Fuel Injector Service

Part of the maintenance I have performed on every Honda and Acura that I have owned is to send out the injectors for cleaning. The little bottles of fuel cleaner are a scam; ultrasonic cleaning is the only effective way to restore an injector's flow rate and pattern. Servicing the injectors makes the car rev and idle smoother, get better fuel economy, lower emissions, and ensures you get the same amount of fuel delivered to each cylinder. I estimate this service should be performed every 80k-100k miles.

I have used RC Engineering in the past but the last time I did they sent me back a faulty injector. Not a huge deal, but some years have passed since I've needed this service so I decided to see what other companies are out there. Originally I planned to evaluate several companies, but Injector Rehab did a great job and were easy to communicate with, so I ended up have all three sets serviced there. Their customer service is fast and responsive, the turnaround time fast, the pricing competitive, and the injectors all came back working flawlessly. Their packaging is good and the report they send back is easy to understand.

Injector Rehab

I chose three cars for this article: A 1997 Acura Integra GSR coupe with 184k miles, a 1994 Honda Accord LX automatic with 176k miles, and a 1998 Honda Civic HX manual with 255k miles. .

1997 Acura Integra GSR

My daily driver is a stock GSR coupe. I have been keeping track of the fuel economy on every fill up since purchasing the car in June of 2009 (four years at the time of this article), which is an ideal foundation to report any effect on miles per gallon.

Swapping the injectors is very easy and requires no special tools. Care should be taken as it is very easy to cause a fuel leak. If ignored, it could lead to a total loss of the vehicle.

To avoid downtime, I sent a spare set of injectors in for service. After installing these injectors, I will then send my original injectors in. Once I get the second set back, I mix and match them so I have two sets that are within the ideal balance of less than 2% variation in flow.

Tools and Supplies

Injector Resistance

The OBD2 B Series engines use high impedance, saturated injectors that should be between 10 - 13 ohms. Measure their resistance with a multimeter. Any that aren't within the specified range should be tossed in the trash.

Torque Specs

Before / After Videos

Before Cleaning - showing the received condition of the Injectors. Injectors 2, 3, and 4 all leaking under pressure. 20.9% out of balance with injector 3 being the worst and having a poor spray pattern

After Cleaning - no leaks and spray pattern on injector 3 restored back to good operating condition.

The B18C1 is a 1.8 liter DOHC VTEC with a two-stage intake manifold making 170hp. I'm able to achieve 33mpg in my stock GSR.

Allow the vehicle to sit for at least an hour after driving in order for the engine to cool and the fuel pressure to decrease. Remove the fuel cap.

Release residual fuel pressure at the fuel filter, careful to catch the fuel in a rag. There's usually a 6mm service bolt that you loosen one full turn.

Undo the crankcase ventilation hose and push it to the side.

This particular engine has a clear path to the injectors due to the upside-down design of the intake manifold.

Remove the two nuts and unclip the two clips for the plastic wiring protector.

Remove the fuel rail mounting nuts. In addition there are two 10mm bolts to remove, one on each side of the fuel rail.

Pull upward on the fuel rail until the fuel injectors pop out. There is a lot of resistance to pulling the injectors out of the fuel rail. Be careful not to smack them against the intake manifold as this will break the pintle caps.

The outsides of the injectors are quite dirty, but even greater concern is the contamination inside.

I neglected to send in the seal rings with my injectors, so Injector Rehab had to guess what size to provide. There are lots of variations between all the different Honda manifolds. The supplied replacement seal rings (right) were far thinner than the originals (left). Luckily I had the replacement seal rings that were sent with my Accord injectors (center) which were wrong for that application but perfect for this one.

Mark each injector on the underside to correspond with the printout your received. I use an A-B 1-4 designation because I usually send in two sets and mix and match the sets for the best balance.

High-end engine management systems like the AEM EMS actually let you enter the flow rates for each injector in order to get a perfect balance of fuel between each cylinder.

Spray a small amount of throttle body cleaner in each intake manifold injector hole to clean up some of the gunk that has built up there. Don't overdo it! The only way to get it completely clean is to remove the manifold. Spray too much carb cleaner in there and the car wont start.

Spread a slight amount of oil over each O-ring and seal ring. I get it from the dipstick, but technically you should use clean oil. Put the injectors in the fuel rail first. There is a lot of resistance and it is easy for the O-ring to get pinched and leak fuel. If this happens, reuse one of your the O-rings that was returned to you.

Dry up any fuel that spilled when you initially removed the injectors.

Once the injectors are installed, plugged in, the fuel rail bolts torqued down, and the bolt on the fuel filter is tightened, turn the key forward 2 clicks to prime the fuel pump without starting the engine. Repeat this several times so that the fuel pressure reaches the injectors. Now closely inspect each injector for fuel leakage. No amount of leak is acceptable! Remove and reinstall the offending injector, replacing the O-ring if necessary.

