1970 SIIA Missing/Backfiring - Defender Source
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  #1  
Old August 12th, 2017, 09:09 PM
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Baird M. Gehring
1997 D90 ST #1558
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1970 SIIA Missing/Backfiring

Truck starts missing upon acceleration. Idles fairly good but misses sporadicly when I give it gas driving down the road, seems like an electrical issue. Referenced green workshop manual electrical wiring diagram and checked everything out from the battery back, nothing obviously suspicious looking. Blew a hole in my muffler the other day it backfired, y'all might have noticed my wanted ad for a new muffler. At my wits end! about to just order points and condensor and see if that does anything, of course that will take a week to get parts!
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  #2  
Old August 12th, 2017, 11:57 PM
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Rob Wollschlager
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Sounds like a points adjustment/timing issue. How is the shaft in your distributor, any wobble? Are the contacts in your distributor cap worn unevenly?
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  #3  
Old August 13th, 2017, 07:41 AM
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Abraham Bell
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Quote:
Originally Posted by BMGmotors View Post
Truck starts missing upon acceleration. Idles fairly good but misses sporadicly when I give it gas driving down the road, seems like an electrical issue. Referenced green workshop manual electrical wiring diagram and checked everything out from the battery back, nothing obviously suspicious looking. Blew a hole in my muffler the other day it backfired, y'all might have noticed my wanted ad for a new muffler. At my wits end! about to just order points and condensor and see if that does anything, of course that will take a week to get parts!
I would skip the points and get an electronic ignition system like pertronixs. Regardless if that's the problem or not. If I recall correctly , even if your distributor shaft has wobble the pertronixs system will keep firing.
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  #4  
Old August 17th, 2017, 10:55 AM
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Peter Shaw
1965 SIIA 88"
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I had this same problem on my 65SIIA, ended up changing the distributor assembly because someone had frankenstined a rover car version into it. I suspect the real problem was with the vacuum advance and points.
Blew the muffler into a taco, and the later backfires would make your ears ring from the megaphone effect.
BTW has anyone tried the 123ignition.nl looks like it would be an excellent upgrade?
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  #5  
Old August 17th, 2017, 01:02 PM
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Robert Davis
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You first need to verify consistent voltage to the coil.
You could have burned contacts in the IG SW.
Then make sure your coil is both good and stock.
If someone installed a hotter coil for HEI, then the voltage is way too much for your points and condenser.
The points will melt and the condenser will fail with a later coil.
Abe's EI suggestion is valid, but only if the rest of your distributor is OK.
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  #6  
Old August 19th, 2017, 10:50 PM
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Baird M. Gehring
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A new set of points and condenser solved it for me! I don't suspect the points were bad as they looked ok but replaced them anyways. New rotor arm wouldn't work even though it looked more like an OE Lucas rotor than what was on there, put my old rotor back on and it fired up! Now I've got to replace the exhaust system cause it sounds baaaaad with a blown muffler!
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