Undriveable due to massive flat spot below 5000rpm



  • hi mate think i have seen your car parked outside the church ?! I am on creek road but i don't have any vsix parts I'm afraid but if you need any tools or a hand gimme a yell



  • @youdirtyfox

    Great, thanks for the offer! And, yes, it is the one outside the church :P



  • Do all the basic checks to rule them out, then….

    Could be the VAF or TPS.

    If it was crank sensor I wouldn't expect it to still work ok at higher revs, same for the fuel pump.

    Is there anyone near enough to pop down and swap some parts over?



  • Might be worth checking for leaks around the variable resonance induction system (vris), those should open at idle but then close after about 1500 then open again at 4000, cant remember the exact values but not far off, its odd to have something effect such a large range of the revs, but the vris does effect a large range of the revs and with v6 engines its very common to have a flatspot thats due in part to the way a v6 works and its need for a variable induction system.

    At idle itd make minimal noticeable difference as theres no load on the engine, but once load is applied and the vris is in the wrong state for the rpm/demand then the fuel to air ratios would be squiffy and bogging your car down ie flatspot.



  • This is now fixed and currently relisted on fleabay



  • Sorry for late replies to you all but have been busy with other things. Car is now fixed and on eBay, 20 watchers but no bids at yet :(

    I checked out the induction system, changed the fuel filter and went to the diag box after making up a test lamp. Unfortunately the box was unmarked and it took me a while to find a pin out for it.

    Plugs were changed and I have been driving it daily for the past week to see if any problems recur. Take the long route along Southwood Road Hayling just to check on the MX-3 parked there.

    I have updated the ebsy ad to point out that if no bids received by Thursdasy it is being withdrawn, I am very impressed with the car now it runs well and will put an MoT onit and keep it.

    thanks to you all dor your helpful suggestions, guided me in the right direction and taught me a bit about modern electronics.

    My other car is a 1954 Daimler Ferret



  • Do we know what the fix was?



  • First off tried to find any air leaks in induction area - no leaks and nothing different when put back together.

    Battery then needed charging - all the while the car was in the layby outside Hayling Church, about 3 miles from home so there were brief visits each time I was passing.

    Tried it with newly charged battery, started ok but hideously flat before about 5k when accelerated hard, would run ok with very gentle acceleration.

    Found it impossible to try and hold multimeter probes on TPS while playing with it on the car so that came bake home to be tested, next the VAF - both tested out ok.

    Ordered a fuel filter from Japarts though filter on car seem clean and shiny on outside, slight improvement but still hesitant.

    Pulled all six plugs, a couple of tubes had oil in them. Replaced plugs and it seemed a lot better. Been driving around the island and brief bursts on the M27 and seems fine.



  • So it was a misfire?



  • Originally it was far more than a misfire.

    I picked the car up and it seemed fine. Got on the M27 at junction 1 and came off at the base of the A3 to go the back way to Tesco to put some fuel in. At that point, pulling away from the traffic lights, it failed to respond to the throttle. It was just driveable by accelerating to 3000 in neutral, putting it in gear and dropping the clutch.

    After filling to see if fresh fuel would help it was just as bad and became worse when trying to get onto Hayling. Eventually stopped to call the AA who were unable to do anything except drive behind as I kangarooed the rest of the way home.

    I think it could be a combination of low fuel/ bits blocking the filter (though it was fairly new), tired plugs and removing, cleaning, replacing components making the electrical contacts more secure.

    No one fault as such but just a combination of things which together made the car sick. As each cause was investigated and eliminated the car got progressively better.



  • You never mentioned the misfire before, just a flatspot



  • No you called it a misfire - to me not responding to the throttle at all above idle and then coming in with a bang at 3000 or more revs is a massive flat spot.

    One thing I forgot - VRIS was operating, gave the linkages a good does of WD-40 and anything else that looked like it could do with some got a squirt too. That may have helped.



  • @24751c52fd=macspite:

    misfires really badly or doesn't pick up at all when accelerated normally in neutral.



  • Don't care whether it was a misfire, flatspot - as said at the beginning of the thread or a temporary bout of Mazda flu, the car seems fixed and thank you to all who suggested various things that may have been wrong, very helpful.



  • Fair enough, but it makes it difficult for us to help you better if we dont know the proper conditions.


 

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