Fuel Pump relay resistor gone bad?

Max777 · 08-03-2009, 01:53 AM

Ok, so after I pulled apart the intake manifold on my S5 N/A for the umpteenth time to make sureI got no leaks, used gaskesinch to seal my intake gaskets, and replaced all the vinyl vac caps with lengths of hose and 10mm bolts, my car still ran like crap... I adjusted the TPS, tried to mess with the idle, and did some other stuff when I happened to find this in the FSM:

"Check the fuel circuit resistor located in the right hand corner of the engine bay" check the resistance, it should be 5~7 ohms"

Well, my resistor read 1.2 ohms.... with a DVOM.

all this time, could this have been my problem? How much can a bad resistor pack affect the drivability of the car?

NoDOHC · 08-07-2009, 06:41 PM

The S5s had high-impedance injectors and did not use a resistor pack on the injectors, this would have to be for the fuel pump.

You should check your fuel pressure. If the fuel pressure is good (about 40 psi) then your fuel pump is working fine.

I know you know what you are doing, but any one of us could overlook something simple.

You could also put a wideband in the exhaust to see if it is rich-misfiring or lean-misfiring.

How does the car drive? Is the idle the only problem it has?

Sometimes other symptoms will clue you in to what the problem is.

Please give more details.

Max777 · 08-12-2009, 11:38 PM

edited.

Max777 · 09-09-2009, 11:52 PM

Ok so I rechecked my compression, and it is at 82~88 psi. Even bounces and all.

Will too low compression make an engine stall at idle?

Turns out it was NOT the fuel pump resistor after all, I got another one and it also read 1.3ohms... I guess the FSM is wrong then...

NoDOHC · 09-10-2009, 10:54 PM

Those compression numbers are fine (s5s will start at 60 psi and idle fine).

I don't think is it a mechanical problem.

Is your AFM mounted level?

Has someone tampered with the idle mixture adjust screw on the passengers side shock tower?

Max777 · 09-13-2009, 02:25 PM

"idle mixture adjust screw"

I dont have any such thing on my pass side shock tower... S4 cars seem to have this my car does not.

Also, the S5 AFM... it has a spring loaded plunger inside, not the barn door like the S4 cars, so I am not sure that this will afect my car that much...

08-03-2009, 01:53 AM	#1
Max777 Pirate Join Date: Mar 2008 Location: Central IL iTrader: (5) Posts: 1,323 Rep Power: 18	Fuel Pump relay resistor gone bad? Ok, so after I pulled apart the intake manifold on my S5 N/A for the umpteenth time to make sureI got no leaks, used gaskesinch to seal my intake gaskets, and replaced all the vinyl vac caps with lengths of hose and 10mm bolts, my car still ran like crap... I adjusted the TPS, tried to mess with the idle, and did some other stuff when I happened to find this in the FSM: "Check the fuel circuit resistor located in the right hand corner of the engine bay" check the resistance, it should be 5~7 ohms" Well, my resistor read 1.2 ohms.... with a DVOM. all this time, could this have been my problem? How much can a bad resistor pack affect the drivability of the car? __________________ Rotaries:They are NOT that complicated! Last edited by Max777; 08-12-2009 at 11:38 PM..

08-07-2009, 06:41 PM	#2
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	The S5s had high-impedance injectors and did not use a resistor pack on the injectors, this would have to be for the fuel pump. You should check your fuel pressure. If the fuel pressure is good (about 40 psi) then your fuel pump is working fine. I know you know what you are doing, but any one of us could overlook something simple. You could also put a wideband in the exhaust to see if it is rich-misfiring or lean-misfiring. How does the car drive? Is the idle the only problem it has? Sometimes other symptoms will clue you in to what the problem is. Please give more details. __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

08-12-2009, 11:38 PM	#3
Max777 Pirate Join Date: Mar 2008 Location: Central IL iTrader: (5) Posts: 1,323 Rep Power: 18	edited. __________________ Rotaries:They are NOT that complicated! Last edited by Max777; 09-09-2009 at 11:50 PM..

09-09-2009, 11:52 PM	#4
Max777 Pirate Join Date: Mar 2008 Location: Central IL iTrader: (5) Posts: 1,323 Rep Power: 18	Ok so I rechecked my compression, and it is at 82~88 psi. Even bounces and all. Will too low compression make an engine stall at idle? Turns out it was NOT the fuel pump resistor after all, I got another one and it also read 1.3ohms... I guess the FSM is wrong then... __________________ Rotaries:They are NOT that complicated! Last edited by Max777; 09-10-2009 at 12:26 AM..

09-10-2009, 10:54 PM	#5
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	Those compression numbers are fine (s5s will start at 60 psi and idle fine). I don't think is it a mechanical problem. Is your AFM mounted level? Has someone tampered with the idle mixture adjust screw on the passengers side shock tower? __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

09-13-2009, 02:25 PM	#6
Max777 Pirate Join Date: Mar 2008 Location: Central IL iTrader: (5) Posts: 1,323 Rep Power: 18	"idle mixture adjust screw" I dont have any such thing on my pass side shock tower... S4 cars seem to have this my car does not. Also, the S5 AFM... it has a spring loaded plunger inside, not the barn door like the S4 cars, so I am not sure that this will afect my car that much... __________________ Rotaries:They are NOT that complicated!

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