Persistent misfire under load only

[scapistron]

Just the bank. I'd probably start launching the parts canon, but I'm more of a replacer than a proper technician.

1. Low pressure fuel pump and low pressure sensor.
2. Fuel injectors.
3. High pressure fuel pumps.

I'd probably go in that order.

 

[Jimmy Brooks]

I replaced both the High Pressure and Low Pressure Fuel pumps with my recent build.

This does seem like it could be an issue with the fuel supply and the symptoms are identical to work trucks I drive (land cruisers) which, due to very poor fuel, get the fuel strainer/filter in the fuel tank clogged. That causes a host of issues like this.

Fortunately, in that case, the filters just need to be replaced which requires "only" dropping the tank and doing a service.

Meanwhile, I am working through my own low pressure fuel pump and fuel tank issues.... which you can check out at the thread:

Fuel Gauge Reading Off

Tribe, An update on this job from my side. So I went ahead and ordered “Fuel Sender and Hanger Assembly” - Part Number: LR042974 (Supersession(s): LR015937) from the Team at Land Rover Palm Beach. They were super helpful and did a great job boxing everything up and sending it out. Photos...

www.landroverworld.org

The short of it is that I am replacing the pump and sending unit as well as both fuel level sensors / float assemblies.

Hopefully that will resolve the current issue - which in my case is now the fuel gauge reading zero.

Good luck!

If the fuel filter is built into the low pressure pump then wouldn’t I have to replace the whole unit or could I clean the filter?

Luckily for me this is a D5 which means I should be able to get to the low pressure pump through the cabin without having to drop the whole tank (unibody).

 

[Jimmy Brooks]

It's a mystery. Fuel trims really look like a vacuum leak, but the failure under throttle really looks like fuel delivery issues (or spark issues). You also have fuel trim issues on both banks, but a misfire issue that appears to be only on one bank. Maybe there are two different problems happening at once.

Very strange that there is no code after having the check engine light and restricted performance set. If you have another scanner, even a generic one, I'd try it to make sure the Gap tool is not malfunctioning. Or maybe have autozone or oriellys scan it for codes.

I would run the fuel trims again - make sure they really are cleaning up at high RPMs. Maybe also record fuel trims under load, but cruising, not under acceleration. When you accelerate, the car will go back into open loop, but if you are cruising with steady throttle at highway speed, you will be under load and should be in closed loop - at least that's my understanding. If they are worse under load, then it really does point to fuel pumps.

Looking back at your smoke testing post - did you have the smoke test running key on or key off? If the throttle body was closed up, you might not have tested for leaks between the MAFs and the throttle body (I think that purge valve connection is on the engine side of the butterfly valve, thought I'm not sure).

Still other things to consider: Maybe the fuel pressure regulator - we've seen reports of these failing in this forum. Fuel pressure driver module is another point of failure. MAP/MAPT sensors might be another issue (actually two sensors on this car I believe), but I don't know if there is a way to check that on the GAP tool. Electric throttle body...not sure how this would affect fuel trims or how to test exactly, though I think you can get some parameters from the GAP tool.

To answer your earlier question on o2 sensors, car needs to be warm so it's in closed loop.

Misfires on one bank should only affect that bank - fuel control is bank by bank, so it can certainly affect any cylinder on that bank, but it would not explain the fuel trims on both banks.

Ran fuel trims after the whole experience. Ran it up to 2000 rpms and they were cleaning up, pulling I believe negative 16-18% on the STFT with about 23% on the long term on both cylinders.

When I did the smoke test through the purge valve in the intake I had the intake duct all duct taped and when I pulled the duct tape off smoke poured out so it was making its way into the space between the throttle body and the MAFs.

The misfire thing confuses me, to my understanding I think it’s random on any cylinder which is why the computer won’t catch it 90% of the the time under any type of throttle. I find it odd that it finally recognized it and it happens to be on the same bank and involve one of the same cylinders.

I doubt it has a code stored because no check engine light but I will stop by an auto parts store to get the codes read. I’ll yeah the lambdas between the O2 sensors and I’ll get live values on the fuel trims at consistent throttle under highway speeds.

 

[Land Rover Joe]

If the fuel filter is built into the low pressure pump then wouldn’t I have to replace the whole unit or could I clean the filter?

Luckily for me this is a D5 which means I should be able to get to the low pressure pump through the cabin without having to drop the whole tank (unibody).

So there is a strainer on the fuel sending / low pressure fuel system - highlighted in red. However, what you are really concerned with is the fuel filter itself, which is integrated on the fuel tank seal / cap assembly - which is the white plastic thing behind the sending unit in my photo attached (003). You can see this a little more clearly on the workshop manual diagram attached ("Fuel Delivery Module Diagram") - #7 is the plastic "sock" and #10 is the actual fuel filter integrated inside the fuel tank cap/seal.

