Misfiring Cyl 2/4/6 ?? 2015 LR4

[scapistron]

Didn't have a ton of time last night, but measured compression on 1 and 4 because they're the easiest. Cylinder 1, 180psi. Cylinder 4, 190psi. The engine was warm, throttle was wide open, fuel pump relay had been pulled. Earlier in the day while the motor was cold I pulled the plugs on bank 2 so I could have a look. 4 was obviously rich with a very small amount of oil near the washer. 5 looked good aside from the insulation cracking because I dropped it. 6 looked okay as well. This was after about 1000 miles. In the picture plugs are from 4, 5, and 6 from top to bottom.

Computer also through the codes again. Confirms that my scan tool doesn't know the cylinder numbering. P0304,5, and 6. Also got a P0173. So anything I wrote above about 2, 4, and 6 should be read as 4, 5, and 6.

Some drivability observations are that it will drive fine on the highway with only a very occasional misfire. Most typically when you need to let off the gas because of traffic and the engine goes full lean (lambda 2.0). This is typically only 1 recorded misfire event which clears out of the data on it's own. After an hour or two of highway driving and hitting stop and go traffic I'll get a lot of misfires. When it misfires bad (counts greater than 10 per cylinder) I can see the MAF signal get very noisy. At first I thought this was an input problem, bad wiring, bad sensor, etc. Thinking about it more, I'm not so sure.

 

[djkaosone]

@scapistron I typically see individual or an entire bank misfire. For it to misfire between both banks is uncommon, but not unheard of. For oil to drip onto your plugs, it sounds like your spark plug and valve gaskets are starting to go.

Have you tried smoke testing it? I'm guessing that could introduce unregistered air into your engine and your O2 sensors are compensating for it by adding more fuel.

 

[jlglr4]

Not sure, but I think going lean when you let off the throttle and coast down (in gear) is probably normal. ECM is pulling back fuel faster than the engine is slowing down. A single misfire event on the counter is nothing really to worry about. If it’s setting a code at that point, then it would be a different story.

As for drivability, when it’s misfiring “badly,” you can feel it running rough and hesitating, etc., correct? Or is it just the misfire counter showing misfires without drivability issues?

Also, has the car been misfiring since you got it, or did it show up out of the blue or maybe after doing some work on it?

The single plug fouling faster than the others seems to be a good piece of evidence. Doesn’t look badly fouled, but certainly different than the others. Trying to think of all the things that could cause that. Weak spark, leaking injector, intake valve not fully opening, maybe lean condition in the rest of the bank and ECM increasing fuel to all and causing rich condition in that one cylinder (not sure how likely that is). Valve stem seal leak could cause it, but that should give you a little smoke and maybe some misfires at startup - shouldn’t get worse with driving. In fact, I don’t really see why any of these things I mention would get worse with driving, except maybe the weak spark.

Going back to djkasone‘s comment, vacuum leak somewhere would cause more misfires at idle and it would get better with increasing throttle/speed. So, maybe something to rule out. You checked the PCV? I suppose an exhaust manifold leak also could be messing with the air/fuel ratio detected in the O2 sensors. No easy way to check for it though. Tough problem.

 

[powershift]

What software are you running?

 

[scapistron]

I have not done a smoke test.

When it misfires bad you can feel the vibration and get a little bit of hesitation when applying throttle. Lambda equivalence is always rich during bad misfires. So not enough oxygen and / or too much fuel. Been like this since I got it. I don't smell an exhaust leak, but could take a look. I don't think it would be a vacuum leak because of the richness. I can try disconnecting the PCV next time it is happening and cover the port by the intake.

Combustion gas getting past the intake valve would probably make the MAF reading go nuts. What should the manifold pressure be at idle? I'm thinking I should see this in the boost pressure.

Is there any way the timing is off such that the intake valve isn't closing in time? Does this have variable timing that might make this intermittent?

Maybe a mild exhaust restriction in the cat that only shows up when things are very warm, 1000F in the cat?

Thinkcar platinum S8 from Costco.

 

[powershift]

Thanks

 

[jlglr4]

I agree that rich points away from vacuum leak, but it seems like sometimes you’re showing lean and sometimes you’re showing rich (I remember it was at 2.0 in one of your posts). (i edited this post to delete some of my own poor logic. misfire itself will not cause o2 sensor to show rich).

