                    Disconnect the battery for at least 30 mins then re connect it and take the vehicle for a drive around the block, don't have the airconditioner on.

                    I had the same problem with two of my Mitsi magna's when i changed batterys, the car used to come up to a set of lights and nearly stall, then the revs would jump up to about 1500 to 1800 revs and then hunt up and down. sometimes would even stall. disconnecting the battery for about 30 mins then connecting it again would reset the system.
                    NP 03 Exceed. 3.5l petrol. Injected LPG. 2in lift, Poly air at rear, custom rear storage, 10 wheeels, 5 tyres looking for some new tyres,

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                    • #11
                      Thats what I orginally thought to begin with, but i tried it and it made no difference.

                      Originally posted by sinbad View Post
                      Have you disconnected the Battery at some time, if you have try this,
                      Disconnect the battery for at least 30 mins then re connect it and take the vehicle for a drive around the block, don't have the airconditioner on.

                      I had the same problem with two of my Mitsi magna's when i changed batterys, the car used to come up to a set of lights and nearly stall, then the revs would jump up to about 1500 to 1800 revs and then hunt up and down. sometimes would even stall. disconnecting the battery for about 30 mins then connecting it again would reset the system.

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                      • #12
                        Cheers for that,

                        At least a magna 3.5 intake thing should be easier to track down. My car probably backfires on average twice a week, so I don?t really want to buy a new one to break that until the problem is fixed. Is there any suggestions as to what else I could shove in there instead of the honeycomb, some kind of pipe or something, even if it just works a little better as opposed to being 100% fixed. Although I did a test on petrol, and my fuel economy doesn't seem to have changed at all from when the honeycomb was installed. So apart from being annoying to watch the rev counter, and occasionally stalling if I leave it idling for a while, is it doing any damage if I just leave it?

                        Cheers
                        Shane



                        Originally posted by wrexed03 View Post
                        The 3.5 engine in the magna has the same AFM the 3.0 slightly different 2 less pins on the connector from what i remember i believe the honeycomb will be the same in both. You may have a difficult time pulling it out without damaging it so be careful. If you can get a complete MAF from a 3.5 Magna just plug and play. Note you will need to sort out the backfires first otherwise you will blow this one up as well.

                        With mine so far the unit itself hasnt been damaged just the comb all up i have had up to 7 or 8 backfires with the old lpg system.

                        Regards

                        Comment


                        • #13
                          If its running rich it may foul your plugs and eventually ruin your cat convertor.

                          Regards

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