That filter is the one that is likely to get gunked up and then restrict flow from the LPFP pushing fuel to the HPFP's located on the engine (bottom right hand side). Without adequate fuel to the HPFP's...they simply cannot get more gas to the engine. This is one possibility....

The last photo shows my "Box of Parts" from Atlantic British. The short story is that when I had the failure of fuel level...I went forward to replace everything in the fuel tank. However...little did I know that the (two!) float level sensor assemblies were not included (!!!) So we replaced the LPF, cover/filter, and o-ring but not the parts that were actually the problem. Fuel pump is on the right, the cover with filter on the left, and the O-ring on top.

While a bit wasteful, I feel this was time to go ahead and do anyway given the life of the truck so I am not too worried about replacing parts early (dropping the tank is a pretty big PIA).

But...there apparently is an upgrade for the fuel tank cover (separate threads on that from @gsxr ) and I ended up buying the older variants....

Hope that helps and this is vastly different than on a diesel Land Cruiser which has these great purge fuel filter assemblies which use a centrifuge filter system. Those are really easy to deal with and in my opinion, far superior in overall design for ease of maintenance. The Land Cruiser I spoke of with weird power issues was a gasoline engine and has a media filter (like the Land Rover). The issue I was having with my work Land Cruiser was that I would get to about 40 mph and then 2,000 rpm; I would hit the gas (to go uphill or pass)....and nothing would happen. Nothing: 2,000 rpm. It wouldn't make a difference no matter what I would do, I couldn't get more power (rpm) out of the truck. The problem, I found out from our fleet mechanics, was due to using a terrible fuel point with water and rust and who-knows-what in the tank which then wrecks the gasoline fuel filter, which just needs to be replaced periodically. Would be better to get a new storage tank....

 

[RossN1999]

Also used a smoke machine to check for vacuum leaks but turned up nothing. Check engine light came on again and still only had two codes, p0483 (fan performance, frequency too low) and p0430 (bank 2 cat efficiency). No misfires codes but definitely feels like it.

 

[Jimmy Brooks]

Sorry for taking a bit. I just replaced the rear upper control arms on my LR4 so I’ve been focused on completing that. Finished that all up, drove to the alignment shop to get my car aligned and found out that the rear toe links are completely seized and the shop can’t adjust them… great! (I can’t win)

ANYWAY,

Took some live values today the first one is of the fuel trims at 61 mph under consistent throttle. The fuel trims clean up really well. At about 3.5 I let off.

The second and third are low pressure and high pressure desired vs actual pressures. The high pressure pump seems to consistently be about 10psi lower than desired. At idle the it ranges from 416-424 when desired is 434. However the low pressure is a bit all over rhe place. Maybe this is normal?? The first screenshot is the biggest low pressure difference that I saw under load, this was during the point where misfires were getting worse. The second is a random difference that I saw and was not sure if it is normal

For the lambda values on the O2 sensors should the car be idling in park when I take the log?

 

[jlglr4]

My rail pressure looks about the same from past logs. I don’t have much data on the low pressure side. But seems like fuel rail pressure is what really matters. If your low pump is misbehaving badly enough to cause a misfire, you should see it in the rail pressure as well. If it’s not affecting rail pressure, then it shouldn’t be affecting drivability.

For lambda values, idle is fine. Car should be warmed up. I think some people also check at higher RPMs, but you need to hold the throttle steady to keep the car in closed loop mode.

 

[Jimmy Brooks]

Hey all, sorry for the week late response. I had surgery on Tuesday and have been recovering since. Today was the first day I felt like a human again so we are back to diagnosing!

Here are the lambda values at idle and 2000 rpm. You described them in a wavy fashion and that seems like exactly what mine are putting off.

I’ve been thinking about things that are upwind of the engine that would make the whole engine run this way. As all the sensors seem to be reading right I thought of something that hasn’t seemed to happen on this forum but would be interesting. What if the purge valve was stuck closed?? Would these symptoms makes sense

 

[Jimmy Brooks]

Tested the purge valve and it works just fine. Any more ideas, what would make the entire engine run odd.

 

[jlglr4]

Sorry to hear about the surgery, but glad you are recovering. The o2 sensors do seem to be responding. I’m trying to think of all the things that would cause a lean condition on both banks. Seems like the most common would be vacuum leak, MAF, fuel pump/pressure, fuel rail pressure sensor. Could also be dirty injectors on both sides, coolant temp sensor, MAP or MPAT sensor, supercharger bypass valve.