Heres the lowdown..

I have an S4 TII. Fuel Pump rewired to 12v and I also have a fuel switch wired aswell.

Now when I go to start my car it will run but only for a few seconds then die.
Just stops. No sputter.

Oddly enough..when I jumper the two pin yellow bypass connector it will start and run and stay running. I can free rev and all. I thought maybe the MAF was possibly faulty as im aware theres a form of a kill switch built into it, so I had a friend come by and we swapped the MAF out of his TII and no change.

Next I checked voltage at my rewired fuel pump. The multimeter shows my 40amp relay is receiving power when its running for that brief moment. but then the multimeter shows the power just disappear in relation to right when the motor starts to die.


Anyone have any pointers>? Why does my car run only with the bypass jumpered? Id imagine that means the fuel pump opening relay under the steering column is faulty...yet my switch is wired to that relay and the switch works with starting the car...IM SO CONFUSED!!!!!!!!!!!!!!!!!!!!!!!!

 

The Circuit Opening Relay has two relays, one for starting and the other for running the engine. The Brown wire in the relay wiring comes from the AFM and provides a ground to the relay when the engine is running, otherwise the wire would have voltage on it close to 12 volts w/key to on. Jumpering the fuel check connector forces the Brown wire to have a ground. If the car runs properly w/the jumper in place then the relay should not be your problem so the focus should be the signal on the Brown wire.

 

Brown wire.....brown wire....ok. I remember seeing a brown wire at the mag plug...and I think one under the dash. I'm assuming those are what you are referring to. So since that brown wire needs to be grounded to run the engine, where does it ground at? Or does the relay ground it?

 

The AFM fuel switch does the grounding. There are two wires in the fuel check connector, one is Black and the other Brown. The Black wire is a ground wire which runs to the AFM. The Brown wire also comes from the AFM. This Brown wire waits for the fuel switch to close, caused by flapper opening, and the ground on the Black wire passes onto the Brown wire which then runs to the Circuit Opening Relay.

 

Okay I apologize ahead of time if I'm not completely understanding just yet. So when I start the car, I have power for a few seconds, during that moment the brown wire is waiting for the AFM to to move which triggers the fuel switch in the AFM. When that happens it passes over to the black wire.

So it sounds like my problem is the brown wire is broken? Is that the right assumption?

 

A poor connection to the AFM might be your problem.

 

So I did some testing and so far I have continuity from both the brown and black wires. To and from the AFM and relay.

I swapped relays just got kicks and suddenly it runs..but low and behold my dumbass left the AFM unplugged.

So I understand that the car will run regardless with it unplugged, but what or where else should I be looking? The car runs only with the jumper, all wires tested fine aswell as the AFM. What wire does the trigger signal travel through(the one that passes the ground over) on the AFM? I feel like everything is working but the passing ground over is not making it to my relay

 

The engine would run w/o the AFM but it would require the fuel check connector being jumpered as w/o the jumper, the engine cannot possibly run while the AFM is unplugged. Seems like the problem resides at the AFM as the plug connects to the sensor. The two wires in the check connector need to be making a proper connection at the AFM. W/ AFM plugged in, no jumper in place, the two wires in the check connector should have continuity w/the the flapper door to the AFM opened.

 

Did some searching and found this.

"actually, it sounds like the AFM is bad, or the fuel switch in the AFM isnt working.

Here is a test for you. Jumper the fuel pump test connector (I assume you have a stock ECU harness). Its a yellow plug normally located around the passenger strut tower. Install a jumper there, and the ECU will "IGNORE" the signal its supposed to get from the AFM.

Reasoning behind this...

The AFM has in "interlock". This interlock is bypassed when the key is in the "start" position, and allows the pump to run. Once you return the key to the "ON" position, the ECU needs a signal from the AFM stating that the motor is running. If the signal isnt present, it shuts the fuel pump back down. Hence why your car only starts for a second, then dies.

Rat"


Someone else also mentioned a bad ground too.

 

Nothing new here.

 

Kick me if im wrong but are you referring to continuity by touching the flapper door or a specific pin.

I have a wire diagram now and am trying to understand where everything goes and what does what

 

The flapper door is physically pressed open. The fuel check connector has two wires. W/the flapper door opened the ground on the Black wire is passed to the Brown wire thus there should be continuity between these two wires at the check connector w/the flapper door of the AFM opened.

 

Ok. I will do some more checking when I get home. Thanks

 

No continuity. . :/

 

If you have no continuity between the two fuel check connector wires w/the AFM door opened then either the fuel switch inside the AFM is damaged or the connection to the AFM is poor or there is a flaw in the wiring. You said that you switched out the AFM temporarily and the problem persisted. This would lead one to believe the fuel switch is not the overriding contributor to your problem.

 

I'm sitting here trying to comprehend the Haynes diagram and I see a b/w wire that powers the relay and it looks like it goes straight through a coil solenoid to the brown wire..there is some form of a switch that is apart of that that goes to the blue wire for the fuelpump. That's as much as I'm understanding.

 

So I've eliminated the fuel switch by swapping AFM. I've tested continuity through the brown signal wire from the AFM to the relay and it's ok. As for the fault in the wiring..Idk. Does continuity necessarily rule out "damaged connection"?

 

To test the Brown wire found at the AFM (same wire as found in the fuel check connector) for continuity w/the connector to the AFM on one side of the continuity test, and on the other side of the test being the Brown wire at the relay, would require unplugging both items thus you're not ruling out a connection.

 

Gotcha. Headed to the garage now.

 

Ok I've tested the brown wire and it's a ok. I also started testing the relay voltage per FSM AND ALL SPECS fine except the Fc wire (aka brown wire from afm). It registers 12v at on but still holds 8v while cranking on start.

 

As per,

 

The car has to start and clear 500 rpm for the Brown wire to then have a ground otherwise it would have voltage close to 12 volts w/key to on and the voltage is dragged down to a lower value while starting because the start circuit requires a lot of voltage/amperage. If you unplugged the AFM to do the continuity test then you have to focus on the CONNECTION to the AFM.

 

Hey Watch I just want to say I really appreciate all the help and patience you have. I am normally very good this stuff but wiring is my weak bone. By chance I had left my AFM plugged in and set it on the fenders. I went to test the check connector and what the hell, there's cont.

I looked over at the AFM and poked the door with my finger and immediately I hear fuel priming the rails.

Broken connection at the AFM is the problem.

Thanks again for the help. Also I did fix my driver turn signal aswell from my last thread. It ended up being a severed ground wire!