W212 Insufficient gas pressure

Benny_Cornwall · Mon May 25, 2026 11:06 am

Hello, my 2012 E250 CDI W212 is up for sale. I keep getting the P0252 fuel quantity control valve code whenever I accelerate rapidly, and the EML light comes on. Yesterday, I changed the valve, but the EML light came back on after only two minutes of driving with the code P08791, meaning the fuel pressure was too low! Even if it enters limp mode when the light is turned on, I still need to figure out what the issue is. The pressure on fuel rail A is 22,000 kPa. At idle, the pressure from the gasoline pump in the tank is 3 bars, and at 2800 rpm, it rises to 3.7 bars. The gasoline filter has been changed as well.

I would really appreciate any advise you could offer.
Many thanks

LiamTheGreat · Mon May 25, 2026 11:06 am

Conduct a test to determine the injector's leak off. Despite acting normally otherwise, this is often the case with injectors that have a high leak off rate.

Benny_Cornwall · Mon May 25, 2026 11:07 am

I am grateful for that piece of data. Yeah, I'll give that a go throughout the week.

lumperjack · Mon May 25, 2026 11:07 am

A little low, at 3.7.

Benny_Cornwall · Mon May 25, 2026 11:08 am

I appreciate it, and I plan to check for injector leaks this week.

lumperjack · Mon May 25, 2026 11:08 am

be careful to also examine the low pressure pump.

Benny_Cornwall · Mon May 25, 2026 11:09 am

Thank you. I will take care of it. A few years ago, I had an issue with a B6 Passat. I removed the pump from below the rear seat, and to my surprise, the tank had a lot of gel or sludge.
Once I got everything cleaned up, it was ideal.

Benny_Cornwall · Mon May 25, 2026 11:09 am

What does this fuel rail pressure mean while the engine is at idle? The value fluctuates between 26000 and 32000. Many thanks