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Old 04-25-2015, 01:21 PM   #1
henrymartin OP
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Question Any Nissan techs? Xterra puzzle

I have an 05 Xterra manual with 110k on the clock. About a week ago, the car threw a code - random misfire. I checked the oil, and it was a tad over, which could have dirtied up the MAF. Drain the excess oil, cleaned the MAF, and rode. Threw another code - a/f sensor 1, bank 2. With a 3 hr trip to the airport, there was no time to fix it, so we drove. Car misfired along the way a few times, especially under load.

Returned yesterday, drove 3 hrs back from the airport, and the SES light did not flash once.

Hooked up to a scanner, code p0300 - random misfire. No pending codes.

Changed the plugs with OEM plugs, thinking that was it (at the mileage). Car started fine, but ran more rough with odd idle (500-1500rpm), no codes. When it gets above 2500rpm, the SES will flash, but no code, plus it will go blank after the rpms drop to idle.

Pushed the truck a bit, code came up - 0300 again. All plugs and coils are solid, and engine speed drops when unplugging cylinders one by one.

Hearing a hiss, as if a vacuum leak, but spraying carb cleaner everywhere does not change rpms at all, so stumped where the leak could be. Alldata says to look at PVC valve first, but that is working and not stuck. All butterflies operate correctly, it seems, as is the spiral valve. No loose hoses, no knock sensor codes....

I'm at a loss for ideas.
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Old 04-25-2015, 01:25 PM   #2
JakeOfDaytona
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IAC? I had alot of those symptoms on my ram, especially the hissing and rough idle. IAC turned out to be sticking. Easy $12 fix. Hopefully yours turns out to be as well
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Old 04-25-2015, 07:08 PM   #3
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Originally Posted by JakeOfDaytona View Post
IAC? I had alot of those symptoms on my ram, especially the hissing and rough idle. IAC turned out to be sticking. Easy $12 fix. Hopefully yours turns out to be as well
Thanks. The IAC is a little dirty, but I doubt that is what it is. I'll clean it. I'll be taking the plenum off tomorrow and replacing the PCV Valve. Damn, I just mastered replacing spark plugs without removing the plenum and now I have to take it off anyway.
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Old 04-25-2015, 07:48 PM   #4
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That truck doesn't have an IAC. It is drive by wire.
Crank and cam position sensors are things I would strongly suggest you research.
Stock air cleaner housing or a "cold air" aftermarket thing?
Check the intake hose from the MAF to the engine very carefully. Any cracks or splits will cause problems.

That's about all I can think of at the moment. Still leaning toward the crank/cam sensors.
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Old 04-26-2015, 06:11 AM   #5
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Originally Posted by broncobowsher View Post
That truck doesn't have an IAC. It is drive by wire.
Crank and cam position sensors are things I would strongly suggest you research.
Stock air cleaner housing or a "cold air" aftermarket thing?
Check the intake hose from the MAF to the engine very carefully. Any cracks or splits will cause problems.

That's about all I can think of at the moment. Still leaning toward the crank/cam sensors.
I know. The throttle plate is dirty a bit, so that is what I meant by cleaning. It never threw a code for crank sensor, but the plugs were worn. I am taking the plenum off this morning and checking the pcv valve. The rubber between maf and throttle had small cracks which I fixed temporarily. Nissan does not have that piece available until mid week.

The hissing sound is what droves me crazy as I cannot find the source. I will also check the valve covers for any cracks.
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Old 04-26-2015, 03:54 PM   #6
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Cleaned the MAF again with MAF cleaner, replaced the rubber connectors to eliminate the option of an intake leak. The PCV valve was dirty and not closing - replaced with new one. Took the upper plenum off, inspected gasket, plug boots, coils. Checked all hoses and connections for leak. Nothing. With truck running, sprayed crab cleaner all over to check for any leaks, but nothing again. Still getting p0300 random misfire whenever under load. At neutral, I can rev it up 5k without the MIL flashing. Under load, at 2k rpm it starts flashing. No other codes. Starts fine and fast.

No excess pressure in crank either, and no noticeable oil consumption.

111000 on the clock, stock air intake, cats replaced about 20k ago.
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Old 04-26-2015, 04:49 PM   #7
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Originally Posted by henrymartin View Post
The hissing sound is what droves me crazy as I cannot find the source.

That says plugged cat to me.
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Old 04-26-2015, 05:54 PM   #8
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That says plugged cat to me.
It sounds more like a vacuum leak, and it is the most audible near the upper plenum on the passenger side. But spraying carb cleaner did not change rpms at all. We tried pinching and unplugging the various hoses, and the sound did not change at all.

