This is long, so please bear with me. I've included a wide variety of info that might be relevant to point me in a direction. I'm pretty mechanically competent, or I can at least eventually fix most issues.
I'm trying to chase an intermittent misfire/rough idle. To be clear, this is an intermittent problem that does not always present itself, and it does not occur within a certain unique window of conditions. It is not p0300, random misfire. There's a lot here, because I can't find a common symptom to point me in any direction of a faulty part.
Background - 2008 FX35 195k miles, daily driven. We've owned the vehicle from 79k, Zero mods. Occasionally in cold weather over the years the car would need an additional attempt or two to start. Cranks strong but won't catch. I've assumed it's the AC amplifier, but as it's never stranded us we've driven around it. Spark plugs changed about 9 months ago (NGK LFR5AIX-11), along with maf sensor and TB getting cleaned, all for the probably the vehicle's first time in life. I was chasing a high idle and wanted to improve fuel mileage. Worth noting there was no oil in any of the plugs where there shouldn't be. After the pedal dance, an air idle flow code came up, but eventually resolved itself after regular use. Idle lowered, but still a little high (~950rpm).
We coincidentally took the FX out of daily driver duty in July. After a week or so, I drove it to work. When leaving for lunch, there was a very evident misfire. Code was p0305, cylinder 5 misfire. A few on/off cycles didn't resolve the issue, as some of the rougher idle starts (cold weather starting trouble related) have fixed before. Think parking for lunch, and coming out 5 minutes later. No change during hot restarts that day. I had the car towed home. Tow truck driver, a self professed Nissan guy, said coil pack after starting it and feeling the idle. It's a pretty easy thing to say and sound smart, but also relatively cheap for a single cylinder.
With the spark plugs relatively new, I replaced the coil pack (Hitachi) on #5 and cleared the code. Immediate test in the garage was successful. Started smooth and idled up to temp. Idle was also down to 675rpm.
Next morning, before I got out of the neighborhood, misfire was back. No code. Drove home, and the misfire was gone. Within about 60 seconds. Smooth idle. Drove on to work. On the way home the start was a little rough, but drove home fine. As a precaution, I replaced the cylinder 5 spark plug and car battery. The battery was at least a few years old, and I wanted that out of the equation knowing the FX would only be driven once every few days as I worked to fix the misfire. Also threw some b12 chemtool in the fuel tank. (Maybe a stuckish injector?)
Drove to work just fine the next day, decent fuel mileage. On the way home, moments after leaving the parking lot, bad misfire was back. Code this time, but cylinder 6 now. With a basic code reader I watched the fuel trims. Short term fuel trim bank 2 was a little wacky. Pulled over, cleared the code and restarted. Drove home fine. STFT was mostly ok, nothing over 10% long term.
Thinking that an immediate successive coil pack failure on the opposite bank was unlikley, I figured there was an issue affecting both banks. Vacuum leak? Smoke test revealed no vacuum leak.
I started in the garage to try to watch the fuel trims. Bank 2 definitely has some issues. Rough start but no code. Bank 2 stft was quite high, over 20% briefly. Once it hit a certain temp the trims flipped to -8%. I wasn't watching that line so don't know what that temp was. Maybe 135/140? Definitely not full operating temp. I feel like that points to some vacuum leak, but I couldn't get smoke to come out anywhere.
So now, I'm not positive what to test. I don't want to replace ever single part blindly trying to chase I problem that I can't define. Most of my searching leads to p0300, random misfires and a vacuum leak with some other issue seemingly quite unrelated to my issues. Or I've encountered something that strikes out that particular culprit.
Here's what I'm thinking next steps should be:
- Test O2 sensors? The wild swing in fueling for bank 2 is concerning.
- Verify all bank 2 coil packs are getting proper signal? Not sure how to do that. Basically to highlight a wiring harness issue
- Send out injectors for cleaning? The car is really just waiting to be sold until this is fixed, it's not relied on in any way. This feels a bit shot in the dark through and potential wasteful spending.
- Swapping coil packs around doesn't feel like a good use of time as the misfire has never felt like it occurs with any regularity. Maybe I could swap 6 with another on that side? Unplugging one at a time while running doesn't seem worthwhile. The engine will eventually idle smoothly, so there won't be any issue to isolate during such activity. It'll only create problems during a time when everything is working properly.
- PCV? I know it's old in mileage and age, but I don't have anything pointing me there. Just spitballing consumables.
- Accept my smoke test was inconclusive, take car to shop. Pay too much for a fix that didn't have any evidence but was whatever the tech wanted to do. Drive home and develop misfire.
