How to Diagnose a Bad ATV, Motorcycle, UTV/Side-by-Side Fuel Pump
Understanding the symptoms and how to diagnose a bad fuel pump on an ATV, motorcycle, or UTV/SxS is handy knowledge for any enthusiast and precisely what we’ll be discussing below. When a fuel pump fails to operate within its designed specifications, your EFI-powered vehicle can suffer in a few ways. Expect lowered performance, causing it to run poorly, or failing to start at all.
A properly functioning fuel pump is one of the many crucial components in your ATV, motorcycle, or UTV/Side-by-Side (SxS).
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Whether we’re talking about two or four-wheeled vehicles, testing a bad fuel pump, or issues related to your fuel system are similar. It doesn’t matter if you drive an Arctic Cat, Can-Am, or Polaris, ride a Harley-Davidson, Honda, or Husqvarna. Fuel pumps can fail anytime, anywhere.
What does matter is that you’re referencing your vehicle-specific service manual to confirm any necessary technical specifications, as those figures can change depending on the vehicle year, make, and model.
Luckily, troubleshooting a bad fuel pump follows the same general principles, and we’ll be covering a few basic and advanced methods.
QFS does not intend this article to be a strict guide. As always, we recommend that only those confident in their mechanical abilities perform maintenance, repairs, and diagnosis on their vehicles.
If you do not feel comfortable performing this work, please consult an authorized and licensed service technician.
Tools You’ll Need To Diagnose Fuel Pump Problems
- Eye protection
- Nitrile gloves
- Hand tools (socket and screwdriver set)
- Multimeter or voltage meter
- Pressure testing gauge
- Contact cleaner
Symptoms of A Bad Fuel Pump
Let’s dive into it with how to diagnose a bad fuel pump and review some tell-tale symptoms of an underperforming or failed fuel pump.
Not Starting/Won’t Idle
Not starting when all systems appeared to be in regular working order is a good indicator that fuel is not making it through the fuel system. If the engine does start but fails to maintain idle, that is another sign that the pump is on its way out.
All fuel pumps produce a low audible hum when operating. When they reach the end of their lifespan, you may notice a loud whining sound, pointing to a fuel pump motor stressing itself to function.
Surging occurs when traveling at a constant speed and feels as if your ATV, motorcycle or UTV briefly accelerates with no input from the user. Typically, excessive pressure buildup can momentarily deliver excess fuel. In this case, we strongly recommend replacing the pump and filters immediately.
Power Loss Under Load/Cut outs
Does your bike, quad, or SxS accelerate normally only to begin losing power as the rpm climb or at higher rpm? That is often a signal of a fuel pump that cannot deliver the correct amount of fuel pressure to meet performance demands. Alternatively, you may experience power cut-outs at random, demonstrating a fuel pump operating sporadically.
Diagnosing a Failing Fuel Pump
Pinning-down fuel issues can be complex, as fuel systems and electrical systems are interdependent. Problems with one system can cause the other to malfunction. Our goal here is to isolate variables and help you determine the root cause of your issues.
Before you turn a single wrench, start with the basics and confirm a few things:
- Is there fuel in the tank, and does your fuel gauge (if applicable) register accurately?
- Is your battery adequately charged, and does your electrical system appear to be fully operational?
- Is the kill switch in the “run” position?
- Is your bike, SxS, or quad in neutral?
If you’ve answered yes to all those questions and you’re still experiencing issues, then it’s time to start investigating.
Fuel Pump Won’t Prime
Fuel pumps can fail with or without warning. We go to fire up our ATV, motorcycle, or UTV; the engine cranks, and it simply won’t start. Our first step is to observe if the fuel pump is operational and “priming.”
Priming means that the fuel pump engages for a short time, pressurizing the fuel lines and providing adequate fuel flow for the injectors.
To test this, cycle your key to the “on” position and listen intently for an audible hum coming from the fuel tank. The hum should only last a few seconds.
If you’ve repeated this multiple times and don’t hear a mechanical whirring, chances are the fuel pump has failed or is not being supplied electricity.
If you are performing this test on a dirt bike (Motocross or Enduro) that doesn’t have a keyed ignition, press the starter button and quickly release, which will trigger the fuel pump and allow you to determine if the fuel pump is operational.
Check the Fuel System Fuses & Relays
Fuses and relays act as bridges for electrical current. If they fail, the current can’t reach its proper destination and provide power. Consult your service manual to access your fuse box and relays, and then remove them to inspect them for any damage visually.
A healthy fuse will have its metal “bridge” connected, and a functional relay will “click” when power is delivered. You can also use a multimeter to check the resistance of a relay or fuse, which is more accurate.
Confirming Your Fuel Pump Has Power
If your fuel pump is not priming, you must determine if this is an electrical problem or a fuel pump failure. To do that, you will need to gain access to your vehicle’s fuel pump assembly. Consult your model-specific service manual for instructions to perform this safely.
Once you have clear access to the fuel pump assembly, you will want to test if power is coming down to the fuel pump itself with a multimeter or voltage meter.
Disconnect the wiring from the fuel pump assembly. Again, you will need to consult your service manual and wiring diagram to determine which terminal connections to measure.
Once you’ve done that, confirm that adequate power is available by cycling the key to the “on” position and measuring the voltage — it should rise to the cited technical specification in your service manual, then fall to zero after a few seconds. If you don’t have power or insufficient voltage, you know that the issue is not related to your fuel system.
If all is in order with the wiring harness, perform a continuity test with your multimeter on the fuel pump itself. Locate the positive and negative leads going to the fuel pump and check if an electrical connection is capable.
If it isn’t, rest assured that the fuel pump motor is dead.
Pressure Testing a Fuel Pump
Pressure testing is crucial when faced with lean and rich conditions, power loss, or surging, as irregular pressure in your fuel system can cause these issues. This test requires one of the few specialized tools mentioned here since it will need a gauge with model-specific connections to be installed between the vehicle’s fuel pump and fuel lines.
Once you’ve determined your vehicle’s fuel pressure specifications and installed the pressure tester, cycle the key to the “on” position. Pressure must raise and hold at the required specification.
If that checks out, start the engine and increase the rpm gradually. Once again, pressure should not deviate outside the recommended range.
If pressure is excessively high, your pressure regulator has failed, and we offer replacement options. Conversely, clogged fuel filters can lower fuel pressure and create flow issues.
Inspect all relevant filters thoroughly, although we recommend replacing them during this type of service. To accurately diagnose a bad fuel pump, all other fuel system components must be thoroughly checked.
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- Understanding the symptoms and how to diagnose a bad fuel pump on an ATV, motorcycle, or UTV/SxS is handy knowledge for any enthusiast
- When a fuel pump fails to operate within its designed specifications, your EFI-powered vehicle can suffer in a few ways — robbing performance, causing it to run poorly, or failing to start at all
- Pinning-down fuel issues can be complex, as fuel systems and electrical systems are interdependent
- Priming means that the fuel pump engages for a short time, pressurizing the fuel lines and providing adequate fuel flow for the injectors
- Pressure testing is crucial when faced with lean and rich conditions, power loss, or surging