Misfiring Cyl 2/4/6 ?? 2015 LR4

[scapistron]

Posting my problem here because it sounds pretty similar to mine. Looking at the live data I'll get some intermittent misfires on 2, 4, and 6, which is strange with it not all being on one bank. Did some of the simple obvious things, plugs, coils, air filter, cleaned the MAF. Still there. When the CEL comes on it says misfires are on 4, 5, and 6. It really seems to come and go. The truck runs great at times, sometimes it is just a rough idle, sometimes it presents during driving as well.

Other stuff I've checked on in the live data stream is as follows. One of the MAF sensors is on the fritz, I've seen it drop to 0 and bounce around very erratically. Swapped the sensors from side to side, definitely the sensor. Two new ones are in the cart to be ordered. When it is misfiring I can see the short term fuel trim drop to -25% on bank 2, corresponding high value on the 1st O2 sensor on bank 2. I need to get fewer data streams going at once so I can just focus on MAF, O2, and trim % to see which is moving first. I've also checked the engine coolant temperature, one of them reads normal engine operating temperature (210F, 98C) the other is less than half last I checked. I've got one of these in the cart too, no idea where it is in the engine bay though.

Thoughts?

 

[jlglr4]

You have two ECTs, one is on the hot side of the system coming out of the block (back of the engine - rear crossover), the other is on the cool side of the system coming out of the radiator (on the radiator hose just below the t-stat in the front of the engine). The cool is side supposed to be considerably lower temp than the hot side, so your ECTs are probably okay.

Definitely need to get the MAF fixed, but I’d also suspect the pre-cat O2 sensor as the misfires seem to be primarily on one side of the engine (the info from the two MAFs are combined - they are not right/left specific; but the O2 sensors are specific to fuel control on the right/left bank.

Might also take a look at fuel trims when it’s not misfiring. Might give some clue.

 

[scapistron]

Two new MAFs and two new pre-cat O2 sensors, two new post cat O2 sensors problem seems to be persistent. Bank 2 is still running rich, long term trim has been around -25 to -20 with the short term bouncing between -3 and +3. I'll catch a lambda of 0.900 or less at times sitting at idle.

I did clear the adaption values, about how many miles for the computer to relearn everything, I've probably only done 10 so far. I've got a new DTC (P0430-00), catalyst system efficiency below threshold. Pretty sure that means I need a new one. Silly to fix the cat until this is sorted though.

If I get on it, 3-4000 rpm the lambda values look good, right around 1. Replace the injectors next? Could I have some valve seating issues on bank 2?

As I sit here idling trying to do some troubleshooting while I type this the lambda for bank 2 has pegged itself at 2, strange. I assume that this is the computer ignoring the pre-cat O2 sensor as the short term fuel trim is also pegged at 0.

Shouldn't be a boost leak or faulty boost sensor because it would show misfires across all cylinders.

 

[jlglr4]

I mssume you rechecked airflow numbers to confirm the new MAFs are working. If you’re still getting dropouts on that one MAF, could be wiring issue.

From your description, it sounds like the engine is missing mostly at idle. You are showing rich on Bank 2, but we don’t know if that‘s cause or effect of the misfire. Is bank 1 fuel trim normal at idle?

Maybe check fuel trims at idle, 1500 RPMs, and 2500 RPMs (in park or neutral, just holding the throttle steady). See if the fuel trims even out at the higher RPMs, or if they are still really rich on that one bank. (Is the other bank normal?). Make sure the engine is warmed up when running the tests.

Might also check your fuel rail pressure to make sure you have good pressure at both rails.

No other codes, right? Just the misfire on Bank 2 and the catalytic converter code? Are you using a GAP tool or something else?

I think the rich condition is more likely a symptom of the misfire rather than a cause. A leaking injector can cause a misfire and rich condition, but seems like you’re getting misfires on the whole bank. I suppose it’s still possible. A valve problem also is a possibility as you mentioned. Could also be ignition wiring problem.

A failed cat also can become clogged and cause a misfire condition on the whole bank. But running rich can cause the cat to start failing as well…so, again, not sure if that cat code is indicating a potential cause or effect of the misfire.

Is this car new to you? Misfire just showed up, or slowly got worse? If it’s a new-to-you car, I guess it could be something like a head gasket leak from a prior overheat that you didn’t know about.

The coming and going of the misfires that you mention makes me think of two other things: (1) Is it tied to the engine warming up and going into closed loop fuel control? and (2) Could it be tied somehow to the purge valve that vents the charcoal canister? There is a tube that connects at the throttle body and runs down the side of the engine then along the valve cover and back towards the firewall. Somewhere in that run, there is an electronically controlled purge valve. The valve sometimes fails, and you’ll get rich vapors being sucked up into the engine when its not expecting it. Or, if your canister has liquid fuel in it (which it should not), you’ll get a really rich condition even when the valve is operating normally. This should not be a bank-specific effect, so I think this is a bit of a long shot, but you should be able to test for this by just removing the purge line from the throttle body, plug the opening in the throttle body, and see if your fuel trims or misfire condition improves.

Sorry - feel like I’m not really being helpful and just giving more possibilities and less direction.

 

[scapistron]

Vehicle is new to me, it may have overheated. I was told the crossover pipes were replaced. I've been using a thinktool with the big touch screen. I do have a GAP tool as well, I'm just more familiar with the thinktool. It is possible that the thinktool doesn't have the right cylinder ID. So when I read misfires on 2,4, and 6 it could really be 4,5, and 6. I don't know how to check for misfires in the live stream with the GAP tool.

