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Missing at speed

Last post 05-27-2008, 8:00 AM by Darrel. 13 replies.
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  •  04-11-2008, 5:59 AM 13898

    Missing at speed

    998 engine.  Accelerates smoothly to 50/60 miles an hour and cruises there with no issues - as long as the road is flat.  As soon as you hit a hill and place more load on the engine it starts to "misfire".  I place it in inverted commas as I am not sure this is what it is doing - but that's how it feels.  The following has been checked/adjusted/replaced - valve clearances, float, dashpot oil, points and condensor replaced with magnetronic, dizzy cap, rotor, spark plugs, carb mixture, timing (not sure if I got this right, hence previous post).

    The problem occured before all these changes and persists.  Someone has suggested that the petrol/gas tank may not be breathing adequately?  Can anyone help?

  •  04-12-2008, 6:26 AM 13911 in reply to 13898

    Re: Missing at speed

    Wow, you've covered all the possibilities that come to MY mind.

    Testing the tank breather is easy, go for a high speed drive with no gas cap. If your car still "misses", it's NOT the breather.


    On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"
  •  04-13-2008, 10:27 AM 13922 in reply to 13911

    Re: Missing at speed

    Hey...one more thought.

    Have you checked to see that your vacuum advance is working correctly? It may be hanging up somehow. Make sure that your vacuum line is intact and that the mechanism in the dizzy moves freely.

    Good luck!


    On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"
  •  04-14-2008, 6:19 AM 13931 in reply to 13922

    Re: Missing at speed

    Yes it is.  The distributor was serivced about 2500 mi ago.  The vacuum unit was replaced and I put in a new vacuum tube with new ends.
  •  04-15-2008, 10:54 PM 13950 in reply to 13931

    Re: Missing at speed

    Darrel wrote the following at 04-11-2008 7:59 AM:

    "998 engine.  Accelerates smoothly to 50/60 miles an hour and cruises there with no issues - as long as the road is flat.  As soon as you hit a hill and place more load on the engine it starts to "misfire".  ...."

     
    Were the valve guides replaced recently?  This sounds like a valve sticking open when the guide gets hot and expands (inward) under higher load and heat conditions.  Bronze guides are particularly susceptible to this as they expand more than iron, so they need a tad more running clearance.
  •  04-27-2008, 6:51 AM 14097 in reply to 13950

    Re: Missing at speed

    The more I think about this as I keep this thread in the back of my head, I must agree with Barneymg. Actually, I had the same thing happen to me with my Sprite! 

    I too had a stuck valve. Initially it was only while on the highway. When this happened, I took my foot off the gas then hit it hard, and the valve freed-up. Eventually, it stuck solid and I had to re-do the guides.  


    On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"
  •  05-01-2008, 1:13 PM 14168 in reply to 14097

    Re: Missing at speed

    Seeing as how you seem to have done just about everything on the ignition side of things, have you thought about an air leak in the suction side of the fuel system?

    According to the book of words, if you have an electric pump you can check for an air leak by disconnecting the fuel line at the carburettor and immersing it in a half filled jar of fuel. With the ignition on and pump running, if you get air bubbles you have a leak on the suction side of the pump somewhere.


    Mini 40....its a wicked ride
  •  05-09-2008, 2:52 AM 14322 in reply to 14168

    Re: Missing at speed

    This problem disappeared for a while - but reappeared about 2 days ago.  An interesting development was that with winter approaching my trip home was in the dark - so had the headlights on.  When I felt the drag/hesitation the head and dash lights went dim.  When the problem went away - the head and dash lights were bright again.  Interestingly too - the problem occured intermittently all the time - so irrepsective of whether I was climbing a hill or not - was just more noticeable climbing the hill as you need all that the 998 can give you at times :)

    I did some basic checks when I got home, like the tension on the fan/v-belt, checked all earth points for tightness and cleanliness - all seemed ok.  Any other suggestions??  I am running an alternator - replaced the gennie about a year ago.

  •  05-15-2008, 9:31 AM 14409 in reply to 14322

    Re: Missing at speed

    Just give you spark plugs another check over! I had a misfire recently and it was one of the plugs I had just replaced a week earlier...I had a crack across the porcelain right at the bottom...just a thought? I can't think of any thing else pal?? what was actually replace? and what was just checked?

     


    Oz Cooper
    Classic Mini Product Manager UK


    Helpful Links:
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    Moss Europe Ltd

    Disclaimer: Working on automobiles is inherently dangerous. Moss Motors, Ltd. is not liable for injury or damage due to incorrect installation or use of their products. All products are sold with the understanding that the safe and proper installation and use of the products is the customer’s responsibility. Follow factory workshop manual procedures and instructions, but use current shop safety standards and common sense. Some tasks will require professional advice or services which Moss Motors cannot provide.
  •  05-22-2008, 6:12 AM 14522 in reply to 14409

    Re: Missing at speed

    Took out the whole system and took it to a distributor specialist.  They bench tested it for me.  I have recently converted to Lumention Magnetronic ignition system.  With the ballast on the spark is poor.  With the ballast off the spark is good.

    Question:  Can I run this Lumenition system without the ballast?  Or will it damage the module?

  •  05-22-2008, 7:45 AM 14528 in reply to 14522

    Re: Missing at speed

    Darrel,

    You haven't been running the module itself from a ballasted source, have you? I don't think it was meant for that. Only the coil itself may, or may not, need a ballast. Do you have the instructions for the Luminition? Check them over carefully. If the spark is lousy with a ballast and good without, I think you have an answer to that part of it, at least!


    Motorbill
    From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon
  •  05-22-2008, 8:25 AM 14529 in reply to 14528

    Re: Missing at speed

    Thanks motorbill.

    The lead from the ignition is attached to one side of the ballast.  That side has the red lead from the module too.  The other side of the ballast goes to the coil.  And the black lead from the module to the other side of the coil.  We thought the ballast may be faulty - but two other ballasts gave us the same result.  So it seems to me that the module is picking up it juice directly from the ignition?  Car electrics not my strong suite :)

  •  05-27-2008, 6:15 AM 14601 in reply to 14529

    Re: Missing at speed

    Darrel what year is your car again? If you are ballast I personally would bypass it and replace the coil with a 12volt one! usually the ballast on a Mini is the wire itself and only one or two were fitted with an acual ballast risistor. To swop over to 12v is easy find a swiched 12v feed on the ignition side (so it goes off when the key is out) and swop the coil...thats it. I wasn't aware Luminition did a 6v unit?

     

    Oz


    Oz Cooper
    Classic Mini Product Manager UK


    Helpful Links:
    Code of Conduct
    FAQs
    Moss Europe Ltd

    Disclaimer: Working on automobiles is inherently dangerous. Moss Motors, Ltd. is not liable for injury or damage due to incorrect installation or use of their products. All products are sold with the understanding that the safe and proper installation and use of the products is the customer’s responsibility. Follow factory workshop manual procedures and instructions, but use current shop safety standards and common sense. Some tasks will require professional advice or services which Moss Motors cannot provide.
  •  05-27-2008, 8:00 AM 14602 in reply to 14601

    Re: Missing at speed

    Thanks for all your help on this one.  I removed the ballast and put in a new set of ignition leads (2 had a higher than should be resistance), connected it all up.  Started her - on the first twist of the key she purred into life - having stood for over a week.  A quick adjustment of the timing and I was up and running.  No starting issues since.

    Just waiting to see if the problem that originated this post re-occurs.  So far, so good.

    It is a 1968 Mini Estate/Wagon/Traveller.  Not running 6V, running 12V.