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Had a misfire in 2nd to 5th gears as soon as I hit 1.4-1.5 Bar of boost. Tested TPS as per Clark’s. Ok. I read some posts that it was plugs. This is what I discover. Plugs are gapped at 0.035 and corrosion in #1 & #2 connectors at the plug. Was running BPR7ES. Replaced with BPR6ES gapped to 0.028” Cleaned up connectors. Misfire is gone. Plugs may have been OK but the ignition system was probably too weak for the 7’s at 35 thou.
New wires on the way. Distributor and rotor look fine.
What do do you all recommend for wires? I had 7mm Bosch Premium on now. The connection to the plug is pretty sketchy as the little clip in there gets pretty mangled when trying to install. Maybe I’m doing it wrong?
If you run higher than15psi boost, you may want to run the BPR7ES as they are 1 heat range colder than the BPR6ES.
The problem was with the plugs gap, 0.035 is too large. A tighter gap 0.028 with the stock ignition system works better. If running high boost, you may need to narrow the gap 0.025 or tighter if needed.
I'm a big fan of the Clewett wires. I run the BPR7ES at .026 gap at 20psi with no issues (although I also use an MSD6 ignition box and their 8253 coil). The bigger the gap, the fewer miles I get out of plugs before they start misfiring.
I'm a big fan of the Clewett wires. I run the BPR7ES at .026 gap at 20psi with no issues (although I also use an MSD6 ignition box and their 8253 coil). The bigger the gap, the fewer miles I get out of plugs before they start misfiring.
Interesting, I thought that with a MSD box you could run bigger plug gaps, which are actually desirable given the short-duration spark of that style of CD ignition.
I think the fact that Bosch and NGK heat range ratings numbers are of an opposite scale (Bosch: lower number=colder, NGK, higher number=colder) causes some confusion.
I also changed to the BPR7ES when I went larger turbo/fuel injectiors and VEMS just to be on the safe side.
Interesting, I thought that with a MSD box you could run bigger plug gaps, which are actually desirable given the short-duration spark of that style of CD ignition.
I think the fact that Bosch and NGK heat range ratings numbers are of an opposite scale (Bosch: lower number=colder, NGK, higher number=colder) causes some confusion.
I also changed to the BPR7ES when I went larger turbo/fuel injectiors and VEMS just to be on the safe side.
Well, I'm a sample size of 1, so not dispositive of the issue, but I've noticed a pretty consistent pattern. (I also run E85 and water/meth injection, so lots of variables in play...)
I always change the plugs for smog tests, so haven't had the same set of plugs in the car for more than 2 years in a very long time. If I open the gap up to say .03", I don't get the full 2 years out of the plugs before they start misfiring, but at .026 they run great for the full two years. I can't tell the difference in gap from the driver seat, so I now just stick with .026 to .028. I used to run WR-6DC plugs, but the car just seems happier to start and smoother to drive on the BPR7ES plugs, though maybe that's all in my head -- hard to validate. It seems like the BPR7ES is about half way between the WR6-DC and the WR7-DC....
06-15-2019, 01:51 PM
Misfire at 1.5 Bar (Solved. For now)
I run the BPR7ES at .026 gap at 20psi with no issues (although I also use an MSD6 ignition box and their 8253 coil). The bigger the gap, the fewer miles I get out of plugs before they start misfiring.
