Misfiring Cyl 2/4/6 ?? 2015 LR4

Salanizi

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Hello

My car (2015 3.0 SCV6 w/70k miles) has never idled properly since i bought it last may.

It is idling rough however the rpm is constant no fluctuation, and whenever you press the gas and brake pedals together, it sometimes throws a CEL and always starts misfiring on cylinders 2/4/6...

I have replaced almost all the usual culprits (pcv/brake vacuum hoses/coils/plugs/replaced MAFS/ most O2 sensors/ high+low pressure fuel pumps/ high+low fuel pressure sensors) - after which the car has gained considerably with regards to performance and fuel economy, but still this misfire and rough idle would not go.

Along with misfiring 2/4/6 cylinders i also get a p0156 code for O2 bank 2 sensor 2, however the mechanic says this is a symptom not the cause of the problem, which he has no idea what it is??? I dont know whether to replace this last sensor or is it something else?

I would appreciate any insight on this as I have spent A LOT of money so far chasing this issue to no avail.

Regards
 

mm3846

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what are your LT and ST fuel trims? you could have a vacuum or EVAP leak.
 

Salanizi

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what are your LT and ST fuel trims? you could have a vacuum or EVAP leak.

Unfortunately i do not have an OBD reader however my mechanic has one that is how I identified the misfires and the P0156

I saw on the live scan function the ST and LT fuel trims unfortunately i did not think to take a shot of those...

In any case, i replaced all the fuel pumps + filter and pressure sensors on the vehicle, as well as running 3 bottles of injector cleaner through it. Assuming the fuel trims are off, what more should I do in that case?
 
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Salanizi

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jlglr4

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Ditto mm3846‘s advice. Check your fuel trims - you need to look at both ST and LT (add them together to get total). Check at idle, at something around 1500 rpms, and at something around 2500 rpms. Hold steady at those RPMs (in park/neutral) and record. Then check to see how they are changing. It can give you lots of valuable info. E.g., positive trims (lean condition) that trend back to normal with increasing RPM points to vacuum leak; positive fuel trims that get worse with higher RPM points to fuel delivery/starvation issue; etc.

The code on cyl 2/4/6 is a bit odd because I think the cylinder numbering in the V6 does not follow normal even/odd bank. But maybe the code reader is misinterpreting. With the bank 2 code on the o2 sensor, I assume you’ve got something going on that affects one bank only - if true, that can help narrow it down as well. Could still be o2 sensor - possibly a problem with the wiring harness if the sensors themselves are good, fuel delivery on one rail, exhaust manifold leak, valve cover leak, VVT solenoid. With multiple misfiring cylinders, I wouldn’t normally expect injectors, but if you had the injectors reinstalled, they could be leaking if they were not replaced properly (new seals). That might make sense with misfires under load - it also would cause the CEL with excess fuel dumping.
 
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Salanizi

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Ditto mm3846‘s advice. Check your fuel trims - you need to look at both ST and LT (add them together to get total). Check at idle, at something around 1500 rpms, and at something around 25000 rpms. Hold steady at those RPMs (in park/neutral) and record. Then check to see how they are changing. It can give you lots of valuable info. E.g., positive trims (lean condition) that trend back to normal with increasing RPM points to vacuum leak; positive fuel trims that get worse with higher RPM points to fuel delivery/starvation issue; etc.

The code on cyl 2/4/6 is a bit odd because I think the cylinder numbering in the V6 does not follow normal even/odd bank. But maybe the code reader is misinterpreting. With the bank 2 code on the o2 sensor, I assume you’ve got something going on that affects one bank only - if true, that can help narrow it down as well. Could still be o2 sensor - possibly a problem with the wiring harness if the sensors themselves are good, fuel delivery on one rail, exhaust manifold leak, valve cover leak, VVT solenoid. With multiple misfiring cylinders, I wouldn’t normally expect injectors, but if you had the injectors reinstalled, they could be leaking if they were not replaced properly (new seals). That might make sense with misfires under load - it also would cause the CEL with excess fuel dumping.

