Fuel Pressure Help

Hey all, got a 95 Grand Am GT, 3.1 v6. 140,000 miles. Having some fuel issues and need some help / recommendations.

First, fuel mileage has dropped considerably. We were getting ~30 mpg on the highway and ~25 in around town. Now we're getting a max of 25 on the highway and as bad as 13 in the city (usually 15-17 now).

Replaced fuel filter, checked fuel pressure regulator for fuel in the line. The line wasnt wet, but you could smell gas (normal I presume?) Fuel pressure is 35 psi at idle. Moving the throttle body plate causes the psi to spike 3-4 psi and then drop 3-4 psi also ... is that normal?

What should the pressure drop off rate be once the engine is shut off?

It also has a rotten egg smell after idling a short time and I tend to see exhuast gases alot more than I should. The local shop says that the O2 sensor is reacting a little slow, but appears ok. They also say that the CAT looks and sounds fine (no rattling). I'm guessing that the O2 sensor may be bad and causing excess fuel to be injected. Thoughts?

The thing that gets me is that the engine appears to be running just fine. Not hesitation, but sometimes it starts hard when cold.

Any thoughts or recommendations would be appreciated. I did search, but didnt find a topic specific to fuel pressure tests. Thanks.

Silverado

The rotten egg smell is from sulfur in the gas, probably caused by it running rich. Check your air filter, maf sensor, o2 sensor. Air filter is least expensive, maf sensor probably the most expensive, o2 sensor most difficult to replace.

I didnt think about the MAF. I'll do a check on that tonight. I'll agree with you on the O2 sensor. It's bad enough getting back there to replace the 3 rear spark plugs! :D

The rotten egg smell coming from the exhaust indicates that the catalytic converter is breaking/broken down and needs replacement. When the catalytic converter becomes clogged this will increase exhaust back pressure and cause the engine to breath very poorly (low volumetric efficiency) and also makes the engine work much harder to do the same amount of work. I would re-consider the catalytic converter even though they are quite expensive. Good Luck.

The rotten egg smell coming from the exhaust indicates that the catalytic converter is breaking/broken down and needs replacement.

The smell tells you its working. Brand new ones are more smelly.

Thought this sounds like a fuel issue. Those seals on the injectors might be leaking air in and fuel out, since you said you smelt gas under there. An or be dirty/clogged.

Try some Lucas Oil Injector cleaner.
35 psi is a little low on for fuel pressure, should be around 45 running and hold that for a little after you shut the engine off.
THe plugs and wires, how are they?

If you run the injector cleaner through and its still getting bad milage try those O2 sensors, that is if the MAF checks ok, and it should clear up.
The converter can be checked a shop to make sure its working correctly, they are expensive to replace when its not bad.