Lean Fuel Condition – P0171

Injector Tester on VehicleA fuel system lean condition can be broken down into three subsections: fuel pump performance, fuel quality, and injectors.  A good starting point is to check the fuel pump assembly for pressure, volume, and amperage.  It’s also important to check the fuel quality as the customer could accidentally pump E85 into a regular engine.  The last item to check would be the injectors. They should be checked for both electrical and mechanical integrity.

How To Check Fuel Injectors Effectively

To effectively check for electrical integrity, it is recommended to use an oscilloscope to view the voltage and current waveforms. The final analysis comes with the following realities: injectors can be clogged, leaking or possibly installed on the wrong engine family. Injectors of the wrong family will have poor flow rates, and can be difficult to isolate.


Cylinder 5 Misfire ReadingThe example of this pulling codes case is a 2004 Pontiac Grand Prix with a 3.8L supercharged engine. There were five codes stored in the PCM memory: P0128 – Engine Coolant Temperature below thermostat regulation (due to low coolant level), P0131 and P0137 – Low Voltage Code for Oxygen Sensors (even after replacing the sensors, codes did not go away), P0171 – Lean Condition (the post oxygen sensor readings confirmed the engine was running lean), and P0300-Random Misfire (a misfire was created to see how the engine would react). On a side note, the oxygen sensor’s voltage went low, and stayed low.
Photo 2The next area to check was the fuel pump. The fuel pump was working as designed displaying satisfactory pressure, volume, and amperage readings.Photo 3 The fuel quality was also within operating standards. The final test was verifying the proper flow rate of the injectors using an active fuel injector tester. The tester is meant to work on GM product and Duramax injectors.Gray Fuel Injector The tester allows one to test the flow rate of the injectors using the engine as the test bench. The tester is attached and some automated test are performed. Photos 2 and 3 show the test results. Photo 3 indicates that injector #3 has a higher flow rate than the other injectors. The hypothesis was that injector #3 was leaking and should be replaced. The obvious answer to this mystery was incorrect though.Black Fuel Injector Under further inspection, it was noted that injector #3 was gray, and all the other injectors were black (See Photos 4 and 5). Instead of having on rich injector there were 5 lean ones. When the injectors on this engine were replaced, the wrong type of injectors were used. The black injectors are meant to be on a 3.8L non-supercharged engine, while the gray ones are used with the supercharger. This explains the lean condition code pulled when one cylinder misfired. This Pulling Codes case is now closed. If you would like to offer any comments on this, e-mail the author at carlton196100@yahoo.com.