So I swapped my alternator to a fd alternator and it wouldnt start. I found I had no spark and I tested for voltage and im only getting 3 volts to my coils and injectors. I swapped my alternator back to my s4 one and same issue. Im guessing I shorted something but all of my fuses are intact. I have 12 volts going into the ecu from the black and yellow wire but only 3 volts coming out in the pins for the injectors and coils. The car is a s4na with a s4 t2 swap. Na chassis harness with t2 engine harness. Any thoughts?

 

Also I only have 3 volts going to the main relay in the black white wire

 

Are you measuring 3 volts at the ECU pins or at the coil plugs?

The ECU is powered by the B/W wire from the Main relay.

The Main relay should have battery voltage on the "two wire" relay plug w/key to on.

 

check for corrosion on the EGI fuse.

 

so i should check for power on the b/w wire on that two wire plug?

and i tested for voltage on the wire after the egi fuse, and im getting 12volts.

its weird because on the main relay, i tested for voltage on the four wire plug, and im only getting 3 volts.

and im measuring 3 volts at both the coil plugs, and the ecu pins. does anybody know the routing for power for these? like battery-main relay-ecu-coils and injectors?

 

did you install the Fd alt correctly on the Fc Harness?
..when you install the Connector for the FD harness,One wire on the connector is to get 12 volts.( I put that one directly to the Big Black wire on the Nut).The other goes to the Dash gauge via the harness.
So One wire that was originally hooked up to the OLD s4 connector is now NOT hooked up,is taped and tucked aside.The other is hooked up to harness and supplies dash gauge.
you can just barely see it in my Pic.where one of the Pigtail connector wires is hooked up under the Big Black wire(12 volts) under the nut on top.That gives it 12 volts.

 

At the Main relay there are two plugs. One plug has 2 wires while the other plug has 4 wires. The 2 wire plug supplies voltage to the relay via the B/W wire and the second wire in the 2 wire plug is a ground wire. Thus the B/W wire in this 2 wire plug needs to have battery voltage w/key to on.

The four wire plug at the main relay has 4 wires but 2 of these are constant power. The Black/Green wire and the White/Blue wire are the 2 wires which have constant voltage. The other 2 wires have voltage w/key to on. These 2 wires are Black/Yellow which you already tested at the coils, and the B/W wire (this is another B/W wire that is different than the B/W wire in the 2 wire plug).

Since B/Y has voltage then it should be a given that part of the relay works. When you find battery voltage on the B/W wire in the 4 wire relay plug w/key to on it will tell you if both aspects of the relay are working properly.

EDIT: If the B/Y wire has battery voltage w/key to on then it is a given that the B/W wire in the 2 wire plug has battery voltage w/key to on.

 

i forget but isn't there a connector junction for the EGI under the brake master cylinder?

 

Im getting no power at the black white wire on the two wire connector at the main fuse. on the four wire connector on the main relay im getting 12 volts on the white-blue wire and black-green wire. However im only getting 3 volts o

 

Sorry im updating u guys from my droid phone. However im only getting 3 volts from the black-white wire and .8 volts from the black-yellow wire

 

Does anybody know where the power comes from until it reaches the main relay on the black-white and black-yellow wires?

 

Did you test for voltage on the B/W wire in the 2 wire plug w/key to on or not? The key needs to be on when testing the B/W wire in the small relay plug.

I stated already which wires in the 4 wire plug have constant voltage w/no key necessary and which 2 wires in the larger plug will have voltage "only" w/the key to "on." So White/Blue and Black/Green have voltage all of the time so no key is necessary but the relay passes the voltage from these 2 wires to the B/Y and B/W (same plug) only when the key is at "on" or better.

 

Key was on during these tests. The small black-white wire on the 2 wire connector only has about .05 volts. The black-white wire on the 4 wire connector has 3 volts and the black-yellow wire has .05 volts

 

The B/W wire in the 2 wire plug to the Main relay is supplied voltage from the 15 Amp Engine fuse found in the interior fuse box. The key being turned to on takes constant voltage off of the Black wire in the ignition switch and passes the voltage onto a B/W wire running from the ignition switch to the interior fuse box where the Engine fuse is. The Engine fuse then passes voltage onto the Main relay via a B/W wire.

 

So in theory I could run a switch and give the black-white wire on the two wire connector 12volts from the battery and see if it solves the problem. Of course run a fuse

 

Or you could focus on the 4 wire Main relay plug and jumper the B/G to B/Y and the W/L to the B/W wire. Or you could check the Engine fuse! Unless I'm missing something, running an additional switch should not be necessary.

 

Well ill probably jump the wires and see if it lets me start the car. Ill have to run a 12volt source to the small black white wire since I believe I have a short

 

The engine fuse on the interior fuse panel is good

 

Using the 2 jumpers bypasses the Main relay so there is no need to activate it. Jumpering the B/W wire to voltage is not a good idea. When you turn the key to on do the turn signals work?