What do we really need to think about when filling our tanks?

First and foremost, it is typically not a good idea to fill our tank when there is a fuel truck filling the underground tanks at our favorite gas station. The primary reason is that when the fuel tanks are delivering fuel, the sediments inside the underground storage tanks can be agitated due to the pressure of the incoming fuel causing those sediments to be kicked up and thus pumped into our vehicle’s fuel tank while pumping our gasoline. It is always a safer bet to allow that sediment to settle back down to the bottom of the underground storage tank before filling our vehicle’s tanks whenever possible.

Across the United States, most States have allowed up to 10 percent alcohol blended fuel. This blend is used for a couple of reasons. First, alcohol is used to help prevent fuel line freezing in colder climates during the winter months. More importantly, when alcohol is present, the Hydrocarbons and NOx pollutants are reduced. In fact, E-85 (which can be as high as 85% alcohol, has been known to significantly drop those pollutants by as much as 20-25% when compared to tradition 10% blended fuels!

The three main reasons why manufactures don’t just switch to 100% flex fueled production vehicles are that it requires more fuel to get the same power range when compared to a lesser blended fuel (which means even though E-85 is cheaper, you will need to fill the tank more often).

The alcohol has a tendency to break down the hoses at a faster rate when introduced to oxygen and finally, causes a corrosion concern on the hard line components such as fuel pumps and injectors. Most E-85 flex fueled vehicles have a sensor usually located on the fuel rail that will inform the PCM of the alcohol content of the fuel so it can then use this information to adjust the fuel and spark curves as needed to obtain optimum performance and emissions calculations.

While there are some specific tools out in the market place that are designed to not only test the alcohol content of the fuel, but also if there is any water present in the fuel , they do come at a hefty price. A great

In step 1 of the test we fill the cylinder with water to the water fill line. Step 2 we will finish filling the space with an actual fuel sample taken from the vehicle in suspicion. Step 3 would be to shake the cylinder and then let sit on a flat level surface for a few minute. As it sits, the water would gradually float to the bottom while the alcohol will set on top of the water and then finally the fuel or gasoline will rest on top. This cylinder is really nice because of it’s graduations showing the percentage of alcohol present once the test sample has settled accordingly.

While we are on the subject of fuel, an often overlooked principle concerning gasoline is called Reed Vapor Pressure. The nuts and bolts explanation of this principle is that when we have gasoline in a sealed container such as a fuel tank, it’s pressure will rise. If we think about our old lawn and garden gas cans we can remember that they, along with an older vehicle’s gas tank, would have a vent going directly to the

atmosphere to relieve this rising pressure. While items such as heat and sloshing of the fuel would normally create a higher reed vapor pressure, we could not allow the hydrocarbons to vent directly to the atmosphere due to their detrimental effect on the Earth’s atmosphere. The auto manufacture’s first started sealing the fuel systems on vehicles back in the seventies by eliminating the vented gas caps and installing a rather rudimentary EVAP system by today’s standards , which allowed those rising pressures to be stored into an Evaporative emissions canister , which when the vehicle was started , would allow those hydrocarbons to be sucked out of the canister and burned through the act of combustion.

Another modification the auto manufactures went to in later years was the introduction of return less fuel systems. While both carbureted and early injected vehicles would typically have a fuel return line allowing the fuel pump to pump higher pressures to the fuel rail and then return what was not needed back to the fuel tank, this principle actually aggravated the Reed Vapor Pressure containment process by the fact that when the fuel was pumped to the fuel rail, it would pick up unnecessary heat from the engine and then introduce hotter fuel back into the tank of the vehicle. The added heat and the sloshing fuel effect caused the pressures to rise thus putting an unnecessary strain on the vehicle’s evaporative emissions system.

Once the manufacture’s started using the return less systems , along with a fuel pump that was controlled by varying the RPM of the pump (usually by the use of a driver module), we could then send just the needed amount of fuel pressure to the fuel rail as determined needed by the engine’s operating conditions. This allowed for less strain on the evaporations emissions systems by helping to eliminate the extra heat and fuel slosh that used to occur.