Cats were replaced at 80 something thousand miles at a dealership (with oem)

I replaced the rst of the exhaust last fall. Had I not dumped a lot of new parts to it last year, I wouldn't have worried about it so much. But I replaced exhaust, suspension, front wheel hubs, alternator, fan clutch, idler pulley, belts, trailer harness . . . all within the past twelve months.
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Old 04-26-2015, 08:18 PM   #9
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Originally Posted by henrymartin View Post
It sounds more like a vacuum leak, and it is the most audible near the upper plenum on the passenger side. But spraying carb cleaner did not change rpms at all. We tried pinching and unplugging the various hoses, and the sound did not change at all.
Ahh, ok. There should be a vacuum regulated fuel pressure regulator right in that area. Find it.
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Old 04-27-2015, 06:23 AM   #10
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Reading through all that again...

Fuel pump. Lacks volume at load but has the volume and pressure for idle and light loads. For that generation you have to drop the tank to access it. The FSU is a pump, fuel level gauge (a common failure that will set a check engine light), filter, and regulator all built into one unit. It is not a vacuum referenced fuel pressure regulator, those died out in the early 2000's.

There is no test port for a pressure gauge. You have to use a kit that puts one in line if you want to really test it right.
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Old 04-27-2015, 09:04 AM   #11
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Reading through all that again...

Fuel pump. Lacks volume at load but has the volume and pressure for idle and light loads. For that generation you have to drop the tank to access it. The FSU is a pump, fuel level gauge (a common failure that will set a check engine light), filter, and regulator all built into one unit. It is not a vacuum referenced fuel pressure regulator, those died out in the early 2000's.

There is no test port for a pressure gauge. You have to use a kit that puts one in line if you want to really test it right.
That unit was replaced as part of a recall about four years ago. The MIL flashes only between 2k-4k rpm. Rev it higher and it stops flashing, so I don't think it is fuel pressure.

I'm puzzled because I only get a random misfire code, no other codes.

Anyway, after spending two days bolting and unbolting stuff, having it hooked up to a scanner for countless times, and a mechanic I trust not being able to determine the issue, I set up an appointment at Nissan to have it diagnosed.
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Old 04-27-2015, 12:30 PM   #12
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Let me know what you find. I am interested in what it is.
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Old 04-27-2015, 02:00 PM   #13
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Let me know what you find. I am interested in what it is.
Will do. I'm leaning toward crank sensor, cam sensors, or MAF sensor. But I want to be sure before dumping money into it, as, judging by the new plugs I just installed and checked, it is happening on both sides, so it is not a single cam issue.

Since this started after oil overkill, it could be one of the sensors is dirty but not toast, throwing wrong values without being too far off to throw a code, as the MIL only catches voltage.
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Old 04-27-2015, 02:34 PM   #14
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I would check the EGR valve if it has one. And check out the coil packs real closely. It sounds like a vacuum leak, though.

I had a misfire problem recently that was a bad coil. Which I didn't figure out until I tested & replaced the crank position sensor and fuel pump. (The freaking stupid thing (CPS) required removal of the starter and front engine mount). It tested out of range, but it wasn't the problem. Generally, the CPS is a pretty simple magnetic pick up.

Turned out there was a nice crack in the coil, only found it as I was pulling my hair out, checking everything over. Just a small crack under the coil HT wire, but it had nice carbon build up around it. Dumb on my part, as the coil is a common failure, I even had one in the trunk, just in case.
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Old 04-27-2015, 04:49 PM   #15
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Originally Posted by mjydrafter View Post
I would check the EGR valve if it has one. And check out the coil packs real closely. It sounds like a vacuum leak, though.

I had a misfire problem recently that was a bad coil. Which I didn't figure out until I tested & replaced the crank position sensor and fuel pump. (The freaking stupid thing (CPS) required removal of the starter and front engine mount). It tested out of range, but it wasn't the problem. Generally, the CPS is a pretty simple magnetic pick up.

Turned out there was a nice crack in the coil, only found it as I was pulling my hair out, checking everything over. Just a small crack under the coil HT wire, but it had nice carbon build up around it. Dumb on my part, as the coil is a common failure, I even had one in the trunk, just in case.
Doesn't have an EGR
It is a coil on plug ignition, so no coil packs. A single bad coil will show that cylinder misfire, not random cylinder misfire.
Crankshaft position sensor is real easy to access, remove the passenger tire and the fender liner. Staring you in the face. If you try it top or bottom side it will be a battle.
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