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Pelican Technical Article:

Fuel Flow Delivery Test

Steve Vernon

Time:

1 hour1 hr

Tab:

$0

Talent:

**

Tools:

Flathead screwdriver, relay jumper, rags, measuring container

Applicable Models:

Porsche 944 Turbo (1986-89)

Hot Tip:

Use all precautions when working around gasoline

Performance Gain:

Ability to diagnose fuel delivery problems

Complementary Modification:

Fuel pressure test

All internal engines need three things to run; air, fuel and spark. As engines have become more complicated, powerful and emission regulation dependent, keeping the fine balance of a proper running engine has meant tighter tolerances on the air, fuel mixture and timing of the spark.

After you have checked your fuel pressure, you will need to check the actual volume of fuel flowing through the fuel rail. This article will walk you through how to check your fuel flow for Porsche 944 engines.

You will be working around gasoline so make sure to take the proper precautions. Always wear proper gloves and eye protection. Work in a well ventilated area and keep any open flame, spark or heat (shop lights) away from the area.

There is going to be some gas spillage so be prepared to collect it in rags and dispose of the rags in accordance with your local regulations. NEVER store gas soaked rags as they can become very combustible.

If possible let the engine rest for at least a couple of hours before preforming these tests to allow the system to depressurize.

Locate the fuel pressure regulator.
Figure 1

Locate the fuel pressure regulator. It will be different on some models (turbo, 8-valve and 16-valve) but it is always on the fuel rail and most times on the rear of the rail (red arrow). Follow the line out from the regulator to make sure it is the return line and not the supply line (yellow arrow).

Use a flathead screwdriver and carefully disconnect the rubber return line from the metal line (red arrow).
Figure 2

Use a flathead screwdriver and carefully disconnect the rubber return line from the metal line (red arrow). On some models it is easier to remove the line from the fuel pressure regulator.

Use a container that will hold at least 50 ounces (red arrow) and place the return line from the regulator in the container (yellow arrow).
Figure 3

Use a container that will hold at least 50 ounces (red arrow) and place the return line from the regulator in the container (yellow arrow). Fuel will come out quickly and with some force so if you are doing this by yourself make sure to have the container well braced.

You are going to want to jump the relay so you can test the flow rate without the engine trying to start.
Figure 4

You are going to want to jump the relay so you can test the flow rate without the engine trying to start. Remove the fuse/relay panel (red arrow). On older cars it is located inside the vehicle under the dash. On newer cars it is located in the rear left side of the engine compartment.

Locate and remove the fuel pump relay (red arrow).
Figure 5

Locate and remove the fuel pump relay (red arrow). You are going to want to jump terminals 30 and 87b. The terminals should be clearly marked on the bottom of the relay.

While you can directly jump the two terminals by running a direct shielded wire between them, I like to make a jumper that includes a fuse (red arrow, to prevent damage to the electrical system) and a switch (green arrow).
Figure 6

While you can directly jump the two terminals by running a direct shielded wire between them, I like to make a jumper that includes a fuse (red arrow, to prevent damage to the electrical system) and a switch (green arrow). The switch will give you more control over the testing. If you jump the terminals directly the pump will start immediately and stay on. You are going to want to run the pump for 30 seconds so having a switch here is a really good idea.

Using your fused switch or the jumper wires run the pump for exactly 30 seconds.
Figure 7

Using your fused switch or the jumper wires run the pump for exactly 30 seconds.

Pour the gasoline into a container where you can measure the amount of fuel.
Figure 8

Pour the gasoline into a container where you can measure the amount of fuel. Most pumps should put out 850ml or 28.7 ounces in 30 seconds; the green Bosch pump should put out 750ml or 25.4 ounces in 30 seconds. If you have substantially less fuel measured than either of these two amounts, you probably have a problem with your fuel pump, lines or filter.

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