so i'm having ignition issues, a few weeks ago i was getting a bad missfire, and i was pretty sure it was an opti because i had caught a puddle while driving and i know it got wet. i put a new lifetime warranty opti in it from chandler motorsports and it was better but still had a miss. i did some more checking and decided to put a set of plugs in it, plugs that were in it were TR55's, had about 20-25K on them so i figured that isnt unreasonable to need new ones, when i pulled them they were all around 55-58 thousandths gap so a bit wide. i put new TR55's in gapped between 46-48 thousandths. car ran great. when i put the opti in i also replaced the water pump, since replacing the water pump the car seems to run slightly warmer. it has a 165 stat in it and never used to get over maybe 170-175 tops even on a hot day in a traffic jam, now on hot days or when running the a/c or stuck in traffic it will get to 180-185. i have blead it and i'm not getting any more air out so i dont understand why its running hotter, but now any time it gets over about 170-175 degrees it develpoes a missfire between 2,000 and 3,000 rpm. you can hear it dropping and picking back up cylinders, at idle its fine and above 3,000 its fine. and when its below about 170 its fine. so i thought maybe the module was going bad, i put a new module in it with new dialectric grease of course, and also for grins i put an MSD coil in it too. i figured it couldnt hurt as long as im in there. the car already has MSD 8.5 wires with OTVC setup and the wires all look good, but even after the new module, coil, plugs, and opti i'm still fighting this miss that only happens between about 2,000 and 3,000 rpms and only when the car is about 175 degrees or warmer. my head is getting sore from beating it against the wall here guys, any ideas or suggestions would be greatly appreciated!!!

 

Do you have any mods done to the car? Has it ever been tuned?

 

yea the car is modded, 355ci, cam, injectors, LT's TD's no cats ect. it is tuned.

 

any ideas guys? the only two things i can think of are maybe my 5 and 7 plug wires are too close and cross firing, which to me doesn't make sense with it only happening when warm, and also they are good MSD wires and are not very old, plus i routed them the same after the opti install as they were before and it didn't do this before the opti install. the only other thing i can think of is that i got a bad opti out of the box. the car never did this before i replaced the opti, i replaced the opti and plugs because it had a dead miss all the time. this miss thats affected by temp and rpm didn't start until after the opti and plugs were done.

 

what kind of compression you have if its over 11:1 i would go with a ngk t6 i had the same problem with my new motor it just was looking for the right heat range and the ngk t6 at about .35 - .40 work and fixed my problem. Or i hear the autolites104 are good as well some one will chime in and say something

 

Check the resistance of each plug wire. They may look good on the outside but you may have a bad one. My #8 wire went bad and caused a miss and also caused the #8 primary to burn extremely hot. They were MSD wires and had less than 4K miles.

 

the engine i believe is almost right at 11:1. i don't think it would be the wrong plug because i drove the car for about 15-20000 miles with those same plugs in it with no issues when i bought the car. i will test the resistance of the wires then to make sure they are all okay. is there a certain resistance they should be under or should i just be looking for one that is much higher then the rest?

 

You might be able to contact MSD and see what the expected resistance is but yeah, just look for one that reads higher or stands out from the others.

 

alright, yea i would assume it would be a spec like x ohms per foot or less is acceptable. i will just test all of them and see if any stand out from the rest first. after doing some more thinking i did think of one other thing. i don't think this would cause an intermittent problem like i have, i think it would be all the time, and i don't think it would be affected by heat, but when i replaced the opti i did notice just a little bit of corrosion in the end of the extension harness that plugs into the optical sensor, but i used electrical cleaner and cleaned it thoroughly before reinstalling it so i think it should be okay.