420A injectors not getting 12 volts

[brannflakes]

420a..So the injectors no longer get the constant 12 volt power supply. I've checked it all the way back to the PCM and nothing. but all the other sensors are receiving the correct voltage. Is there something that would stop my PCM from sending out the 12 volts to the injectors? Side note.. I swapped another PCM in and it did the exact same thing, and I find it hard to believe they both had the exact same problem, so I am ruling out the PCM....for now.

 

[luv2rallye]

The injectors (and many other stuff) get their +12v from the ASD relay (on firewall) - not the PCM. The PCM pulse grounds the other side of the injectors to operate them (note that when it's not grounding them, it floats the wire so you will see +12v on both sides of the injectors). So if the other stuff (eg. O2 sensor, coil, etc) are getting +12v then you have a wiring problem between the injectors and ASD relay.

 

[brannflakes]

But the power wire runs from the injectors to the PCM.... So how does it connect to that relay as well?

 

[brannflakes]

the relay has a 12 volt input to the PCM, I am getting 12 volts there. But nothing is coming out of the pin that gives power to the injectors

 

[brannflakes]

Okay weird thought.. with the key on (engine off) the oil pressure light stays on and doesnt turn off. The oil is full.. so could this be a bad sensor sending a signal that is stopping the injectors?

 

[luv2rallye]

No. There is no oil pressure with engine not running so that light is on.
The injectors have one side all connected together which goes to the ASD relay - this is the power source for all of them. The other side of each injector has it's own separate wire to a PCM pin - this is the control side which the PCM pulse grounds at the proper time (based on CAS signal).

 

[brannflakes]

Mine has one side all connected together that goes to the PCM.. does that mean its wired incorrectly? (remember this is a 420a)

 

[luv2rallye]

Yep (or you traced it wrong, or there's really 4 wires inside a harness that's going to the PCM). Where do the other side of the injectors go?

 

[brannflakes]

I have the 4 "ground wires" ruining from each injector to the PCM.. Then the Constant power wire runs to the PCM as well. The car ran for years with this setup... so is it really wrong?

 

[luv2rallye]

Well if the constant power wire goes to a PCM pin that goes to the ASD relay then it's fine. What pin does it go to and what year is the car?
I bet it's pin 6 if a 96-99 or pin 2 if a 95.

 

[brannflakes]

its a 98 rs.. I believe it is 6.. Its black/red stripe and is the "Auto shutdown Relay Output" according to the diagram I found. (that one connects the PCM to the Injectors) and then there is a "fused B=", pin 46 which I believe s traced back to the relay if I'm not mistaken

 

[luv2rallye]

That all sounds correct except pin 6 is the one that actually goes to the ASD relay and your injector commons. 46 is the PCM battery backup and goes to a 30A fuse (it has power all the time). Bottom line it's wired correctly. If you have no power at the injectors the common wire must be broken somewhere or injector connector is bad.

 

[brannflakes]

I have continuity from pin 6 to my injector wiring harness. However 12 volts is not present at pin 6 so if I am understanding you correctly this means the injectors will also not get power.. Any idea why the 12 volts wouldn't be present at pin 6?

 

[brannflakes]

And like I said before.. I've tried a second PCM and i find it hard to believe they have the same problem..

 

[luv2rallye]

See if you have +12v on the ASD relay's pin 2 black-red when key is turned on (note pin 8 is red-black but that should have power all the time and is the one the ASD relay connects to pin 2 when it activates).
If with key on, you have power on ASD pin 8 but not pin 2, then measure voltage on pin 4 (red-white). If it's not zero, the PCM is not turning on the ASD relay.