Fuel injector not firing (but connector is pulsing)

I have a problem with my #1 cylinder, so I was mucking with the injector wires. Before I started screwing around, all injectors were working. I was testing voltage/current/pulse frequency to the injector connectors, and then put it all back together and started it back up. Now #2 isn't firing. I checked with a stethoscope. When I plug #1 connector into #2 injector, the injector works. When I plug the #2 connector into #1 injector, #1 doesn't fire.

So, I know the #2 connector isn't firing, but when I check for voltage/pulse, its all there.
The voltage is 12.4V, and the frequency on the negative side is 6.4Hz (same as all the other injector connectors) which equals 384 cycles per minute (* 6 cylinders is 2000 cycles. divide by 2 cause each full cycle is one on and one off, for a grand total of 1000rpm).
There is no continuity between the positive and negative terminals of the connector, so there is no short.

I suspected I may have accidentally shorted the positive to the negative while testing, so I thought the PCM may have a short code, and I tried resetting by disconnecting my neg bat terminal and grounding it for a bit, but didn't help.

WTF? The connector physically looks good. What is happening?

loose connection inside the plug...try the super wiggle trick?

I've been messing with it for 2 hours. I don't think its goona wiggle back together .

As an aside, the neg cable is already grounded- you won't clear the PCM via touching the ground wire to the chassis.

the female end inside the plug might be messed up. id try bending the tab in with a safety pin...:dunno:

No other idea's?
Anyone have any input on how to properly test? I'm just guessing at stuff.
I do notice that when i measure voltage across both injector terminals while plugged in and running, working injectors give me a fluctuating response, where the non-functioning injector gives me nothing.

Back up a couple of inches from the connector, open area, and pin into wire. May be bad right at the connector.Reseal wire. Connector: bent pin? bent open socket? corrosion?

I wish I knew more about electronics. :gonnablow
I've tried everything I can think to try aside from plugging in an OBD reader.

I guess the next step is to just cut the connector off and manually connect the wires, but this doesn't make much sense as I get the same response from ALL connectors as long as they're disconnected.
I have to be missing some basic test...

in the original post you stated "So, I know the #2 connector isn't firing, but when I check for voltage/pulse, its all there." so right there you narrowed it down to a bad connection/bad injector prongs.

I agree. I'm going to cut the connector off tomorrow and try touching the wires directly to an injector. Still can't figure out why the readings are all the same with the connectors disconnected though.

maybe you pulled a prong out of that injector when you pulled the connector. :dunno:

Pull the connector at the pcm and switch two injector output control wires, 1 with 2, see if the problem follows.

High resistance in a wire will show voltage, but not allow enough amperage to fire the injector. An injector driver in the pcm could have failed also.

I've seen problems in the past with bad splices on the positive line. All the injectors (HO era assumed here) get their +12 volts from a common source at the coil, branching out via splices in the harness. The PCM pulses the negative. In the one I got, the voltage was low even with the injector unplugged, but I could see the possibility that you could get voltage drop only when the injector is putting a load on the circuit. The injector will stop firing if the voltage goes below about 9 volts.

I was thinking of checking amperage by tying the 12V lead from the connector and then tying the pulse together with my multimeter. Sorta short on spare wire and hands (damn I could use some alligator clips).

Anyone have a pin out schematic for the PCM fuel injector plug?

Ok, I've verified that the pulse is not actually happening on the #2 connector. I've also tested the pulse wire all the way back to just after it come out of the PCM connector, so either the wire is broke right as it comes out of the PCM, or the PCM isn't sending a signal. Anyone have any idea's how to test either?

Sure, pull the hardshell connector all the way off the pcm. Use a small pointy probe so you don't damage the wire terminal. Check for continuity from the pcm side of the connector out to the fuel injector end of the harness. If there's continuity, look closely for a pin-fit issue. If the terminal isn't messed up, try a known good pcm.

Well, I pulled the connector, traced every injector pulse lead, and did a bunch of tests. In the end, I just swapped the #1 pulse lead to the #2 right at the PCM to verify that the problem wasn't' wiring. Problem wasn't wiring. The new wire didn't change anything.

When I pull codes, all I get is 202 (injector circuit shorted or open), and eventually 302 (#2 misfire).

Can anyone confirm that the 12V lead is common to all the injectors?

At this point I'm guessing my PCM is fried...

After much XXXXing around, I decided the PCM was probably hooped and figured I couldn't hurt anything any worse, and I wanted to rule out the possibility of the 12V lead not being able to supply the amperage I needed. So... I back probed the #2 pulse lead to my multimeter and connected the other side to the frame, started the engine, and got 1A steady. This of course made the injector very hot and puke fuel all over the cylinder. I smelled gas and shut everything down. Disconnected the probe and jumped the #1 pulse to the #2 injector and started the engine back up. Still nothing. Shut down, removed back probes, started up again and stethoscoped again. #2 is XXXXing working now! WTF?

All I can think is that something in the PCM desoldered itself, and when I shorted it with 1A, it resoldered...?

At any rate, problem is fixed for now. Goona track down a spare PCM just in case.

Xwhatever, sounds an awful lot like a hosed injector driver in the ECU. I agree with picking up a spare, just shove it under the back seat along with a cheap set of socket wrenches and a ratchet and keep it there till the old one blows, swap it out on the side of the road and keep going.

I'm not sure how giving it electroshock therapy helped, but I guess it did :dunno: might last a decade, might last five minutes.