250xs Air Pressure Leak In Rail

[jbutah]

250 xs 0T998486

Twin engine center console. The engine has a rough idle, but seems to be making power other than lagging behind the other engine about 200 RPMs at WOT. I tested the fuel and air pressures on the rails. Fuel pressure was about 104 and air pressure about 94 at idle. Fuel pressure held after shutdown, however air pressure immediately dropped after shut down. I automatically assumed it was a bad tracker valve and replaced it with a new one. After replacement the pressure drop and rough idle is still there. What is the next step I should take?

[EuropeanAM]

It is theoretically impossible for air pressure to drop and fuel pressure to remain steady after shutdown.

Fuel pressure is equal to air pressure + 14.7 psi. Please recheck and make sure you have the fuel pressure on the STB side rail (top) and air pressure on the PORT side rail (back).

[jbutah]

Checked the pressures again, you are correct Don. Fuel pressure does drop after shut down, but much slower. Fuel pressure about 104-105 at idle, 90 15 seconds after shutdown, 75 at 30 seconds, and 50 at 1 minute. Air pressure 94-95 at idle, 75 at 15 seconds, 50 at 30 seconds, and 25 at 1 minute.

[EuropeanAM]

Is there any LIQUID FUEL in the air side?

Using an external air source (regulated to 90-94 psi), apply air pressure to the port-side schrader valve. Check for air leaks in hoses, fittings, listen at spark plug openings (plugs out) with a piece of hose held to hear, plug air inlet of air compressor with finger to see if that is the source of the leak, and- if none are found, pinch off the Air RETURN line and see if the air pressure loss ceases.