To replace or not to replace fuel pump

[drewnashty]

Hi all, I'm working on a 96 Q45 that was leaking fuel through the fuel lines gromet under the trunk and the customer said the vehicle stalled on her once and that was also when she noticed the smell of fuel. I found that one of the screws for the fuel pump to the tank wasn't even fastened all the way and when I attempted to fasten it I noticed it wasn't even getting slightly tight. I pulled it out and it's stripped. So now I'm certain it was leaking fuel because of lateral force sloshing the fuel towards the rear where this stripped screw was and it would leak due to lack of seal.

I have a few questions; Could this leak have caused an intermittent lack of fuel pressure to stall the car and maybe damaged or put wear on the pump due to lack of seal and vacuum? There are no service records stating when the pump was replaced, all though it's obvious it has been and the tech stripped the screw during replacement. I also removed the fuel control module which looks fairly new; I removed the cover plate and the solder points all look good. I'm wondering if I should just get a new screw to fasten the pump securely to fix the leak or have her buy a new pump, and put the new one in and call ti a day. The customer is young and doesn't have a lot of money to throw here and there and just bought this car 2 weeks ago from a private seller with 133k miles on it and the prior owner doesn't have a clue about what's been done to it. I'm just worried about the pump putting excessive current draw on the fuel control unit if the pump is going out, especially with 110+ degree weather right around the corner here in Phoenix.

Thx

[Skibane]

Could this leak have caused an intermittent lack of fuel pressure to stall the car and maybe damaged or put wear on the pump due to lack of seal and vacuum?

The tank maintains a slight vacuum for emissions reasons, not to assist the pump in moving fuel. I can't see how lack of a vacuum would hurt the fuel pump in any way.

I also removed the fuel control module which looks fairly new; I removed the cover plate and the solder points all look good.

Be sure to check for signs of overheating on the printed circuit board pads that are soldered to the leads on the power transistor. The transistor runs hotter when the fuel pump starts to fail, due to higher current draw. The pump also draws more current if the fuel filter is obstructed, so replacing the filter is a good idea.

I'm wondering if I should just get a new screw to fasten the pump securely to fix the leak

If the threads in the tank are also stripped, a new screw might not grip any better than the old one. If so, you might be able to use a self-threading sheet metal screw instead.

I'm just worried about the pump putting excessive current draw on the fuel control unit if the pump is going out, especially with 110+ degree weather right around the corner here in Phoenix.

You could advise her to keep at least half a tank of fuel in the tank at all times, in order to help keep the pump cool.

[Infinitiguy19]

If the threads in the tank are stripped, installing a new screw might not help. If so, you might be able to use a self-threading sheet metal screw instead.

I'm just worried about the pump putting excessive current draw on the fuel control unit if the pump is going out, especially with 110+ degree weather right around the corner here in Phoenix.

You could advise her to keep at least half a tank of fuel in the tank at all times, in order to help keep the pump cool.

Make sure if you decide to hack it and use a self tap screw that its not longer than the screw that came out of the tank.

Another member on this board says the fuel pump is cooled by the fuel that runs through it. Is that not true?

[Skibane]

Another member on this board says the fuel pump is cooled by the fuel that runs through it. Is that not true?

Partly, but it's also cooled by being immersed in fuel. It will run hotter if it's not immersed.

[drewnashty]

Thx for the helpful response.

Be sure to check for signs of overheating on the printed circuit board pads that are soldered to the leads on the power transistor.

The pads on the control unit and the power transistor look new with no signs of overheating, warpage or discoloring

You could advise her to keep at least half a tank of fuel in the tank at all times, in order to help keep the pump cool.

Definitely.

Make sure if you decide to hack it and use a self tap screw that its not longer than the screw that came out of the tank.

I got some new screws and fastened them down just enough to be snug. They were about 4 mm longer than the originals, that was all I could find at the Home Depot. Will this be a problem. They didn't run out and kept fastening with ease until flush with the pump surface

[drewnashty]

Alright no more fuel leaking through the grommet but it's still stalling. I had her drop it off at our shop and we closed and now i'm working on it and after it sat for several hours I reparked it and it was already stalling. I checked fuel pressure and it seems to be just below 2.5 bar so around 34-35 psi at idle. At part throttle it drops closer to 2 bar. How much should these engines dip in pressure when you give it throttle.

I'm about to check codes.

[drewnashty]

Looks like there's a few other things going on of course.

P0100 for Mass Air Flow Circuit
P0340 for camshaft position sensor A circuit
and P0325 for Knock Sensor

[Skibane]

The plug on the mass air flow sensor has a reputation for developing poor connections over time, which can cause stalling problems. The customary fix is to unplug it, and then hose it down liberally with contact cleaner. WD-40 works OK for this purpose.