Dead 1,3, and 5 cylinder 89 m20b25

[///Muffin]

So originally I had a dead cylinder #3, and simply couldn't figure out why. I did a compression test on all cylinders and came out with 150 across the board, aside from one that was at 130. After that I checked spark and all wires and plugs are good. Changed out the #3 injector, still dead. Swapped injectors with another cylinder, still dead. I saw that one of the wires providing power to the injectors was a bit worn, so I did a test on all of those and they're good, but immediately after doing that, I lost #1 and #5.
I know the firing order is 1,5,3... so I thought distributor, popped that off and everything looks alright. I didn't have the battery unplugged when I popped the test light in, so I could understand maybe messing up something in the CPU, but I have absolutely no understanding of electrical anything.

Any ideas?

[SpecM]

I'm going with "the connector under the intake manifold for $500, Alex"

;) try cleaning it out with electronics cleaner

[///Muffin]

The screw on one that's threaded really weird and a pain to get off that directly connects to the black plastic piece that provides power to the injectors?

[SpecM]

The screw on one that's threaded really weird and a pain to get off that directly connects to the black plastic piece that provides power to the injectors?

yes

[2.5-12]

.. for $500, Alex...

"suck it trebek!"

[///Muffin]

I'll be trying this out later tonight, most likely. It just seems weird that I was getting power to that #3 injector and it still wasn't firing.

[///Muffin]

Well, thank you very much, this did get me back to 5 cylinders, but #3 is still dead.

So just a review: I have spark, I have a working injector, I have compression, I have no explosion.

[PeaveyBassist]

You know the injector is opening while the car is running? If you have the right timing, spark, fuel, qnd compression, you should have a firing cylinder. I believe the ecu grounds the injectors to open thrm. They should always have 12v. You might want to take out the injector harness and check the wiring inside if 1 and 5 stopped working for a min.

[StereoInstaller1]

^hot sig pic, yo.

[jlevie]

The injectors are organized as two banks of three. Bank one is cylinders 1, 3, & 5 and Bank 2 is cylinders 2, 4, & 6. Power is common to both banks and the DME grounds each bank to fire those three cylinders. A common failure point that can take out either, or both banks, is C191 and/or the DME. Failure of a single injector is a bad injector or a bad connection to that injector.

[///Muffin]

The injectors are organized as two banks of three. Bank one is cylinders 1, 3, & 5 and Bank 2 is cylinders 2, 4, & 6. Power is common to both banks and the DME grounds each bank to fire those three cylinders. A common failure point that can take out either, or both banks, is C191 and/or the DME. Failure of a single injector is a bad injector or a bad connection to that injector.

(I'm now firing on 1,2,4,5,6)
I used one of the injector electrical test lights that you hook up to the electrical harness and it lit up. I've swapped injectors between cylinders and it's always #3 that is dead. Any chance it could be injector timing.

[jlevie]

If a noid light shows that injector connector to delivering a firing pluse and the failure doesn't follow the injector when you swap parts around, I'd look to the ignition for that cylinder or for low compression on that cylinder. I'd do compression and leak down tests and if they are okay I'd replace the plugs/wires/cap/rotor.

[///Muffin]

Problem found, sheared rocker arm. Pulling the head should be fun =)