3.0 SCV6 - Multiple misfires around 1000rpm

Salanizi

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Hello

I am now on week 2 ownership of my 2015 LR4 (60k miles) and so far, have fixed most issues and also done alot of preventative maintenance (full overhaul of cooling system).

I am now faced with a continuous misfire and hesitation only around 1000rpm (no CEL tho, no smoke), once the car takes off it goes away, it also idles smooth with no issues

I already changed:
oil+filter
air filters
techron+sea foam bottles in the tank
cleaned throttle body
replaced spark plugs
replaced PCV
oxygen sensors

- all original LR, still did not resolve this issue.

On the OBD it shows many misfires on both banks - to which they replaced 4 coils with used ones from their shop (dubious origin/condition) which made the car run worse. I resorted to going back to my original coils, with less of a misfire/vibration.

Should i bite the bullet and pay $700 for a new set of coils(original LR) or am I missing something? My indie says it could be that the piston sleeves have widened and are the cause of the misfire - changing the coils would not sort that out.

I would appreciate any insight on the matter
 
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jlglr4

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So, to be clear, you have OBD codes for misfires, or are you judging by the misfire counter on an OBD tool? If you have codes, what are the codes?
 

Salanizi

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So, to be clear, you have OBD codes for misfires, or are you judging by the misfire counter on an OBD tool? If you have codes, what are the codes?

Mmm, i believe i was looking at the misfire counter, which showed misfires on all cylinders...

May I ask what difference it would make? I mean is this where the misfire would be a symptom, and the coils might not be the problem? (Already changed plugs/o2 sensors)
 

jlglr4

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I haven’t really done much with the OBD misfire counter, but my understanding is that the misfire counter detects misfires based on the position of the crank just after ignition and determines whether a misfire has occurred based on that position (I imagine the crank moves slower in a misfire than an proper detonation and, thus, in a different position at a given instant following detonation). The counter operates on a timer or reference frame of some kind, and if enough misfires are detected within the reference frame, it throws a code. Thus, there are an acceptable number of “misfires” within a time frame. Because of the way this whole thing operates, I believe the threshold for code generation takes into account erroneous misfire calculations.

So, if you are truly having a misfire situation, you should see a code. If you are not seeing a code (and not having any drivability issues), then I think you are still within the threshold for normal operation. Again - that’s my understanding, but I’m no mechanic.

Your hesitation and vibration at a specific RPM could very well be engine mounts. I’ve seen a couple of reports on these forums about the engine mounts getting sloppy - and I think it was close to your mileage. That particular RPM might be hitting the frequency that causes it to start bouncing. When the drivetrain is engaged, you might not notice it much. You might watch the motor as someone hits the gas or puts it in gear and see if there’s any detectable shifting of the motor.

Generally, causes for real misfires don’t happen at a narrow RPM range. It would generally happen at low RPMs (e.g., vacuum leak) or high RPM (e.g., fuel supply problem). But I can’t really think of what would cause a misfire at right around 1000 rpms, only out of gear. I suppose it could be a harmonic balancer, though I haven’t heard of any problems with them. I also don’t have enough experience to know if it would only vibrate at a specific RPM.

I can’t really make any sense of the theory on piston slop . I think that’s highly unlikely. Why would that be tied to a specific RPM? You’d probably be seeing oil consumption as well.
 

Salanizi

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I haven’t really done much with the OBD misfire counter, but my understanding is that the misfire counter detects misfires based on the position of the crank just after ignition and determines whether a misfire has occurred based on that position (I imagine the crank moves slower in a misfire than an proper detonation and, thus, in a different position at a given instant following detonation). The counter operates on a timer or reference frame of some kind, and if enough misfires are detected within the reference frame, it throws a code. Thus, there are an acceptable number of “misfires” within a time frame. Because of the way this whole thing operates, I believe the threshold for code generation takes into account erroneous misfire calculations.

