Misfiring Cyl 2/4/6 ?? 2015 LR4

Salanizi

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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.

The issue is that acceleration on my vehicle is great and silky smooth, i only have issues when idling and low speed traffic driving (below 1000rpm) where i get the occasional misfire and CEL
 

Salanizi

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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).

I felt that the mechanic gave up and sounded defeatist, along with the fact that a new engine is an expedient option for them...

Rates are around $60 per hour whereas parts are about 15% more expensive than the States/UK


Anyway...

I replaced the last remaining O2 sensors that werent already replaced (bank 1 s1+s2) and i believe it fixed the fuel trims (please see attached pics) - even though oddly my misfires were mostly on bank 2 - numbers are much closer to 0 now

I am starting to suspect the MAP sensor for some reason, as you can see the MAP is around 5.55 psi - what should the reading be? Is that normal?

Reason is if you remember I had a heavy metal clunking noise in the supercharger, which did not go away even when replaced the isolator...

If the MAP pressure is ok my next plan is to check the CATS and any manifold/exhaust leaks...
 

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djkaosone

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Here's my 2 cents and take it with a grain of salt. With all those new parts, have you tried clearing all the adaptation values? This will force the ecu to relearn new values, which means that it will reset to factory fuel trims. It will relearn all the fuel curves over a few days of driving. Some people will argue that all new vehicles and ecus are adaptive learning, and I will argue that a computer still needs to be reset (like clearing the cache to stale data) to perform properly every once in a blue moon.
 

jlglr4

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I don’t know the normal MAP values - I’ll try to check mine tomorrow. But it does seem like MAP should be changing more than it is with increasing RPMs. I don’t remember the heavy metal clunking noise in the supercharger, and I can’t imagine what part of a supercharger would be making a heavy metal clunking noise. Is it still making that noise? The supercharger does have a bypass valve - I wonder if that might be malfunctioning.

But the fuel trims look better, so you’re making progress. I’ll try to report back map values tomorrow.
 

Salanizi

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Here's my 2 cents and take it with a grain of salt. With all those new parts, have you tried clearing all the adaptation values? This will force the ecu to relearn new values, which means that it will reset to factory fuel trims. It will relearn all the fuel curves over a few days of driving. Some people will argue that all new vehicles and ecus are adaptive learning, and I will argue that a computer still needs to be reset (like clearing the cache to stale data) to perform properly every once in a blue moon.

Hello Sir

How do I do that?
 

djkaosone

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Hello Sir

How do I do that?
From my understanding, you don't have a Gap IID Tool. So, you'll probably have to ask someone that has the proper tool to do this for you. IF this costs money to clear the adaptation values, then I would suggest putting that $$ towards the Gap IID Tool. It seriously pays for itself and you'll have a vast amount of peer support for the product to get you through things like this.

Here's a snipit of Gap's reasoning of why you should clear the adaptation values, which is why I suggested doing so.

Screen Shot 2022-11-16 at 9.53.25 AM.png
 

jlglr4

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Just reporting back on the MAP values. Mine look similar to yours, about 5.8 psi at idle and 5.3 psi at 1500-3000 rpms steady throttle. It does change quite a bit if you blip the throttle.
 

Salanizi

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Just reporting back on the MAP values. Mine look similar to yours, about 5.8 psi at idle and 5.3 psi at 1500-3000 rpms steady throttle. It does change quite a bit if you blip the throttle.

Then i guess the last act would be to check the cats

I will have a specialist dismantle them and see what they can find, and clean them if possible

The exhaust specialist i went to yesterday suspects that the right side cat has been emptied for the stuff inside (theives steal cats here or empty the insides to sell whatever precious metal there is inside)

However he confirmed no leaks on the manifold nor the exhaust (i actually went to two garages just in case)

Weird thing is that i never got a cat code on the reader, could an emptied out cat cause a rough idle?
 

jlglr4

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Not sure what an emptied out cat would do. I assume that would increase exhaust flow, which is the opposite of what I was thinking. But how/why would a thief carefully disassemble the cat, empty it out, and put it back together installed on the car? That just doesn’t make much sense to me. Here people steel cats all the time, but they just cut them off and take the whole thing.

Did the exhaust specialist give you some reason they think the cat has been emptied? Did they do some sort of diagnostic? Usually they look at temp or backpressure at least.

I’d drive it for a while - maybe 50 miles or so - now that you replaced that last o2 sensor and the fuel trims improved. The engine will learn new adaptations and might sort out the rough idle.
 

Salanizi

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Not sure what an emptied out cat would do. I assume that would increase exhaust flow, which is the opposite of what I was thinking. But how/why would a thief carefully disassemble the cat, empty it out, and put it back together installed on the car? That just doesn’t make much sense to me. Here people steel cats all the time, but they just cut them off and take the whole thing.

Did the exhaust specialist give you some reason they think the cat has been emptied? Did they do some sort of diagnostic? Usually they look at temp or backpressure at least.

I’d drive it for a while - maybe 50 miles or so - now that you replaced that last o2 sensor and the fuel trims improved. The engine will learn new adaptations and might sort out the rough idle.

What happens is sometimes when cars are left at a garage, the garage owners themselves are the thieves...

My theory is that either the internals of the cats were stolen or some idiot hollowed out the cat to solve some problem.


We dont have garages with backpressure testing equipment and such wizardry . lol

Im taking the car in an hour to the garage to physically dissassemble the cat and try to clean them as much as possible... ill report as to what happens.
 

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