Reset the ECU by removing the 7.5A "backup" fuse in the fusebox under the hood. Tap the brake or flip the headlight switch to remove the residual electrical charge, then reinsert the fuse.

Driving Impression

The car revs and idles noticeably smoother. It's comparable to setting the ignition timing, changing the oil and spark plugs on an engine that has been neglected. This effect alone is enough to justify having the injectors serviced.

Fuel Economy Conclusion

Shortly after writing this up, I bought an STi and stopped driving the GSR regularly. Now my son is driving the car so I can't say conclusively what the change in fuel consumption was.

1994 Honda Accord LX

This has to be the most common car found on the road today. I have never been near a public road for more than 10 mins without seeing a 5th generation Accord go by.

Tools and Supplies

Injector Resistance

94-97 Accords use low impedance, peak and hold injectors with a resistor box. Each injector should be between 1.5 - 2.5 ohms. Any that aren't within the specified range should be tossed in the trash.

Torque Specs

Let the engine set for a couple hours if it has been driven. Remove the gas cap.

Use a rag to catch any residual fuel when you release the residual fuel pressure at the service bolt.

Get the PCV hose out of the way, then remove the harness protector from the rail.

Use a pick tool to remove the metal clips on the injector plugs. Don't drop them! I have gathered extra clips from the junkyard just in case.

Remove the three fuel rail mounting nuts.

Make sure the clean injectors end up in the corresponding cylinder. I use a sharpee to mark each injector. Other injector service companies sometimes use a parts etcher to mark them.

Again, since I didn't provide the original seal rings, Injector Rehab had to guess what size to send. The provided seal rings were too thick to use. They worked well for my Integra, and the seal rings I got for the Integra would probably have worked for the Accord, but these projects took place weeks apart so I simply reused my old seal rings.

Insert each injector into the fuel rail first, then put the seal rings in the manifold and slide the fuel rail/injectors in. Reinstall everything else, then turn the key forward two clicks several times to build fuel pressure.

Inspect each injector for any leakage. The slightest leak is a major problem. It's common for the O-rings to get pinched inside the fuel rail. They will have to be replaced. You can reuse an old one if you remove it carefull from an old injector.

Reset the ECU by removing the 7.5A "backup" fuse in the fusebox under the hood. Tap the brake or flip the headlight switch to remove the residual electrical charge, then reinsert the fuse.


I can't conclude anything about this car before and after because it wasn't running when I got it. I replaced the injectors at the same time as I removed the auto transmission for a rebuild. The car passed smog easily, runs great, and gets 35mpg highway.

1998 Honda Civic HX, 5 speed

My roommate asked me to find her a car so I tracked down this HX with 255k miles on it. The D16Y5 makes 115hp to the 106hp of the Civic DX/LX, and this car is capable of 45mpg. If fuel economy is of great concern to you, I recommend the 1996-2000 Honda Civic HX manual over any other car available. It is more common to find, more reliable, and has more creature comforts than the 1992-1995 Honda Civic VX, and it gets better fuel economy at a lower entry level cost than a modern hybrid.

Tools and Supplies

Injector Resistance

OBD2 D series engines use high impedance, saturated injectors between 10-13 ohms. Measure their resistance with a multimeter. Any that aren't within the specified range should be tossed in the trash.

Torque Specs

Push the clips in and release the plastic harness cover.

Unclip each injector plug.

Unplug the Evap Purge Control Valve. It's difficult to see until you lift up the harness cover.

It's apparent in this picture that I also removed the fuel line to the rail. The pulse dampener requires a large wrench. I used a crescent wrench on the widest setting.

Lift the rail away from the valve cover so you can pop out the injectors without banging them on it. It's easy to break the pintle caps by accident.

Only the VX and HX had EGR until the 7th or 8th generation Civic. If you have a Civic HX (D16Y5), now is a good time to clean the EGR system.

The supplied seal rings were far too thick. I wasn't expecting to get seal rings with the service so I already had a kit that included new O-rings, seal rings, and cushions. Later, when I contacted Injector Rehab to let them know, they told me that you should send in your old seal rings for them to reference.

This pic demonstrates the thickness of the seal rings that were supplied (left vs oem in the center). There is no way they can be used.

Injector Rehab seals each injector in a marked bag, but puts no marking on the injectors themselves. I recommend marking each with a sharpee or parts etcher, then putting them in the corresponding cylinder. The cylinder on the crank pulley side is #1.

Reset the ECU by removing the 7.5A "backup" fuse in the fusebox under the hood. Tap the brake or flip the headlight switch to remove the residual electrical charge, then reinsert the fuse.


The car runs great and gets killer mileage. With my roommate driving the car, and no mpg history prior to purchasing it, I can't make any solid conclusions before and after. I hope to use this car for a road trip so I can report its maximum fuel economy.

In all three cases I failed to verify an improvement in fuel economy. I plan to revisit this in the future.