Low Fuel Pressure

This is a 96 Buick Riviera, 3.8 that had a suspect fuel pump replaced and instant fuel leak as new gasket wasn't used. Rest of a botched job unknown how bad.

OK - Fuel pressure gauge screws onto fitting on fuel rail Damsel and just key on engine off (KOEO) you should have it up to spec quickly.
Shutting key back off that pressure should hold where it was or mention that.

Sorry to butt in, just had to state the car and the fuel pressure tool. If incorrect say so and I'll edit it to correct,

T

Ok, what you want to do is hook up the fuel pressure gauge and take a reading. Now look for a section of the return line that is rubber (not plastic) and with the engine running, momentarily pinch off the return with pliers and see if the pressure spikes up. If it does, then you have a bad regulator. If not, we are still looking at pump issues. If you happen to have plastic fuel lines, we will have to find another way to restrict the return line because you can't pinch plastic line. It will damage it.

Is there any chance this guy never actually put a new pump in?

The fuel pressure spec for this is 41-47 lbs. The pump could be a dud, but I wonder since this guy was a hack that worked on it for you if he even changed the fuel filter. Its on the left side of the car against a frame rail and is has one line with a quick-disconnect that will look like a plastic clip and one end which is threaded. See if it looks shiny. Its about $11 for a new one but you will need a line wrench to remove it without damaging the end. It should've been replaced when the fuel pump was. If it was clogging up with junk, it could've been what killed the last pump. At the very least for the age of the car it is routine maintenance.

You may also have an issue with the fuel pressure regulator. It is mounted on the fuel rail on the engine and is what creates the pressure in the fuel rail that you are reading with a pressure gauge. They can fail, and there are some tests that can be done to determine if this is the cause that are rather simple. There is a vacuum line on the top of it, and you should pull that line off and see if there is any wetness in it. If so, you have a bad one for sure as it is leaking fuel past its diaphragm.

If you don't have a second pair of hands you can put vice grips on it with the engine off and then cycle the key on. Make sure you only do this long enough to see the pressure spike up because the high pressure is not good for the regulator.

Yes, that's exactly what I mean.

Also the spec I have for this car is 333 to 376 kPa (45 to 55 psi) I don't know where Nick got his spec from.

No, you have to cycle again after restricting it.

Yes, that would be correct. Are you sure it was the return line and not the feed? If it really was the return, then we are still looking at a problem in the fuel pump. I assume you replaced the entire assembly, right? Not just the motor itself.

That could have been the vapor line The is another line the runs from the fuel rail back to the tank as a return. It's usually one size smaller hose than the feed line. The fuel pump- has 3 lines going to it. A feed, a return and a vapor that carries no pressure.

That looks like it might be broken off but is should have a line going from there to the charcoal canister. Either way, the return should be attached to the tank but it will be made up of a combination of steel and plastic, just like the feed. If you can rig a way to run the feed directly into the gauge with no outlet, it would tell us the same thing.