Strange Misfire Issue

[QuasarDecimari]

Hello Everyone! Curious if anyone has a similar experience or advice for this situation I’m having. I’ll give my vehicle details and cut to the chase.
 
2001 Nissan Pathfinder LE
3.5L VQ35DE
196,000+ Miles
Engine Overhaul @ 182,000 Miles
(Timing, head gaskets, plugs, and so on changed)
 
Summary: The engine, whether hot or cold, rough-starts/misfires for a few seconds (first 1000 revolutions), then levels out and runs “fine.”
 
Short Story, for those who don’t like to read:
•Rough Start/Misfire in first 1000 revolutions
•Cold or Hot engine doesn’t affect it
•Very strong fuel smell in exhaust
•Runs perfectly smooth after it levels out
•DTC only showing Cyl. 4 Misfire
 
•Ignition coils
•Spark Plugs NGK Laser Platinum @14,000 miles, gapped to 0.044
•New Fuel Filter
•Changed injector on Cyl. 4
•Compression in range on all 6 cylinders
•Not losing coolant
•Oil smells like gasoline, but isn’t milky
 
 
Slightly more detail:
The issue started within the last 500 miles. I cleaned out and overhauled the engine about 14,000 miles ago, with new head gaskets, studs, seals, and so on, and up until these past couple weeks, it has been running great.
The engine rumbles a little, inconsistently when starting (the issue doesn’t occur every time), but it does start instantly with no problems. Just for the first 10-15 seconds of running, it rumbles and idles rough, then levels out and runs perfectly smooth. There is a slight power bog at higher loads, but this rig is also lifted on 33s.
I waited until the computer would finally throw a code, which showed up after 4 rough starts. The DTC only gave information that Cyl. 4 was misfiring, so I cleared the code to see if it remained consistent. Over time, the light came back, and the code remained the same (P0304), 3 times. I ran a full bottle of seafoam and some premium Shell gas in the tank for good measure, but the issue remained.
Naturally, I pulled off the intake manifolds and started to check for signs of failure.
 
When relieving fuel pressure, the FSM asks that you pull the fuse to the fuel pump and run the engine until it sputters out. When I pulled the fuse and went to run the engine, it attempted to start for a moment, then died instantly (usually it runs for several minutes until it dies off).
 
I decided to change all the coils with new ones, as well as changing the Cyl. 4 injector with a brand-new (NAPA) injector. Looking at the spark plugs, they didn’t show abnormal wear, the gap seemed a little larger than when installed (being now 0.047). Noticeably, however, the plugs were wet with fuel, and smelled really strong like gasoline. No other strange buildup was noticeable on the plugs, so they were reinstalled, but the plug for Cyl. 4 was swapped with Cyl. 2 just or good measure. The engine was then reassembled, and started. I took it to get a full tank of 91 Octane fuel, and it ran fantastic the rest of the day, with no starting issues.
 
24-hours later, the problem returned, and the idle is rather high (900-1000 RPMs in park/neutral). I’m lost as to what the issue could be, but I do have a few ideas.
 
 
 
So, does anyone have any advice or ideas? Seen this problem before? I’ll be happy to answer any questions, or try most any tests I can. In the meantime, I will drive a different vehicle, and leave the battery disconnected in the Pathy in case the computer just needs refreshed.
 
Thanks everyone!
 
 
 

[onespiritbrain]

Does the VG35 have a MAF sensor? If so I’d try to clean it or replace it.

I am a little more curious about a possible intake leak. Not from improper gasket or installation but from a crack in the manifold. Look very closely with a bright light everywhere that you can see near #4.

So you’ve got new plugs, coils, and injectors.. there’s not much left to look at. Check the contacts in each connector.

I wonder about the injector bleeding fuel into #4.. so is the issue intermittent or can you reliably cause the issue over and over? If it’s the latter, see if the issue is less severe following a shorter time with the engine off and more severe following a longer time with the engine off.

[QuasarDecimari]

Does the VG35 have a MAF sensor? If so I’d try to clean it or replace it.

