How To Test The Fuel Pump (1994-1999 2.0L Mazda 626)

The fuel pump, on your 1994-1999 Mazda 626 can be tested to find out if it's bad or not. There are 2 basic tests to test the fuel pump. One is done with a fuel pressure gauge and the other is done with starting fluid.

I'm gonna' explain both in a step-by-step manner so that you'll be able to find out if your 2.0L Mazda 626 is not starting due to a bad fuel pump.

Symptoms Of A Bad Fuel Pump

When the fuel pump fails, it usually just stops working completely. Every now and then, the fuel pump will fail in such a way that it supply just enough fuel to start the engine, but not enough to keep it running optimally when you're driving down the road under load.

Here are some specific symptoms you'll see when the fuel pump fails completely:

1. The engine turns over but will not start.
2. The ignition coil pack feeding spark to all 4 cylinders.
3. The PCM will still pulse (activate) all 4 fuel injectors.
4. Engine starts, although momentarily, if you spray starting fluid into the throttle body and then crank the engine.

When the fuel pump is starting to fail and under-performing, you'll probably see one or more of the following symptoms:

1. Lean air/fuel mixture trouble codes.
2. Rough idle.
3. Engine starts after extended cranking.
4. Lack of power when accelerating the vehicle down the road.
5. Back-fires thru' the intake manifold when accelerating your pickup or van down the road.

Both of these conditions can be tested with a fuel pressure gauge. Alright, with this info under our belts, let's get testing.

Where To Buy A Fuel Pressure Test Gauge

One of the most important tools any serious DIY'er should have in his/her tool box is a fuel pressure test gauge. The cool thing is that you can buy them in just about any auto parts store (although at a higher price).

The following fuel pressure test gauge kit includes the adapter (the M12 X 1.25 test fitting) to tests all 2.0L Mazdas covered by this tutorial:

TEST 1: Checking Fuel Pressure With A Fuel Pressure Gauge

A fuel pressure gauge can be connected to your 2.0L Mazda 626 by removing the banjo bolt that connects the fuel pressure line to the fuel injector rail.

You then substitute this banjo bolt with a fuel pressure test fitting (usually known by its measurement as: M12 X 1.25 fitting).

It's to this fitting that you can then connect your fuel pressure gauge to. You can see the fuel line's banjo bolt in the photo here: Where To Connect The Fuel Pressure Gauge Adapter.

The cool thing about using a fuel pressure test gauge, to test the fuel pump's fuel pressure, is that we can find out if the fuel pump is behind the no-start condition or behind a lean condition (if your Mazda starts, runs, but runs with a lack of power).

The fuel pressure specifications with the key on engine off (KOEO) is: 30-45 PSI.

NOTE: If you don't have a fuel pressure gauge, take a look at the section: Where To Buy A Fuel Pressure Test Gauge.

OK, let's get started with this test:

1. 1

   Place a shop towel around the fuel line's banjo bolt. The shop towel's job is to absorb any fuel that may leak when doing step 2.
   
   To see the location of the fuel line's banjo bolt, go here: Where To Connect The Fuel Pressure Gauge Adapter.

2. 2

   Remove the fuel filter's union bolt. Careful the union bolt's 2 copper washers don't fall and get lost in the engine compartment. You'll need to re-install them when you get done with the fuel pressure test.

3. 3

   Install the fuel test fitting in the banjo bolts place and tighten it. Make sure that you use the copper washers since these are like gaskets that keep the fuel from leaking out.
   
   Now, connect the fuel pressure test gauge to the fitting you just installed and tightened.

4. 4

   When ready, ask your helper to cycle the key on and off several times but don't crank the engine while you observe the fuel pressure tester's gauge.
   
   Check the connection at the fuel pressure test fitting for fuel leaks and if any tighten the fuel pressure a bit more (by hand only) to eliminate them.

5. 5

   Your fuel pressure gauge should register the specified KOEO fuel pressure of 30-45 PSI if the fuel pump is OK.

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

CASE 1: If the fuel pressure gauge registered 0 PSI: This confirms that the cause of your 2.0L Mazda 626 no-start problem is caused by a lack of fuel.

CASE 2: If the fuel pressure gauge registered the specified fuel pressure for your vehicle's model year. This test result lets you know that the fuel pump is working and delivering enough fuel to the fuel injectors. The reason your 2.0L Mazda 626 is not starting is due to another reason. The fuel pump is OK.

TEST 2: Using Starting Fluid To Confirm Lack Of Fuel

Testing a 'no-start' problem, to see if it's being caused by a lack of fuel, with starting fluid is an old mechanic's trick.

The accuracy of this test depends on making sure that all 4 cylinders are getting spark. So, if you haven't already checked, you should check for spark first. If you get a 'no spark' test result from all 4 spark plug wires, then you can forget about the fuel pump being behind your 626's 'no-start' problem and you should focus your troubleshooting efforts on the ignition system.

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.

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

   You'll get one of two results with this test:
   
   1.) The engine will start momentarily and after a few seconds will die or.
   
   2.) The engine will only crank but not start at all.

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

CASE 1: If the engine started and ran for a few seconds. This test result tells you that the no-start problem is due to a lack of fuel.

Your next step is to check to see what the fuel pressure is with a fuel pressure test gauge. Go to: TEST 1: Checking Fuel Pressure With A Fuel Pressure Gauge.

CASE 2: The engine did not start, not even momentarily. This usually means that a lack of fuel IS NOT the reason your car is not starting.

Now, remember what I said about this test not being very accurate? Well, I suggest you do one more test and this is to check the fuel pressure with a fuel pressure test gauge. Go to: TEST 1: Checking Fuel Pressure With A Fuel Pressure Gauge.

Where To Connect The Fuel Pressure Gauge Adapter

NOTE: The photo above is of a 1997 2.0L Mazda 626.

The orange arrow points to the banjo bolt that must be removed and replaced with the fuel pressure gauge fitting. This banjo bolt has two copper washers that seal against fuel leaks. As you're removing the banjo bolt, you need to be careful they don't fall down in the lower engine area. These copper washers are re-used when installing the banjo bolt back in its place (after doing the fuel pressure test).

Where To Buy The Fuel Pump And Save

The fuel pump in your 2.0L Mazda 626 is located inside the fuel tank. The fuel pump can be bought in any auto parts store, but I think you'll find the better price online. The following fuel pumps are pretty good deals:

Not sure if the above fuel pumps fit your particular 2.0L Mazda 626? Don't worry, once you get to the site, they'll make sure it fits by asking you the specifics of your vehicle. If it doesn't fit, they'll find you the right one.