Liquid gold It started out a few billion years ago, roaming around the plains, eating whatever it could find. Calamity struck and wiped it off the face of the earth. After lying under the earth for all these years, it became oil, was then pumped up, filtered, refined, trucked around and finally ended up in your customer’s fuel tank. And that’s where all the fuel system problems began.
Once upon a time, fuel systems were pretty simple to diagnose. If there was fuel in the tank, and the filter was not plugged up, you could safely assume that the vehicle had a bad fuel pump. Two bolts, 15 minutes and 20 bucks later, your customer’s vehicle was back on the road and everyone was happy. Nowadays, things are just a little (a lot!) more complicated.
In the following paragraphs, I will try to address some major areas of focus for diagnosing and repairing fuel systems. In addition, I will cover some of the tools that can help you quickly and accurately diagnose and repair those problems. As a professional tech, you will recognize some of the following comments on ROs: “vehicle stumbles on acceleration,” “vehicle shut off and won’t re-start,” “vehicle won’t go over 45 mph.” All of these should be red flags to fuel-related problems. That is the easy part. Now it is up to you to use your experience, technology, knowledge and diagnostic skills to figure out what the problem is.
Some of the major areas to be concerned with in fuel diagnosis are: electrical/electronic signal failure, fuel pressure problems and fuel volume problems. One way to remember these three items is the acronym EPV: Electrical, Pressure, Volume.
It is always best to start with electrical. Is the system communicating with the fuel injectors? Is the signal arriving at the appropriate time?
There are some great simple diagnostic tools that every tech should have in his or her box. Noid lights are high on the list of must haves. This simple item is an LED light that plugs into the wiring harness in place of the fuel injector. This tool gives a visual indication that there is an electrical signal coming to the injector. While this doesn’t confirm that the signal is arriving at the correct moment, at least you know that part of the system is functioning. Noid lights will only let you know that some electricity is reaching the injector. You may find at this point that you need to use a good DVM or Digital Voltage/Multimeter to determine that the injector is receiving the correct amount of voltage.
Fuel pressure is an important part of the EPV equation. In fact, for many years it was safe to assume that if you had pressure on a fuel system, you could safely make a diagnosis on that system. The fact is, you need an accurate pressure test kit to verify how much pressure is on the system. What looks like good pressure to the naked eye, may not be enough pressure to overcome a regulator or get past the injector itself.
While pressure isn’t the only thing to concern yourself with, it is still a very big part of diagnosing fuel systems. There are some really great fuel pressure test kits available on the market today. The difference between an “okay” fuel test kit and a “great” kit comes down to adapters and applications. Your goal(s) as a tech should be: speed to “hook up” (connect) to the customer’s vehicle; minimize the risk of damaging expensive lines and components; and, of course, get good test results.
Another less obvious, but very important consideration about fuel injection test kits is selecting a kit that offers a logical organization system for the many different adapters, connectors, hoses, valves etc. that make up these large kits.
When making your buying decision about these kits, be sure you look for a kit that includes at least two different pressure gauges low pressure and high pressure. This can be accomplished either with a single gauge with multiple scales or different gauges.
Another attribute that is really a nice feature is quick disconnect fittings. This allows you to choose a main manifold and hose kit and then add the appropriate end fittings for the vehicle you are working on.
The better pressure test kits will also include some sort of bypass system such as a diverter valve, and an overflow tube. This arrangement will allow you to conduct basic volume/flow tests.
One other item to consider when making a buying decision is looking for kits that include repair parts for fuel injection systems. Common repair items such as valve cores, clamps, fuel connector lock rings, electrical sockets etc., are all great additions to the better fuel injection test kits.
With the advent of tank-mounted fuel pumps on late-model vehicles, it has become more and more important to verify the pump’s health before going to the trouble of dropping a fuel tank to get at the pump. Many times, it turns out that a pump can make plenty of pressure, but can’t move enough volume to allow the vehicle to operate as designed.
When shopping for a fuel volume tester, ensure that the tester has a good method for measuring and quickly identifying the amount of fuel that has been pumped out of the system. The best systems have large, well-marked reservoirs with clearly marked increments. This allows you to do time vs. volume diagnosis tests.
This test has become especially important with the advent of so many diesel-powered vehicles on the road today. Once used primarily in heavy-duty vehicles, diesel engines are now found in a large portion of cars and light-duty trucks.
The best fuel injection testing systems out there are calibrated to work on either diesel or gasoline engines. These kits have instructional literature, markings, fittings as well as technical specs on various makes and models of vehicles to help you determine if the results you get fall in an acceptable range.
Service Tools and Equipment
There are several other items to consider for servicing fuel systems. A great source of revenue for repair shops is fuel injection cleaning. This service is one that should be offered to every customer who comes into your shop. Fuel injection cleaning equipment can range from a small canister rig that uses individual cans of cleaning solution, all the way up to large, cabinet-style cleaners that are microprocessor controlled and offer multiple passes of the cleaning solution. The canister-style cleaners are a great option for lower volume shops and can be used in conjunction with your fuel injection pressure test kit.
You will want to make sure you have a large assortment of fuel line disconnect tools for doing fuel service work. There are multiple types and some vehicle-specific disconnect tools you will need to add to your box, depending on the types of vehicles you see most often in your shop. There are several styles and materials of disconnect tools. You will have to determine which tools best suit your needs. There are universal tools made to fit a specific line diameter. They can also be manufactured from different materials. Some are made of plastic, others from various types of metal.
If you do a lot of fuel service work, you may want to consider investing in a fuel line repair kit. These kits allow you to make repairs to fuel lines that would otherwise have to be replaced. The better kits will have hydraulic crimpers that allow you to repair high pressure fuel lines. You will also need a special bubble flaring tool to make repairs to the fittings associated with fuel injection lines.
Fuel system testing and repair can be a great source of income for you and your shop. It is just a matter of being prepared and equipped to deal with the problems as they arise. If you are able to do that, you will be able to take home the gold.