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Hello all! My 2015 S63 cuts off power under hard acceleration, check engine light comes on and gives code P0087 - fuel rail/system pressure too low. A local shop did testing and said that the low pressure fuel pump shorts out and drops to 0 under hard acceleration. Check engine light goes away after 2-3 cycles of start/stop. Anyone else have this issue? If so what’s the fix?
18 AMG GTC and 22 F150 Limited. Past owner 16 Maybach, 17 Brabus Smartcar, 06 Ford E150, and 22 G70
Think I would attach a mechanical fuel pressure gauge to the fuel rail and run the line into the cabin and then drive the car and see if you are experiencing the low pressure. If so then its probably time for a fuel pump. If you dont have fuel pressure drop perhaps you have a bad pressure sensor.
All Cars Lost To Hurricane Isaac (W124 E420 revived - added 88 Allante 14 S550, 17 S63
Originally Posted by Katie22
Think I would attach a mechanical fuel pressure gauge to the fuel rail and run the line into the cabin and then drive the car and see if you are experiencing the low pressure. If so then its probably time for a fuel pump. If you dont have fuel pressure drop perhaps you have a bad pressure sensor.
removed - not relevant..
see bulletin posted elsewhere
Last edited by kafklatsch; 04-16-2021 at 01:11 PM.
Reason: removed post due to better information posted
Hello all! My 2015 S63 cuts off power under hard acceleration, check engine light comes on and gives code P0087 - fuel rail/system pressure too low. A local shop did testing and said that the low pressure fuel pump shorts out and drops to 0 under hard acceleration. Check engine light goes away after 2-3 cycles of start/stop. Anyone else have this issue? If so what’s the fix?
The referenced TSB seems a bit misleading into saying the car acts low on gas... then finally change the tank.
Nothing too interesting besides the 50% duty cycle to build up pressure.
sample low pressure pump control
I believe this problem has its roots in a wiring issue that disrupts CAN signaling.
Last edited by CaliBenzDriver; 07-24-2021 at 12:13 PM.
Hello all! My 2015 S63 cuts off power under hard acceleration, check engine light comes on and gives code P0087 - fuel rail/system pressure too low. A local shop did testing and said that the low pressure fuel pump shorts out and drops to 0 under hard acceleration. Check engine light goes away after 2-3 cycles of start/stop. Anyone else have this issue? If so what’s the fix?
My former 2017 S63 did this exact same thing at 70,000 miles on it. Fortunately it happened when I was only 3 miles away from the dealership. I limped it into the service bay, they checked it out and couldn't reproduce the issue and did not find anything wrong. It happened earlier that same day several miles away. I drove it another 10,000 miles with no reoccurrence of this problem and then I decided to trade it off for an S560 due to the expense of rotors, brake pads, tires, etc. The only thing I could blame the problem on was bad gasoline as I did fill it up that morning.
On my M276, the LPP OUTPUT PRESSURE IS FLAT regardless of Rpm.
3k Rpm LPP pressure: 4.5Bar (+/- 0.3)
The FSCU manages the pump output to keep up with the gas HPP has used up.
It seems like LPFP is NOT involved with boosting pressure for acceleration. Injectors duty cycles is used for enriching acceleration mixture with a fine granularity.
LPFP output PRESSURE SENSOR is connected to R-SAM, not directly tied to FSCU.
** nop: I think pressure data gies direct into controller. Both fuel gauges go to R-SAM **
Last edited by CaliBenzDriver; 07-04-2022 at 12:53 AM.
The referenced TSB seems a bit misleading into saying the car acts low on gas... then finally change the tank.
Nothing too interesting besides the 50% duty cycle to build up pressure.
sample low pressure pump control
I believe this problem has its roots in a wiring issue that disrupts CAN signaling.
I initially had a p008a/CEL, no noticeable performance issues, although since then I might have gotten the jerking once. I had 30-60psi at rail. I changed fuel filter fuel pump and fuel pressure sensor, in that order, a tank of gas between each part. Filter did nothing to codes. Pump got pressure to 65psi, but caused P0087 to confirm, although never permanent or setting off CEL. Fuel pressure sensor got rid of the p008a, but p2540 and p0087 persist in the background, no CEL. Gas light comes on at 1/8 of a tank, a little earlier than expected.
Edit: What makes you think it's electrical? Anyone ever get anywhere with this?
I initially had a p008a/CEL, no noticeable performance issues, although since then I might have gotten the jerking once. I had 30-60psi at rail.
