Rep Power: 0

Got a 2004 Civic Si and all but one of the fuel injectors are reading 13.8 volts when the car is running, the last one (the cylinder second from the left, or passenger side) is only reading 1.5 volts. All fuel injectors read at 11 ohms. Unplugging the power to the fuel injector or the ignition coil for the offending cylinder has no effect on the engine, runs the same (bad idle, nearly impossible to start on cold days).

Is there anything else besides the ECU that could cause this? Sorry for what is probably a worn out question, but I don't have a service manual for this car. None of the wires to the ECU are of the same gauge as the wires connected to the fuel injectors, so I'm just wondering if there is something else in between the two that could cause the voltage drop.

 
Rep Power: 517

The ECM (ECU, PCM, whatever) controls the grounds to the injectors, not power...
Power comes from a main relay and runs through splices to reach each injector....

You sound like you probably have a wiring problem instead of an ECM problem.



USA Si car, or Canadian Si?
What engine?
2, 3, or 4 doors?
Etc?

Wait wait wait (clicks handle) Ah, it's a US Si 3 door 2.0
That would have been handy to know sooner.
0_o

On a 2.0, the power side for the injectors is yellow/black, the splice pack (junction connector C104) is on top of the plastic harness holder that runs along the end of the head, almost directly under the forward air breather box mounting screw(?) Can't find a good pic, sorry.
There's like more than 20 wires in the connector and they all go in only one end. Looks like 7 of them should be yellow/black, all those are supposed to be connected together within the pack.


If you truly have 12v+ to only 3 out of the 4 injectors, then your problem should be somewhere between (and including)that splice pack and the injector affected.

 
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Well, I located C104 and did find one Yellow/Black wire that was nicked, most likely whenever the previous owner put the cold air intake on it. I clipped out the nick and soldered the wire back together which did get the 12 volts back to the injector, but that hasn't solved the problem of the engine running the same whether or not the injector is plugged in.

I manually grounded the red wire on the injector without the engine running (with the key in the run position) and I can hear it click. Tried it again with the engine running and I can apparently flood out the cylinder because it will start to accelerate for a split second and then bog down the engine. So, I would think that means the injector is good. But, I am not what I would consider an auto mechanic, so I could be wrong.

Is there any possible way to test the computer before I decide to send it in to be repaired? http://www.foreignecurepair.com/ advertises that they can repair them for $195, that's a heck of a lot better than any replacement price that I've been able to find.

 
Rep Power: 517

So you restored the B+ side to the injector.....What about the other side?

Use a (noid light, LED test light, duty meter, meter set for mS, labscope) to see if there is a pulsed ground signal at the injector. Whatever you find should measure identical with another injector.

If no signal, then repeat the same test right at the PCM (to eliminate wiring as a possibility). Get a good wiring diagram.

I know I'd hate to waste coin on a PCM repair only to discover it still is broke and its a wire problem.


Plug it in to a known good car.
If you don't have that luxury, then you eliminate all other possible causes first.


Hondas stuff is pretty dang reliable, so I'd not suspect a bad PCM or injector right off the bat. I'd expect more wiring issues at the top of the list, especially if someone has been in there modding at all.

 
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Borrowed a noid light from a mechanic, obviously the ECU is working. Lovely, I get to figure out how to take off a fuel rail and remove injectors. I'm an air-cooled VW guy, this is going to be a new adventure for me.

 
Rep Power: 517

Ohm test the bad injector, compare it to a good injector.

If they measure the same (they likely will) then run the engine and tap on the dead injector. Maybe you can get it unstuck and start working again.

Use common sense, don't break the injector in half!

You might just start with tapping on the injector.
EDIT: Nevermind this. I forgot the injector was able to squirt fuel manually.
You might check compression and valve adjustment? IDK