J-44175 Fuel Composition Tester

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A vehicle's fuel economy, driveability, and emissions, and the condition of fuel system components, are affected by the quality of the fuel in the vehicle's fuel tank. Two of the factors that define fuel quality may be easily observed and analyzed in your service department -- fuel contamination and amount of ethanol in the gasoline. These will help you diagnose fuel related concerns.

The essential tool Fuel Composition Tester J-44175 (fig. 1), a microprocessor-based handheld device, allows you to accurately analyze gasoline and gasoline/ethanol blends.


IMPORTANT: When using the Fuel Composition Tester J-44175, always observe the safety practices and procedures explained in the user manual, and in SI. Refer to the manual for test procedure details. The following information contains highlights only.

IMPORTANT: The user manual has recently been revised. See details in the accompanying box.


You will use a pressure gauge, either J-34730-FF or CH-48027, to obtain fuel samples from the vehicle's fuel rail pressure connection.

To properly sample fuel, you must first flush out the fuel pressure gage hose that is used to obtain the fuel sample. Any fuel that remains in the gage hose from a previous vehicle must be flushed with fuel from the vehicle being tested.

You will take TWO separate fuel samples from the vehicle. Each sample is tested separately. Perform all testing in accordance with appropriate service information (SI) procedures and applicable diagnostics.

First Sample -- Use the first sample to observe any particulate matter or gross water contamination. Allow the sample to settle for a few minutes and then visually observe for water separation or sediment. The first sample must NOT be placed into the J-44175.

Second Sample -- Only the second sample taken should be placed into the J-44175.


When using J-44175 to test E85 fuel for ethanol concentration, there are several factors which can have an effect on the accuracy of the test reading.

Effects of Humidity -- When testing in high ambient humidity and temperature conditions, it is possible for humidity to be absorbed into the fuel. This can adversely affect your reading. Remember that ethanol will absorb a certain amount of water. There is a connection between the fact that ethanol will easily absorb water and the effect it has on accuracy when testing E85 for ethanol concentration.

TIP: This is the principle used by ethanol-based fuel additives to prevent gas line freeze in the winter. Those products are effective because the ethanol in the additive absorbs water in the fuel.

Depending on the level of humidity in the air and how long the fuel sample is exposed to it, the tester's AC frequency reading may begin to slowly increase. Readings taken after 15 seconds will not be accurate. If the fuel sample sits longer than 15 seconds before it is tested, do not test that sample. Collect a new sample of the vehicle's fuel and test it within 15 seconds.

Effects of Cleanliness -- Keep the J-44175 as well as the 100mL sampling beaker as clean as possible. Do not use the shop's compressed air to clean any of the surfaces that will touch the fuel sample, including the 100mL beaker, the tester's fuel bowl or test ports. Compressed air may contain small amounts of water or other contaminants. Sweat, fingerprints or other materials can also adversely affect accuracy of the readings.

Effects of Temperature -- The tester automatically compensates for fuel temperature. If the temperature of the fuel is drastically different from the temperature of the tester, the automatic compensation may not react within the 15 seconds required to test a fuel sample. For instance, if the fuel being tested has just been pumped from an underground storage tank, it can be considerably colder than the tester. For best results, a vehicle that has just been filled with cold fuel should be allowed to normalize before sampling.

TIP: Allowing a fuel sample to warm up in the 100mL beaker before being tested is not acceptable because the fuel sample will be exposed to the air for too long, as explained above.


The Fuel Composition Tester J-44175 tool is primarily intended for technician diagnosis and use with SI diagnostics, not analytical testing of fuel samples.

Here's a brief (and somewhat technical) explanation of the differences between of the
J-44175 test results and those obtained in laboratory testing.

The J-44175 is designed to have an accuracy of +/- 5%, and testing of existing tools in the field indicates that they perform well within that specification. When comparing J-44175 test results with a laboratory test, it is important to understand that the lab reports must be stated in Volume Percent to be meaningful and the lab results typically will be 4%-5% lower than levels you will obtain in the shop (at typical E85 alcohol concentration levels). This is due to the addition of denaturing agents in ethanol produced as a fuel additive in the United States.

TIP: The new, revised user guide for J-44175 and SI both mention that, when using the tester, measured ethanol values between 60% and 91% are acceptable for E85. These figures take the tool's +/- 5% accuracy into account. DO NOT add another 5% to the 91% indicated by the tool.

So, it is possible for a test result from the J-44175 to be as much as 10% higher than a laboratory report on the same fuel sample. This is an entirely normal and expected result due to the reasons stated above.

TIP: SI diagnostics are designed to work with the J-44175 test results and not necessarily those of a laboratory.

If for some reason you suspect your J-44175 is not reading fuel samples accurately, there is revised tester verification procedure in the new version 2.0 manual which uses acetone as well as the air test previously used. Also, there is a test cell cleaning procedure which uses acetone, if the test cell or fuel bowl should become contaminated. When using acetone for
J-44175 diagnostics or cleaning, always be sure it is fresh acetone from a sealed container.

- Thanks to Ken Peacock and Jack Woodward


SPX/Kent Moore is releasing an updated user guide for the J-44175 in early 2007 for distribution to all dealers with the J-44175 tool. The new manual is version 2.0 with a yellow cover 
(fig. 2) and should be placed with the J-44175 when received.


All earlier versions of the manual must be destroyed.

Take a few minutes to read the revised tool usage and sampling procedures before using the tool. Some of the points you should review from the new manual are:

- Tester setup.

- Tester verification with air and acetone.

- Gage hose flushing.

- Importance of testing the second fuel sample quickly because ethanol absorbs moisture from the air.

- Taking TWO different fuel samples, with different test procedures for each.

- New acceptable levels of ethanol percentage.

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This page contains a single entry by techeditor published on February 1, 2007 8:12 PM.

Know-How Broadcasts for February was the previous entry in this blog.

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