2003 Wrangler Sport, 4.0/auto, 3.73 gearing, 22,000 original miles, clean CarFax. known owner and use/service history, off-the-showroom floor stock/no mods
Recently purchased. Hard starting but ran well otherwise. 80 mile drive on Forest Service/County gravel roads and notice I had a CEL. Plugged in my scanner and found logged P0301 fault - Cylinder 1 misfire - still running OK. Some internet research and decided to pull spark plug on #1 cylinder. Tan, normal-appearing plug, no evidence of arcing or spark tracing. A little more research and decided to replace plugs with Champion Dual-Platinum 7034 plugs. Gapped to .035", anti-seize on the threads (none on plug tip) and torqued to spec. Reinstalled coil pack and started engine - started easily but ran really poorly! Stumbling, missing, rough. Pulled codes again; P0300, P0301, P0303, P0304. Cleared codes, pulled and checked plugs, reinstalled and torqued plugs - ran poorly again on start-up. Same codes reappeared. Checked coil pack - front and rear packs were cool to the touch - center pack was HOT!
More research and found a YouTube check for coil pack - basically seeing if there is spark from all plug contacts/springs. to a grounded steel rod. Good spark from 1, 2, 5 and 6. No spark from center pack serving cylinders 3 and 4. Checked continuity between contacts/springs 1/6, 3/5,and 2/5. All read very close to 15.5/15.6. No continuity between any other combination of the contacts/springs > leads me to think secondary circuits are good/not open, and no shorts between coil packs. Don't have/can't find what the resistance readings should be between the four connector contacts at the rear of the coil pack.
I'm thinking the coil pack is bad at this point. I'm suspicious of the timing; CEL > P0301 code > new plugs > more and new error codes > lack of spark. The 'no spark' on #3 and #4 seems to be a good reason for the P0303 and P0304 codes. I know the 4.0 can be sensitive to odd spark plugs, but the 7034 plugs seemed to be on the "OK to use list". Doesn't seem like the wrong plugs would kill the coil pack.
What am I missing?
Recently purchased. Hard starting but ran well otherwise. 80 mile drive on Forest Service/County gravel roads and notice I had a CEL. Plugged in my scanner and found logged P0301 fault - Cylinder 1 misfire - still running OK. Some internet research and decided to pull spark plug on #1 cylinder. Tan, normal-appearing plug, no evidence of arcing or spark tracing. A little more research and decided to replace plugs with Champion Dual-Platinum 7034 plugs. Gapped to .035", anti-seize on the threads (none on plug tip) and torqued to spec. Reinstalled coil pack and started engine - started easily but ran really poorly! Stumbling, missing, rough. Pulled codes again; P0300, P0301, P0303, P0304. Cleared codes, pulled and checked plugs, reinstalled and torqued plugs - ran poorly again on start-up. Same codes reappeared. Checked coil pack - front and rear packs were cool to the touch - center pack was HOT!
More research and found a YouTube check for coil pack - basically seeing if there is spark from all plug contacts/springs. to a grounded steel rod. Good spark from 1, 2, 5 and 6. No spark from center pack serving cylinders 3 and 4. Checked continuity between contacts/springs 1/6, 3/5,and 2/5. All read very close to 15.5/15.6. No continuity between any other combination of the contacts/springs > leads me to think secondary circuits are good/not open, and no shorts between coil packs. Don't have/can't find what the resistance readings should be between the four connector contacts at the rear of the coil pack.
I'm thinking the coil pack is bad at this point. I'm suspicious of the timing; CEL > P0301 code > new plugs > more and new error codes > lack of spark. The 'no spark' on #3 and #4 seems to be a good reason for the P0303 and P0304 codes. I know the 4.0 can be sensitive to odd spark plugs, but the 7034 plugs seemed to be on the "OK to use list". Doesn't seem like the wrong plugs would kill the coil pack.
What am I missing?
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