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.
TEST 1: 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:
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.
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).
Crank the engine once the air duct is back on and you're clear of the engine compartment.
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 2: 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 2: Checking Fuel Pressure With A Fuel Pressure Gauge.