Model 45565 On-Car Injector Flow Bench

How does it know the flow?

Question:
Hickok claims the On Car Flow Bench (OCFB) can measure the flow rate of a fuel injector on the vehicle and that the measurement can be compared to the manufacturer's specification. How do they do it?

Answer:
The flow of the fuel injectors in an engine is critical to proper operation. The actual fuel flow depends on a number of things including the fuel pressure, fuel viscosity, the size and shape of the pintle of the injectors on-time of the computer signal etc. etc. So, when a manufacturer specifies the flow rate of fuel injectors they do so under a very specific set of conditions including specifying pressure, the calibration fluid viscosity, temperature etc. etc. How can the service technician duplicate these very specific conditions to tell whether the injectors on the vehicle are within manufacturer’s specifications? Answer, he can't. The only alternative until now was to remove the injectors and test them on a professional Flow Bench. The reason Flow Benches have been used is until now they were the only way to even get close to duplicating the conditions that a manufacture uses when specifying the flow rate of fuel injectors.

Hickok has developed a patented alternative that measures the flow rate of fuel injectors to manufacturer's specifications and does it on the vehicle without special calibration fluids, pressure settings or needing to see the spray pattern. The Hickok On Car Flow Bench combines two well known measurement techniques to accurately measure flow rates in a way that is directly comparable to the manufacturer’s specified flow rates. In addition, the unit includes certain other tests to completely cover all the characteristics an injector must have to operate properly on the vehicle as the manufacturer intended.

The two measurement techniques that the OCFB uses to measure Injector Flow Rate are:

1. MEASURING RATE OF PRESSURE CHANGE: Flow volume can be determined by measuring the time it takes for pressure to change from one value to another within a closed system. (This measurement also depends on knowing (or being able to measure) the viscosity of the fluid, (gasoline), the change in volume of the vessel (fuel system lines), temperature and several other parameters but as you will see the OCFB takes care of this problem.)

2. COMPARISON OF KNOWN TO UNKNOWN: Because all injectors are substantially similar, determination of specific characteristics of an unknown commodity to a commodity that the characteristics are known is accurate and efficient. (Ex.; A voltmeter measures voltage by dividing the voltage being measured by an accurate internal reference voltage and converting that comparison to what is read on the LCD.)

The On Car Flow Bench combines these two techniques to measure fuel injectors. It works like this:

When the On Car Flow Bench is connected to a vehicle the connections allow it to turn on and off the fuel injectors, turn on and off the fuel pump, and to measure the pressure in the fuel lines. What it does to measure the flow factor of an injector on the vehicle is pressurize the fuel system by turning on the fuel pump while the injectors are turned off. Once pressure is reached the fuel pump is turned off. The unit waits until it sees that the pressure has stabilized (usually less than one second). Then it turns on one of the fuel injectors and starts a stopwatch. When the pressure drops by a certain amount it stops the watch and records the time it took for the pressure to change between the two points. Next it re-pressurizes the system by turning on the fuel pump and again waits for stabilization. Next it turns on a fuel injector in the Fuel Management Unit (FMU) of the On Car Flow Bench. Again it measures the time it takes the pressure to drop between the same two pressure points that it used for the fuel injector on the vehicle and records the time. The time recorded for the injector on the vehicle and the time for the injector in the FMU are related to the flow factors of the two injectors. The measurement uses less than a thimble of fuel so it doesn’t create any kind of problem in the engine. It doesn't even wet the spark plugs enough to make the engine hard to start after testing. The On Car Flow Bench repeats this sequence three times for every injector on the vehicle and remembers the times it measured for each pressurization and pressure drop sequence. Next it averages the readings and calculates how the flow factor of each injector on the vehicle relates to the flow factor of the one in the Fuel Management Unit. The equation is:

Vehicle Injector Time	=	FMU Injector Flow Factor
FMU Injector Time		Vehicle Injector Flow Factor

Or another way to put it:

Vehicle Injector Flow Factor	=	FMU Injector Time x FMU Injector Flow Factor
		Vehicle Injector Time

Because of the relationship above, the microprocessor in the OCFB knows how the flows of the injectors on the vehicle compare to the injector in the FMU. As example; If the time measured on vehicle injector #1 and the FMU injector is the same, vehicle injector #1 has the same flow as the FMU injector. If vehicle injector #2’s time was _ that of the FMU injector vehicle injector flowed twice as much. The OCFB microprocessor is told, during its manufacture, precisely the flow rate of the injector in the FMU when tested the way the injector’s manufacturer specifies. Because the actual flow rate of the FMU injector is known, the comparison of flow factors is actually a comparison of flow rates. Notice that the OBCF has actually calculated the flow rate of the vehicle injector without knowing the volume of the fuel system, the viscosity of the fuel, the temperature or any other characteristics that can affect the flow rate because all those other things were the same when the time / pressure change of the vehicle injector and the FMU injector were measured.

Hickok has tested this patented concept over numerous vehicles using many different gasolines and even modified fuel systems to create a broad range of test conditions. As all the mathematics predicted, IT WORKS!!

Spray pattern observation has been a mainstay of injector flow testing since the beginning. The spray pattern is determined by the shape of the pintle. As stated earlier, shape of the pintle has a direct influence on flow rate. After extensive testing and consultation with fuel injector experts, Hickok has proven that alterations of the spray pattern caused by deposit build up or broken pintles also alter the flow rate of the injector. Measuring the flow rate of the injector and comparing to the manufacturer’s specs will detect injectors that would have bad spray patterns. The OCBF detects the problem without having to see the spray pattern.

Besides Flow Rate there are other important characteristics to determine if a fuel injector is operating properly. Electrically is it OK? How about dynamic characteristics like stickiness when opening or closing, does it leak when closed, etc? The OCBF incorporates tests that determine all these other characteristics required for proper operation on the vehicle.

The OCBF performs a resistance test and an inductance test on the injector coil. Inductance? What is that all about? Electrical coils like those used in fuel injectors have a failure mode that doesn’t affect the resistance much but renders the coil unable to open the pintle. Current recommended diagnostic techniques to detect this problem involves looking at the “kickback” using a scope. Inductance measurement detects it even better but Inductance Meters are not readily available to the automotive technician. The OCBF has an Inductance Meter built in to detect these failure modes.

The OCBF buzzes each of the injectors on the engine monitoring the time it takes for the pressure to drop between the same points used for the flow rate test. It compares the resultant measure of flow of the injectors to one another. If one is sticking or leaking its flow will be different than the others. The OCBF graphs this dynamic flow so the tech can determine if one or more are not acting the same as the others because of some dynamic problem. What if they are all screwed up? If they are, it will always show up in the static flow test when compared to the manufacturer’s specifications.

Bottom line: The OCBF patented technology truly tests fuel injectors to the manufacturer’s specifications without removing the injectors from the engine. It only takes about 5 minutes for the automated test to run and generally hookup is pretty quick, by connecting directly to the injectors if they are easily accessible or the PCM I/O connector if they aren’t accessible. Automotive technicians now have at their disposal a test unit that is quick and easy to use that provides laboratory grade information on the performance of fuel injectors.