Fuel delivery problem on my S5 Turbo
 

Hey guys... so I've run into a problem with my car recently. As most of us know, when you turn the key to the on position (not cranking) you'll hear your fuel pump prime and buzz to its little motor heart's content and then proceed to start the engine. My fuel pump is not doing that anymore and not allowing the engine to start up.

It happened out of nowhere, I drove the car earlier the day that it happened with no issues, boosting around and all... went back in, cranked it up, didn't make it out of my driveway when it just shut off.

I checked for power going to my fuel pump, and I'm getting around 5 volts at the relay under the steering wheel, and at the plug for the fuel pump when the key is in the on position. I've replaced the relay in hopes that may have been the problem along with the fuel pump and still no luck.

I have tried hard wiring the fuel pump straight to the battery to see if the pump turns on, and it does. However it doesn't build up more than 10psi of pressure according to the gauge on my FPR.

I'm running a microtech ltx8 ecu, Aeromotive afpr, and a Walbro 255lph. I'm stumped on what else it could be...

I am sure that the pump doesn't turn on until you go to Start..then the AFM kicks the relay to keep the pump running.
Have you checked the pressure while jumping the fuel connector?
Is the stock fuel supply still wired as stock?

Sounds like a bad fuel pump to me, as long as the gauge on your FPR is accurate.

Not running an AFM. And yes, when I turn the key, pump goes on. Happened every single time. All the wiring looks stock to me.


Weird though because the fuel pump is brand new.

If you're not running an AFM, it's not wired stock. The AFM generates an output which triggers the fuel pump relay.

Good point. Well I did mention I am running a LTX 8 Ecu. So it's on map sensor.

Does your main relay function? It's two relays in one. One side powers the coils and injectors, the other side powers the fuel pump. Make sure you have power in and out of the main relay.

https://cimg5.ibsrv.net/gimg/www.rx7...2da55dd8c8.jpg

https://cimg3.ibsrv.net/gimg/www.rx7...a7e52f9a40.jpg
So these are the only relays I see in the engine bay besides the head lamp and lamp motor relays ... Which of these are fuel related?
https://cimg2.ibsrv.net/gimg/www.rx7...d1656cd3cd.jpg

The relay under the steering wheel is the circuit opening relay. Which wire did you measure 5 volts on. Was it the Blue wire?

The main relay is the one directly nest to the clutch master. Gold colored with a metal strap bolting it to the fender.

So I went back in the car to test the relay on the steering column, and used a separate ground to test for power and got 11.xx volts on two pins. Now, what I'm thinking is that maybe the ground for the relay is no good. Does that sound like a possible cause for this lack of delivery in voltage?

Are you testing w/key to start and which wires have power. You're being ambiguous and it's hard to get a handle of what you are doing. Top left has voltage w/key to start. Top center has voltage w/key to on. Top right wire (remember, that Blue wire) has power w/key to start and key to on if the fuel check connector is jumpered. Bottom left wire is the constant ground.

Yes, key was in the on position. I ran the external ground and started hearing the pump priming when key is turned as it used to do before it stopped working.

Went ahead and replaced the fuel filter because the pump wasn't producing enough fuel pressure, but that didn't clear my problem. I'm narrowing this down to my fuel pressure regulator. Gonna check in a bit to see if that is my problem.

Which wires tested out properly versus which did not as stated in post #12.

Brown wire, and black w/ red wire are getting up to 11.xx volts. Other two I have nothing. This is that the relay with yellow plastic just to be clear on what I'm testing.

The Brown wire is a temporary ground and only grounds when the car is running . The top center wire should be 12 volts w/key to on and it should be Black/White. The B/R wire should be at the top left position and has voltage only w/key to start. When the B/R wire has power w/key to start then the Blue wire should have voltage as it powers the fuel pump. Does the Blue wire have power or not w/key to start? If the bottom two wires (Black and the Brown wire) are jumpered then the B/W wire (again, top row center position) and Blue wire should have voltage w/key to on. Does it? This will tell you if the relay is good or not and takes but a couple of minutes to doi.

Nah no power from blue wire. And just for my sake of remembering, you're referring to the blue wire that is right outside the fuel pump right?

The blue wire on the top row far right position of the relay you've been testing.

So I'm getting power to all the right connections. Everything works as it used to. Was able to pump out 42psi of fuel and got the car running for maybe 5 seconds. Then lost fuel pressure again. Since then, I haven't been able to figure out why my pump isn't putting out the necessary pressure. It primes and everything but only to 10psi. I checked the connection for the signal wire that goes from the plug on the pump to the relay for my microtech and it seems fine. I cleaned the contacts and put some electrical grease to help the connection but still nothing. Even went and got a new battery. I'm lost lol

Jumper the bottom two wires of the circuit opening relay and see if this helps. Also, the car has an additional fuel relay under the AFM which could be problematic. If you jumper both Blue/Red wires at this relay it will bypass it.

And if the car starts and cuts out then leave the key to the on position and look for the Green check connector with 3 wires near the lead coil and make sure the Black/White wire has 12 volts. If it does not then the relay is shutting off (this would kill the engine).

Not running an AFM. And I'm using two trailing coils

Is your fuel pump pickup clogged?

...Is the gas tank empty?