Fuelish persuits.
Hello Rustlovers, Welcome to the Free Model T. Today I present to you a mostly pictorial guide to test and recondition fuel injectors. Please wear any and all necessary safety gear and exercise caution when working with pressurized air/liquids.
First of all, what the heck is a fuel injector anyway? The answer is absurdly simple: it is a tiny spray nozzle with a tiny electric switch on it. On an electronically fuel injected system (EFI) the fuel pump provides fuel pressure to the top of the injector and the computer sends a 12 volt pulse to the electromagnetic switch when it wants some fuel for that cylinder. When the injector gets its pulse, it opens, spraying fuel out of the bottom of the injector into the intake port.
Three other types of fuel injection are:
- Mechanical. An injection pump turned by a belt or gear pushes the fuel into each cylinder as needed through separate fuel lines per cylinder.
- Throttle body. One or more electric injectors are positioned at the throttle body to act more as an electronically controlled carburetor.
- Direct. Fuel is shot directly into the cylinders at several thousand PSI just in time for ignition. The high pressure is to overcome the cylinder pressure as the fuel is injected during the compression stroke.
Step 1: grab a fuel injector.
Step 2: Ohm check it across the terminals both ways, the readings should be the same. If they are repeatably different by more than 100 milliohms the injector should be replaced.
Every good injector I’ve ever checked had between 12 and 19 ohms. All injectors should be within a few decimal places of exactly the same ohm value. If one injector reads wildly different than the others it is bad.
Step 3: Clean the injectors. Look how nasty these are! I lightly wire-wheeled the metal bits and sprayed the plastic parts with solvent.
Step 4: stick a #8 sheet metal screw in your vice.
Step 5: spin the fuel rail side of the injector onto the screw and give it a tug, the filter basket should stay on the screw.
Step 6: connect a pressure regulator to some fuel injection hose with fuel injection hose clamps.
Step 7: carefully fill the fuel line with your favorite “fuel system safe” “non flamible” solvent. Attach injector.
Step 8: slowly pressurize only to the appropriate pressure for your fuel system. Check injector tips for drips or moisture around the spray nozzle. If there are any signs of moisture the injector is bad.
Step 9: connect some leads to your injector with a push botton and a 9 volt battery. Point it into a container and press the button. It should have a nice, solid strong beautiful spray.
Step 10: place the new filter basket into the injector and give it a couple of firm taps on a clean block of wood. You don’t have new filters???? See step 11
Step 11: go back in time a week and order the filter baskets. Seriously though, I like to make sure my injectors are good BEFORE I order parts.
Now put your o-rings on and install them!
The one part I left out is a flow test and it’s because I don’t care and will only be using these as emergency spares. Basically it can be done with similar components but you would need a larger volume of pressurized fluid (I would use an automotive paint gun for this), a stopwatch, and a collection container with measuring lines.
Injectors are rated by how many lbs. of fuel per hour (I’m in the U.S.) they can deliver at proper pressure assuming they are unrestricted and open the whole time. Therefore you can flow the injector for 1 minute and should get 1/60 that capacity. As my injectors are 19 lbs, after 1 minute I should have about 5.07 oz. by weight NOT volume.
Are you confused yet because here’s where it gets slightly tricky. The solvent coming out of the injectors doesn’t necessarily weigh the same as gasoline so you can’t tell by weight if it’s accurate or not. Most solvents WILL be similar in viscosity to gasoline so you SHOULD be able to tell by volume. Since 1 fluid oz. of pump gasoline weighs exactly .75 oz. by weight, my injectors should have put out almost exactly 6.75 fluid oz. in 60 seconds.
For my Rustlovers in any of the other 40 countries that I have readers in, you’re in luck. Your injectors are rated by volume in cc’s per minute so you don’t need to do any of these stupid conversions. Also I’m in luck because I don’t feel obligated to do them for you.
Until next time Rustlovers, use the metric system. It’s just better.
