EFI: Fuel system

FUEL SYSTEM

The fuel system in my Beretta is pretty typical. The fuel pump is electric and is located inside the gas tank. It sends fuel to the filter near the gas tank and then to the fuel rails on the engine. The injectors are mounted on the fuel rails. A fuel pressure regulator that is vacuum controlled returns unneeded fuel back to the gas tank. When the engine is idling or under low load, a lot of the fuel sent to the engine compartment is directed back to the gas tank. When fuel demands are higher and then engine is consuming more fuel, less is returned to the gas tank. The main advantage to this design is that extra fuel is instantly available to meet increased fuel demand. I also believe a constant flow fuel pump is less complex and more reliable.

The Fuel Filter

If you're past due, replace the fuel filter. (Another part your local AC/Delco distributor has cheaper than the dealer.) A clogged fuel filter can cause fuel starvation; I'm told that some aftermarket fuel filters are too restrictive (they filter too well). A marginal fuel filter may pass fuel fast enough to maintain the desired fuel pressure at idle but not when the demand is higher.

Fuel filters are designed to flow in one direction; I've heard installing one backwards will result in a lack of fuel pressure.

When I change a fuel filter, I like to cut it open to look for junk. However, they can be full of goo that restricts the fuel flow and still look ok. So if there's any question, I think it's best to just replace it. Be sure to follow the safety instructions found in the service manual; the fuel system can be under pressure even when the engine is off.

Fuel Pump Relay

The fuel pump relay allows the ECM to control when the fuel pump is on. There is also an oil pressure switch that acts as a backup to the relay. If the relay isn't working, you can crank the engine with the starter motor until the oil pressure comes up and then the oil pressure switch will kick in and power the fuel pump.

The main symptom of a bad fuel pump relay is that it takes a lot of cranking for the engine to fire. The ECM normally engages the fuel pump for a few seconds when you turn the ignition on to pressurize the fuel rails. If you don't hear the fuel pump run for a few seconds when you turn the ignition on, you should suspect there is a problem with the fuel pump relay.

Fuel Pressure Testing

Test the fuel pressure. You can either buy the $175 TPI fuel pressure test kit with the right fittings, etc. or else get a 0-50 PSI pressure gauge from the local speed shop for $30 and use a short piece of rubber hose and a couple of hose clamps. Perhaps this is not as safe as using the proper test gear so make sure you know where your fire extinguish is and have an assistant sit behind the wheel in case you need to have the fuel pump turned off quickly.

The manual says you should see 40.5 to 47 PSI when you turn the car on (without starting it). You should hear the fuel pump come on for a few seconds and then shut off. When you start the car, it's supposed to drop 3-10 lbs. Mine started at 40 and dropped to 37. I also hooked the MityVac to the fuel pressure regular and convinced myself that it was working. (No vacuum boosted the pressure to about 45 and other vacuum values produced numbers between there and 37 lbs.)

Injector Testing

Although the factory service manual shows them, I did not do any injector tests. You need some test equipment and also must remove part of the air intake and I didn't want to mess around with the gaskets. 99% of the time I use name brand gas (Chevron) from a local station that I know has had its tanks recently replaced so I don't really worry about injectors getting clogged. Also, injector problems seem to be much more common with imports than domestics.

If you decide your injectors are bad, there is apparently an alternative to just buying new ones. I've heard you can have your injectors rebuilt at many performance shops. This sounds attractive since the rebuild includes testing.

I did run one bottle of injector cleaner through the car. I'm sure Richard Petty and STP appreciate my purchase but I was unable to detect any improvement. This might be because there is already injector cleaner in name brand gas. And as I've said, I believe the domestic injector design to better.

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