I am a little more curious about a possible intake leak. Not from improper gasket or installation but from a crack in the manifold. Look very closely with a bright light everywhere that you can see near #4.

So you’ve got new plugs, coils, and injectors.. there’s not much left to look at.

Good points, and the MAF is nice and clean, fairly new (I baby the heck out of this engine, most external parts are new).

Someone on the Facebook page for this group actually made a huge point I hadn’t considered, the PCV valve. While it’s also new, looking at all the symptoms of a bad PCV points mostly to this. While it doesn’t explain the loss of fuel pressure, or the exact reason for a single cylinder misfire, I have noticed a small amount of oil around the valve cover gaskets (only 14,000 miles on those too), oil in the spark plug tubes, and weeping around the bottom of the engine. Taking the little filter off the Valve Cover PCV inlet tube (the one connected to the throttle side of the engine), I noticed blowby residue (yellow sludge) in the tube, and the filter was saturated. I wonder if excessive pressure is building in the engine’s crankcase, and it’s not able to let off pressure from blowby, causing the rich fuel smell, and performance lag. Plus, excessive pressure would explain the source of the weeping along the engine.

[Slartibartfast]

My guess is that the #4 injector has a slow fuel leak. When the engine's off, it's leaking fuel from the rail into cylinder 4 (or just its intake runner, if the valve's shut), flooding it and making it misfire when you start it up. Some of the fuel seeps past the rings to contaminate your oil. Because the leak is small, you don't notice it when the engine's running, at least not after the puddled gas has blown out of #4. I don't know the VQ computer too well but I wouldn't be too surprised if the high idle was trying to compensate for something.

 

The mucked up PCV sounds like something to address, but unless the PCV is dripping goo into the runner for #4 or something, I doubt it's causing your misfire.

 

Don't forget to change the oil after fixing the injector (if that does turn out to be the issue). Good luck!

[QuasarDecimari]

So here’s a followup on the issue:

This was a user-induced issue, as I modified the PCV system slightly when changing my intake for a snorkel setup. I put a small breather filter on the PCV breather inlet, instead of reconnecting it to the intake. By doing so, crankcase pressure and gasses caused oil to buildup in that filter until it was barely breathing and clogged. The engine only had one area it could vent crankcase pressure, which was the PCV. With the PCV constantly blasting pressure into the intake manifold, oil could be picked up at that velocity, spitting oil into the intake manifold.
If you look at the lower plenum, before the manifold collector on the VQ, the PCV releases pressure and gasses through a tube right above the intake valves for cylinder 4 and 6. Noticing a small trickle of oil draining into cylinder 4, that would explain a lot. The oil would get into that cylinder and take a moment to burn off when starting the engine, causing the misfire. That would also explain why cylinder 4 was the only culprit.

By fixing the PCV intake so that it is connected to the air intake, as originally designed by Nissan, all the small oil seepage around the engine has stopped, the intake doesn’t have oil in it, and it seems happier altogether. The misfire still persisted after doing this fix, until I changed the spark plug for cylinder 4, which would make sense if it was burning the oil off in that cylinder.

Lesson learned? The PCV system is important and designed the way it is for a reason. Don’t mess with it. If you suddenly have a misfire upon starting, and it points to cylinder 4, check your PCV intake for blockages, and replace the $2 PCV valve. For just a few hours and a couple dollars, it saves a bit of headache.

[QuasarDecimari]

Unfortunately, I have bad news. The issue isn’t gone completely, just seems less drastic. I’m running out of ideas, and slowly getting cornered in the dreaded “Blown Head Gasket” realm.

New spark plugs, new coils, new Injector, PCV system fixed, new fuel filter, new MAF. Just yesterday, I added about half a quart or coolant to the radiator, even though there was plenty in the reservoir. Under the oil cap looks fine, and pulling the dipstick, the oil is nice and clean, no milky substance signs still.

