Testing injectors, ? Options

[Hammy]

How do I do a visual test/check on fuel injectors outside the car on the bench? Any way to tell they're spraying right? I don't want to install this engine and find the injectors are crap.

[jk76.914]

I've tested mine a couple of times. Generally, when I had the time to work on it, I didn't have the bucks, so I had to figure a lot of things out. No 914world.com back in the 80's when I got started.

I use a long length of hose- maybe 6 feet. You don't need the spensive fuel injector hose, as you're using it for such a short time and outside the engine compartment. Regular American fuel hose works OK. Maybe $4 for 6 feet at NAPA.

Also, I made an extension cord from an old leaking injector- broke it apart and used the electrical socket, soldered to the end of a 6 foot piece of wire. The other end is a fuel injector pigtail that I cut off a VW bus in a junk yard. Cost me 50 cents plus a round trip to the junk yard on a Saturday morning.

Disable the coil, and ground the center wire. Hook up the injector using the long hose, with hose clamps on each end (don't have to be expensive FI clamps for this), and the extension cord you built. Stand as far away from the car as you can, point it at a piece of brown paper, and have someone else crank the engine. When you've had enough- probably 3 or 4 cranks, tell them to stop cranking. The thing you'll notice right away is how loud it is. Don't let it startle you into dropping the injector into the dirt.

There are four tests you can do yourself-
1. pattern. Check it out as it squirts, plus the pattern it leaves on the brown paper. You want to see small small droplets, coming out in a cone shape. Do all 4 and you'll see right vs. wrong. It's highly unlikely that all 4 will be bad, so you can learn what's OK by experience. It's pretty likely that all 4 will be OK. (reference- Bosch Fuel Injection and Engine Management Manual)

2. leakage. Unplug your extension cord to the injector you're testing, but keep the hose attached at both ends. Crank the engine. This will build up fuel pressure. With the injector pressurized, but not opening, you may see a drop of fuel form on the tip. Two drops every minute is a max acceptable. (reference- Clymer 914 manual) Use a watch to time it. Ideally it doesn't drip at all. Don't crank the engine for the whole minute though!!! You'll burn something out, like your starter. Several turns will pressurize it and the check valve in the fuel pump will hold it long enough for the test. If you're getting into EFI tuning, you really should own a fuel pressure gauge, and it should be hooked up for this, because it's possible your check valve isn't checking.

3. While you're waiting for drops to form at the tip, carefully check around the body of the injector for seepage. The body is formed from a few tubular pieces, stacked on top of each other and sealed with o-rings. They can leak, which is dangerous, in addition to causing hot start problems by bleeding off the residual pressure in the system. (reference- Bosch Fuel Injection and Engine Management Manual)

4. resistance. This is the easiest and safest test. Just measure the resistance across the two pins on the injector. The spec is 2.4 ohm, but anywhere between 2 ohm and 3 ohm is OK. (reference- Porsche factory shop manual.)


Things you can do- for #1 and #2- put it all back together, and then run a can of Chevron Techron Fuel Injector Cleaner through with about 8 gallons of gas. It's amazing stuff! There's a good chance that's all it needs and you're done. If you still have the problem, you can try sending it off to a fuel injector cleaning service, or you can put that money towards new injectors.

For #3 and #4- replace the injectors. I'm currently having no problem with my Niehoff injectors for 1974 Mercedes 450 SEL. They were only $49.99 at PartsAmerica.com brand new- not refurbished. I only have 2000 miles and 2 years on them though, so it's early to tell how the reliability stacks up.

There's no such thing as a "rebuilt injector", though some advertise them as such. The cleaning services clean them in solvent, back flush them, and replace the inlet screen, but they don't "rebuild them", which implies replacing worn parts. Important to note though- they also measure fuel volume and assess spray pattern. Fuel volume you can't easily or safely do at home, in my opinion.

That's what I've learned after 24 years with my '76 2.0.