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L405 Low Fuel Pressure- Not HPFPs
Hey guys,
I have a 2014 L405 with 96k miles on it. I had about four codes relating to the fuel pressure so I changed both HPFPs with two known good units but I am still getting these codes: P0087- "Fuel rail/system pressure - too low" P228F- "Fuel Pressure Regulator 1 Exceeded Learning Limits - Too High" If it was a bad injector, I would expect high or low fuel trims or a misfire code, but I don't see any of that. Does anyone have any ideas or any direction you can point me in? Thanks |
Seems to be pretty clearly pointing towards a fuel pressure regulator issue, or an issue with fuel flow through through the lines. Have you done a fuel pressure test?
Any reason you've ruled that stuff out? And have you run BG44k through the system? |
SOLVED
I'm not aware of any fuel pressure regulator on these? I thought the fuel pressure was controlled by the metering valve on each of the high pressure fuel pumps. I have not attempted to clean the injectors out. I did not see any particular misfires, just the low pressure code. The issue ended up being the fuel pump camshaft being out of time! I checked it and the shaft appeared to be about 180deg out of time. I took the front cover off after some work and fenagled the timing back in spec and it works great with no codes! I have had the same issue on a 2014 LR4 with the 3.0L engine. That one had codes for high fuel pressure and no issue running. This one had the same issue with the fuel pump camshaft being out of time but different codes. I do not know the cause in either case and neither one has had an issue since.... |
That's awesome. Good sleuthing. I should have said fuel pressure regulator *or sensor* - I haven't chased fuel problems very many times with these. Looks like the sensor was telling the truth though on this one.
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Nice description of the diagnostic process from another thread.
Post by LR Techniker: This is where diagnostics come into play. You actually have three pumps: Low pressure pump mounted in the tank and two high pressure pumps (HPFP) mounted on the side of the block. HPFP usually are the cause for extended cranks and fault codes, but every time a tech just assumes it needs HPFP and doesn't test, it ends up being the low pressure pump. The low pressure pumps generates about 70-80 PSI and feeds the HPFPs fuel, they in turn generate a few thousand PSI to feed the injectors. HPFP can't do their job if they don't have any fuel. With a scantool and the engine having sat overnight, look at live fuel pressure data as you turn the car on, but DO NOT CRANK. HPFP only work when engine is rotating. So with KEOE, the rail sensors will read low pressure pump, should be around 70-80 PSI. If you can't generate this, you either have a bad low pressure pump or a leaking injector. Typically a leaking injector will also induce rich faults or even misfire as a single cylinder becomes flooded. If low pressure is good, then crank and watch what rail pressure sensor does. It should go up considerably. I'm not at work, so I don't have my notes in front of me, but I think cold start-high idle should generate over 2,000 PSI. Factory diagnostics (SDD) has a test plan to isolate a faulty HPFP, but if I have come to the point where I"m sure its one of them, I just do them both. It seems silly to do the labor to access them, to not just do the other considering how inexpensive the pump is and the frequency that they fail. You will also want to remove the tappet down inside to inspect for damage. Occasionally they wear out and need replaced as well. One last thing that needs checked is fuel pump camshaft timing. We really don't see this too much, but we have the tool to check it just to be sure before we sell pumps. The HPFP is driven by its own shaft, chain driven off the crank. It has to be timed correctly to generate pressure when its needed, otherwise the pressure will be low. |
Originally Posted by hlang52
(Post 870077)
Hey guys,
I have a 2014 L405 with 96k miles on it. I had about four codes relating to the fuel pressure so I changed both HPFPs with two known good units but I am still getting these codes: P0087- "Fuel rail/system pressure - too low" P228F- "Fuel Pressure Regulator 1 Exceeded Learning Limits - Too High"If it was a bad injector, I would expect high or low fuel trims or a misfire code, but I don't see any of that. Does anyone have any ideas or any direction you can point me in? Thanks |
Originally Posted by adamolan
(Post 873422)
Seems to be pretty clearly pointing towards a fuel pressure regulator issue, or an issue with fuel flow through through the lines. Have you done a fuel pressure test?
As far as a fuel pressure regulator- I am not aware of any regulator on this system. All I know of is the two fuel metering valves on the high pressure pumps that regulate fuel pressure by increasing or decreasing the volume of fuel flowing through the pumps. |
I think that "adamolan" you're replying to is a spammer - I reported the post but they just copied part of one of my replies up above and reposted it. Maybe to get their post count up so they can post spam links? Not sure...
Just fyi, I clarified later I should have said fuel pressure sensor not regulator. |
I've also seen elsewhere that there is a programming update that loosens the code set criteria for the pressure sensors. Apparently to get rid of some nuisance faults like these.
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Seems to be pretty clearly pointing towards a fuel pressure regulator issue, or an issue with fuel flow through through the lines. Have you done a fuel pressure test?
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