Those negative LTFT indicate that you are flooding your cylinders with excess fuel and the ECU is trying to reduce fuel. Since it is with both banks, the problem isn't with a single cylinder 1.

Did you say you replaced your HPFP?

 

Didnt replace HPFP, I replaced the passenger side in tank fuel pump with a used OEM one because the car wouldn’t start with the aftermarket one, driver side in tank fuel pump is still aftermarket didn’t touch that.

 

Reread every post again. You have done the standards swaps, visual of cylinder 1. Compression and leakdown tests?

Can injector 1 be blocked, and ECU increases amount uniformly -> too rich because #1 is clogged?

Recall West's clogged fuel rail at cyl 1? Someone polluted the fuel rail?

Just a guess

 

You have an M276.9XX engine which uses a single HPFP on the passenger side (Bank 1) to pressurize the fuel rail to both banks. Could the prior owner have also replaced the HPFP as well and there is a chance he bought it off of AliExpress or Temu? (AliExpress does sell them.)

 

The HPFP seems to be original

 

It may be hard to tell without removing it. It's kind of buried on the back of the engine. I'm not doubting you, but how to tell? I was going to replace mine and decided to wait until I had symptoms that it needed replacement. I have 130,000 miles on my 2014 C350 (same engine) and knew it was going to be more work than I was in the mood for at the time.

It's apparent that there is a fuel delivery or monitoring problem, and you seem to have addressed the more probable problems. Apparently, the previous owner was also having fueling problems. Otherwise, why replace the in-tank pump and filters?

 

When I had the intake removed earlier I inspected the HPFP.. I bought the car as a no start.. found both in tank pumps aftermarket. I replaced the passenger side and the car started. The driver side is still aftermarket, could this be causing fuel delivery issues..?

 

if someone took the fuel rail out already, all the bets are off . A piece of a seal could end up at the entrance of the injector. It has happened already here

 

I don't have an E-Class, but I'm sure @S-Prihadi could tell you. My understanding is that you have a saddle tank and one of the two pumps you have is a filter and the other is the pump feeding fuel to the HPFP. I'm not sure which side is which. The HPFP also acts as a fuel pressure regulator (FPR) that traditional fueling systems use. So, I think anything tank-side of the HPFP would have no effect on what we are seeing.

If your fuel trims were limited to only one bank, then maybe a bad injector, etc. But since both banks are having excessive fuel, I would look closely at what affects both banks: HPFP, ECU, ???

 

Or, bad fuel, dirt, debris contaminating the fuel rail.

 

The HPFP runs from cams on the cam shaft. If there is a fuel delivery issue could it be the lobe on camshaft for cylinder #1 is worn.

Then, if the roller lifter of the HPFP is damaged it would mean not proper fuel delivery (but this would go to all cylinders). This should show in the fuel rail pressure. Can the scanner OP use read that?

 

I think this is where Xentry becomes necessary to read engine data beyond what Foxwell exposes.

We could focus on...:
HPFP duty cycle
VVT gear PWM solenoid activity
CPS positions
....

Xentry won't give us codes the ECU has not flagged but will give us data to doctor wicked condition.

 

Fuel rail pressure is 14870 kPa

 

I'm trying to find what the rail pressure should be, but 14870 kPa is approximately 2160 psi. Did you mean 1487 kPa?

 

2160psi is about right

 

 

Never mind. 14870 kPa is equal to 148.7 bar. I need confirmation, but I think the lower and upper limits of the fuel pressure are about 180 to 220 bar, making the rail pressure less than the lower limit. There is something definitely wrong.

 

Thanks. I also found that. The warning is even more scary!

Still, 2160 psi is far less than the expected 3000 psi. Something is wrong. The HPFP test in XENTRY is expecting to see 180 to 220 bar.

 

So my HPFP could be bad?

is there a way to confirm?

 

If you have XENTRY, there are tests you can perform. I'm not sure you can run the tests with Foxwell. That's why I really encourage people to reach out to @BenzNinja for XENTRY and diagnostic support. Below is the test report when using XENTRY Simulation, so it doesn't show actual measured values, only the boundary values.

 

I don’t have xentry just have an Autel scanner

 

Fuel pressure for M276.8 3.0 Turbo, which should be similar to M276.9 3.5 NA is between 120 to 190 BAR.
Depending on being at idle or WOT or light load.
If WOT or deeper accelerator pedal, it will be reduced to approx 150 BAR as certain high enough throttle body opening.



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All above from a single log.

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This is from another log. WOT event



Hope this data helps

 

Any idea on what can be causing both banks to run rich..?

 

Here is my thought :
AA. The combustion control for AFR is done by two sensors : B17 Intake Air Temperature Sensor and B28/7 Pressure Sensor downstream of throttle body, we call this as MAP ( manifold absolute pressure sensor )
BB. The VERIFICATION of AFR is done by the front wide band o2 sensors.

AA assumed that the injectors are injecting fuel properly in terms of spray pattern, open and close at the proper time ( quantity ) as per command by the ECM and the COP is also firing properly and Ignition timing is also proper.

AA and BB work together, when in CLOSED LOOP.
BB or front 02 sensors are ignored when in OPEN LOOP, as the ECM is using the prepared fuel MAP in its memory/database.


What if-s :

01. What if the AA sensors are not showing actual true value, particularly the B28/7 Pressure - MAP ?
To test it, at least in reference to ambient air pressure is easy. to test it full pressure spectrum you need more special tools.
Test at ambient atmospheric pressure : Engine OFF, Ignition Key ON, read the Manifold Absolute Pressure, it should be within 3% of your actual barometric pressure of your car location/garage.
If you have a hand vacuum pump and assortment of clear hoses, you can suck the sensor with vacuum pump to the hand pump maximum capability and check the pressure
as read by scanner vs the analog needle gauge of the hand vacuum pump. Not the most accurate, but if B28/7 can't read to 29 inch HG, that is an alarm bell.

The B17 Intake Air Temperature Sensor is easy to test, current room temperature and use hair drier gently.


02. What if the front o2 wide band sensors reading wrong ? Its service life is supposedly 100,000 miles and 15 years in non racing application. It is a Bosch LSU4.9.
https://www.boschautoparts.com/docum...20Brochure.pdf

The only way to know or test is to go to an Emission Test center, where their unit has Lambda sensor too. Go and compare.
BTW, now is a good time to renew all 4 o2 sensors anyway. Yours have hit the mileage and 10 years being blown by exhaust gases at up to 900C is a severe working condition.


03. What if the High Pressure Fuel Sensor and Temperature sensor is out of calibration ? This is called B4/25
You can only test at ambient pressure if it is reading proper ambient pressure or not. Can't test full spectrum pressure without special bench tester.
Read here, mine drifted 7 BAR when supposedly at zero BAR.
https://mbworld.org/forums/e-class-w...re-sensor.html


04. What is the High Pressure Fuel pump Quantity Valve is not operating properly ? This is called Y94
If the B4/25 high press fuel sensor is good from a known good sensor, pressure reading while under load like my log can tell if Y94 is bad or not.


So, there you go............ AA and BB components are the one you must verify.

 

When I start the car the fuel rail pressure is at about 20000 kPa. After a few minutes it drops to 14000 kPa and starts misfiring.