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78 Posts
Hi,
I like to think I'm pretty good with engines, but this one has me scratching my head. This is an 09 V sedan. Mild mods. Just recently, Dash Boss started reporting that the engine was knocking under VERY light throttle. Not at WOT ... just at very light throttle ... enough to keep a steady speed and just cruising at 30 mph (and other slower or faster speeds). So more scanning and found that cyl 5 is misfire continuously. So I pulled the plug and it looked fine except it was dirty black and fouled looking ...
1. Put a new gapped plug in. Same problem on 5.
2. Swapped coils with another cylinder. Same problem on 5.
3. Swapped injectors with another cylinder. Same problem on 5.
4. Performed injector balance test from Tech 2 ... injector performed perfectly.
5. Pulled plug, reconnected it to the coil, set it on metal and turned the motor ... nice big heavy visible spark.
6. Pulled valve cover and turned the motor ... valves fully actuate up and down.
7. Pulled and Inspected rocker arms, push rods, and valve springs. No issues found.
8. Ran a compression test ... 150 psi in 4 valve cycles.
9. Ran a leak down test. Held 100% of the pressure ... no loss.
Everything I've checked seems to be perfect, but yet cyl 5 continuously misfires on every firing cycle.
Anyone see this kinda thing before with everything checking out like it does?
Any suggestions??
Bill
I like to think I'm pretty good with engines, but this one has me scratching my head. This is an 09 V sedan. Mild mods. Just recently, Dash Boss started reporting that the engine was knocking under VERY light throttle. Not at WOT ... just at very light throttle ... enough to keep a steady speed and just cruising at 30 mph (and other slower or faster speeds). So more scanning and found that cyl 5 is misfire continuously. So I pulled the plug and it looked fine except it was dirty black and fouled looking ...
1. Put a new gapped plug in. Same problem on 5.
2. Swapped coils with another cylinder. Same problem on 5.
3. Swapped injectors with another cylinder. Same problem on 5.
4. Performed injector balance test from Tech 2 ... injector performed perfectly.
5. Pulled plug, reconnected it to the coil, set it on metal and turned the motor ... nice big heavy visible spark.
6. Pulled valve cover and turned the motor ... valves fully actuate up and down.
7. Pulled and Inspected rocker arms, push rods, and valve springs. No issues found.
8. Ran a compression test ... 150 psi in 4 valve cycles.
9. Ran a leak down test. Held 100% of the pressure ... no loss.
Everything I've checked seems to be perfect, but yet cyl 5 continuously misfires on every firing cycle.
Anyone see this kinda thing before with everything checking out like it does?
Any suggestions??
Bill