Check with ohm meter from battery negative terminal to the spot on the frame it grounds to. Check alternator voltage with a multimeter at the alternator. Check the ohms from the battery positive(red) to the alternator.

What are the brands of parts you are using?
Here is a list of recommended brands. http://www.pontiacbonnevilleclub.com/fo ... 16991.html

Sounds like the motor brushes are worn. When it does not work, press the window up and bang the middle of the inside door panel repeatedly, like a jack hammer. If the windows goes up its the brushes. I replaced the brushes in a window motor. You can also buy a new motor.

Spray starter fluid through open throttle. If the car sputters then it is a fuel problem. If it just cranks suspect electrical problem.

Fuel pressure was never the issue. MPG still low. Rear O2 sensor wire frayed. Replaced O2 sensor, mpg still low.

Plug wires are 3 years old. I did do an ohms test recently and they all tested good. The new egr seems to respond linearly between duty cycle and egr volts. The other thing I did was run the engine in park to 3500 rpm. No kr in park. I also filled the tank with 16 gallons of 93 octane. Drove for ...

I was averaging 30 a year and a half ago. And the lower mpg has happened through all the seasons. I drive at 72-75 mph.

2002 Bonneville SE 3800 NA 200,000 miles. My knock count(22125e) is always 1, even during KOEO. My KR goes up to 5 and my rpm is below 2200 rpm. Sometime kr is 0 on the highway. My fuel trims are under +- 5, ltft +stft. In the last year I have changed plugs(xp606), maf(denso), map(ac delco), fuel ...

The backfiring seems to point to timing. Could it be crankshaft position sensor or camshaft position sensor? I have never had this situation so I am not sure.

Fuel pressure is 48.

Mike, You were right about the pressure gauge. It does not go high enough. I will find a gauge that goes to at least 60. Did a vacuum test. At idle, 750 rpm, vacuum was 19. The needle moved about the width of a hash mark line. My elevation above sea level is 500 ft.

Wires are belden 3 years old. Will redo fuel pressure test. Tonight while stopped at a light MAF was 5.8, rpm 750, LTFT was -7. I thought the MAF was high. The downstream O2 sensor was 0.3, better than during the weekend which was 0.1.

No stored codes. Spark plugs are iridium autolite. AcDelco MAP and O2 sensors. Denso MAP. Temp sensors are correct. Tried fuel pressure once but the gauge popped off the rubber hose so I thought it was good. Checked fuel pressure regulator, no gas smell. LTFT is about -5, STFT goes 1 to -3 at idle ...

I have had a decrease in MPG to 22, it used to be 27 and on long highway drives 30. I then changed upstream O2 sensor, spark plugs, map. Cleaned injectors and downstream O2.
Checked for brake drag and tcc slip was ok.
I always use OEM parts or premium brands when replacing parts.
Here is my test of ...