How To Clean Fuel Injectors?

Each year, millions of dollars are spent on different cleaning methods for fuel injectors. The question now is which one among all works the best. To help our readers make an informed decision, we have performed a hands-on review for the most popular injector cleaning methods present for the general public.

Most Popular Injector Cleaning Methods

  • Ultrasonic fuel injector cleaning
  • Injector/Injection Cleaning (Pouring in the fuel tank)
  • DIY Injector Cleaning
  • Injector Cleaner Induced by Rail (Usually used by most dealers and retail shops)

Having a load-bearing chassis dyno and an accurate air-fuel ratio analyzer available, we tried the most popular injector cleaning method. 

Performing Ultrasonic Fuel Injector Cleaning

Vehicle Used: 1993 Ford Mustang Lx

For this test, we used a 1993 Ford Mustang having 135000 miles, on an odometer. Before the experiment, the ca have not been driven for almost two months.

Step 1: Performing Leak Down And Compression Test

To begin with, a leak down and a compression test was performed which resulted in a fine. The fuel tank was then drained. The fuel was nevertheless discolored slightly, but it did not have a bad odor and no indication of phase separation was present.

Step 2: Attaching Tailpipe With Autronic Model B Air-Fuel Analyzer

The tailpipe was hooked up with an Autronic model B air-fuel analyzer, and 10 gallons of fresh gas was poured in the tank. On starting, the engine stumbled a bit but once it warmed up, it ran fairly smoothly. The throttle response was although fair but had some misfired under the free-revving. We then took the car on a road trip which included both an open road and some stop and go driving.


The engine ran fairly smoothly on the cruise, but the Air Fuel Ratio was indicating constantly that it was running between rich and lean. Huge lean-rich fluctuations were displayed in the stop and go driving. Finally, the wide-open throttle acceleration produced certain misfires and was quite sluggish.

The fuel tank emptied into a 5-gallon measuring can, back at the shop and 1.85 gallons were recorded. On the basis of this, 8.15 gallons of gas were used for the trip which was 102.7 miles and resulted in average fuel consumption of 12.6 miles/gallon.

Injector Cleaning Methods Compared.

Considering the engine size, fuel type and fuel injector size, etc. it was calculated that the car is able to produce 85-90 horsepower to wheels.

5 gallons of fresh gas was entered into the fuel tank, and the vehicle then runs on a load-bearing chassis dynamometer. Lean engine conditions were indicated by the AFR ratios, and the vehicle then produced a horsepower of 72, which is approximately 15% less than expected.

The old spark plugs indicated a lean condition when removed and checked. The new spark plugs gaping to appropriate size was installed once again and the car now produced a horsepower of 72. After this, the air filter was changed but again 72 hp. Following this, the fuel filter was replaced yet the car still produced just 72 hp/

The fuel pressure under load stayed at a constant pressure ranging between 43 – 45 psi during a dyno testing, which indicated a healthy fuel pump. On the basis of these, it was felt that the fuel injectors were quite dirty and needed a cleanup. They were then removed and a flow test was conducted on them. the results were then 156, 168, 180, and 172 cc/min.

Fuel Injector Cleaner

Fuel Injector Cleaner as the first method we put to test, which is also called injector cleaning additives. This cleaner is added and mixed to the fuel. The fuel injectors were then reinstalled without cleaning them, and the tank was drained. We added a good brand’s fuel injection cleaner to the exact specifications mentioned by the manufacturer, with 5 gallons of fresh fuel, and was then poured in the fuel tank again. The cost of fuel injector cleaner was around $12.5. in a matter of just a few minutes after starting, we noticed that the engine was now running somewhat rougher than before.

The car would now produce only 63 hp on the initial dyno pull, but it wasn’t able to complete the second dyno pull as the engine started misfiring badly after bogging down. The AFR turned lean and indicated a 17:1 and above AFR.

The engine was now unable to maintain idle and was to be kept alive just through additional throttling. The fuel injectors were now removed and put to test again, which this time flowed a 128, 162, 136 and 122. Moreover, two of the fuel injectors were leaking this time.


The dirt in rail and fuel line is loosened while the injectors are partially clogged by the injector cleaner. They may be inexpensive but one should stay careful as it may also cause disastrous consequences. 

Fuel Rail Induced Injector Cleaner

Now the injectors were reinstalled without being cleaned. This time a fuel rail was used with high pressure induced injector cleaner. This procedure may cost between $225 to $350 when done by an auto repair shop or mechanic. The engine managed to start without any additional input after the procedure, though once the throttle touched the engine would again die. The startup became tough and a smell of fuel was noticeable while cranking. In fact, strapping down the car on the dyno was just a waste of time.

It was revealed during the injector flow test that the output was 142, 154, 146, and 128 but all four injectors were now leaking. It was noticed that two injectors had caused damage to filter baskets now. The remaining damaged filter baskets were now removed from the injectors and they were then proceeded back to flush them. besides the expected regular dirt, there was filter basket material present in the debris. The two injectors were again tested for leaks and flushed back. The flow increased to 168 and 180 this time with no leaks.


