Spark Plugs-Long Story Short
 

Wife's 91 with 47K miles on it.
Been driving years with a slight misfire.
Got progressively worse over the last few months.
Owned it since 2002 and never had the plugs out.
***Odd discovery*** (4) FR2LS left side (4) FR3LS right side
Replaced with AC Delco 41-602.
Huge difference and runs smooooooth now.:dancing

Re: Spark Plugs-Long Story Short
 

Good for you!!

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Re: Spark Plugs-Long Story Short
 

Honestly, I can understand the difference in heat range for the two sides

Re: Spark Plugs-Long Story Short
 

:confused: I "get it" too, but beg to know: is it the dissimilarity is a "fix" to some anomaly - perhaps with the O2s?? (See left/right comparison below)


Shrek: I believe you meant to say AC Delco 41-602s (instead of "91-602") But, you're right: Pete recommended the 41-602s and I love 'em.

AC Delco 41-602s

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Re: Spark Plugs-Long Story Short
 

IIRC, the FR3s are “hotter”, which would make sense since the right side (passenger) seems to run richer than the left, particularly at lower rpm. The disparity between Right and left bank BLMs gets smaller as u climb up the rpm scale. “Split BLMs” aren’t just an LT-5 issue. The ECM is modifying fueling based on an “average” since there is only one VE table for both banks.
My thought would be to run the fuel supply feed in parallel to each of the fuel rails rather than in series. I suspect that u would find that fuel pressure is slightly lower on the left side than the right. The Xfire was like that and they came from the factory w a larger injector on the left side of the motor to offset the lower FP.

Re: Spark Plugs-Long Story Short
 

Thanks! Fixed it!! :cheers: