Engine Misfire

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pete0rz

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First, just want to say that I've lurked in these forums forever and learned a lot from fellow owners. Thank you everyone for your passion and posts. That said, hoping y'all can point me in the right direction. I have a 2012 LR4 with 137K miles, purchased at 11K miles, and the vehicle's been properly maintained. I've changed oil (every 5K miles), always used the right gas, replaced failing parts immediately, and done all the regular services per schedule. To date this truck has been beyond rock solid, that is, until 3 months ago.

Been dealing with a pesky CEL and need some advice. Initial DTC was a single p0305 and p0316. So swapped coil, misfire didn't follow. Replaced plug, wire, and injector on cylinder 5. Made it ~400 miles before I got yet another CEL. Had additional misfires all on the same bank. Swapped those coils, misfires didn't follow. Ran BG44 thru system and replaced injectors 1,3, and 7. Then took it for a 70 mile extended ride, got no DTCs and felt the issue had been addressed. Not 10 miles later and after gassing up, I got another CEL. Since then been seeing p0305 and p0316 together consistently. These misfire DTCs, p0316 and p0305, seem to happen immediately after refilling gas tank. Though I've also had a p0316 only and also had one p0153. No other codes.

FYI o2 sensors, PCVs, and MAFs haven't been changed. Idle has a little bit of a shake to it, but no restricted performance, and don't believe idle shake is due to vacuum leak. No smoke out of the pipes. If anything, the vehicle drives and feels great; no lag or hesitation whatsoever.
A part of me thinks this issue stems from getting bad gas in February. Suspect bad gas because I had an engine knock, after refilling in an off grid location, and then the car drove differently for about a month. The gearing was off and it felt like injectors were sticking. FYI I got that 1st CEL, the single p0305 and p0316, a month or so after that.

Do you think the current DTCs could be the result of a bad o2? Again, seem to get p0305 and p0316, only after refills and wondering if that bad gas back in Feb messed them up. Any thoughts? I love this truck and had hoped to get to 200K miles...
 

jlglr4

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I think the o2 sensor would be the first thing I’d try at this point seeing as you had one o2 sensor related code pop up in the past (p0153), and at 137K, they should probably be changed anyway. That also would be consistent with misfires all on one bank (not sure why its primarily number 5). MAF and vacuum leaks (PCV) will typically affect both banks.

Any differences when the car is warm vs cold with respect to the idle shake/codes?
 

pete0rz

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No real difference in terms of idle shake. It continues to throw the same codes whether cold or warm. What's odd is that in between fill ups I have stretches with 0 codes. For example I had 0 DTC for probably 20 or so engine starts over 3-4 days. Then as soon as I gassed up, it started throwing those same codes again. It will do that for a while and then throw 0 DTC for stretches.
 

jlglr4

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The only thing I can think of relating to filling the tank is the purge valve. If that’s not closing tightly, the full tank might be pushing more fumes up into the intake when the tank is full. Not sure why that would cause a misfire on just one cylinder - and always the same cylinder, but I guess it’s possible.

Next time you gas up, you could disconnect the purge valve and block off both open ends of the connection (the throttle body inlet and the purge valve exit) so the purge valve is effectively closed, and see if that helps. The car might throw some kind of evap system code, but shouldn’t really affect anything otherwise. Don’t leave it that way too long because the vapors in the tank need to get out. You could leave the purge valve side open - then you’ll for sure throw an evap leak code at some point - but again, I don’t think it will affect anything else.

You don’t happen to top off the tank past the click do you? I’ve seen some reports of gas getting into the charcoal cannister that way and messing up the evap system - that also will drive a lot of vapors into the engine.
 

Michael Conley

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All 4 O2s we're replaced? If your seeing it one side, I'd start by checking the O2s there. I had a similar issue where I had fluctuating idle, misfires on one bank, lurching acceleration, and couldn't pass emissions because my evap and egr wouldn't "ready" because of the O2 monitor.

No codes but the Indy noticed anomalies in the upstream O2 voltage. Once he replaced it, acceleration and idle we're good and my monitors clicked back-to-back.
 

pete0rz

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I almost always top-off past the click. I'll stop and see if that changes anything. Have heard of that cannister issue, but when unscrewing my gas cap there's no suction sound which I heard is a symptom.
 

jlglr4

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Whether or not canister has gas in it, disconnecting the purge (and blocking throttle body inlet) should tell you whether the evap system is involved. Not topping off won’t change anything short term.
 

rolledover

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I was dealing with almost exactly the same issue, except on Cylinder 7. I changed plugs, injectors, swapped coils, walnut blasted the intake valves in hopes of fixing it. I then had a leak down test which confirmed a leaking exhaust valve on cylinder 7. I also had the shake while idling but no noticeable issue when driving. I could confirm with the Gap Tool that misfire would stop as soon as rpm's were raised above idle. If you have a way to check live values I would imagine you're getting a constant misfire on idle, then on the subsequent startup it throws a CEL because of the P0316 code. I'm currently in the process of tearing the motor down to have a valve job done. This is what the passenger head looked like when removed.
 

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f1racer328

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I was dealing with almost exactly the same issue, except on Cylinder 7. I changed plugs, injectors, swapped coils, walnut blasted the intake valves in hopes of fixing it. I then had a leak down test which confirmed a leaking exhaust valve on cylinder 7. I also had the shake while idling but no noticeable issue when driving. I could confirm with the Gap Tool that misfire would stop as soon as rpm's were raised above idle. If you have a way to check live values I would imagine you're getting a constant misfire on idle, then on the subsequent startup it throws a CEL because of the P0316 code. I'm currently in the process of tearing the motor down to have a valve job done. This is what the passenger head looked like when removed.
How many miles do you have on the engine? I had a very small shake at idle (No CEL, no misfires) but it has since gone away. I'm running a few bottles of Sea Foam through my fuel system and might do the intake version as well... but having a valve stick sucks... I'm at 94k miles.
 

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