An intake valve that is stuck open or closed might mess with both fuel trim and MAF readings, but I’m not sure why you’d be seeing it only after driving for a while. A stuck open/leaking valve all the time would give you low compression, so it doesn’t seem to be that. Valves that get “sticky” (open or closed) tend to give more problems when cold and less problems after driving for a while, not the other way around. So that doesn’t really seem like the problem.

I’m wondering if the erratic MAF is just reflecting a bad misfire, i.e., the engine kind of stuttering and causing a very brief interruption in airflow that the MAFs are picking up.

The car does have variable timing, and the VVT solenoids do go bad sometimes. They are easy to change from all reports I’ve seen. They are located right up front - mounted externally on the timing chain cover. Timing problem would affect the whole bank and not cause just one plug to start fouling, but I guess you are showing misfires on the whole bank (although not sure about that with the discrepancy in cylinder numbering).

Partially clogged cat also would affect the whole bank and I think it would give you problems all the time, not just after driving a while. You can check the cat function with an IR temp gun. After warming up, the front of the cat should be lower temp than the rear of the cat by a significant amount.

 

[scapistron]

I was just looking around to see what else I can monitor in real time. Cam position sensor for the inlet and exhaust on bank 2 are both sloppy compared to bank 1. Adaption values are also fairly different. Ordered a new cam solenoid and o-ring.

Possible the motor is telling me I need a new timing chain, it is at 97,*** miles.

 

[JaJp]

Didn't have a ton of time last night, but measured compression on 1 and 4 because they're the easiest. Cylinder 1, 180psi. Cylinder 4, 190psi. The engine was warm, throttle was wide open, fuel pump relay had been pulled. Earlier in the day while the motor was cold I pulled the plugs on bank 2 so I could have a look. 4 was obviously rich with a very small amount of oil near the washer. 5 looked good aside from the insulation cracking because I dropped it. 6 looked okay as well. This was after about 1000 miles. In the picture plugs are from 4, 5, and 6 from top to bottom.

Computer also through the codes again. Confirms that my scan tool doesn't know the cylinder numbering. P0304,5, and 6. Also got a P0173. So anything I wrote above about 2, 4, and 6 should be read as 4, 5, and 6.

Some drivability observations are that it will drive fine on the highway with only a very occasional misfire. Most typically when you need to let off the gas because of traffic and the engine goes full lean (lambda 2.0). This is typically only 1 recorded misfire event which clears out of the data on it's own. After an hour or two of highway driving and hitting stop and go traffic I'll get a lot of misfires. When it misfires bad (counts greater than 10 per cylinder) I can see the MAF signal get very noisy. At first I thought this was an input problem, bad wiring, bad sensor, etc. Thinking about it more, I'm not so sure.

Anything changed? Just did a timing job and experiencing the same problem misfires at 2,4,6 only at 1000 rpms or somewhere around that range

 

[scapistron]

Funny you ask. Remember that generic scan tools can show a misfire on 2, 4, and 6 but if it actually throws a code you'll see that it is indeed 4, 5, and 6. Land Rover changed the cylinder numbering and a lot of aftermarket scan tools will be off on cylinder identification. I have swapped in a fresh set of plugs and drove for a bit. Things were okay for a while, but the misfires came back. Eventually I sat there with the truck idling watching continuous misfires on 5 and 6. I checked for spark using a coil wand, spark confirmed. Pulled the plugs. 4 was sooty, 5 and 6 had a reddish coloring to the tips. So 4 was rich and 5 and 6 were lean. I ran compression on 4, 5, and 6, they were all good and within 5 psi of each other.

My working hypothesis at this point was that the #4 injector was leaking fuel, O2 sensor could tell and was pulling fuel back on that bank. To confirm I put the plugs back in and looked at the long term trims while it was misfiring at idle. Sure enough bank 2 was at -25% long term trim. At this low of fueling cylinder 4 would ignite and 5 and 6 would misfire due to too lean. Lambda equivalence would float around 1, so essentially cylinder 4 was getting enough fuel for all three.

I replaced the #4 injector (driver's side front) today and did a couple of longish trips, total of 45 miles. Things seem really good. Fingers crossed.

If you just changed your timing chain, I'd first look for something that you might have neglected to plug back in. Maybe the cam solenoids? Is it actually throwing any codes? I'd also be a little concerned that the timing is off on bank 2. If you're very confident that the timing work is good, look at your plugs and check your fuel trims. That will help narrow it down.