Hi Richie, I wish GM never published that coilpak resistance value range for indication of OK - good to go. As Chuck noted, coilpak & ign module can behave differently when hot and can certainly behave differently under load. Also, odd spark conditions exhibit if there is something amiss with the charging system (battery & alternator) whereas system voltage is less. bench testing known good coilpaks and ign modules at 12.6 VDC using just a battery and Casper's tester would have you believe all coilpaks were defective. However, adding a charger to raise the voltage to 14.1 VDC, the coilpaks all tested perfectly.
I covered this scenario in this thread:
help interpreting electric arc variations using Casper's C3I to test coilpaks & ignition modules
that Casper's tester is invaluable. John has it currently on sale for 11 more days...maybe something nice to add to your toolbox. it's the only way to test these things.
CCCI Ignition Simulator
On the coilpak, cylinders 3 and 6 are together. it's a waste-spark system. but you noted that #3, like the others looked fine. only #6 was running rich or was fouled. so that should eliminate any issues with the coilpak & ign module.
Years ago, Mr. Clark flowed intake manifolds.
interesting numbers
for the hot air's, on a stock intake, it was #4 that flowed 14 - 19 percent less than the others. #6 flowed the same as #2; and were +- 4cfm to #1, #3 and #5. So I don't think it's an air volume (or lack thereof) causing #6 rich fouling.
a compression test is OK but a leak down test would tell more. these folks already covered it...
Compression test PSI
Help with compression test #’s and spark plug reading
if you don't like the harborfreight leak down tester, there are plenty of others on Summit, Amazon, etc. I use the total seal version.
You may find after all this diagnosing and testing that #6 just runs that way. And the suggestions from Jerryl and Earl and Chuck are your key.
I pulled all of my 1K mile spark plugs ( AC R45TSX's ) . All look pretty good white / light tan , Except for # 6 . its slightly flack , black soot. I ordered NGK 6630 UR4's , per Earl Brown's reccomendations. Any way , I'll do a compression check , but I'm pretty sure that it's gonna be Ok? I did notice what I think is a " weak " Spark at & 6 . Coil pak resistance , At he towers , is within spec. ? I've read that does not mean much because that could change under load ?
, but I always follow what I read from you guys.
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