Problem - Misfire



  • Hi,

    My 1993 v6 seems to have a very strange missfire at low and high revs.

    When i try to accelerate it sometimes pulls away ok but other times it coughs and splutters all over the place. Its a little tricky to drive especially pulling away from lights.

    If you try and rev the engine past 5000 it seem to just die but not cut out.

    I recently changed the Distributor because it broke.

    I have tried changing the Spark plugs and ht leads but still the problem occurs.

    Any ideas?

    Rob


  • administrators

    Hi,

    Try checking the vacum system and the air intake, if that has a crack in it then the ecu will be getting invalid data!

    Also please read the Posting Rules at the top of this forum

    Jono



  • sounds like a lead is dying!


  • administrators

    @0afb08ed3d=irish-mx3:

    sounds like a lead is dying!

    @0afb08ed3d=catman:

    I have tried changing the Spark plugs and ht leads but still the problem occurs.

    irish, I dont think its the ignition system

    Jono



  • was there any oil on the plugs?

    you could try turning the distributor, perhaps when you put on it lost its timing-too far out for the ECU to compensate. Or it slipped since.



  • Thanks for the suggestions….

    I have tried tunring the Dizzy but with no effect other than to degrade / improve performance. I have it set now to the best position.

    I was thinking along the lines of a vacum leak somewhere..

    One other thing that i have noticed is if you set the car in idle then floor it it just coughs and splutters alot where as if you gently press the throttle it doesnt do it so much.

    I have tried the main vacum assembly form filter to inlet and it looks fine so not sure where else would caus ethe problem.

    Would it be a big crack or could it be something really small?

    Rob



  • @dde3a80197=catman:

    I was thinking along the lines of a vacum leak somewhere..
    Would it be a big crack or could it be something really small?
    Rob

    Hmm there's quite a few lines, think you've checked them all?
    I would check the various tubes connected to the y piece to the right of the front cam cover going to the intake box/tube
    the cam cover breather line
    the oil cap (seems silly but it all counts)
    the condition of the black flexible intake
    etc

    I take it you can't hear any hissing anywhere?



  • No hissing noise on idle.

    But i have noticed that if you blip the throttle a kind of sucking noise.

    It kind of emminates from the center of the engine just to the right of the dizzy (if you are looking at the dizzy from thepassenger side)

    Wasnt sure if it was related.

    Ill try and have another look tonight.

    If i cant find it though would a diagnostic check pin point the problem?

    Rob



  • Oh one other thing that i had thought about was if the coil was knackerd.

    Would this cause similar symptons?



  • The coil failing would more than likely start failing at the higher RPM and when the engines hot



  • Hmm, interesting as the car does seem to run alot better when cold.

    The reason i thought about it was because at high revs the engine just seemd to die / backoff which i immidiatley thought would be the coil breaking down.



  • sily ones now
    manifold/ downpipe blowing possibly
    or a bad earth somewhere
    i kept having a missfire at ow revs
    and tured out to be the neg on the battery had worked loose??



  • Doesnt seem like the downpipe is blowing.

    I can hear a kind of sucking when opening the throttle at idle which conicdes with the missfire at low revs.

    If i put my ear over the engine it sounds like it is comming from the air intake gasget where the intake plenum connects to the body of the engine.

    Would this need changing?



  • sounds like that could be your problem! Or at least worth a look… I replaced my IM gaskets, 10er each of probestore. Mine were completely knackered - theyre metal with some plastic coating and the plastic was in bits. Better that than your IM being cracked...

    My gaskets:



  • Thanks for the pics.

    Just purchased gaskets from ford probe.

    Hopefully that will fix my issues…..



  • Np, good luck with the gaskets. If thats not the problem I bet they needed done anyway ;)



    • high revs the engine just seemd to die / backoff which i immidiatley

    • missfire at low and high revs.

    • if you set the car in idle then floor it it just coughs and splutters alot where as if you gently press the throttle it doesnt do it so much

    • I recently changed the Distributor because it broke.

    • I have tried changing the Spark plugs and ht leads but still the problem occurs

    IT SEEMS TO STRUGLE WHEN THE ENGINE IS UNDER LOAD

    1) IGNITION
    First I would have looked at Battery, Sparkplugs and Leads.
    (but you have checked those so we can rule that out)
    And if your getting a decent spark, we can rule out ignition problems.

    2) QUESTION
    Next I would ask about changing the dizzy, did you have this problem before you changed it? How soon after you changd it did the problem start?

    Make sure you put all the leads back correctly!
    (assuming you swaped it ok and put everything back right)

    3) FUELING
    Next I would be thinking is it a problem with fueling as it seems to occur when under load, so maybe you have a sensor out.

    • AIR: VAF sensor?
    • TEMP: Coolant Temp Sensor?

    Let us know how you get on.



  • Thanks for the tips.

    Will double check the spark plugs / leads but im pretty sure they are ok.

    As for the dizzy change, no it was fine before i swapped it. After it was ok for ~6 weeks then faild on the way home from work.

    All the leads are back ok, i made sure that i changed one at a time.

    On the note of sensors. I did a dignostic check earlier and found that it was giving error code 12. TPS Sensor failure.

    Would this give the symptons that i am having? Would the TPS Error be related to the IM Gasget sucking problem?

    How would i check the VAF sensor?

    Rob



  • Yes the TPS sensor is your problem.

    It is the Throttle Position Sensor I'm guessing, and that tells the ECU what position your throttle butterfly is in so that it can alter the fueling when you accelerate.

    It is attached to your throttle body, I'm not sure about the MX3 but on some cars its easy to change just the sensor, but on others just swap the whole lot. You can pick that stuff cheap from a scrappy and they will let you take it back if its faulty.



  • The sensor might not be set right, its adjustable by about 15 degrees, but the sensor can be taken completely off the throttlebody


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