Code P008792 low fuel pressure at the rail.
2012 E550 with M278

I recently had a bad a bad injector that was replaced with a known good used one, and I had an Autel to change the serial number and check everything. Install went smooth and car idled for close to 10 minutes without issue. Went for a test drive and about a mile down the road started getting misfires and weird surging, so I quickly turned around to head home, but the car stalled a couple blocks away and wouldn't restart because the battery was low from sitting a couple weeks. Besides misfires from the lack of fuel, that was the only other code.

Charged the battery overnight and tried it again. It fired up but ran very rough and was smoking. Cleared the codes with my Carly and read again; same P888792 and random misfires.

What's the best way to trouble shoot if it's the low pressure pump or one of the high pressures? I only see one Schrader valve on the rail and it's on the drivers side. Then, how would I tell which HPFP is the bad one?

Missing driving my car, so any help is greatly appreciated.

 

Your ECU has narrowed down a low fuel pressure issue.

> 3 pumps bingo...
either one of the dual HPFP or tank pump/filter.

Confirm the tank pressure data... 60Psi ?
Confirm the rail pressure data... 3000Psi?

You can also confirm the LTFT are rich to rule out bad rail sensor.

 

So, the pressure at the Schrader valve on the driver side was at 70psi at cold start and was pretty smooth. After a couple minutes it started running rough, just like last time, and the pressure would bounce between 50 and 70psi.
LTFT on bank 1 is 13.3% and bank 2 is 16.4% and would indicate a lean condition.
Fuel rail pressure is at 1490 kPa ~ 216psi. I'm assuming that's at the sensor on the passenger side and way out of spec.

A bad HPFP is looking like the culprit. Is there a way to determine if it's the left or right one?

 

Q: Left or right HPFP ?
Both or None.

The HPFP's work and die together doing the exact same job will very little oil pressure at the very end of the conduit.

Your bonus parts are for the nearby PCV maintenance due at the same mileage.

You can need to confirm results with a dial gauge on rail if the 216Psi pressure is valid or not.

Target is near 2500 to 3000.Psi.
There is a case where pressure range is truly correct but sensor is literally toasted.

 

Well, I replaced the HPFPs and there is not change and I am getting a number of codes. I was before but the scanner description didn't make them sound like anything to do with fuel. Here are the codes I am getting now:

P00A1 - Charge Air Cooler Temperature Sensor Circuit (Bank 2)
P0095 - Intake Air Temperature (IAT) Sensor 2 Circuit
P00C2 - Turbocharger/Supercharger Bypass Valve 'B' Control Circuit High
P0087 - Fuel Rail/System Pressure Too Low
P0300 - random or multiple cylinder misfire
P1CCF - fuel high-pressure system fails to build enough pressure during engine startup

Did a bunch of stuff just fail at once or is this all tied to to a specific issue? Started with an injector, then multiple issues. There were no issues I could tell before the injector started. I am kind of lost as to all these failures and tired of spending money.

 

The only way to not replace good parts is to troubleshoot things up front and not jump to conclusions without testing. You had done both.

Your rail pressure was measured from 70Psi to 200Psi with a gauge.
What is rail pressure now ?
What is the tank pressure ?


> Valid faults or not...
Did you clear faults after repairs, yes ??
Are these faults status: current or stored ?


> ELECTRICAL issue..
The following faults read like an electrical issue but here the pressure gauge confirmed pressure was truly low, not sensor issue.

P00A1 - Charge Air Cooler Temperature Sensor Circuit (Bank 2)

P0095 - Intake Air Temperature (IAT) Sensor 2 Circuit

P00C2 - Turbocharger/Supercharger Bypass Valve 'B' Control Circuit High
If I had to guess what these 3x circuits have in common is a shared GND...

Fault says "high" meaning power is there (fuse ok).

Pull the schematic to check these circuit. May be a harness issue: cut up or oily.

 

What is your M278 mileage and what model of Autel scanner are you using ?

For Low Pressure Fuel Filter proper inspection, you can follow my method : Post #12
https://mbworld.org/forums/e-class-w...ml#post8568085


Our fuel filter and low pressure fuel pump flow rate wont be different by much, but your engine can burn more fuel than mine for sure, by at least 100HP more.
So in theory, if you drive hard like I do 100% the same, your fuel filter will clog sooner than mine, because you use more fuel...as simple as that.





Here is something for you to know.
Anyone who replaces their High Pressure fuel pump ahead of their low pressure in tank fuel filter, is not understanding fuel filtration enough.
If you are to replace HP fuel pump, low pressure fuel filter must be replaced too because HP fuel pump life ( for fuel pumping ) depends a lot on how clean your fuel is.
HP fuel pump has 2 sections, above in blue its the 1st section. The 2nd section is the engine oil bath section , this is the easy one but wear and tear on the roller push bearing can happen.

