I just got done doing a full rebuild. Before the car did not have any fuel pump issues (other than a loud as hell walbro).

The car has a rewired Aeromotive Stealth in tank pump in it now, i have 12ga wire running directly from the battery in the trunk and i am using the pigtail that comes with the pump connected directly to the 12ga wire bypassing the stock connector. The tank is full of fresh 93 octane.

If i start the car and let it idle the pump will be nearly silent (i do not have the back seats in) and if i drive the car then everything is normal.

The problem comes in shortly afterwards.

When its just idling i can hear the pitch of the fuel pump change and if i go and rev the car and watch the fuel pressure gauge the fuel pressure dips instead of increasing. If i disconnect and reconnect the pump quickly while its running sometimes i can get the pump to go back to the near silent whine.

When i am driving and it happens i can drive around in vacuum just fine but as soon as i try to go into boost it pegs lean (obviously)

During the rebuild i relocated the alternator to the rear of the block ala the Jays Racing relocation kit. I extended the alternator voltage wires and have a 4ga ground to the firewall.

I have reused the stock 6ga ground wire that goes from one of the starter bolt's to the frame. The battery has a 4ga ground to the "nut" used to hold the spare tire down.

The voltage from the battery is 12.4V (i know its a little low). If i disconnect the battery while the car is running and measure the voltage using the batterys ground wire and the positive battery wire in the trunk i get 13.7v.

Sorry for the essay but i am really out of options.

 

The plastic thing that joins the return line with the hose that draws fuel from the passenger side of the tank has been damaged so i replaced that with a T and ran the extra hose outside of the stock fuel tank sump so it would not aerate the fuel in the sump area. If this is my problem i have no idea.

AEM FPR is using the smallest return restrictor. I disconnected the return line at the tank and fuel was happily ****ing away. Fuel pressure is set to some where around 42-45psi. It will stay there all day long until the pump is asked to flow any volume then dips to 20psi.

Tried disconnecting the alternator to see if that was the problem. The pump got remarkably quiet (i guess 12.4v will do that) and the noise did not change but still the pressure dipped whenever i would rev the car. Negative results

Tried adding resistance to the circuit. Negative results.

Fuel filter in the engine bay is clean

If there was a way for me to see if it is emptying the stock sump too quickly i would love it (but its on a full tank of fuel so that makes no sense).

I am convinced there is a ****ing midget gremlin that is treating my fuel tank like a jacuzzi and hitting the bubble button after he settles in.

Taking the car to some local evo experts and seeing if they can fix it.

 

Tried a new walbro yet??? Simple, stupid are the usual fixes.

 

Last night i double checked everything. The AEM FPR is using the smallest return restrictor, i elongated the return line in the tank in case it was causing any aeration right next to the pickup but still getting the same results.

I have tried 2 walbro's and the stock pump and gotten the same crap.

I have one last shot. Right now since the outlet on the walbro and aeromotive pumps are 8mm vs the 9 or 10mm of the stock pump i am using the stock O-ring with a smaller O-ring to seal it.

I am going to cut the cup off the fuel pump holder that the fuel pump outlet seals against with an O-ring off and weld on an 8mm tube and use some hose to clamp onto both. That way i can be sure fuel is not making its way past the O-ring.

If that doesn't work i am taking it to a shop.

 

tons of people are running drop-in pumps with no housing mods. you're overthinking the situation. sounds like the pump isn't getting enough power, or there is a leak at the pump outlet seal. did you try putting a volt meter across the pump? (pierce the sheath with a needle.) have you observed fuel pressure at shutdown? it should hold 43 psi for at least 20 minutes.

 

The pump is getting the proper voltage.

The fuel pressure does not hold like that at all, drops to 20psi within a few minutes.

I will see if i can get some steel 8mm tubing tonight and weld on where the o-ring holder for the fuel feed line was so i can hose and clamp that to the pump outlet.

 

ok....I now have a leak proof transition from the pumps outlet to the fuel pump cradle/fuel line.

I checked the fuel filter again and there was some small things caught up by it but nothing that would have blocked it. I am using one of the small filters from summit. Maybe i need to use a larger filter?

When i initially started the car the fuel pressure would drop when the motor was revved. I disconnected the feed line from the rail, and cranked a few times to get any air out of the line and reconnected it. Started the car and voila good fuel pressure.

On the drive from my moms house where all my tools are to my apartment (15minles or so) the issue came back after about 10 miles of driving but i turned the car off and started it back it went away.

I am not sure if it is the filter i am using or if i need to step up the return restrictor to a larger one?