You can easily test the fuel pump to find out if it's bad or not with a fuel pressure test gauge.
In this tutorial, I'm going to show you in a step-by-step way. I've also included the instructions on how to do a starting fluid test if you don't have a fuel pressure test gauge.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 4.0L V6 Ford Ranger: 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011.
- 4.0L V6 Mazda B4000: 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009.
IMPORTANT: Gasoline is highly flammable! Take all necessary safety precautions, be alert, be careful. Starting fluid and gasoline can ignite very easily.
Symptoms Of A Bad Fuel Pump
In my experience, fuel pumps usually fail in one of two ways:
- The fuel pump stops working entirely and does not send any fuel to the engine. This lack of fuel causes the engine not to start.
- The fuel pump works but sends just enough fuel to start the engine but not enough to allow the engine to run optimally.
If the fuel pump is only sending enough fuel to start the engine but not let it run optimally, you'll see one or more of the following symptoms:
- The engine takes a long time to start.
- The engine may start but will stall soon after.
- Lean air/fuel mixture diagnostic trouble codes illuminate the check engine light.
- The engine stalls as soon as you accelerate the engine under load.
- Backfire through the intake manifold when accelerating the engine under load.
- Lack of power when accelerating the engine under load.
Where To Buy A Fuel Pressure Gauge
A fuel pressure test gauge isn't an expensive fuel injection diagnostic tool.
You can buy one at your local auto parts store, or you can save some bucks by buying it online.
The following three fuel pressure gauge kits are quality tools I've used myself (no knock-off tools).
TEST 1: Fuel Pressure Test With Gauge
Thankfully Ford made it super easy to check the fuel pump pressure by installing a Schrader valve on the fuel injector rail.
To this Schrader valve, we'll connect the fuel pressure test gauge to check the fuel pump pressure.
You'll need the fuel pressure specification for your particular 4.0L Ford Ranger (Mazda B4000), and you can find it here:
NOTE: If you haven't already checked the fuel pump inertia switch, do so before starting this test. See this section for more info on the fuel pump inertia switch: Checking The Fuel Pump Inertia Switch.
OK, let's get started with this test:
Place a shop towel under the Schrader valve. The shop towel's job is to absorb any fuel that may leak when doing step 2.
Install the Ford Schrader valve adapter on the Schrader valve.
Connect the fuel pressure gauge to the Schrader valve adapter.
When ready, ask your helper to cycle the key on and off but don't crank the engine while checking for fuel leaks.
If no fuel leaks, go to next step.
If fuel is leaking, resolve the leak before continuing to the next step.
Have your helper to crank the engine while you observe the fuel pressure tester's gauge.
Your fuel pressure gauge will register one of the two following results:
1.) The fuel pressure gauge will register the indicated fuel pressure specification
2.) The fuel pressure gauge will NOT register the indicated fuel pressure specification.
OK, now that the testing part is done, let's take a look at what your results mean:
CASE 1: The fuel pressure gauge registered 0 PSI. This confirms that the cause of your engine's no-start problem is caused by a lack of fuel.
Now, I usually take two more precautions before condemning the fuel pump as bad:
- I check the fuel pump inertia switch isn't activated and cutting power to the fuel pump. Look at the following section: Checking The Fuel Pump Inertia Switch for more info on this.
- If the fuel pump inertia switch is OK, I still make sure that the fuel pump is getting 10 to 12 Volts as the engine is cranking. This 10 to 12 Volts confirmation test checks the fuel pump relay and fuse are OK and doing their job.
To check that the fuel pump is getting power (after you have checked the inertia switch), you'll need to:
- Attach a multimeter, set to Volts DC mode, to the wire that supplies power to the fuel pump.
- Have a helper crank the engine while observing the multimeter.
- Your multimeter should register 10 to 12 Volts as the engine is cranking.
- If 10 to 12 Volts are present, you have now 100% verified that the fuel pump is fried and needs replacement.
CASE 2: The fuel pressure gauge registered the correct fuel pressure specification. This fuel pressure gauge result lets you know that the fuel pump is working and delivering enough fuel to the fuel injectors.
Your 4.0L Ford Ranger (Mazda B4000) is not starting due to another reason. However, the fuel pump is OK.
The following tutorial may be helpful: How To Diagnose A No-Start Problem (4.0L Ford Ranger And Mazda B4000).