The roller bearing





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This is how precise the tolerance of the HP fuel filter long thin piston sliding in and out of its sleeve or imagine cylinder bore or cylinder liner.

Part 1

.
Part 2


.

The gasoline itself is the lubrication of the thin piston sliding inside the cylinder wall or liner/sleeve, no piston ring like our engine piston, no engine oil to help lubrication....simply gasoline is the lubrication.
Very much like how diesel fuel pump uses diesel fuel as lubrication and cooling system. So fuel cleanliness is everything.






Close up of Audi aftermarket HP fuel pump upgrade kit for its piston and the liner/sleeve , also a GDI system.
https://www.fcpeuro.com/products/aud...ort-0341066052


Look , no piston ring. It is simply precision machining tolerance.


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If you want me to help you ( I will try my best ) ....
Show me a complete STORED or CURRENT DTC of yours as per your scanner using photos.
Give me your VIN so that I can find the correct wiring diagram for your M278

Here is what you wrote :
01- P00A1 - Charge Air Cooler Temperature Sensor Circuit (Bank 2)
02 - P0095 - Intake Air Temperature (IAT) Sensor 2 Circuit
03 - P00C2 - Turbocharger/Supercharger Bypass Valve 'B' Control Circuit High
04 - P0087 - Fuel Rail/System Pressure Too Low
05- P0300 - random or multiple cylinder misfire
06 - P1CCF - fuel high-pressure system fails to build enough pressure during engine startup

This information is not very useful without the whole back-story, because whenever you remove HP fuel pump/s, the first few seconds of trying to start the engine will be low pressure,
air bubbles which will cause misfire and yada yada, which can cause 04 , 05 and 06.
This is why CURRENT or STORED status of these DTC is a must to know.

If you did not plug back connectors properly after the HP fuel pump job, and you do Ignition Key ON engine off, or key position 2 ( before engine crank ), that alone is enough to produce
01 to 03.

The proper way before any engine start/running when working on an engine is :
01 - Run diagnostic when all connectors are already back in place.
02 - Remove any DTCs.

03A - Prime ( using bi-directional ) low pressure fuel pump to fill into HP fuel pump and its injector rail. This is 5 BAR pressure.
03B - Leak out air bubbles at most distant fuel injectors from HP fuel pump. Prefer each bank you leak out air bubbles from its most distant injector/s.
This process will reduce bad/difficult start or misfire by much. I done this already 4 times.
I have bled dry my HP fuel system 4 times. Thus I must primed it.

04 - Run engine say 3 minutes, shut off engine, cylle ignition.... and see what new DTC/s you get, by now any DTC/s will be STORED one.

This is my engine after 60 days being worked on and fuel system bled dry at both low and high pressure side.
I primed it properly etc etc and started the engine :


.
Yep, the air intake boxes I flipped them forward so that can inspect fuel leak better.
The air intake boxes pressure sensors (2 ) are installed at its connector but not at the air boxes, so no DTC/s.

See how long it took for my engine to crank, but there is no bad misfire because I primed it properly using bi-directional control.
NOTE : fire extingushers ( 2 ) standing by all the time , because I am leaking fuel out of the union nut of the injectors.

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Scanner is only good when you know how to use it properly as in : when a DTC is a true touble DTC or the DTC is self-made DTC because we have not completed the connectors plug in, or similar.
I hope you understand what I am saying.

Also to note : Often it is wiser to let a professional workshop throubleshoot for you rather than doing DIY, when and if your skill is not suitable of the task.
No offence, it is the truth.

Owning a scanner is only one of the many MUST HAVE, the other MUST HAVE is the knowledge if the system you are working on and a few more skills which made
we DIY-er will often need professional workshop help.

Now let me ask you, do you want to carry on troubleshooting your M278 DIY ?
If so, how competent are you reading electrical schematic ?
Do you have access to MB WIS and EPC, the ebay version is OK, same as genuine one anyway.
Are you decent with DC electrical works ?
Do you have proper tools to troubleshoot DC electrical works ?

IF AND WHEN NEEDED :
Do you have access to an at least 4 channels oscilloscope, when and if needed to trace ignition related signals to COP/Ignition of to HP fuel pumps quantity valve or to the piezo injector.
BTW , our piezo injector is very close to 200V, so you need additional accesories for the oscilloscope to handle the high voltage flip flop signal of from engine computer
driving them piezo injectors.

If you are in the US, you are lucky for GDI piezo injector test facility, it exist . My country has only diesel common rail testing facility, not GDI albeit 200 BAR only GDI :
https://mbworld.org/forums/e-class-w...intenance.html


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So, are you up for the DIY challenge ?