How To Test The Fuel Pump (1993-1998 3.0L V6 Nissan Quest)

The fuel pump on your 1993-1998 3.0L V6 Nissan Quest is going to fail sooner or later. And the absolute best way to find out if it's kicked the bucket is to check its fuel pressure output.

In this tutorial, I'm going to show you how to use a fuel pressure test gauge to check the fuel pump's pressure.

With your test results, you'll quickly and easily figure out if the fuel pump is toast and behind either an engine no-start problem or and engine performance issue.

NOTE: This tutorial applies to the following vehicles:

• 3.0L V6 Nissan Quest: 1993, 1994, 1995, 1996, 1997, 1998.
• 3.0L V6 Mercury Villager: 1993, 1994, 1995, 1996, 1997, 1998.

FUEL PUMP CIRCUIT WIRING DIAGRAM:

• Fuel Pump Circuit Wiring Diagram (1993-1995 3.0L V6 Nissan Quest).
• Fuel Pump Circuit Wiring Diagram (1996-1998 3.0L V6 Nissan Quest).

Symptoms Of A Bad Fuel Pump

For the most part, when the fuel pump in your 3.0L V6 Nissan Quest or Mercury Villager decides to quit, it's going to do so in one of two ways:

1. The fuel pump stops working completely and the engine doesn't start.
2. The fuel pump continues to produce some pressure, but not enough. In this case, the engine does start, but it doesn't run optimally.

Here are some of the most common symptoms you're going to see when the fuel pump begins to fail (but hasn't died completely):

• Lean air/fuel mixture trouble codes.
• Rough idle.
• Engine starts after extended cranking.
• Lack of power when accelerating the minivan down the road.
• Back-fires thru' the intake manifold when accelerating your the minivan down the road.

Whether the fuel pump is causing a no-start condition or wreaking havoc on engine performance, a fuel pressure test will let you know if the fuel pump is the culprit.

Where To Buy A Fuel Pressure Test Gauge

To check the fuel pump's pressure on your Nissan Quest or Mercury Villager, you're going to need a fuel pressure test gauge kit with a T adapter. The kits below have the adapter you'll need to tap into your minivan's fuel system. They're reliable and don't cost an arm and a leg:

TEST 1: Checking Fuel Pressure With A Fuel Pressure Gauge

In a nutshell, to check your fuel pump's pressure output, we need to install a T-adapter between the fuel filter's outlet port and the fuel hose that connects to it (this hose is the one connecting the fuel filter to the fuel injector rail).

In the illustration above, you can see the T-adapter already installed on the fuel filter. The key thing to keep in mind is that the T-adapter goes on the side of the fuel filter that delivers fuel to the fuel injector rail, not on the hose that supplies fuel to the fuel filter from the fuel pump.

Once the test is set up, we should see between 34 and 43 PSI with the key on, engine running. These are the specifications shown in the table below.

Without Vacuum to Fuel Pressure Reg.	With Vacuum to Fuel Pressure Reg.
43 PSI	34 PSI

NOTE: Before you begin your fuel pressure test, locate the fuel pump inertia switch and make sure it hasn't been tripped. If the inertia switch has been tripped, reset it and crank the engine. If the engine starts, there's no need to check fuel pressure, since the switch itself was the cause of the no-start.

OK, let's get started:

1. 1

   Release the fuel pressure built up inside the fuel line. You can accomplish by removing the fuel pump relay and cranking the engine for about 5 seconds.

2. 2

   Place a shop towel around the fuel filter. The shop towel's job is to absorb any fuel that may leak when disconnecting the fuel hose.

3. 3

   Disconnect the fuel hose that connects to the outlet side of the fuel filter.
   
   NOTE: The "outlet" side of the fuel filter is the side that sends fuel to the engine (the fuel injector rail).

4. 4

   Install the T adapter and any additional fuel hoses (that come in the fuel pressure test kit) to the fuel filter. Tighten all hose clamps. Your set-up should look like the illustration above.

5. 5

   Connect the fuel supply hose to the T adapter.
   
   NOTE: This is the fuel hose that you disconnected from the fuel filter in step 3.

6. 6

   Re-install the fuel pressure relay and ask your helper to cycle the key on and off but don't crank the engine while you observe the fuel pressure tester's gauge.
   
   Check your T-adapter connections for fuel leaks and if any tighten the hose clamps a bit more to eliminate them.

