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S4 T2 Dies when hot

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Old 05-16-17, 06:17 PM
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AB S4 T2 Dies when hot

Gentlemen! I hope all is well with everyone. Hoping to get some help and insight. I've searched and searched for answers but I'm getting nothing that's definitive.

My wifes S4 T2 has been having this issue where the car runs fine on startup but then when you drive it for about 20 minutes or so it just decides to buck and try to stay alive but then eventually dies.

I've replaced the fuel pump with an Aeromotive 340 and I've added an Aeromotive A1000 FPR. When I installed the FPR everything seemed fine and my wife even drove the car for a good cruise for at least an hour around the city without any issues.

The very next day it starts doing the very same thing.

I haven't done any solid electrical diagnosis but I'm guessing its either improper voltage going to the pump which indicates a bad fuel pump resistor, or just ollld corroded wiring. OR a bad AFM since those two parts work hand in hand.

I'll be doing some electrical diag sometime this week but I'd like to know if you guys have had any similar experiences that could point me in the right direction before i start doing the whole fuel pump rewire that I've stumbled across in my research.

THANKS GUYS!
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Old 05-17-17, 12:49 AM
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Do you still have the old fuel system(rails) attached to the Aeromotive and NEW FPR?
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Old 05-17-17, 08:50 PM
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Originally Posted by misterstyx69 View Post
Do you still have the old fuel system(rails) attached to the Aeromotive and NEW FPR?
Yeah I haven't touched anything else with the fuel system. I did get the injectors flow tested and cleaned about 4 years ago when we first built the car. Fuel dampener removed as well.

I forgot to add that when this problem last happened, I pinched the fuel return line after the FPR and the pressure was not going up on the gauge while trying to start it up afyer it's died. But the car still fired revved up - barely - and dies again.
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Old 05-18-17, 03:40 PM
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*update*

This thread title should be changed now lol. Turns out that the car being hot has nothing to do with this problem.

After about an hour of electrical diag and more research I'm still at the same spot. Car has been sitting for a week and I tried to start it. Car starts for 5 seconds and dies. I've seen some other threads about this problem but I get no conclusive answer as to what the culprit actually is.
I tested the circuit opening relay (yellow and black relay to the right of the steering column) and it tested good.
Fuel pressure is at 40psi and holding.

There's nothing else in the fuel system that i can test.

Any help would be appreciated

Last edited by misterstyx69; 05-19-17 at 12:53 PM. Reason: don't need profanity to explain a problem.
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Old 05-18-17, 08:27 PM
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Starting for a few seconds and dying sounds like an AFM issue.

Have you jumped the fuel test connector and observed the same behavior?
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Old 05-19-17, 12:03 AM
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Originally Posted by DC5Daniel View Post
Starting for a few seconds and dying sounds like an AFM issue.

Have you jumped the fuel test connector and observed the same behavior?

The test connector on the passenger strut tower? Not yet. That's the one that would bypass the AFM in starting conditions right?
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Old 05-19-17, 12:51 AM
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Yes, should be a two pin connector (I think yellow), and the wires are black and brown. This will bypass the AFM switch which triggers the fuel pump. If the car stays running with this connection jumpered you either have a discontinuity in your harness from the AFM, or more often a bad AFM.
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Old 05-19-17, 12:44 PM
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Stupid suggestion..but it happens.
The AFM door gets corroded and will stick..
Check the movement of the AFM door to see that it moves freely.Corrosion can get in between the aluminum and make it do funny things.
I had one that just plain stuck on me and I had to take it apart and wire brush,wheel and lube it back to operational condition.
I came across this by accident too,as you do not think that AIR would have anything to do with the problem..!
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Old 05-20-17, 12:05 AM
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Originally Posted by misterstyx69 View Post
Stupid suggestion..but it happens.
The AFM door gets corroded and will stick..
Check the movement of the AFM door to see that it moves freely.Corrosion can get in between the aluminum and make it do funny things.
I had one that just plain stuck on me and I had to take it apart and wire brush,wheel and lube it back to operational condition.
I came across this by accident too,as you do not think that AIR would have anything to do with the problem..!
The flapper inside the AFM moves very smoothly. No binds or irregular appearance to me. I did a resistance test on all the prongs that the factory service manual says to test and all results were within range.

The ONLY value that I tested that was a little e strange was the resistor relay. Prongs E-F tested at 1.2 ohms whereas the fsm states one single value of 0.64 ohms.
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Old 05-23-17, 12:47 AM
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This thread title needs to be changed lol...

So after some more work this weekend I've made one step forward but two steps back.

I tried to do the AFM jump with the yellow connector down by the passenger strut tower near the frame rail. I jumped the connector and the car started! Then tried to run the car normally without the jumper and lone behoid the car started, held idle at 1000 and fuel pressure was at a solid 40spi and it ran smoothly.

Here's what takes me back a few steps. I cant give the car any throttle. If i press the gas just a BIT it starts to stumble and die until i close the throttle plate and continues to idle smoothly.

I replaced the TPS sensor with a brand new unit about 2-3 years ago but its only seen about 2000 km of use.

I've re-grounded all of the common grounds except for the starter ground shared with the battery ground on the drivers side strut tower.
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Old 05-25-17, 10:26 PM
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you have a bad airflow meter, because your fuel pump switch inside is making intermittent contact, which is why the initial test jumpering the test connector passed but again reverted to some original symptoms when not.

it's a common problem.
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Old 05-29-17, 02:18 AM
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Originally Posted by insightful View Post
you have a bad airflow meter, because your fuel pump switch inside is making intermittent contact, which is why the initial test jumpering the test connector passed but again reverted to some original symptoms when not.

it's a common problem.
Even if all resistance tests for the afm turn out within range it can still be bad?
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Old 05-29-17, 10:19 AM
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i said what i had to say, you can believe it or not. the fuel pump switch in the AFM is a very common failure, you already proved that theory with the fuel pump test connector bypass.

i locked my old account so i could care less if you take my advice, since no one really gave a **** about me anyways.

Last edited by insightful; 05-29-17 at 10:21 AM.
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Old 05-30-17, 11:51 AM
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Originally Posted by eklips3 View Post
Even if all resistance tests for the afm turn out within range it can still be bad?
The fuel pump switch check is halfway down the FSM page attached. I had one that was similarly affected by heat, so testing it when cold may not show the problem.
Attached Files
File Type: pdf
AFMCheck.pdf (230.7 KB, 10 views)
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