So, I recently removed the EM harness from my turbo swapped S4 GXL. I depinned all of the wires and connectors that I didn't need. (2O, 2P, 2M, 2N, 2K, and 3D)

Yesterday I reconnect everything and try to start the car. I noticed that the fuel pump didn't prime. The car sputtered and tried to start about five times. Pressing the throttle a bit didn't help because it felt as though there was no throttle pedal.

Today I remove the three ECU plugs and check voltage to a few wires with key to "ON"... The main thing that really stood out was the 'V ref' voltage reading full voltage as opposed to the 4.5~5.5V that it should be seeing. Just to be sure, I check the boost sensor V ref, the AFM V ref, and the TPS V ref. They all read full voltage. (Roughly 12V.)

The car ran great about two weeks ago, before I had "cleaned-up" the wiring harness. This is the same issue that ruined my old Power FC. I now have stock components. (N333 ECU) - I don't understand where the 'V ref' wire gets it's signal.

 

it comes directly from the ECU. you have some cross continuity still going on for it to be seeing 12v so the wiring harness is faulty somewhere.

remove or temporarly cut the 5v ref from the ECU and check to see if it is still putting out only 5v directly from the ECU or the stock ECU may be fried as well. from there continue disconnecting anything that has a Vref connection to see if something may be shorting out internally that also has a 12v input like OMP(if it was an S5), AFM, pressure sensor, etc. if with them all disconnected it still showing 12v then it's obviously the Vref wire in the main harness is touching a 12V hot wire somewhere and will need to be cut open and dissected or replaced.

 

Luckily the ECU is okay. I've found that when the atmospheric pressure sensor (near passenger side kick panel) is plugged in, the voltage is well above the necessary 4.5~5.5V. With key to "ON" and pressure sensor unplugged, I get ~4.9V at the 'V ref' wire on the atmospheric pressure sensor plug. My problem lies somewhere in that bit of wiring... Maybe even the sensor itself.

 

Make sure the B/W wire which has 12 volts w/key to on is not rubbing up against the Brown/White wire (Vref) and picking up its voltage.

 

Where would it be rubbing at? At the sensor plug or something??

I just checked the 'V ref' pin at the ECU plug with key to "ON" and now it is showing ~12V. It wasn't doing that before... So, I unplugged the boost sensor and it went away. This is starting to become a clusterfuck.

 

The Boost sensor also is fed power by the B/W wire. So it sounds like the B/W wire is coming in contact w/the Br/W wire more than it should. Where? I don't know.

 

I'll keep looking around.

What would cause the fuel pump not to prime? I jumpered the check connector yesterday, and it runs. It just won't prime when I turn the key to the "ON" position.

 

You might want to check pin 2R which is a ground thus w/key to on it should have 0 volts. This ground is associated w/the ground of the AFM and its related fuel check connector, which if poor would prevent the fuel pump from turning on after the check connector is jumpereed and key to on.

 

the pump only primes after the AFM moves to tell the ECU that the engine is cranking, your old PFC did have a priming sequence though.

 

doesn't prime, it either runs with the key in "start" or when the ECU sees RPM and the AFM is not fully closed

 

^ That's interesting. My car has always primed for a few seconds with key to "ON". It primed two weeks ago when I drove it. Perhaps I don't have an issue when it comes to that. I still have the V ref issue. :-/

I checked 2R with key to "ON" at the ECU plug and at the AFM and got 0V. So, that checks out to be just fine.

I have yet to look in the FSM at the two orange plugs near the atmospheric pressure sensor. I only get this problem when the connector with 13 wires is plugged in. Those plugs connect to the dash harness?

 

If the plug has 13 wires but 8 pin positions on the row w/the most pin positions then that would be FEM-01. This connects the Front harness w/the Emission harness. Can you verify that this is the problem plug before other advice is offered. If the plug though has only 7 pin positions on the longest row then that would be FEM-02. Now some wires might not be used depending on how a person wired their car so the number of wires in the plug is not the best way of describing the plug unless some of the wire colors were stated so the best way to describe it is by the number of pin positions on the longest row. If -02 was disconnected then that would cut power to the ECU from the Main Relay so it makes sense that you would be talking about -01.

 

My apologies. It definitely has 7 pin positions on the longest row, meaning it is FEM-02. I know for sure that it has two black/white wires with 12V with key to "ON". That is the plug that is giving me issues. I've checked the EM harness and haven't found any open wires. I've also inspected each plug with a V ref wire... Nothing touching any other voltage sources.

 

Well if you disconnect that plug then the ECU cannot have power so how would you know what is going on w/the Vref wire if the ECU is not powered? It should result in zero voltage on the Vref.

 

It does result in zero. I don't know what the ECU is doing without that plugged in. Perhaps I am just making things more complicated in my mind. I figured maybe that the front harness was feeding voltage through the FEM-02 connector to the wrong wire in the EM harness. I cannot find the FEM connectors in the FSM.

 

I think one thing which would be of assistance is to depin 2A and place the meter through the plug and into the ECU and see if it registers 5 volts w/key to on as this is an output signal. If it does then that would suggest that there is 12 volts on the depinned wire, the Brown/White wire. If this were the case, then diagnosing your problem becomes easier.

 

~5V from the V ref pin on the ECU and ~12V from the depinned ECU V ref wire.

Are there any other items that use the V ref signal other than the AFM, TPS, boost sensor, and atmospheric pressure sensor?

 

Another thing of importance is the Vref wire "does not" run through either FEM -01 or -02 so it is erroneous to single out one of these plugs as the problem. You singler you.

 

Your results make much sense. Variable Resistor is the 5th item supplied w/Vref voltage.

 

In case the resistor is not the problem.

Both the Boost and ATP sensor have a B/W wire that has voltage of 12 volts w/key to on. So perhaps you might depin one of these B/W wires and recheck the voltage on the depinned Vref wire and see if the voltage drops from 12 volts or not. If not, then depin the B/W wire at the other sensor and once again check the voltage on the depinned Vref wire. If it drops then repin the 1st B/W wire that was depinned and w/all of these sensors connected except for the one recently depinned make sure the voltage is still not 12 volts. If so then you probably narrowed down your problem.

 

I depinned the B/W on the boost sensor first and read ~12V on the depinned V ref wire.

I depinned the B/W wire on the ATP sensor while the boost sensor B/W wire was still depinned... 0V on the depinned V ref wire.

I repinned the boost sensor B/W wire. ~12V on the depinned V ref wire.


This would mean that it is this particular B/W between the ATP and Boost sensor that is giving me issues then. Correct?? Wait... I've not yet tried the variable resistor.

 

And just for the heck of it measure pin 2C w/key to on.

 

2C is a ground... I'm getting ~12V on that wire. Not good.

 

That ground supplies the 5 sensors that are supplied Vref voltage in addition to the Water Thermosensor and the Air Intake Sensor. This is likely your problem.

And you measured 2C while it was still plugged into the ECU I hope?

 

... No. I just plugged it in and don't see voltage on 2C.