Spark Plugs-Long Story Short - ZR-1 Net Registry Forums

Shrek · 09-30-2018

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.

jss06c6 · 09-30-2018

Good for you!!

Sent from my XT1585 using ZR-1 Net Registry mobile app

XfireZ51 · 09-30-2018

Quote:

Originally Posted by Shrek

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 91-602.
Huge difference and runs smooooooth now.

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

Paul Workman · 10-03-2018

Quote:

Originally Posted by XfireZ51

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

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

.

XfireZ51 · 10-03-2018

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.

Shrek · 10-03-2018

Quote:

Originally Posted by Paul Workman

Shrek: I believe you meant to say AC Delco 41-602s (instead of "91-602")

.

Thanks! Fixed it!!

09-30-2018	#1
Shrek Join Date: Sep 2010 Location: Currituck, NC Posts: 246	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. Last edited by Shrek; 10-29-2018 at 09:16 AM.

09-30-2018	#2
jss06c6 Join Date: Aug 2015 Location: Magnolia, Texas Posts: 884	Re: Spark Plugs-Long Story Short Good for you!! Sent from my XT1585 using ZR-1 Net Registry mobile app

10-03-2018	#5
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,685	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.