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Employee training inspection procedure
No problem Disc Brake Job Part 1
No problem Disc Brake Job Part 2
Fuel pump testing 101

1) Pressure test
2) Volume test
3) Static test
4) Wave pattern test

This a wave pattern of a faulty fuel pump that is not giving problems, yet! Figure 1

Testing fuel pumps have become one of the first things technicians have leaned to check for a driveability problem. We as technicains should be familar with a pressure test on all fuel injected cars. Without having proper fuel pressure a car may not start when cold or perform badly when driving. A Lot of driveabilty problems can be traced to improper fuel pressure. Whether it is too little or too much fuel pressure. Each type vehicle has it's own specification that it must be within. Some GM trucks and cars with as little as 5 pounds too little pressure will cause them not to start when cold. Sometimes too much fuel pressure can cause a simular problems with starting.

Wave pattern of a new fuel pump. Notice the top of the wave pattrn is rounded! Figure 2


Wave pattern of another good fuel pump! Static in the pattern or noise does not indicate it is a bad pump.Figure 3

The next test that is the easiest to do. It is a static fuel pressure test. All you have to do is watch the fuel pressure after the engine is shut off. The fuel pressure should rise slightly when shut off (on most cars). It should maintain this pressure for several minutes without dropping. If the fuel pressure drops this could indicate fuel injector leakage as well as possible fuel pump check valve failure. Another area that could be faulty is the pressure regulator. They can get "stuck" open by debris, allowing the static fuel pressure to drop. Symptoms of a vehicle not holding pressure is excessive cranking before starting. Mainly seen when a vehicle has set overnight and you try to start it the next day. Sometimes you may even smell "raw gas" when it runs.

The volume test is the same on ALL fuel injected vehicles. The amount of volume should be 1/2 of fuel in 15 seconds or a full pint in 30 seconds. No matter the make of car, this test is a constant. Audi, Chevrolet, Mazda it doesn't matter!

Fuel pump waveforms This test will make sure that your fuel pump is NOT going bad. If you look at enough good known waveforms the bad ones will stick out like a sore thumb.

Figure 2 and 3 are normal patterns. Figure 1 is a bad fuel pump pattern. You can only get these patterns using a lab scope and a low amp inductive clamp.
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