Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.
Diagnosing a Clogged Fuel Filter
You may have a clogging fuel filter if your car:
- feels sluggish at highway speeds
Fuel filters don't last forever.
Over time, the filter element clogs, restricting and blocking fuel flow. That's why most manufacturers suggest fuel filter service intervals as part of your car's preventive maintenance.
Check these signs of bad fuel filter symptoms to avoid getting stranded in the middle of the road and paying an expensive repair bill.
Signs of a Clogging Fuel Filter
The fuel filter removes abrasive particles, sediment, rust, dirt, and other contaminants from the fuel stream that can upset the operation of a carburetor, fuel injector, or diesel injection pump, and ultimately affect engine performance. As driving miles accumulate, these particles spread over and stick to the filter element.
- Engine hesitation or misfiring: As particles start to clog the filter, the rate of fuel supply begins to decrease. You may not notice it while driving in stop-and-go traffic, but as soon as you accelerate to highway speeds, the engine hesitates or misfires—the rate of fuel fed to the engine can't meet the most demanding needs of your engine.
- Engine feels sluggish: As proper fuel flow diminishes, the fuel filter starves the engine of the needed fuel during acceleration, making it feel sluggish.
- Engine stalls: Soon, you won't go too far from your driveway before your engine dies as you accelerate.
- Fuel pump damage: At this point, your fuel pump might have suffered some damage since the restricted filter is putting too much pressure on the pump.
Why a Worn-Out Fuel Filter Might Not Show These Common Symptoms
You might be lucky if your clogging filter gives you these signs of wear. A few years ago, some manufacturers decided to install a check valve in some of their filters. This valve begins to open whenever working pressure inside the filter starts to rise, so that fuel bypasses the clogging filter element. This way, the engine doesn't lose power or stall, which in a way is a good thing. However, this can have catastrophic results for your engine over time if you are not paying attention to your car maintenance schedule.
Allowing unfiltered fuel to pass can wreak havoc with your engine, as hard particles can scratch cylinder walls before impurities begin to shut off your carburetor or fuel injectors. Later on, you'll have to deal with a more expensive repair.
Clogging Fuel Pump Restrainer
You can see similar symptoms to those of a restricted or clogged in-line fuel filter when the in-tank fuel pump restrainer (or mesh filter) begins to clog as well.
The restrainer catches big particles inside the tank to protect the fuel pump. However, you may have a harder time troubleshooting for a clogging restrainer than a bad fuel filter. Soon after your engine stalls, the restrainer may partially clear and allow your engine to start, until it clogs and your engine stalls again. If you replace the fuel filter and the problem continues, you might not realize the restrainer is the one clogging.
|Common Symptoms of a Bad Fuel Filter|
Car feels sluggish at highway speeds
Replacing the Fuel Filter
If you haven't changed the fuel filter in more than a year, chances are your problem lies in a partially restricted or clogged fuel filter. And even if this is not your main problem, you got nothing to lose by replacing a filter with an overdue service date. Most in-line fuel filters are pretty straightforward to replace.
Unfortunately, many modern vehicles now come with the fuel filter inside the fuel tank. Some models make it easy to service the fuel pump and filter by providing an access panel under the back seat or trunk; otherwise, you'll need to lower the fuel tank and pull out the fuel pump to replace the filter. Even then, some models require replacing the whole fuel pump assembly as part of the fuel filter replacement service, usually when reaching the 100,000 miles. If you have some mechanical experience, you might be able to replace this in-tank filter. Check the repair manual for your particular vehicle, if necessary. It'll show you the proper procedure for your particular model.
On some vehicle models (both gasoline and diesel), you may find a bowl fuel filter. This is a device in the engine compartment. Maintenance requires opening the canister, cleaning the bowl, and replacing the filter element. And some diesel engines may use a canister fuel filter, similar to the bowl-type filter and requires the same type of maintenance.