The filter baskets on some injectors were damaged by the rail induced injection cleaning procedure. Debris chunks were forced past some injectors’ filter baskets while some chunks were loosened from the pintle shafts. These chunks were too large to pass through the seat and pintle and were lodged between the seat and pintle leading to the leak in the injector. Meanwhile, the filter basket and debris of other injectors lodged between the pintle seats. This is exactly what was told to the dealer that was happening when the cleaning process was being performed.

DIY Injector Cleaning

Without sidestepping the DIY cleaning process’s proponents, we went into a 12V car battery with a syringe, carburetor cleaner, and a 12V auto battery with a push-type switch. The procedure was then followed as shown in some tutorials over YouTube. In order to ensure a thorough job was being done, the process was repeated around 5 times for each injector and then back to the flow bench. The results this time were 172, 174, 180, and 174 cc/min. A slight improvement was noticed from the original flow test, which was quite small but not enough to warrant any additional dyno time.


In our opinion, the DIY fuel cleaning methods can remove some of the loose debris but since the actual cleaning fluid does not remain in contact as much with the internal injector components for longer time periods, the baked hydrocarbons or and hard shellac cannot be loosened or dissolved by it.

Ultrasonic Injector Cleaning Method

Finally, the fuel injector was put through a full ultrasonic fuel injector cleaning process. This injector cleaning method requires about 45 – 60 minutes in the ultrasonic bath. Afterward, the injectors were flow tested, and this time the results were 192, 192, 194, and 192. New filter baskets and O-rings were installed. The injectors were installed using PTFE O-ring grease on the O-rings on both the manifold and fuel rail side.

The gas tank was drained and 5 gallons of fresh gas were added and again we installed a new fuel filter.  The engine fired up immediately and ran smoothly. Throttle response was good with no misfires. Free revving produced no misfires. Air to fuel ratios (AFR) stayed within 14.2: 1 – 14.9:1

The vehicle produced 87 HP on the dyno and AFR’s stayed within an acceptable range during full power loads.

Once again we drained all the gas and re-added exactly 10 gallons of fresh gas. We proceeded to complete the exact road and city trip we did in the beginning. This time we used 5.1 gallons of gas thus recording an average fuel consumption of 20.13 MPG. A fuel consumption decrees of 80%.


Although fuel injection cleaners are cheap and “might” work, extra precaution should be taken especially when used on older fuel systems. We recommend fuel injection cleaners for maintenance items and a precautionary solution on newer cars rather than a solution to cleaning fuel injectors.

Based on our test on the above vehicle and subsequent newer models, a whole new range of variables are introduced when using high-pressure fuel rail induced injector cleaner.  Some of these variables can have costly results. It is expensive and we do not recommend its use on older fuel systems. We also caution its use in newer fuel systems.

Proofed by our “injector cleaning steps” comparison test we believe that ultrasonic cleaning of the injectors when removed from the engine delivers not only the best results but is the only method that can actually guarantee a better result.

Advantages and Disadvantages of  These Injector Cleaning Methods

Fuel Injection Cleaners


  • Inexpensive.
  • Easy to use, anyone can do it.


  • No way of accurately knowing if any or all the injectors have been cleaned or how well each one is performing.
  • Internal injector components, O2 sensors, and catalytic converters can be damaged due to the harsh chemicals. Some automakers advise against the use of these products.
  • Problems such as partially clogged filter baskets, leaking injectors, weak pintle springs, and more cannot be identified.
  • Poor spray patterns cannot be determined
  • Uneven and or correct injector flow cannot be measured.
  • Filter baskets and pintle caps are not replaced
  • O-rings that have become hard and cracked cannot be replaced.
  • It can cause more clogging which can lead to serious engine damage such as detonation and knock.

Warning: do not use on older fuel systems or fuel systems that were contaminated with old or bad gas.

In Car Pressure Induced Injector Cleaner Method.

This method is used by many dealers, repair shops, and quick oil change places. A cleaning solution is forced into the fuel rail to clean the injectors while the engine is running.


  • Expected to deliver results more rapid than in tank cleaners.


  • Very costly
  • Greater risk of damaging the injector components, catalytic converters, O2 sensors, and other electrical components due to the high concentration of harsh chemicals.
  • Particles building up in the filter dislodge and can be forced between the shaft and pintle housing that may cause the pintle to be stuck in an open position.
  • Parts like pintle caps, O-rings, and filter baskets not replaced.
  • Not able to identify partially clogged filter baskets, weak springs, leaking injectors, poor spray patterns, and any other potential issues.
  • Cant check how well each injector can be cleaned or how good is each one performing.

Ultrasonic Cleaning With Fuel Injectors Removed from the Engine.


  • Can detect weak pintle return springs
  • Determines accurate flow rates
  • Tests were done for leaks, coil resistance, flow rate, and spray pattern.
  • Check and confirm proper spray patterns.
  • Side by side testing of injectors allows accurate flow comparison
  • Determines accurate flow rates
  • Provides before and after data sheets
  • Installed new parts like filters, o-rings, and pintle caps
  • Injector components can not be harmed by the cleaning method
  • Injector RX uses cleaning solutions that are biodegradable, safe and can never enter the engine
  • The best and safest way for cleaning injectors
  • The only method is able to guarantee cleanliness and good functioning of injectors.


  • Injectors to be removed from the car and sent to the specialist.
  • Extended downtimes.