A long shot but known to be a problem is the intake manifold gasket. These start to leak for some reason and all sorts of weird things will take place since the air/fuel ratio is always trying to correct itself.

A quick and actually safe way to find such a leak is to pick up a tool that looks like a long thin pipe on the end of a hose. The other end of the hose connects to a propane tank like the propane torches use. Start the engine and crack the valve on the propane tank so that a very small amount of propane is coming out.

Then wave the end of the pipe with the propane feed close to the intake manifold bolts and runners. If you hear an increase or decrease in RPM you have found a leak where the engine is sucking in air and, in this case, propane. Check all the vacuum connections in the same way. Any change in RPM is a leak because the additional propane screws up your air/fuel ratio.

Mechanics do this all the time. It sounds risky but I don't think you would have any problem with doing this in a safe manner. This also has the advantage of being repeatable. You engine may change RPM at odd times but with this method every time you move the pipe to the same spot the RPM will change.

This should be moved to P&R since it will take hopey and prayer not get blowed up :D

Interesting test, but I have no propane on hand... I already have the (improved metal) gaskets, so it's just a matter of time before I install them. I figure, though, that the smell of fuel is probably due to something else.

Just hooked up a fuel pressure gauge I rented from AutoZone to the fuel rail, ran the car, got the fuel pressure up to 38 PSI (spec is 37-48, IIRC), and shut down... within 5 minutes, it had lost 2-3 PSI and was going downhill, so I guess that means there's a leak somewhere. I'm now alternately clamping off fuel lines to try to track it down.

Oh, and I noticed a mild oil leak that's consistent with the lower intake manifold gasket going.

If thats a 3.1 v6 - I can gurantee that the lower manifold gasket is shot, replace and remember to use proper GM engine sealant or toyota FIPG on the blank space between the 2 gaskets. If you dont and use pep boys/autozone/FLAPS etc gasket maker then you get back to square one faster than a veyron accelerates from 60-100 mph.

The rich running issue is usually a bad MAP sensor or bad fuel pressure regulator.

Another tip - if you are changing the ATF and dont fancy bathing in it then undo the supply line for cooler - (small circlip) and install a hose on it and dump into a bucket. Start engine and allow it to empty the transmission pan for you - now you can get under the car and remove the transmission sump neatly.

If your radiator has the smaller type cooler line fittings then you can buy a barb for it from autozone etc - its about 3 dollars - shove a hose on it and do the same as above.

Make sure you have that hose well attached, the fluid comes out at about mach speed.

GM has been trying to 'fix the buick' for decades now, what makes you think you can do it :D

the fluid exit speed is not that bad - takes about a minute for a gallon. There is negligible pressure as the hose is open on the other end (in bucket)

Why cannot American automakers install drains on most of their automatics.

Not sure about JL's combo, but I did it on a Jimmy, and just starting it and shutting it down cost me real money in replacement fluid. ( was checking for rad sediment/blockage) (wasn't any :D )

My experience backs everything this guy said. I previously mentioned the MAP sensor. Did you check it with a vacuum pump and electric meter?

Your manual has a section for driveability issues, should cover rich condition and give a flow sheet of tests.

OK, so with both the supply & return lines clamped, fuel pressure still goes from 38 PSI to 20 PSI in less than half an hour. My understanding from what I have read is that this identifies the injectors as the leakers -- is that correct?
But the guy at Pep Boys is great! He said his sealant works on any car!

JK. I'll be sure to use the proper sealer.

Holy cow, there's no drain plug? Seriously? What on earth...

Thanks for the tips!
It's a MAF, and it appears to be in good working order.

Yeah, I've been working with the stuff in the manual while also blazing my own path. I am an independent thinker auto diagnoser.

Clamped?

To make sure it's not leaking out of some other part of the fuel system.

so you did not actually catch the fluid in a container?

GM also use a MAP sensor, it would be a 3x1 inch plastic rectangle with a green connector on it and a vacuum hose attached to it, They are known to go bad. Cheap too. The MAF on that vehicle is tested by measuring Hz - and the two tests for it idle and high rpm actually show the correct working, replacement Delphi MAF elements are not the same design as original.

If you are seeing loss of fuel pressure with captured fuel in the rail - the only two points of leakage are the regulator diaphragm or the injectors - btw injectors are 'spensive' on this car. hunt the yellow pages for a place that sonic cleans and tests gasoline engine injectors.

If you plan to replace the lower manifold gaskets, along with the previous posts you also need to replace the oil pump drive gear O ring (I believe the 3.1 also has it) It lives under the manifold and causes vacuum leaks if its old.

I did catch it all.