Regardless, that doesn’t mean I’m in the clear. I’m starting to think that the cooling jacket is leaking into cylinder 4 from the head gasket, so when the engine is shut off, the residual pressure in the system depressurizes through the cylinder and the small amount of coolant sits in there until it doesn’t have the force to push any more in. Then, by starting the engine, it has issues in that cylinder until it’s burned off. The 127 PSI of compression in that cylinder trumps the 13 PSI cooling system, making it run perfectly while the engine is in motion...

Does this sound pretty feasible? I’m running out of ideas as to anything else it could be. I’d hate to have to tear it down again after just changing the head gaskets 16,000 miles ago

[onespiritbrain]

Unfortunately, I have bad news. The issue isn’t gone completely, just seems less drastic. I’m running out of ideas, and slowly getting cornered in the dreaded “Blown Head Gasket” realm.

I know the feeling... I sure do hope it’s not a BHG.

Let your engine warm up all the way from cold with the radiator cap off and then have someone rev the engine to 2500 and hold it there while you look for a small stream of bubbles coming up in the radiator filler neck.

I was adding a gallon of coolant every tank of gas before I finally decided it was a BHG. I also put 200psi air pressure into each cylinder(during each cylinders compression stroke) and there were no bubbles in the radiator at all.

Check out this thread: Blown/Seeping Head Gasket?
http://www.nissanpathfinders.net/forum/index.php?/topic/43908-Blown-Seeping-Head-Gasket%3F&share_type=t

[QuasarDecimari]

I know the feeling... I sure do hope it’s not a BHG.

Let your engine warm up all the way from cold with the radiator cap off and then have someone rev the engine to 2500 and hold it there while you look for a small stream of bubbles coming up in the radiator filler neck.

I was adding a gallon of coolant every tank of gas before I finally decided it was a BHG. I also put 200psi air pressure into each cylinder(during each cylinders compression stroke) and there were no bubbles in the radiator at all.

Check out this thread: Blown/Seeping Head Gasket?
http://www.nissanpathfinders.net/forum/index.php?/topic/43908-Blown-Seeping-Head-Gasket%3F&share_type=t

Sounds like a plan. In the recent coolant flush (a bit of a mishap with the freezing temps in Colorado...), I never observed any small bubbles while running. One thing I hate about these engines and cooling system stuff is I have never had luck with running the engine without the radiator cap. It overflows as it warms up very quickly, and even with a very large funnel, it’ll erupt once it hits operating temps. Dunno if that’s normal, but its a PITA.

[onespiritbrain]

Edit: you must be on an incline and a very steep incline reduces eruption.

 

Yeah, if my cooling system isn’t already low then it starts going everywhere when I start the engine and then again when the thermostat opens up. I just let it go all over the place and it’ll eventually calm down. If you park on as steep of an incline as you possibly can then it’ll reduce the eruption a bunch.

 

I didn’t see any bubbles until mine was all the way warmed up and the thermostat had opened. I did have bubbling in the coolant reservoir AFTER I shut off the engine though.

 

I did not have:

-Boiling over

-Uncontrollable overheating(replace missing coolant and all returned to normal)

-White smoke at the tailpipe

-Oil in coolant

-Noticeable coolant in oil

-Misfires

-Noticeably cleaner than the others spark plug

-External coolant leaks from head/block mating areas

-Sweet smell in exhaust

 

I did have:

-Many gallons of unexplainable disappearing coolant

-Bubbling coolant reservoir(only after shutting engine off— then eventually while engine was running also)

-Almost completely clogged radiator

-White film on spring of radiator cap

-Clean #6 piston surface

-Greenish yellow goop on oil cap

-Swollen radiator hoses

 

 

[QuasarDecimari]

So, this continues to get more interesting and frustrating as time goes on. I’ve verified that I don’t have a head gasket problem (whew), but even with the past several starts with misfires, my engine refuses to throw and codes. For some, that’d be a good thing I guess, but to me, especially when I know something is wrong but the computer doesn’t, it bugs me.

