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Old 02-25-2013, 09:45 AM   #1
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Default Major misfire

Lately my 98 bonneville has had a misfire problem. When it is humid or raining it had trouble accelerating, completely random misfire, never threw a CEL, would go away above 3000rpm. Then it went to constant misfire. Replaced all 3 coils and ICM. Worked fine for a week then started doing it again. Grabbed a spark tester and found the 3/6 coild was weak, so grabbed my old 3/6 and put it in and solved the problem. 2 weeks later, back in the same position. CEL flashes when runing at all rpms, have a feeling its a coil again No vacccum leaks, plugs and wires are 6 months old, 172k miles. When it runs good, its perfect.
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Old 02-25-2013, 09:47 AM   #2
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Also exhaust smells phosphorus
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Old 02-25-2013, 10:58 AM   #3
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sounds like you put poor quality parts in if the new coils are bad. what did you use for plugs/wires/coils/icm? your profile says l36 they dont like to run on anything but platinum plugs and high quality wires.
you try squirting things with a spray bottle to see if it arcs?
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Old 02-25-2013, 11:34 AM   #4
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The funny exhaust smell is indicating you are not burning all over your fuel. I suggest replacing all of your plugs and plug wires with high quality parts as Justin mentioned.
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Old 02-25-2013, 11:43 AM   #5
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Plugs are platinums and wires are napa premium 8mm. Pulled it into our school shop and checked codes. #3 misfire, evap and sensor 1 bank 1 o2 heater. Found it was arching at the coil post butwe didnthave any dieelectric grease.
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Old 02-25-2013, 11:49 AM   #6
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Having this issue when it is humid or raining is a sure sign a wire or spark plug insulator has a crack in it. With the extra humidy in the air something is sparking to ground instead of firing a plug. You may be able to duplicate it by spraying a mist of water in various parts of the engine bay at night with no lights and with the engine running at higher RPM'* than idle (2,000 RPM?). If you see flashes of blue light you found the problem.

You can also help narrow down the problem by getting the car scanned for diagnostic trouble codes. Autozone will do it for free. The codes may tell you which cylinder is misfiring.

What plugs/wires/coils are you using?
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Old 02-25-2013, 11:51 AM   #7
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Oops, posted before you responded.

If you are sparking between the coils posts you likely have a cracked coil. Dielectric grease may help, but that is not the problem.
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Old 02-25-2013, 01:54 PM   #8
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i agree dielectric grease isnt an insulator. the wires and coils have to hold the HV from going to ground
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Old 02-25-2013, 03:36 PM   #9
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Reasinim goung to try it is because I cannot see a crack on either the coil or the wire. Ill also check the plug because thatshould be the optimal ground in the first place. Should I also check the ICM'* ground?
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Old 02-25-2013, 04:56 PM   #10
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If it is arcing at the coil post, the coil is cracked. The crack can be very fine, to the point where you can't see it. Usually there will be a very fine carbon trace line along the crack. Look for the carbon trace line.
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