It would be hard pressed to find a technician that doesn’t understand the need for adequate fuel pressure on an internal combustion engine. After all, without having proper fuel pressure, not only would our fuel trim tables be affected but so would the engine’s performance. Often times however, a tech over looks the

importance of fuel volume testing. Something as simple as a restricted fuel filter can often times lead to an adverse affect of performance due to the fact that we would essentially not have enough fuel to operate the

The best way to test both pressure and volume is to use a fuel pressure gauge that has the ability to measure both such as the one pictured above. By attaching the gauge in series with a fuel line, as opposed to parallel like an ordinary fuel pressure gauge one can accurately measure both pressure and volume and then compare the readings to the manufacturer’s specifications engine under loaded conditions. Fuel pressure can remain the same while fuel volume becomes restricted!

 

Typically the best practices I like to perform when testing the fuel pump’s pressure are as follows:

1. Key on engine off (This tests the fuel pumps prime pressure usually controlled by key on engine off closing of the fuel pump relay) Pay attention to make sure the pressure peaks up to specs and that it doesn’t immediately bleed down.
2. Relieve the pressure
3. Crank engine and allow to start and note reading and compare to specs. Also pay attention how long it took to build pressure. This could be the cause of an extended crank complaint.
4.  A dead head pressure test would be in order next to view fuel pump maximum pressure. Older vehicles with rubber return lines could simply be pinched off to obtain this reading while newer vehicles with variable speed fuel pump’s will require you to open the fuel bleed valve at the gauge to create a condition where the PCM will demand the pump’s speed to increase to 100%.

If one has access to a lab scope and a low amp current probe, he/she can perform a fuel pump RPM test. Basically one would obtain a fuel pump current waveform such as the one shown in the example. Look for a unique characteristic hump and count the humps until it repeats.

This will let you know how many commutators the fuel pump has. Once we know that and we measure how long it

takes to repeat that signal we can determine the both the speed and amperage of the fuel pump.

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This information can be used to help confirm a suspicion of a restricted fuel filter or a kinked fuel line.

Remember, when there is a mechanical restriction present within the fuel system two things will happen. The RPM will slow down while the amperage that the fuel pump draws will increase! Be sure to use this quick test
before you risk breaking some rusty fuel lines trying to change a fuel filter that may or may not be the issue!

CONVENTIONAL FUEL PUMPS QUICK TIP

Even though the auto manufactures are slowly evolving into the newer three phase pump designs, there are still many conventional fuel pumps being used on the vehicle’s entering our repair shops for service.

If you have ever had a vehicle that was a no-start due to lack of fuel pressure but once you tap on the tank with a rubber mallet the problem magically disappears, then you are experiencing a fairly common condition on all types

of motors including starters, blower, and fan motors where the brushes aren’t making good contact with the commutators of the motor. This small vibration that occurs with the hammer trick allows for a temporary fix to the problem.

The motor in question may continue to work for several attempts until it stops in that same position where the lack of contact happens again! See the waveform showing this condition caught in the act. Use this type of testing for those hard to find intermittent complaints that we all see from time to time in our repair shops.

THREE PHASE PUMPS

Starting in about 2011 we started to see brushless 3-phase fuel pumps enter the market. These pumps actually have 3 power wires originating from a fuel pump driver module. The driver module will pulse a signal very fast to the individual phases of these pumps at typically more than 10 thousand times per second!

The best way to test a no start– no fuel pump activation complaint on these systems is to use a 4 –channel oscilloscope and a bi-directional scan tool. The first three channels can be attached to the individual phases of the wiring coming from the module to the pump while the fourth channel of the scope can be used to view the A/C current that the pump is creating if its operating. That’s right, A/C current!

Using your scan tool commanding the pump to run, the first three channels should show each of the 3 120 degree phases of operation while the 4th channel should show the three phases working together creating that A/C current of the pump proving whether or not the pump is good. Typical A/C current measured in amps of a functioning pump is about 4-7 amps of A/C current.

FUEL INJECTORS

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