first off, I'd like to apologize for constantly whoring up the tech sections with awful tech Q's. I'm a bad mechanic, and my car is in horrible shape. It's not a good combo.

I got my engine back together, and my #7 cylinder isn't firing. WHen I spray water on my header primaries, the water instantly evaporates from all of them but #7.

First, checked the spark wire's resistance. It was 11.03K ohms.

Next, I pulled the spark plug out and ran the engine. I visually watched the spark plug fire, and..... I sniffed the air being compressed out of the open spark plug hole. It had no fuel odor at all.

Next, I pulled the injector harness off of #7 and hooked a multimeter to it. With the engine running, it was showing me a constant 12.8ish volts. My multimeter couldn't keep up with the rapid injector pulse signal, so it was just showing a constant voltage.

Finally, I put everything back together, and physically touched the injectors. I could feel the good injectors clicking. I couldn't really tell if the bad one was clicking or not though. If it was, it was weak.

Any ideas or additional diagnostics before I pull of my fuel rail?

CLIFF NOTES: #7 injector won't pulse even though it has an elec signal. WTF?

 

Get a noid light and check to make sure the current is pulsing. If it is then the problem is a bad injector. An injector is really just a small solenoid....apply current and it open allowing the fuel to flow. The computer controls both the timing of the opening and the time it stays open, fuel pressure determines how much fuel flows.

 

Didn't see where you tested the injector coil with the meter. They should be in the 12 ohm range. The injector could also be clogged. When you have the rail off, you could swap it to another location and see if the trouble follows.

 

Good point, Rob.

Try switching the #7 wire with number 5 and see if 5 acts up. If it doesn't, it's injector related, if it does, it's wiring related.

 

Well.....

it must have been clogged with debris or something. I turned the key to the "on" position, and pressurized the fuel system to 40psi. THen, I touched a 12 volt wire to the injector, grounded of course, and watched the fuel pressure bleed down rapidly. I think that blew out the scuzz in the injector.

I dry cycled the motor for a minute, then re-assembled everything. It is running and firing on all 8 cylinders now....... FOr the first time since thanksgiving. WIERD!!!!!!!!!!

 

The injectors have a little screen pressed into the inlet. If it's semi clogged it might start acting up again. I think you can fairly easily remove the screen if you're careful, and brake clean any crud out.

 

I'm glad it worked out for you but I have to warn folks against doing what you did. In this case, applying 12V won't hurt because the injectors are operated as a 12V saturated system with high impedence coils. Low impredence injectors operate on a diferent voltage and use a peak and hold driver and would have been damaged by applying 12V to the connector....

I looked at the spare stock injectors I have an there is no screen at the spray end. There is an internal screen but nothing external. I, personally, don't recommend doing anything to the injectors as even scratches around the spray holes will alter fuel spray, atomization and, perhaps, power.