I changed fuel filter fuel pump and fuel pressure sensor, in that order, a tank of gas between each part. Filter did nothing to codes.
Pump got pressure to 65psi, but caused P0087 to confirm, although never permanent or setting off CEL. Fuel pressure sensor got rid of the p008a, but p2540 and p0087 persist in the background, no CEL. Gas light comes on at 1/8 of a tank, a little earlier than expected.
Edit: What makes you think it's electrical? Anyone ever get anywhere with this?
The 3-Phase LowPressureFuelPump module in GDI engines is signalled directly by the ECU CAN-C. This is an extremely noisy setup with little filtering and extra long leads for GND at trunk and Positive feed from footwell.
Can you pls translate your fault codes into english description so things make a bit more sense.
The part I understand is you used to get 30 psi and now back to 60Psi but still with some faults including faulty tank gauge, right?
Tank gauge level is a different can of worms because the fuel level is a CALCULATED VALUE by R-SAM using both sensors of saddle tank sides.
The 3-Phase LowPressureFuelPump module in GDI engines is signalled directly by the ECU CAN-C. This is an extremely noisy setup with little filtering and extra long leads for GND at trunk and Positive feed from footwell.
Can you pls translate your fault codes into english description so things make a bit more sense.
The part I understand is you used to get 30 psi and now back to 60Psi but still with some faults including faulty tank gauge, right?
Tank gauge level is a different can of worms because the fuel level is a CALCULATED VALUE by R-SAM using both sensors of saddle tank sides.
This attachment PDF is the known problem, and all three codes are explained in full there better than I can rewrite. This is absolutely the heart of the issue, precisely what's going on is the question.
I know the new fuel pump was required given the low pressure, but I'm still not sure I'm up to the required low side pressures. I just measured it at idle. The old pump got as low as 30 and the new one stayed around 65. I didn't correlate that with any idle speed. I'd have to borrow another fuel pressure gauge again, as well as find specifically what the PSI is supposed to be at what RPM and check to be sure.
Since the pump filter and sensor are all new I'm curious if some slight scorching marks on the lp pump harness could cause this.
Fuel pressure is a really interesting topic made confusing. I don't get the TSB mix up between fuel pressure faults, tank level issues, filter and a new tank. It's all wrapped up.
The tank pump output stays constantly flat regardless of RPM. That's the regulation the controller does.
When it's extremely bad the pressure drops under heavy acceleration demand.
You can read the pressure through scanner without hooking external dial gauge.
Once HPFP supply is proven stable, the engine has a better chance to hold near 3000PSI under load.
Last edited by CaliBenzDriver; 02-26-2024 at 10:16 PM.
Fuel pressure is a really interesting topic made confusing. I don't get the TSB mix up between fuel pressure faults, tank level issues, filter and a new tank. It's all wrapped up.
The tank pump output stays constantly flat regardless of RPM. That's the regulation the controller does.
When it's extremely bad the pressure drops under heavy acceleration demand.
You can read the pressure through scanner without hooking external dial gauge.
Once HPFP supply is proven stable, the engine has a better chance to hold near 3000PSI under load.
I have a blue driver scanner, I can see high side pressure, which has never dipped below 2140 and has been as high as 2950. I don't think I can read low side pressure with it, unless you can tell me how. And I've read conflicting information on what the fuel pressure low side is supposed to be. 65 or 100 psi.
I can say this TSB is as vague and off the mark as the one put out for the very common Mercedes startup rattle that's due to an upper hydraulic timing chain tensioner not getting its oil quick enough ala to oil starvation, which then buggers the VVTs due to chain slap that is the "rattle". Mercedes solution is to put a check valve in the block behind the tensioner 🤦🏼 They think the problem is the oil draining from the tensioner after shut off rather than it not getting the oil quick enough to begin with. A quart of ATF in the engine for 500 miles would fix this better. Anyway, I fixed that issue 3000 miles ago and now I'm on to this one.
Since I saw some scorching on the pins, I'd love to replace the in tank wiring harness that goes from the top of the fuel pump (passenger side) to the underside of it's corresponding left side cover A2044700494, but I'll be damned if I can figure out what it's called for the part number. GLK 350 2013. Is there a way to scan over all the parts and pick what you need?
You can read the tank low pressure pump from the FSCU Module. It's directly connected to the main engine bus.
60Psi supply pressure needs to hold regardless of ECU demands on HPFP.
The pump harness connections are known to get oxidized... perhaps from not being effectively water sealed.
Check your old pump for any signs of electrical stress.
04-15-2021, 02:15 AM
