P0087

What the Code Means

P0087 sets when fuel pressure in the rail drops below the required level. The DME calculates the pressure needed for correct mixture formation and compares it to the actual value: if the actual reading stays consistently below the calculated one, the fault is stored.

Causes of the pressure drop are a failed fuel pump, a clogged fuel filter, a problem with the fuel pressure regulator, or a leak in the fuel system. The code applies to N52 engines.

Symptoms

• Hard starting (long crank), especially after the car has been sitting — the system needs more time to build working pressure;
• loss of power under load, when fuel demand exceeds what the weakened supply system can deliver;
• engine stalling, including while driving;
• Check Engine light on the instrument cluster.

Diagnosis and Repair

1. Measure fuel pressure with a gauge. For the N52, spec is 50–60 psi. A reading below that range confirms a fuel supply problem and points to the pump, the filter, or a leak.
2. Inspect the fuel filter. If it's clogged, replace it with the OEM part 13321403957 — a clogged filter restricts flow and causes pressure to drop under load.
3. Check fuel pump operation: if pressure is below spec with a good filter, the pump isn't delivering the required volume.
4. Check the fuel system for leaks — a leak keeps the system from reaching target pressure.
5. Once low pressure is confirmed, replace the fuel pump.

A common diagnostic mistake is replacing the pump without measuring pressure and checking the filter first: the cause may turn out to be a clogged filter or the pressure regulator.

Secondary Damage

• Low fuel pressure produces a lean mixture: the cylinders get more air than the available fuel can burn;
• a lean mixture causes misfires — unburned mixture ends up in the exhaust tract;
• misfires lead to overheating and damage of the catalytic converter — unburned fuel burns off inside the converter and destroys its honeycomb.

Don't put off the fix: catalytic converter damage is the expensive repair, while the root cause (filter or pump) is fixed on a moderate budget.