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S5 Fc vert
75k miles. Good compression
stock fuel imjectors and fuel system. Replaced fuel pump and confirmed working( when jumped to battery)
no start. Checked voltage at plug harness for fuel pump. I have the 5v signal for fuel level but no 12v constant to pump. Hotwired from the battery to the pump and verify the pump is working. Check voltage at the relay under the airbox. No voltage. Checked the voltage at the relay under the bash on the steering column. No voltage. Checked the voltage at the ignition switch. And it has full voltage. Grounds in the trunk area are secure not rusted and sitting on bare metal.
looked at my Haynes manual and I see that one of the relays has a signal from the AFM. I checked my AFM like the manual suggested. Operating range is 20-100ohm. When checked the reading was .0012 ohms. So it looks like the Afm is toast.
My theory’s is that the Afm is not giving a reading to the ecu to use and the the voltage is not bieng sent to fuel pump.. I dont know if that is the case.
the car was sidelined a while ago for having lack of power when diving. Then when driving it would idle fine but above 3k would have a mean sputter, i originally thought fuel injectors but thought of fuel pump. Eventually the car would not turn over. That’s where I’m at today
Has any one else had an issue like this or any other possible ideas
Key on, push in the flapper door on your AFM - Does your fuel pump turn on?
There should be a yellow 2-pin connector near the AFM / passenger strut tower. If you bridge that connection with a bit of wire, key on, do you hear the fuel pump?
I'm the original owner of a '90 GXL. After owning the car for only a few months, I experienced intermittent problems with the engine shutting down while driving. Wasn't able to restart the engine unless it sat for maybe 15 minutes or so. Since it was new, I took it back to the dealer for warranty repair. The dealer had the car for about a week until this intermittent problem reoccurred. They replaced my AFM under warranty, and I never had that problem again. I suspect that it was the air temperature sensor in the AFM.
Key on, push in the flapper door on your AFM - Does your fuel pump turn on?
There should be a yellow 2-pin connector near the AFM / passenger strut tower. If you bridge that connection with a bit of wire, key on, do you hear the fuel pump?
I did jump the two wire connection and no difference I could find. when I push the cone when I was testing it was not changing values with the cone being manipulated. I fully believe the AFM is toast.
I'm the original owner of a '90 GXL. After owning the car for only a few months, I experienced intermittent problems with the engine shutting down while driving. Wasn't able to restart the engine unless it sat for maybe 15 minutes or so. Since it was new, I took it back to the dealer for warranty repair. The dealer had the car for about a week until this intermittent problem reoccurred. They replaced my AFM under warranty, and I never had that problem again. I suspect that it was the air temperature sensor in the AFM.
the car is in another state. I just came back. When I checked for codes a few months ago it was clear. I should have checked again while I was there. I also suspect that the AFM is the culprit. I wanted to see if my thought process was corrrect. And these responses tend to make me think I was right.
I did jump the two wire connection and no difference I could find. when I push the cone when I was testing it was not changing values with the cone being manipulated. I fully believe the AFM is toast.
My understanding is that when you jump the yellow two pin connector, with key in the "on" position, it bypasses the first relay and AFM. So, unless the relay behind the air box is not working, the fuel pump should be operating.
the car is in another state. I just came back. When I checked for codes a few months ago it was clear. I should have checked again while I was there. I also suspect that the AFM is the culprit. I wanted to see if my thought process was corrrect. And these responses tend to make me think I was right.
On the S5, there's the relay under the dash, the AFM and the relay/resistor combo between the air box and front cowl. If those three items complete the circuit, than you should be getting current at the fuel pump.
check the 15A "engine" fuse inside the cabin by your left foot.
people seem to forget it exists, like all the time. if you're not getting voltage anywhere to the fuel pump circuit this is the logical place to start, since you checked the ignition switch and pump relay and are losing voltage between those 2 spots, and this fuse is.... in the middle of those 2 test points.
why it would blow is the question though, a faulty fuel pump would certainly be the culprit. so i can only assume your old pump was seized up. that or you have a ground fault in the circuit. i have certainly seen my fair share of dumb things though, like stereo systems mounted with screws right through wiring harnesses.
Last edited by notanymore; Aug 5, 2025 at 10:10 PM.
check the 15A "engine" fuse inside the cabin by your left foot.
people seem to forget it exists, like all the time. if you're not getting voltage anywhere to the fuel pump circuit this is the logical place to start, since you checked the ignition switch and pump relay and are losing voltage between those 2 spots, and this fuse is.... in the middle of those 2 test points.
why it would blow is the question though, a faulty fuel pump would certainly be the culprit. so i can only assume your old pump was seized up. that or you have a ground fault in the circuit. i have certainly seen my fair share of dumb things though, like stereo systems mounted with screws right through wiring harnesses.
this is wear I started the fuse was not blown and it was a 15amp fuse. I should have double checked again before I left
this is wear I started the fuse was not blown and it was a 15amp fuse. I should have double checked again before I left
something is off then if you have 12v at the ignition switch but no voltage at the relay by the RF headlamp, somewhere in the circuit between those 2 points you're losing the voltage. so you may want to just go in there with a voltmeter and see if you are getting 12v at both legs of the fuse with the key on.
i assume you mean you are getting 12v out of the switch(on the B/W, Black/White wire), not just into it. i have also seen faulty wipers inside the ignition switch before. it's slightly more rare but it happens, the switch is easy enough to take apart and clean the fingers and wipers on, of course it will need to be regreased with electrical grease if that is the problem.
Last edited by notanymore; Aug 6, 2025 at 01:06 PM.