7. 7

   Crank the engine and check the fuel pressure on the gauge.

8. 8

   Check the fuel pressure on the gauge:
   
   If the engine starts and runs: You should see around 34 to 43 PSI (see spec table).
   
   If the engine doesn't start: You should see a fuel pressure close to or at 43 PSI.

Let's take a look at what your results mean:

CASE 1: The fuel pressure gauge registered 0 PSI. This tells us that, without a doubt, your Nissan Quest or Mercury Villager minivan's no-start problem is being caused by the fuel pump not sending fuel to the fuel injectors.

In most cases, this points to a bad fuel pump that needs to be replaced. But before we condemn the fuel pump as bad, I want to point out that a 0 PSI reading can also be caused by a blown fuel pump fuse or a bad fuel pump relay, since either one will prevent the fuel pump from activating and sending fuel to the injectors.

Your next step is to check the fuel pump fuse and fuel pump relay.

CASE 2: Fuel pressure is present, but it's lower than specification. This result tells you that even though the fuel pump is sending fuel, it's not sending enough.

If the pressure isn't within specification, you're going to see engine performance problems. In this case, the fuel pump needs to be replaced.

CASE 3: Fuel pressure is within specification. This tells you that the fuel pump is functioning correctly and delivering enough fuel to the fuel injectors. If you're troubleshooting an engine no-start condition or an engine performance problem, you can rule out the fuel pump as the cause.

TEST 2: Using Starting Fluid To Confirm Lack Of Fuel

Using starting fluid to check whether a lack of fuel is causing your minivan to not start is a simple and fast test. It's been one of my go-to checks whenever I begin diagnosing an engine no-start on just about any vehicle.

But before you begin, there's something important you've got to verify first. For the results to be accurate, the engine must be getting spark. Specifically, you need to confirm that the spark plug wires are actually delivering spark with a spark tester.

Once you've confirmed that the spark plug wires are delivering spark, spraying starting fluid into the throttle body will give you one of two results:

1. The engine starts and runs for a few seconds –This confirms the engine isn't getting fuel, since the starting fluid is what allowed it to start and run.
2. The engine continues to crank but won't start –This tells you that a lack of fuel isn't behind the no-start condition, since spraying starting fluid into the throttle body had no effect.

IMPORTANT: This is a very fast and easy test but you do have to take one very important safety precaution and this is to reconnect the air intake duct after spraying starting fluid down the throttle bore (although you don't have to fasten it). This will prevent any backfire, that might occur, from scaring the heck out of you when cranking the engine.

FUEL PUMP INERTIA SWITCH: Before you begin your starting fluid test, make sure the fuel pump inertia switch —located behind the lower left cowl panel— hasn't tripped. If it has, reset the switch and crank the engine. More than likely, the engine will start.

This is what you have to do:

1. 1

   Remove the intake air duct from the throttle body. You don't have to completely remove it, since you'll have to reconnect it in one of the next steps.

2. 2

   Open the throttle plate and spray starting fluid down the bore.
   
   As a safety precaution reconnect the air duct after you have sprayed a good squirt of starting fluid (but you don't have to tighten the air duct's hose clamp).

3. 3

   Crank the engine once the air duct is back on and you're clear of the engine compartment.

4. 4

   The engine should start and run for a few seconds and then stall.

OK, let's find out what your results mean:

CASE 1: The engine started and ran for a few seconds. Since the engine did start and run —even if it died after a few seconds— you can conclude that the no-start condition is being caused by a lack of fuel.

CASE 2: The engine did not start at all. This result tells you that the no-start condition isn't being caused by a lack of fuel.

More 3.0L V6 Nissan Quest Diagnostic Tutorials

You can find a complete list of 3.0L Nissan Quest And Mercury Villager tutorials in this index:

• 3.0L V6 Nissan Quest Index Of Articles.

Here's a small sample of the 3.0L Nissan Quest tutorials you'll find in the index:

• How To Test The Ignition Coil And Power Transistor (1993-1998 3.0L V6 Nissan Quest).
• How To Troubleshoot A Cylinder Misfire (1993-1998 3.0L V6 Nissan Quest).
• How To Test For A Blown Head Gasket (1993-1998 3.0L V6 Nissan Quest).
• Common Causes Of Spark Plug Failure (1993-1998 3.0L V6 Nissan Quest).