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OM651 W204 C250 CDI – Heavy Black Smoke at WOT + P0087 (Fuel Pressure Too Low) and P2
Hi everyone,
I’m struggling with a persistent issue on my 2012 W204 C250 CDI (OM651) and I’m hoping someone has seen something similar or can suggest next steps. Here’s the full background:
Car Info:
2012 W204 C250 CDI, OM651
71k miles
Automatic, no EGR/DPF mods until recently
History of the Problem:
After my first Stage 1 remap at JACustomTuning, I started occasionally seeing P0087 (Fuel Rail/System Pressure Too Low Bank 1) under WOT. At that time, there was no smoke at all.
For about 18 months, the car ran fine aside from the occasional P0087 under hard acceleration.
Then, after a hard driving session trying to work out why limp mode sometimes triggered, it suddenly began producing very heavy black smoke under WOT — to the point the car behind me could see it covering the entire road.
Smoke occurs even at full load with MAF unplugged.
After the smoke started, I had a different local tuner do a new Stage 1 map with EGR and DPF delete, but the issue stayed exactly the same.
Codes Seen:
P0087 – Fuel Rail/System Pressure Too Low (intermittent)
P226322 – The boost pressure deviates from the specified value. The signal amplitude is greater than the maximum amplitude.
Note: This occurs mainly from kickdown off the line, typically in 1st or 2nd gear at WOT.
In other WOT pulls (e.g. rolling acceleration), I only ever get P0087, not P226322.
P228100 – Intake Air System Leak (historic, likely fixed by intake repairs)
P246309 – DPF soot content abnormal after forced regen (historic)
What I’ve Tried So Far
Intake & Air System:
Smoke-tested, small boost leak at boost pipe seal fixed – no change
PCV replaced – no change
Air filter replaced – no change
Intake manifold removed, swirl flaps, throttle valve, and EGR cleaned – no change
MAF swapped from another vehicle, wiring checked – no change
MAF unplugged – smoke still present
Fuel System:
Leak-off tested injectors cold & hot – all fine
Injectors tested by Colchester Diesel Injection – all reported fine, not replaced
Y94 Quantity Control Valve (used & new) – no change
Xentry tests for fuel delivery, boost leaks, Y74/Y94 all pass
Replaced Y74 after it fell out of spec on Xentry test – fixed test result but no change to smoke
Stock ECU flash reduces P0087 and slightly reduces smoke
Second remap (Stage 1 with EGR/DPF delete) – same issue, no improvement
Exhaust & Sensors:
DPF slightly falling apart, forced regen done
Exhaust pressure sensor cleaned – no change
Lambda sensor cleaned – no change
Boost sensor cleaned and replaced – no change
Observations:
Heavy black smoke only at WOT
Happens even with MAF unplugged (just less due to limp mode)
Seems unrelated to any air leaks or injector faults
Stock ECU reduces but doesn’t completely stop smoke and P0087
P226322 only appears during kickdown in 1st/2nd gear, otherwise it’s just P0087
Current Situation:
At this point I feel like I’ve checked or replaced nearly everything and I’m going in circles. The car runs fine otherwise but pours out black smoke under load, and I’m out of ideas.
Question to the Community:
Has anyone seen similar OM651 black smoke + P0087 under WOT?
Is there something simple I might be missing, or any deeper mechanical causes worth checking?
Any suggestions for specific live data to log or further tests that could help narrow it down?
Any help or ideas would be massively appreciated — I’m running out of things to check!
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