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HPBG: Engine Builder Fuel Injection Maintenance

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Checking The Fuel Injector Flow
A fuel injector flow bench can be used to check the actual flow from the fuel injectors at any load condition or engine RPM (fuel injector on-time) you chose to simulate. The flow bench also allows the user to observe the injector spray patterns, and you can also measure the fuel flow from each injector so the user can be sure the injectors are truly flow matched.

Ideally, every new fuel injector would be built to the same flow standards but holding a production line to that precise of a tolerance would raise the cost of the fuel injectors substantially.  

Most new original equipment fuel injectors are held to a +/- 2% production flow variance, but some inferior replacement injectors that you buy at your local auto parts store may not hold to the same tight flow standards.

Also, due to part number consolidation, some injector suppliers sell fuel injectors with a flow rate that may vary as much as 25% from the flow rate of the OEM injectors that the engine’s computer is programmed to work with.

If the fuel flow and spray pattern is not the same from each fuel injector used on an engine, the air/fuel mixture delivered to each cylinder will vary.  When the air/fuel mixture varies by more that 6-8% from cylinder to cylinder the engine will have cylinders that are running too rich and cylinders that are too lean.

When a cylinder does not have the correct air/fuel mixture the engine’s power output, drivability and fuel mileage potential will suffer.

The fuel injectors should always be replaced as a set unless you are confirming the replacement injectors flow volume and spray pattern are the same as the original injectors by flowing them on a fuel injector flow bench.

GM’s Multec fuel injectors that were used in its Tuned Port fuel injected engines produced from 1985 through the early 1990s had some known issues. The insulation on the fuel injector coil windings deteriorated and then allowed the injector coil to short circuit as the gasoline caused the insulation to breakdown.

The problems you may experience can vary from an occasional one-cylinder miss (caused by an intermittent short in the injector coil) to a totally dead cylinder (a short in the injector coil that no longer supplies any fuel to the cylinder).

Preventing Dirty Fuel Injectors
The best preventive medicine to help prevent fuel flow restricted injectors is to tell your engine customers to use a gasoline that has detergents in it to help keep the fuel injectors clean and prevent deposit formation before it becomes a problem. Many of the car manufacturers recommend the use of a gasoline that conforms to the new “top tier” gasoline standards to help keep the fuel injectors clean.

“Top tier” gasoline has detergents in it that will help keep the fuel injectors clean as you use it, and many of the major gasoline brands are now being blended to these higher standards. The level of detergents in “top tier” gasoline is not always strong enough to keep your fuel injectors clean, so from time to time your customers may need to add some extra cleaning power to their fuel.

The use of an in-tank fuel injector cleaner such as Chevron’s Techron Concentrate Plus at the same mileage schedule as you change your engine oil is a very good way to be sure your fuel injectors stay clean. A dose of Techron Plus will raise the level of detergents in a tank of gas by about 10 times what it is in a typical “top tier” gasoline.

Techron Concentrate Plus is one of the best in-tank fuel injector cleaners we have used, and the “plus” is that it helps protect the fuel system against the corrosive effects of sulfur that is commonly found in today’s gasoline.

These harmful sulfurs can corrode the fuel level-sending unit in the tank and cause the fuel level gauge to malfunction. The most common symptom of a corroded fuel level-sending unit is a fuel level gauge that may stick or not read the correct level of fuel in the tank. The corrosive effects of sulfur may also create excessive wear to the electric fuel pump(s) that are in the gas tank and thus shorten the fuel pump service life.

The CNG Alternative
CNG or compressed natural gas is an environmentally friendly alternative fuel source in place of gasoline because CNG is a very clean burning fuel. CNG powered vehicles have lower maintenance costs than gasoline powered vehicles but they still need service. The fuel injectors that are used with CNG are much higher flow than the same engine would use with gasoline but it still uses the same tiny filter that a standard fuel injector uses.

Some of the CNG injectors we have serviced have had filters that are much dirtier than any other injectors we have serviced. I have been told that this problem is mainly seen Northern California, but if you work with CNG powered vehicles it would be wise to keep an eye on the injector filters.

The debris that flows thru the fuel system and the oil vapors from the CNG compressor can cause fuel injector flow problems as the filter becomes restricted. The fuel injectors can become so flow restricted that engine damage may happen in extreme cases.

It would a good idea to have the fuel injectors cleaned and flow tested on a fuel injector cleaner/flow bench whenever a CNG powered engine or vehicle is in the shop for a tune-up or rebuild.

The Clean Advantage
When all the fuel injectors are flowing the correct amount of fuel to each cylinder, the engine performance will be at its best supplying the vehicle with maximum power and fuel economy. Fuel injector maintenance and service is a very important part of proper vehicle maintenance.

Choose the fuel injector cleaning method that works best for you, and don’t forget to change the fuel filter.