I'd describe the MAFs as still being a bit erratic. Bank 1 will range from 100-50% of bank 2. Yes to the closed loop fuel control. Misfiring at idle can be stopped by blipping the throttle. Sometimes it is for only 5 seconds, sometimes it will work for a minute or more.

To test the cat function, I swapped the post cat sensors around. Misfires are still present on the same cylinders once up to temperature. Long term fuel trim on bank 2 is a bit better with limited driving around, -12%. Still got misfires on 4 and 6, pending cat damage. Is sensor 3 bank 1 or 2 supposed to be on the blue connector up near the floor board?

Disconnected the purge from the top of the throttle body and stuffed a bolt in wrapped with electrical tape in. Lambda values are much better for now.

I think if it persists I'll do a compression check, kind of a pain given the access to the plugs on cylinders 2 and 3.

 

[powershift]

Low compression wouldn't cause miss-fires, nor would a faulty MAF. Coil packs, spark plugs and the connection between them could cause miss-fires.

 

[jlglr4]

Disconnected the purge from the top of the throttle body and stuffed a bolt in wrapped with electrical tape in. Lambda values are much better for now.

This is interesting. You can’t drive around too long with the purge disconnected or you’re going to get errors on the EVAP system. Plus that system needs to vent. But the fact that your lambda is better suggests a possible problem. I believe the purge should be closed without voltage. So, engine off, you can try blowing into the disconnected tube. No air should go through because the vent is normally closed. Engine on, you can listen to see if you hear a faint ticking from the purge. It will tick when commanded open (pulse-width control), but it shouldn’t be open all the time or for long periods of time. I think it is supposed to open at higher RPMs to vent so it doesn‘t change fuel control values too much. So, could be a faulty purge.

The other thing that I believe happens is the charcoal canister gets liquid fuel in it from people topping off the tank. That causes super rich fumes when the vent is open, which might explain intermittent problems (super rich when the purge opens causing high positive fuel trim, followed by lean when it closes until the fuel trim swings the other way). I also think (my conjecture here) a saturated charcoal container can actually cause the purge to suck liquid fuel and charcoal particles up into the purge valve, destroying the valve as well. If you see any liquid in that purge pipe, not a good sign.

Low compression wouldn't cause miss-fires, nor would a faulty MAF. Coil packs, spark plugs and the connection between them could cause miss-fires.

Not sure why you say this, but low compression can cause misfires, and so can a faulty MAF (underreporting MAF causing lean condition more likely to cause misfires than an overreporting MAF causing rich condition).

 

[scapistron]

I did go around the plug wires on bank 2 and give them all a shake. Engine was too warm to chase the wiring around the back, what I could get to back there was tighter than I'd like for wiring. I did notice that the small ground wire from the firewall to the collection of stuff at the back of the motor was rather loose, tightened that up. Haven't noticed any improvement from that though.

Riding around today I've noticed that the lambda equivalence (pre-cat sensor) seems to be behaving a lot better, always trending towards 1. Behaves just about flawless keeping the rpm between 1500 and 3000 while driving.

I'll take a closer look at the EVAP system this weekend. That valve might be sticking open. I'll see if I can force it to behave badly by getting on it and then coming down to an idle.

 

[powershift]

This is interesting. You can’t drive around too long with the purge disconnected or you’re going to get errors on the EVAP system. Plus that system needs to vent. But the fact that your lambda is better suggests a possible problem. I believe the purge should be closed without voltage. So, engine off, you can try blowing into the disconnected tube. No air should go through because the vent is normally closed. Engine on, you can listen to see if you hear a faint ticking from the purge. It will tick when commanded open (pulse-width control), but it shouldn’t be open all the time or for long periods of time. I think it is supposed to open at higher RPMs to vent so it doesn‘t change fuel control values too much. So, could be a faulty purge.

The other thing that I believe happens is the charcoal canister gets liquid fuel in it from people topping off the tank. That causes super rich fumes when the vent is open, which might explain intermittent problems (super rich when the purge opens causing high positive fuel trim, followed by lean when it closes until the fuel trim swings the other way). I also think (my conjecture here) a saturated charcoal container can actually cause the purge to suck liquid fuel and charcoal particles up into the purge valve, destroying the valve as well. If you see any liquid in that purge pipe, not a good sign.


Not sure why you say this, but low compression can cause misfires, and so can a faulty MAF (underreporting MAF causing lean condition more likely to cause misfires than an overreporting MAF causing rich condition).

If the OP comes back with compression measurements in all cylinders showing a problem or replaces the maf and the misfires in 2,4 & 6 go away, I'll gladly stand corrected.

 

[scapistron]

I've been focused on watching the live data on the air mass meters. Blocked off one MAF at a time so air had to go thru only one while the other read zero. Ran pretty well for a while, then I noticed the measured air come up nominally 20-25% with spikes up to double what would give a good idle and the misfires to follow along. After swapping my blocking plate from side to side, I noticed the same thing. Next step for me is to find a wiring diagram, or chase the wires themselves and see if there's an obvious problem. Worst case I think I'll splice something new in.

I just can't think of anything mechanical with the motor that would cause spikes in measured air. So my current hypothesis is, bad wiring is giving false high air measurements. Leads to a lot of fuel and a measured rich condition on the O2 sensors. This is backed up by the visible soot on the replaced plugs and o2 sensors.