Kent and Al,

Fuel pressure at the top port of the fuel distributor when the engine is turned off is just over 40 psi on my ’92 300E (CIS-E). It’s about 80 psi when running, so what I call a “static” test is an engine off, but fuel system still pressurized at “hold pressure.” (I’m sure it’s call something else, but “hold” comes to mind as I write.) When I did my flow testing/tuning I obviously cut power to the fuel pumps between runs . The injectors stopped flowing, I assume since 40 psi was below their threshold, and they did not leak…not even a drop.

I don’t know how much this means to any of you, but in the process of trying to get my car to run really well (idle has been really rich), I have noticed that fuel puddles at the bottom of the intake manifold, right under the butterfly. IF your injectors did leak, they would only leak until the pressure went to zero, which really is not much fuel. I know this because I have had to use my fuel pressure gauge to bleed the system down to 0 so many times. It’s about half an ounce each time.

1. How do you test new injectors?

I put them on my ASNU bench, cranked the pressure up until the injectors opened (noted that pressure) and then kept cranking the pressure up to watch the patterns. I then ran a flow test at 60 psi on all the injectors (I had no idea what the normal pressure was going to be, still had not installed the tank or new pumps) to see how they compared.

2. Please give more detail on how this is done outside the car.

After #1 above, I tested the entire system on the car. You could do it off the car but that seems harder to me.

3. What do you mean by a "static" test?

See above.

4. Why continue to use injectors that are over 150K miles old?

Because in my case they flowed in the same range as the new ones, both pattern and volume, and they did not leak at 40 psi. Off the top of my head they cracked open at about 50 psi.

I do a bunch of electronic injectors. They have tiny pintles that use their shape to generate a spray pattern. Those pintles wear out and those injectors will blow streams at some point. These injectors seem to have a plate that vibrates to cause the pattern. If they ever leak, my guess is that some good fuel additive/cleaner will bring them back to life since the screen should keep particles out.

Now if the injectors just don’t flow because they are clogged up that is a different story. Do the on car test and see.