Misfiring Cyl 2/4/6 ?? 2015 LR4

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Salanizi

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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).

Could it be that the ECU is toast and it just needs a new one?
 

Michael Conley

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I had a V8 with rough idle, inconsistent acceleration, emission inspection failure, and misfires on one bank. Dealership said it was the the fuel injectors, second option from an Indy was skepticism.

The Indy had an old school diagnostic tablet (all I can remember was it was bulky and blue) and after a LOT of digging he noticed an odd micro-voltage fluctuation in the offending bank's pre-cat O2 sensor. Ended up replacing it, I immediately noticed smooth acceleration and my emissions checks went green after 20 minutes on the parkway. Worth a look.
 

Salanizi

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My indy after consulting with another Indy land rover specialist, both decided that I need a new engine.

I replaced plugs for the 3rd time, coils, all O2 sensors on the offending bank, and the 2nd O2 sensor on the other bank, replaced MAFS and all fuel pumps and both fuel pressure sensors to no avail.

The only thing i havent replaced yet is the pre-cat O2 sensor on bank 1. Indy says its not worth to replace since misfires are on cylinders 4 and 6. Would replacing it make a difference?
 

jlglr4

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Wow - that’s a pretty serious diagnosis to jump to. Did the mechanics say why they think the engine is shot? Did they do a compression test and find a warped head or something? This goes to ftillier’s comment - prior overheating can warp the heads pretty quickly. I’ve never heard of someone scrapping an engine just because they can’t figure out a misfire situation.

Regarding your question about the ECU, I suppose it’s possible that something is going wrong in that department but it would not be my first guess. I would sooner suspect some other electrical problem, like a bad coil harness or something like that, before I would suspect the ECU itself.

Assuming the mechanics don’t have some good reason to call it quits here, I would try to replace that last sensor and try to confirm a good and proper connection on all the o2 sensors to see if that clears up the fuel trims at all. You might have more than one thing going on and it would be good to rule out the o2 sensors if possible.

Aside from that and the things you’ve already done, look at the plugs to see if there is any fouling, check for manifold leaks, do a compression test, maybe a backpressure test on the exhaust to make sure the cats are okay. I might revisit the timing issue as well - you mentioned in a prior thread that one of the cam sprockets and a VVT unit was replaced. Wondering what the problem was there and whether it has returned, i.e., maybe the problem was not the VVT but the wiring.

Seems like there is a lot that can be investigated before resorting to a new engine, but I know its not cheap when you are relying on mechanics (not sure what rates are like in Kuwait).
 

greiswig

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Seems like there is a lot that can be investigated before resorting to a new engine, but I know its not cheap when you are relying on mechanics (not sure what rates are like in Kuwait).
This is good advice, in my opinion.
 

ftillier

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Thinking on this more, can we confirm that we're all using the same cylinder numbering? The SCV6 numbers one bank 1,2,3, and the other 4,5,6. It would make more sense if one bank was misfiring, so when you say 2-4-6 are misfiring, are those numbers referring to just one bank or really across both banks?
 

jlglr4

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ftillier makes a good point, and to back it up a bit further - how are the misfires being detected in the first place? Is there a misfire code being set? Rough idle is almost certainly a misfire of some kind, but I’m wondering how you’re seeing the misfires on 2/4/6.
 

jlglr4

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Just thinking on this a little more, and maybe a partially clogged cat on one side makes some sense. It would explain rough idle with misfiring and consequential rich condition on the clogged side, and might also explain the other side going lean because the airflow into the engine would be out of balance with relatively more airflow through the unblocked side. And it would get worse under load.

If you have a cheap infrared thermometer, you could check the temps of the cats. Warm it up good, and compare the front end temp of one cat to the other (measure in the same relative spot). A clogged cat will run hotter. Also check the temp at the front of each cat and compare it to the temp of the rear of the cat on each side. If the front of the cat (inflow) is hotter than the rear (outflow), that is supposed to indicate a clog.
 

Salanizi

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do you know if the engine was overheated previously?

I really do not know as I bought that car last may, apparently the engine has been replaced with one that does not have an oil pressure sensor...
 

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