So, if you are truly having a misfire situation, you should see a code. If you are not seeing a code (and not having any drivability issues), then I think you are still within the threshold for normal operation. Again - that’s my understanding, but I’m no mechanic.

Your hesitation and vibration at a specific RPM could very well be engine mounts. I’ve seen a couple of reports on these forums about the engine mounts getting sloppy - and I think it was close to your mileage. That particular RPM might be hitting the frequency that causes it to start bouncing. When the drivetrain is engaged, you might not notice it much. You might watch the motor as someone hits the gas or puts it in gear and see if there’s any detectable shifting of the motor.

Generally, causes for real misfires don’t happen at a narrow RPM range. It would generally happen at low RPMs (e.g., vacuum leak) or high RPM (e.g., fuel supply problem). But I can’t really think of what would cause a misfire at right around 1000 rpms, only out of gear. I suppose it could be a harmonic balancer, though I haven’t heard of any problems with them. I also don’t have enough experience to know if it would only vibrate at a specific RPM.

I can’t really make any sense of the theory on piston slop . I think that’s highly unlikely. Why would that be tied to a specific RPM? You’d probably be seeing oil consumption as well.

Hello Sir

I just took it to the garage, replaced coils and plugs (again - suggested that the bad coils might have damaged the new plugs) all original LR.

It runs smoother now, although the shake is still there around 1000rpm.

Indy says thats it theres nothing more to cover, it could be the engine mounts but they seem fine not worth replacing at the moment (i already replaced the tranny mount)

Running the autel OBD showed no codes at all, but the live diagnostics show slight misfires on cylinders 2 / 4 / 6 - it seems as you said that this is normal?
 

jlglr4

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I think your original post said no CEL, so is this new? You said no codes before, so I assume these codes in the screenshot are new. If you are not sure, clear all the codes and see what comes back.

From the codes on that screenshot, looks like you still have an oxygen sensor issue. If they were changed, you still have some kind of issue - maybe the wiring, maybe an intake or exhaust leak, maybe a fuel supply issue. That could easily be the cause of your misfires, although (from what I can see) there is a timing code for bank 1 and o2 sensor/misfire on bank 2, so not sure what is going on with bank 1. Still, if that o2 sensor code keeps popping up, I think you tackle that first.

Will that device show you fuel trims?
 

Salanizi

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I think your original post said no CEL, so is this new? You said no codes before, so I assume these codes in the screenshot are new. If you are not sure, clear all the codes and see what comes back.

From the codes on that screenshot, looks like you still have an oxygen sensor issue. If they were changed, you still have some kind of issue - maybe the wiring, maybe an intake or exhaust leak, maybe a fuel supply issue. That could easily be the cause of your misfires, although (from what I can see) there is a timing code for bank 1 and o2 sensor/misfire on bank 2, so not sure what is going on with bank 1. Still, if that o2 sensor code keeps popping up, I think you tackle that first.

Will that device show you fuel trims?

You sir, hit the nail on the head, needed to change the camshaft and sprocket on bank 1 + fuel pressure sensor + bank 1 valve cover (vacuum leak), CEL's dissappeared completely but the shake was still there, albeit less pronounced.

Indy raised the engine off the mounts, car was silky smooth, upon removing and inspecting the mounts they appeared to be some chinese s h i t e, replaced with original Land Rover.

All sorted now
 

Tbh1981

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You sir, hit the nail on the head, needed to change the camshaft and sprocket on bank 1 + fuel pressure sensor + bank 1 valve cover (vacuum leak), CEL's dissappeared completely but the shake was still there, albeit less pronounced.

Indy raised the engine off the mounts, car was silky smooth, upon removing and inspecting the mounts they appeared to be some chinese s h i t e, replaced with original Land Rover.

All sorted now
jlglr4 is basically the LR4 mentalist. He helped me fix a random electrical issue last summer without ever seeing the car.
 

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