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.
Contents of this tutorial:
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:
- The engine turns over but will not start.
- The ignition coil pack feeding spark to all 4 cylinders.
- The PCM will still pulse (activate) all 4 fuel injectors.
- 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:
- Lean air/fuel mixture trouble codes.
- Rough idle.
- Engine starts after extended cranking.
- Lack of power when accelerating the vehicle down the road.
- 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 kits are pretty good deals and include the adapter (the M12 X 1.25 test fitting) to tests all 2.0L Mazdas covered by this tutorial:
All of the fuel pump pressure test kits above have the fitting that will connect to your Mazda's fuel injector rail.
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:
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.
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..
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.
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.
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.