So I called in a professional.
A super friendly mechanic from a group I’m in (NORAC) decided to swing by and have a look. He hooked up his diagnostics computer and started probing around. Hiding in the computer were two codes, P1110 and P1135, which are the timing codes for bank 1 and bank 2. They’re both out of range, and as he made an attempt to override the CVVTS and advance/retard timing, nothing happened. Interesting, the timing won’t change at all, even at high RPMs or warmed up, and even more alarming, he sees these codes but my check engine light remains off, and my OBD2 reader says all is well.

So there’s a timing issue. The computer is basically guessing at startup, causing some issues temporarily. Plus, the Long-Term Fuel Trim was at 94%... which means it’s DUMPING fuel, consistently, to run... explains the really rich exhaust smell.

Oh and on top of that, I’ve got a really lazy Upstream Oxygen sensor in Bank 2.



Which again, the check engine light has said nothing about.


He proceeded to disable cylinder 4’s injector, to make it misfire, which made the engine hum a little and upset it, but nothing compared to how it misfires when starting (which shakes the whole engine). His explanation on that is that it certainly isn’t just cylinder 4 misfiring at startup, but the computer is only noticing cylinder 4.

So with all this in mind, I have a bit of probing to do electronically. I’ve got a new oxygen sensor coming in tomorrow, and I decided to buy the two camshaft variable timing sensors as well just because they’re not too expensive and easy to replace.
This has turned into something a bit more alarming, though. I’m happy to not have to worry about a head gasket issue, but it’ll be unfortunate if the computer is going out, or something of the sort. It’s just confusing that no codes are popping up at all... ESPECIALLY considering that she just passed emissions too, with no problems or weird numbers.

So there’s my update dump. Anyone else wanna hop on this adventure?

[zenopathy]

I had similar issues with my 2002 SE. It ended up being the POS; rear crankshaft position sensor (the coincidence of this acronym was astounding considering the problems it gave me). I'm not sure if the symptoms would be identical had it been the front (CKP) crankshaft position sensor, but I was experiencing some of the same issues (i.e. shaking and misfiring while starting, something almost sounded clogged; rough idling, fuel covered spark plugs, strong gas smell.) However, I did begin to have starting issues and at one point I was stuck at the top of a mountain with a fully loaded rig because of it. As for the DTC, I'm not sure if it actually threw out a code as my SES light was on before the problem started, and still is on. (I have not yet reset it). After replacing air/fuel filters, spark plugs, an MAF sensor, etc. I was getting frustrated, so I feel where you're coming from on that front. I wish you the best of luck!

Edited January 31, 2019 by zenopathy

[QuasarDecimari]

I had similar issues with my 2002 SE. It ended up being the POS; rear crankshaft position sensor

This is really good to know! I’ll have to pull down the sensor and take a look at it. I remember it bring covered in fine metal shavings the first time I removed it a while ago.

[QuasarDecimari]

New Update:

 

So I let the pathy sit for a few days while I waited for my sensors to arrive. When the weather was nice and warm, I threw on the 2 camshaft variable timing sensors, and a new crank position sensor (rear one to the flexplate). Fired it up and it started instantly, no problems, not a shake or rumble, and it didn’t seem to have as rich of a fuel smell from the exhaust. I have yet to change the oxygen sensor, but I anticipate doing so this week.

 

I let it cool down for several hours, then started it again for a test drive. No problems starting, no misfire.

 

Started it today to drive to work, no misfire.

 

Parked it at work for a few hours, then went to start it and go to lunch... misfired all over the place again. What the heck.

 

When I started it to go home from work, it didn’t misfire at startup then either...

 

 

I’ve started to see a trend. Every drive I have done, it makes it to operating temperatures for a good amount of time, but it seems when I drive it for shorter trips, then start it the next day or hours later, it has no problem. My drive to work is about 14 miles, and takes about 21 minutes, driving at high RPMs on the highways. I tend to see the rough starting condition after driving to work or home from work.

 

I’m really getting baffled by this. I’m losing no coolant, the oil looks fine, coolant looks fine, no overheating, no performance loss, no strange MPG, no check engine light, new plugs, new coils, new injectors, new fuel filter, new timing sensors, passed emissions, and so on... but the issue remains.