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Jerking while cruising with light throttle 2-3krpm

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  • Jerking while cruising with light throttle 2-3krpm

    Posting this here to see if someone has had similar problem and found a solution.

    I have this odd problem with my 95 Mx6 LS MTX, Everything runs excellent, except if your giving it light throttle..say crusing at 2-3rpm, thru any gear.. The engine starts to jerk/stumble/chokeout. I dont know how to describe it, its not constant or causing the engine to loose rpms its just annoying. Anything below that 2k its fine, anything above 3k its fine, if you floor it wot any rpm its fine.

    I thought maybe I had a leaking intake gasket so I replaced them, and also chased back all my vac lines for VRIS and EGR, ect. I readjusted the TPS, then IAC, then the Timing, it idles perfect, got a consitant 20hg of vac at idle, its right on the dot at 10deg tdc in diagnostics.

    Brand new distributor, with new wires, new plugs, new fuel filter, cleaned K&N Filter,new clutch, new crank sensor, new fuel pressure regulator, cleaned and remounted ecu grounds,

    The codes I pulled from the ECU are both L02 Sensor inversion and inactive codes, witch I figured they would only cause it to get bad gas mileage.

    My only leads are maybe the VAF is causing it, but I dont have an extra to try. Or possible the EGR , witch Id probably just unhook.

    Another odd lead: Its really hard to put gas in the tank, you have to manually throttle the gas pump as lightly as possible otherwise it overflows and shuts the pump off. Im guessing the vent for the fuel tank is clogged/rusted, maybe this is "air lock is" restricting the return from the fuel pump however When you remove the fuel cap after the engine is running you can hear the hiss from the vacuum so I dunno.

  • #2
    Not the VAF but a leaking fuel injector. Run it and pull the plugs. See if you get a strong fuel smell out of a particular cylinder.

    As for the gas tank, I think you're right about the vent line. Don't know if there's a check valve in the line somewhere but that might be something to look into. Search the forum and see if anyone else has experienced the same thing.

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    • #3
      Any headway yet, king?
      Some people are living life and some people are just living.

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      • #4
        I've had fuel pump lever issues before but I never thought much of it as it only happened at specific stations. At most I never had an issue.
        ------------------------------------------------------
        93 PGT atx Stock
        94 PGT mtx - KLZE straight neck, rebuilt heads with de components, headers, test pipe, full CAI, RR-Racing engine mount inserts front and back, Extremethings modded ecu, Stage 1 clutch

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        • #5
          is the tank hissing vacuum or pressure? if the evap system plugs/solenoid dies it can cause the tank to pressurize, which mine has done before...

          mine acted like that when my coil first started dying, or I know someone who had the egr vent plug, constantly keeping vacuum in the egr valve, holding it open, so maybe pull the vac line from the egr valve with it not running and see if there's vacuum...just a couple places to start

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          • #6
            Nothing yet, I was thinking the EGR as well, maybe the EGR is partially open and causing a vacuum leak that is only noticeable at partial throttle. Im going to check the vacuum line,might clean or block the EGR off all together.

            I dont suspect leaking injectors, because it would cause a poor idle if that were the case.

            When you remove the fuel cap after is been running you get the common " hiss" from the vacuum caused by the charcoal canister. Maybe it will fill better if I left the car run while filling But I know its because the vent for the tank has to be plugged up.If air cant escape the tank while gas comes in, its going to keep the gas from pumping in quickly and overflow triggering the auto shutoff on the gas pump handle.
            Last edited by KING6; October 30, 2014, 06:59 PM.

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            • #7
              I checked the EGR tonight, pulled the vac line off and nothing is coming thru. While trying to reconnect the hose I leaned on the intake a bit and I could hear a "zapping" so I then started wiggling stuff around and noticed the center of the distributer cover arcing against the K&N Filter housing that was about 1/2" away from it.

              So I pulled the filter away about 1-1/2inchs, then thought hmm, I wonder if thats enough to keep it from arcing, stuck my finger between the two and Zap!, yup still arcs. lol.
              https://www.youtube.com/watch?v=csgv...Vvx7xJVReEsTSg

              This is one of them elcheap ebay distributors so im taking it the covers are poorly made, fortunately I have a few more on hand and hopefully that is the problem.

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              • #8
                The refueling problem is probably the flap at the end of the filler neck, just before the entrance to the tank. It is most likely rusted stuck half open restricting the flow of fuel. Either take out the flap completely or clean up the rust where it swivels and keep the flap.


                edit: (I guess the following does not apply anymore.)
                As for the first problem, I had something very similar, especially while traveling at low speeds. When I wanted to accelerate slightly, the same conditions you described (jerking/stumbling), happened. The only way I could smooth out the acceleration was to use the clutch. After I had a new clutch installed it pretty much disappeared. Although, I also had poly inserts installed on the engine mounts, so that might have helped also.
                Last edited by ZeroR; October 30, 2014, 08:09 PM.
                Canadian 94 MX6 LS Mystere
                #51 Zero Racing

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                • #9
                  I changed the cap out over the weekend, and far as I can tell..that cleared up the jerking. It still doesnt cruise as smoothly as My turbo mx6 but I think with some more tweaking and swap the 02's out I can get it perfect.

                  With more inspection of the disty cap compared to the other OEM cap I had, this one was much thinner and the point where it was arcing, it wasent completely sealed

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                  • #10
                    these distys are so poorly made. Unbelievable. And what's sad is THIS IS THE NORM!
                    ------------------------------------------------------
                    93 PGT atx Stock
                    94 PGT mtx - KLZE straight neck, rebuilt heads with de components, headers, test pipe, full CAI, RR-Racing engine mount inserts front and back, Extremethings modded ecu, Stage 1 clutch

                    Comment


                    • #11
                      Jerking while cruising


                      ... so to speak.

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                      • #12
                        For those of us without girlfreinds. Or those with them but never get any.

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