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Twin Plug Engine Running on Lower Plugs Only
Per the title what would you expect? Start and idle well? Drive normally enough under light load? Are the top plugs primary and the bottom ones secondary or are they the same as each other just opposite sides of the piston crown?
Reason I ask is my engine will start and idle happily on the top set only but on the bottom set only it won't start and while on the starter it coughs and bangs and isn't happy. So we're concerned it has a firing order / spark timing issue on the lower coils / plugs. It's on throttles, EFI, and COP so I'm just pulling relays to disable upper or lower. Appreciate your thoughts and feedback. 
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05-08-2019, 02:51 PM
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Both plugs fire at the same time, so they are equal. You might want to check/replace your coils. Also check to see that the secondary distributor/drive belt is functioning.
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05-09-2019, 02:45 AM
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Join Date: Feb 2005
Location: Jupiter, FL
Posts: 306
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Is that an AEM EPM on your distributor? Can't tell by the photo. If so one signal is being used for both top and bottom COP's.
I would check that the wiring is not mixed up to the bottom COP's. Maybe install one lower COP at a time and try re-start to narrow down which ones are crossed. You could also check electrical continuity at the COP connector. The ECU signal wire should be the same top and bottom. T1 to B1, etc.
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Track: 91 C2 SuperCup wannabe, 08 Cayman S Street: 85 RUF BTR Slant-nose, 70 911 T Coupe Pastel Blue Projects: 82 911 SC 3.6, 72 911 T Coupe, 74 914 Signal Orange |
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05-19-2019, 10:36 AM
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You are exactly right on all counts. I had bottom coil 1 and 3 mixed up and bottom 4 and 6 mixed up. Worked it out checking continuity. Supposedly fixed now and when I get the car back I’ll pull the top coil relay and expect to see it running well on the bottom coils. Cheers.
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05-19-2019, 02:58 PM
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1990 Porsche 964 Carrera 4 3.6 liter
