Fuel Injector Tester

Back when the dot-com boom fell apart and I got laid off from my cushy software tech-writing gig (at a company that had once promised a private chef, rock-climbing wall, and customized surfboards with the company logo for its employees), I fell back on a tried-and-true moneymaking scheme: buying towed San Francisco cars at the City Tow auctions, fixing them up, and selling them. It worked out great until I got a '90 Tercel that just wouldn't pass California's super-stringent smog test, no matter what. Long story short, I traced the problem to bad fuel injectors, but what unemployed ex-dot-commer's got money for brand new ones?

Especially when the junkyard is chock full of pocket-sized Toyota injectors, available for free at a reasonable price? Exactly. But how do you know if your junkyard injectors are any good? Sure, you can tell if one is completely nonfunctional once you start the car, but it's hard to detect one that's just screwing up enough to hose the emissions. Well, the Toyota shop manual refers to some kind of high-tech flow-testing device that basically lets you look at an injector's spray pattern and measure the flow to see that it's within specs. I figured, hey, I'll just build my own! Now, y'all can just hold off on the comments telling me I'm a fucking idiot with a death wish, because I swear I look back with horror at all the different ways this thing could have killed me; my only excuse is that I got locked into the challenge of building it, while not really looking at the big picture. In any case, I figure what I ended up building might be of some entertainment value to our beloved Jalopnik readership. So here ya go!


Fuel Injector Tester

But first, as a technical writer I'm required to scare the daylights out of anyone who might attempt to build this incredibly dangerous device, by providing a disclaimer packed with menacing statements in boldface (and, of course, Walker Canada's warning symbol). So: Warning! If you attempt to build any sort of device that involves gasoline under high pressure, particularly one that resembles in even the slightest detail the device described below, you will definitely be killed. In fact, you will be burned so severely that you will pray for a quick death to release you from your agony, as your arms and legs curl up and fall off like sausages left too long on the barbecue. However, before the gasoline ignites, you will experience the sensation of pressurized gasoline being injected into your eyeballs, exploding them. After the paramedics show up (shaking their heads at the fool contraption that transformed you into a cruel parody of human form) and haul you to the hospital, your relatives and friends will arrive at your bedside and read you long lists of your faults and wrongdoings, each whispering "I always loathed you" in your ear (which will resemble one of those black potato chips from the bottom of the bag).


Fuel Injector Tester

Right, so now that we've ensured that you're not going to, you know, try this at home, we can get on with the description of the device itself. First I started with a late-70s Datsun 280Z fuel pump. This is an amazing fuel-injection pump; not only does it deliver a nice reliable flow, but it's by far the easiest such pump to remove from any car at the junkyard, being located in a very accessible spot just inside the right rear wheelwell (unlike most FI pumps, which tend to be located in difficult-to-reach locations like inside the gas tank or behind knuckle-slicing panels). I bolted the pump to a crude plywood frame and rigged up an intake hose long enough to reach a can of gas.


Fuel Injector Tester

Then I grabbed a fuel rail from a junkyard Tercel (the same one that provided my first four injectors) and plumbed the fuel pump outlet to it. That way I had the same pressure regulator as the one on my Tercel; since the Z pump puts out similar pressure numbers to the Tercel's, I could count on getting similar behavior out of the injectors being tested.


Fuel Injector Tester

I only wanted to test one injector at a time, so I packed the three extra injector holes in the rail with JB Weld, screwed some bolts into them, then packed more JB Weld over the whole mess. I'm pretty sure this arrangement doesn't meet internationally recognized safety standards, but I got lucky and it didn't leak.


Fuel Injector Tester

Once the fuel rail was ready, I bolted it to the plywood top of the frame. I figured clamp pressure against the JB Weld would help seal the holes, so I wedged a precision spacer (a dime) underneath the short one. Yeah, I know, what could I have been thinking?


Fuel Injector Tester

A fuel injector does its thing when it gets 12 volts on its electrical contacts, so I rigged up a Toyota injector connector to the wiring harness.


Fuel Injector Tester

I didn't have any injectors handy when I shot these photos, so you'll just have to imagine an injector being held in place in the fuel rail by this aircraft-grade aluminum bracket.


Fuel Injector Tester


I used drywall screws, choice of hoonic backyard mechanics the world over, to tighten the clamp down on the injector and hold it tight enough to get a good seal in the rail. A graduated cylinder goes underneath the injector, but I couldn't dig up one of those for the photo shoot. Just imagine the setup and you'll get the idea- I mean, if you can imagine it not on fire.


Fuel Injector Tester

Of course, a fuel-injection system needs a return line to go back to the gas can- I mean, fuel tank. I must have scavenged the banjo bolt for some other project, so I'm just laying the line in place for the photo.


Fuel Injector Tester

Then a couple of light switches, both hooked up to a car battery. One activates the fuel pump, while the other activates the injector. Turn on the fuel pump, turn on the injector, time how much fuel it squirts in a given time period, repeat. Try not to spray gas all over the place. Avoid smoking.


Fuel Injector Tester

Here's the finished product. It did solve my problem, in that I was able to identify the two bad injectors and replace them with good ones, but I won't be using it again.