Misfire on 2015 STS - need new plug wires? Ideas?

[VStarRider]

Hi everyone,

I have noticed an occasional misfire on my '15 STS SM5, just shy of 13k miles.

Typically, it happens after decelerating, then re-applying throttle, such as slowing down for a turn, then accelerating up to speed. Today, it did it once while downshifting for a turn. It will occasionally misfire at idle at a stoplight, for example.

No check engine light.

A quick search on this site indicates bad plug wires as a likely culprit. Anything else?

How difficult is it to install new plug wires?

[BajaRon]

It could be other than the spark plug wires. Though they are a worthy suspect. Are you sure you're not getting detonation of unburned fuel in the exhaust system? The throttle body vacuum hoses are also notorious little buggers. The thing is. You'll need to pull the air box to get those changed. And once you are that deep. An ignition wire and plug kit are probably in your best interest. Even if they are not the current offenders.

Also check you PCV valve. A less common, but possible player. That can be done without removing much at all.

Good luck!

[germanspyderrider]

to change plug wires is a bad job, but not difficult.

[VStarRider]

It could be other than the spark plug wires. Though they are a worthy suspect. Are you sure you're not getting detonation of unburned fuel in the exhaust system? The throttle body vacuum hoses are also notorious little buggers. The thing is. You'll need to pull the air box to get those changed. And once you are that deep. An ignition wire and plug kit are probably in your best interest. Even if they are not the current offenders.

Also check you PCV valve. A less common, but possible player. That can be done without removing much at all.

Good luck!

Thanks. How would I tell if it is detonation in the exhaust vs a misfire?

Based on my experience, it feels like a misfire - applying throttle, it get a quick jerk through the drivetrain when it allegedly misfires.

[BajaRon]

Thanks. How would I tell if it is detonation in the exhaust vs a misfire?

Based on my experience, it feels like a misfire - applying throttle, it get a quick jerk through the drivetrain when it allegedly misfires.

The difference is fairly obvious. Sounds like you have a misfire and not exhaust detonation.

[VStarRider]

What’s the labor rate for this site? Since posting this, I have not had a misfire.

[BajaRon]

Could have been a fouled plug. Do not lug the 998. It doesn't like it. Keep the RPM above 3,500 after a shift and try to run 5,500 or above most of the time. The 998 likes to rev. It really doesn't even start making HP until 5,500 RPM.

Did you run some good injector cleaner through the system? If not, I would recommend it.

[VStarRider]

Could have been a fouled plug. Do not lug the 998. It doesn't like it. Keep the RPM above 3,500 after a shift and try to run 5,500 or above most of the time. The 998 likes to rev. It really doesn't even start making HP until 5,500 RPM.

Did you run some good injector cleaner through the system? If not, I would recommend it.

I will do that. I run 90-93 octane in it and average speed on the trip odometers is always 40-45 mph. I run a majority of time at 60+ mph / 4400+ rpm. I shift between 3500-5000 most of the time (manual shift).