- Clean intake manifold? Seems pretty labor intensive without a direct smoking gun.
Any ideas at all?
Thanks!
I'm trying to chase an intermittent misfire/rough idle. To be clear, this is an intermittent problem that does not always present itself, and it does not occur within a certain unique window of conditions. It is not p0300, random misfire. There's a lot here, because I can't find a common symptom to point me in any direction of a faulty part.
Background - 2008 FX35 195k miles, daily driven. We've owned the vehicle from 79k, Zero mods. Occasionally in cold weather over the years the car would need an additional attempt or two to start. Cranks strong but won't catch. I've assumed it's the AC amplifier, but as it's never stranded us we've driven around it. Spark plugs changed about 9 months ago (NGK LFR5AIX-11), along with maf sensor and TB getting cleaned, all for the probably the vehicle's first time in life. I was chasing a high idle and wanted to improve fuel mileage. Worth noting there was no oil in any of the plugs where there shouldn't be. After the pedal dance, an air idle flow code came up, but eventually resolved itself after regular use. Idle lowered, but still a little high (~950rpm).
We coincidentally took the FX out of daily driver duty in July. After a week or so, I drove it to work. When leaving for lunch, there was a very evident misfire. Code was p0305, cylinder 5 misfire. A few on/off cycles didn't resolve the issue, as some of the rougher idle starts (cold weather starting trouble related) have fixed before. Think parking for lunch, and coming out 5 minutes later. No change during hot restarts that day. I had the car towed home. Tow truck driver, a self professed Nissan guy, said coil pack after starting it and feeling the idle. It's a pretty easy thing to say and sound smart, but also relatively cheap for a single cylinder.
With the spark plugs relatively new, I replaced the coil pack (Hitachi) on #5 and cleared the code. Immediate test in the garage was successful. Started smooth and idled up to temp. Idle was also down to 675rpm.
Next morning, before I got out of the neighborhood, misfire was back. No code. Drove home, and the misfire was gone. Within about 60 seconds. Smooth idle. Drove on to work. On the way home the start was a little rough, but drove home fine. As a precaution, I replaced the cylinder 5 spark plug and car battery. The battery was at least a few years old, and I wanted that out of the equation knowing the FX would only be driven once every few days as I worked to fix the misfire. Also threw some b12 chemtool in the fuel tank. (Maybe a stuckish injector?)
Drove to work just fine the next day, decent fuel mileage. On the way home, moments after leaving the parking lot, bad misfire was back. Code this time, but cylinder 6 now. With a basic code reader I watched the fuel trims. Short term fuel trim bank 2 was a little wacky. Pulled over, cleared the code and restarted. Drove home fine. STFT was mostly ok, nothing over 10% long term.
Thinking that an immediate successive coil pack failure on the opposite bank was unlikley, I figured there was an issue affecting both banks. Vacuum leak? Smoke test revealed no vacuum leak.
I started in the garage to try to watch the fuel trims. Bank 2 definitely has some issues. Rough start but no code. Bank 2 stft was quite high, over 20% briefly. Once it hit a certain temp the trims flipped to -8%. I wasn't watching that line so don't know what that temp was. Maybe 135/140? Definitely not full operating temp. I feel like that points to some vacuum leak, but I couldn't get smoke to come out anywhere.
So now, I'm not positive what to test. I don't want to replace ever single part blindly trying to chase I problem that I can't define. Most of my searching leads to p0300, random misfires and a vacuum leak with some other issue seemingly quite unrelated to my issues. Or I've encountered something that strikes out that particular culprit.
Here's what I'm thinking next steps should be:
- Test O2 sensors? The wild swing in fueling for bank 2 is concerning.
- Verify all bank 2 coil packs are getting proper signal? Not sure how to do that. Basically to highlight a wiring harness issue
- Send out injectors for cleaning? The car is really just waiting to be sold until this is fixed, it's not relied on in any way. This feels a bit shot in the dark through and potential wasteful spending.
- Swapping coil packs around doesn't feel like a good use of time as the misfire has never felt like it occurs with any regularity. Maybe I could swap 6 with another on that side? Unplugging one at a time while running doesn't seem worthwhile. The engine will eventually idle smoothly, so there won't be any issue to isolate during such activity. It'll only create problems during a time when everything is working properly.
- PCV? I know it's old in mileage and age, but I don't have anything pointing me there. Just spitballing consumables.
- Accept my smoke test was inconclusive, take car to shop. Pay too much for a fix that didn't have any evidence but was whatever the tech wanted to do. Drive home and develop misfire.
- Clean intake manifold? Seems pretty labor intensive without a direct smoking gun.
Any ideas at all?
Thanks!
