Fuel pressure could be leading to starting problem

by Jim KerrBackyard Mechanic . Oct 27 2017

Question: I have a 2003 Subaru Legacy GT 2.5L with 190,000 kilometres. It had been working great until Sunday, when it turned over but would not start. Eventually, by putting pedal to floor (as if flooded), it would start. First time this happened, it was a rough idle. It happened again and, after much cranking, it caught (like it finally gets fuel to system). When I press down on accelerator to try to start the check, the engine light comes on and stays on. After a few starts, the check-engine light goes out. Once it starts, it idles at about 700 r.p.m. or at times a shade higher. However, once it starts, it runs well, never misses and does not stall. It will continue to start well for several starts over a couple of days, and then acts up again. One mechanic thought it was gas or air-gas mix. Any thoughts?


Answer: While there are many parts on a fuel-injected car that can make starting difficult, this problem sounds like a lack of fuel pressure. When you start the car, the fuel pump will run to pressurize the fuel system, so the injectors can spray the fuel into the intake ports. If fuel pressure is low, the fuel is sprayed from the injectors in a stream or big drops rather than a fine mist and it can flood the engine with fuel because the fuel doesn’t evaporate fast enough.

The first thing to check is the fuel pressure on your car while it is cranking. There should be a minimum of 34 PSI while cranking. If the fuel pressure is low, the voltage to the fuel pump should be checked. If the voltage is low, you have a bad connection in the electrical leads to the fuel pump or a bad fuel-pump relay.

If voltage is good and the pressure is low, then the fuel pump is the likely culprit, but be sure to have the fuel filter checked first. Filters are often overlooked on fuel-injected vehicles, but if plugged, they usually cause a problem at higher speeds first.

In my experience, once a fuel-injected engine has flooded, the spark plugs become fouled and usually do not clean up with engine running. I would recommend changing the spark plugs after fixing the problem.