Bad Fuel Pressure Regulator?

[HardcoreZ28]

I've got a buddy with an LT1 car and he's getting a lot of fuel smell from the car with no external leaks. I'm guessing maybe the fuel pressure regulator went bad or he's got an injector stuck open hosing down the engine. He says his mileage has gone down a bit and he smells it a lot at idle.

What's the best way to test the regulator? Fuel Pressure guage on the rail and clamp the return line to deadhead the pressure and watch the bleedoff when the engine is turned off?

[Injuneer]

Just hook the fuel pressure gauge up and look at the fuel pressure. At idle, with the vacuum compensation line disconnected, you should see 43.5psi. GM accepts 41-47psi as being in spec. Then reconnect the vacuum compensation line. Fuel pressure should drop 6-8psi with a stock cam, less than that with a wilder cam.

Then tape the fuel pressure gauge to the windshield, and take it out on the road, run it up to max rpm/max load, and the fuel pressure should hold within 2psi of the "no vacuum" reading.

While you've got the vacuum line off, check the line for wet fuel or heavy fuel smell. That would indicate a leaking diaphragm in the regulator.

Finally, with the engine off, prime the pump and see how long it takes for the pressure to bleed off. If it does bleed off quickly, you are stuck with 3 possibilities, two of which are easy to rule out. The vacuum line check would rule out a faulty fuel pressure regulator. Pulling the rails up with the system pressurized, checking for drips, would rule out pressure loss due to a leaking injector. That would leave you with a faulty check valve in the pump, which would make it hard to start, but wouldn't cause it to run rich.

By "fuel smell from the car" do you mean the exhaust smells rich, or something else?

[HardcoreZ28]

Fred thanks for the detailed response. I'm pretty sure he means a raw fuel smell like a leak, not a rich condition. I'm gonna try to take a look at it next week for him. Your help is appreciated...I'll post the results next week.

[JL8Jeff]

A lot of times the fuel smell comes from the EVAP stuff going bad or the vent hoses around the tank getting cracks or pulling off. But I don't think that should have much effect on the gas mileage so he might have fpr or injector issue. I have a set of spare 24 lb stock injectors and a set of new SVO 24 lb flowmatched injectors. The SVO's might be sold though.