Hey all,
This morning I experienced an extremely long start leaving for work. I finally got it started, and while driving I noticed a lack of power and faint backfires from the exhaust. The CEL came on, and I was getting P0131, O2 sensor voltage low. Finally the drive-ability got so bad that I pulled over and shut it off. Now it will not start at all.

The truck was still in open loop this morning when all this took place. I thought the O2 sensors didn't even come in until closed loop. Also, could this problem cause a no-start condition?

I'm going to do a fuel system pressure test today, even though I installed a new AC Delco fuel pump less than a year ago. Also new (re-manufactured) spider/regulator and a new "nut kit." Also new fuel filter at that time. Spark plugs, wires, dist. cap, and rotor are AC Delco, replaced at the same time as the fuel components. I replaced the fuel sending unit, also, but it was a no-name cheapie. I figured all it does is the gas gauge, and I can't afford the Delco one. The pump is Delco, though.

 

Test results in. Key on, engine off was around 10 psi. While cranking it would slowly climb up to 45, but go no higher. As soon as the key is switched off, it would drop back down to around 15-20 psi within a few seconds.

So I need a new fuel pump? As I said above, it has an AC Delco pump, less than a year old. But I went cheap on the sending unit. It it for more than just the gauge?

Also, any ideas on what would cause a brand new pump to fail in less than a year? I will let the fuel get down pretty low, but then I fill all the way up, so it's not like it's always operating on empty.

 

Don't worry about the sending unit. Before I dropped the tank i would open up the plenum and jump the pump. See if maybe the fpr or nut kit blew. You said it backfired, that says gas being dumped to me.
A clogged fuel filter can burn a pump.

 

I'll check the spider. That's a good idea. I have noticed my mileage has dropped from around 18-19 to 16. Same driving habits, same route. etc. The filter is also less than a year old, so I don't think it's that. I'll check the pressure at the pump, that will rule out a clogged filter.

 

So now it's running, but still noticeably down on power. I think the autozone gauge is broken, because now it always shows 0 psi, even with the vehicle running. Think I'm going across the street to a different store and see what theirs says.

Also, does anyone know what my fuel trim values should be? Here is what I'm showing:

02S B1 S1 (v) 0.080-0.700
O2S B1 S1 (%) -2.3 to -3.9

O2S B1 S2 (v) 0.170-0.260
O2S B1 S2 (%) 99.2 steady.

I only have two sensors, one just after the "y" pipe before the cat, and one after the cat. I'm assuming that's the sensor 1 and sensor 2 my tool refers to.

Also, it's a '95, but it is fully OBD-II, with the CPI engine. VIN "W". Big orange "Vortec" on the plenum. Hope somebody can help out.