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    Misfire and lack of power when hot

    Hi, I hope someone can help me diagnose a misfire on my 72 stag when the engine is hot and under load. The cad has not been run for a while until last week and it started fine and ran ok for a few miles. However it then started to misfire and lose considerable power. Suspecting the coil, I fitted a new Lucas DLB102 but again the same issue occured when the engine gets hot. I have checked wiring to the coil and ballast resistor, all of which is ok, regapped the plugs, checked the HT side and I am getting sparks. The car has a lumenition ignition system on it.
    Fuel is getting through ok looking at the fuel filter and Icant see any other obvious issues.
    If anyone has any other ideas where to look next, I would be grateful.
    Thanks and regards
    Dave Harris

    #2
    Hi Dave

    just something simple to check, is there enough oil in the carb dashpots....

    Neal
    1972 White Manual and loving it

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      #3
      Hi Neal, just checked at they both have enough oil in.

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        #4
        Dave.
        Another suggestion. Over the years I have had similar symptoms in hot weather, and on both occasions it was the Lumenition system starting to break down. They seem to become heat sensitive with age.
        If you don't find anything else wrong, it might be worth getting it tested, but that might not be easy at this time!
        Mike.

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          #5
          I always suspect the coil have you got another? Not unknown for a new one to be duff and Lucas branded stuff is not always genuine. Otherwise have you got another set of HT leads - one or more might be breaking down and giving a high resistance exacerbated by heat. Hate these kind of faults. Good luck
          Paul - 3 projects, 1 breaker - garage built and housing 2 white Stags. One runs, one doesn't

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            #6
            Had a similar issue recently, would run fine from cold for approx 15 mins then start to misfire as if running only on 6 cylinders, turned out to be the red pick up module on the Stag Webber electronic dizzy, wasn't a perfect fit and too close to the pickup rotation, when everything warmed up and expanded they both touched causing the miss firing issue. I too tried all the usual suspects, had me going for a few days.

            Roger S

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              #7
              Thanks for the advice. Plenty to check out, hopefully I will find the issue.

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                #8
                Just had to fit another powerspark. The pickup could not be adjusted for clearance without filing out the mounting plate. However the car wasn’t missing or misfiring, there was no spark at all.
                +1 for Paul’s comment about Lucas dlb could be the issue.
                fitted a Bosch after the Lucas caused missing when hot.
                There are 2 secrets to staying on top :- 1. Don't give everything away.
                2.

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                  #9
                  Originally posted by Goldstar View Post
                  I always suspect the coil have you got another? Not unknown for a new one to be duff and Lucas branded stuff is not always genuine. Otherwise have you got another set of HT leads - one or more might be breaking down and giving a high resistance exacerbated by heat. Hate these kind of faults. Good luck
                  +1

                  I had leads go and a coil go. New Bosch red coil and Magnecor leads it solved it.

                  Jeff

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                    #10
                    Change the rotor arm.
                    Last edited by mallardstag; 25th May 2020, 18:23.

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                      #11
                      I had similar hot misfiring and replaced the opto sensor on the Luminition and it was fine afterwards. I have heard this is a relatively common problem

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                        #12
                        remember that 90% of ignition faults are fuel related and vice versa

                        On the ignition side and assuming that luminition is in good order.

                        When it starts to misfire, run a wire from battery +ive to the feed side of the ballast resistor, does misfire go away? = break in white feed for Ballast resistor

                        Replace the wire that sits between ballast resistor and coil +ive, just bridge it, no misfire = break in wire that sits between BR and Coil

                        Is the trigger wire for the luminition to -ive sound. I have had terminals that look fabulous but are only one strand away from breaking

                        What rotor are you using in side the distributor? does it have a rivet holding the metal blade to the body? = cheap crap

                        I have more failures from cheapo rotors than anything else, got a box full of the damned things that work fine on the bench test but fail in operation. some even wobble the distributor cap when the engine is running!!! wrong size rotor chaps.

                        likewise for the cap - the market is flooded out with cheap nasty crap

                        Said it before and i'll say it again distributor doctor is the only place I buy ignition components from now. Too many failures, to many fakes, even green boxed lucas is not that great and has let me down

                        All that said, have you lobbed fresh fuel in? a tank full of unleaded that in a car that has not been used for months is pretty dreadful, goes off really quick. Super unleaded lasts a little longer. fresh fuel make make the world of difference
                        Stags and Range Rover Classics - I must be a loony

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                          #13
                          A lot of good advice ^^^^^

                          I would be looking at the rotor arm and the coil. I had a misfire a while back. Bought a new Lucas coil from a respective supplier and it too failed when hot. Bought a Bosch Red coil and no problem since.

                          Another thing to check is the plugs and leads. Both can fail when hot.
                          Dave
                          1974 Mk2, ZF Auto, 3.45 Diff, Datsun Driveshafts. Stag owner/maintainer since 1989.

                          Comment


                            #14
                            Originally posted by jbuckl View Post
                            Just had to fit another powerspark. The pickup could not be adjusted for clearance without filing out the mounting plate. However the car wasn’t missing or misfiring, there was no spark at all.
                            +1 for Paul’s comment about Lucas dlb could be the issue.
                            fitted a Bosch after the Lucas caused missing when hot.
                            Yes I think its a Power spark kit that Stag Weber use. That was the issue with mine, I had to file out the plate fixing holes to get the correct adjustment. This is how I found it, the gap is supposed to be constant at approx 1 mm, I had no further adjustment until i elongated the fixing plate holes.

                            Roger S
                            Attached Files

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                              #15
                              Interesting thread and exactly this happened yesterday when my wife tried driving the Stag for the first time.

                              I had no power at all, could barely get going and not at all on a mild incline. Being automatic, couldn't rev up and slip the clutch.

                              I drove it for a short drive today and it was fine so I'll go through this thread and get some spares to try.

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