If you've decided to change the fuel filter, work in a well-ventilated area and park your car away from appliances that work with natural gas. Fuel fumes are highly flammable and might reach the pilot light in a water heater or clothes dryer and cause a fire.
When Replacing an In-Line Fuel Filter:
- You'll need to relieve system pressure first. On some models with TBI (throttle body injection) systems, you can remove the fuel pump fuse, start the engine and let it idle until it stalls. Then crank the engine for about three seconds and you are ready to replace the filter.
- Multiport fuel injection engines use a Schrader (service) valve on the fuel rail, near the engine (the valve looks like a tire air valve). Although the correct way to relieve pressure through this valve is with a fuel pressure gauge and a bleeder hose attached to it, I've done it by removing the fuel filler cap, and then using a shop rag to catch the small amount of fuel that squirts out through the valve as I depress it with a screwdriver. This works nicely if you are working on a cool engine; on a hot engine, you may cause a fire if you accidentally spray some fuel around.
- Once you've relieved system pressure, you can remove the filter. Some models use a plastic, hairpin clip on each side of the filter to lock the fuel lines in place. On other models, you need to unscrew a threaded fitting using a line wrench to prevent damage to the lines. Still, other models may use a special snap-on connector to attach the line to the filter. This requires a special tool to separate the line from the filter. On some vehicle models, all you have to do is unscrew the filter case cap, pull out the filter element, install a new one, and replace the cap. Check your repair manual, if necessary.
- Take the old filter with you to the parts store and match it to the new one so that you know you got the right replacement.
If your car is showing one or more of the symptoms described in the previous section, you may have a partially or clogged fuel filter. Check your car owner's manual to locate the filter and check the recommended maintenance schedule. And if your car is not experiencing any of these symptoms yet, but your filter has reached the manufacturer service interval, replace the fuel filter now. Always try to follow the filter service interval recommendations in your car owner's manual or a schedule that fits your driving habits and conditions. Unfortunately, some manufacturers don't include a service interval for the fuel filter. If you don't find the service interval in your maintenance schedule, replace it at least once a year to prevent engine performance issues.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: Car idles but does not accelerate. What could be wrong?
Answer: The problem could be in the fuel system. Make sure the fuel filter is not clogged. Also, make sure you got a good spark. Download trouble codes, even if the check engine light is not on. There may be pending codes that can help you here.
Question: I was starting my car after putting in new fuel and a fuel filter. It started right up, then immediately sputtered and died. Then it wouldn't start. What could be the problem with my car starting?
Answer: If the engine cranks as usual but doesn't start, spray some starting fluid in the throttle while someone tries to fire up the engine. If it starts for a few seconds, check the fuel system, there might not be enough pressure in the system. This might help:
Question: I have an ‘89 Chevy 3500 1ton, with a gas motor. It is not getting fuel to the carburetor and the fuel pump is constantly running. What could the issue be?
Answer: First, check the fuel pump relay. It can be stuck closed, keeping the pump running. See what it does and go from there. If there’s no fuel, make sure the fuel filter is not clogged (if older than 1 year, just replace it), and check for fuel pressure. There could be an issue with the fuel pressure regulator.
Question: Which way should fuel filter arrow go?
Answer: The arrow should point towards the engine.
Question: Starting my 95 Chevy Blazer was no problem first thing in the morning, but I'd drive it a mile and turned it off. When I'd crank it again, the Blazer seemed flooded and hesitated before it idled normally. Now I'm having problems with it starting and running. It starts up in the morning but will die a short way down the road when I take off and won't restart. Are these 2 things, the flooding and not cranking, related to problems with my Blazer not running?
Answer: If the engine doesn't turn over when you try to start it, there could be a problem in the starting circuit or the starter motor. The flooding and subsequent stall may point to another issue. This post may help:
If the engine turns over but doesn't start, check fuel pressure and the injectors. There could be too much fuel going in:
There could be a problem with a stuck injector:
If necessary, clean the injectors.
© 2016 Dan Ferrell