Hello Sir

Unfortunately my mechanic is a little more than a grease monkey and wont really know how to read such codes/trims, and I personally do not own an OBD reader to take all those readings and report on them.

In case I have a fuel starvation or lean condition issue, how can I fix it? As I meantioned earlier I already replaced all the fuel system components that I know of, which made the car's perfomance noticably better but still did not fix the issue.

In case I choose to replace that O2 sensor (which i probably will) - is there anything else I can do thats easy/quick to replace that might be the culprit?
 

ftillier

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Is there a distributor for the Gap diagnostics iidtool in your area? Definitely worth the price if you plan on keeping your LR4.
 

Salanizi

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Ditto mm3846‘s advice. Check your fuel trims - you need to look at both ST and LT (add them together to get total). Check at idle, at something around 1500 rpms, and at something around 25000 rpms. Hold steady at those RPMs (in park/neutral) and record. Then check to see how they are changing. It can give you lots of valuable info. E.g., positive trims (lean condition) that trend back to normal with increasing RPM points to vacuum leak; positive fuel trims that get worse with higher RPM points to fuel delivery/starvation issue; etc.

The code on cyl 2/4/6 is a bit odd because I think the cylinder numbering in the V6 does not follow normal even/odd bank. But maybe the code reader is misinterpreting. With the bank 2 code on the o2 sensor, I assume you’ve got something going on that affects one bank only - if true, that can help narrow it down as well. Could still be o2 sensor - possibly a problem with the wiring harness if the sensors themselves are good, fuel delivery on one rail, exhaust manifold leak, valve cover leak, VVT solenoid. With multiple misfiring cylinders, I wouldn’t normally expect injectors, but if you had the injectors reinstalled, they could be leaking if they were not replaced properly (new seals). That might make sense with misfires under load - it also would cause the CEL with excess fuel dumping.

Hello

So i got to spend some time today with the reader, after replacing O2 sensor b2s2 + b2s1, which did not fix anything and I later got a CEL with b1s3 as malfunctioning, and got some interesting readings:

FUEL TRIMS
* Bank 1
- stft hovers around +3% and only goes up to a max 10% when around 3000rpm
- ltft is a constant 0%

* Bank 2
- stft starts at +3% at idle and goes down to negative 13% with increasing RPM up to 3000pm
- ltft is around -7%

- fuel rail pressure fluctuates from 510 to 540 psi higher rpm higher pressure

If i understood how fuel trim works correctly, i am in normal lean range for bank 1, but bank 2 is screwed up with an injector stuck open or something else?

I still did not replace O2 sensor b1s1 though...
 

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jlglr4

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It’s odd that the two banks are the opposite of one another. I think you are correct that Bank 1 is technically staying within a normal range, but it’s still indicating an increasingly lean condition with increasing RPMs, whereas Bank 2 starts in a normal range (just a little rich) and then gets increasingly richer with increasing RPMs. You are looking at the numbers when holding the throttle steady, correct? You need to hold it steady for a good 15 seconds or so and let the numbers kind of come to rest (more or less). When you accelerate, it kicks out of closed loop, then goes back into closed loop when the throttle is held constant.

Assuming the numbers are correct, is there any chance the wires got mixed up on the o2 sensors? I haven’t changed the o2 sensors on mine yet, so I don’t know what chance there is of it happening. I assume you’d have more codes, but it’s just something that occurred to me so thought I’d mention it.

If the o2 sensors are working and the numbers are correct, I’m not sure what‘s going on. Originally I was thinking maybe an injector, but if you are misfiring on all cylinders in the bank randomly, that doesn’t sound like an injector. Could be a problem with spark I guess. Not sure, gonna need to dwell on this one some more. Two people on this forum had a sheared off bolt on the exhaust manifold, but I don’t think that would cause a rich condition (not entirely sure though). That occurs to me because you did have a motor mount problem in the past, and bad motor mounts can sometimes put stress on the exhaust manifolds (as the engine moves around too much).
 

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