P0131 & P0151, open loop, no power when floored

[lkrasner]

2002 Tahoe 4WD, flex fuel, 5.3 Vortec

Was driving along at ~50mph today when the car just stalled out, felt kind of like running out of gas. Started right back up and was running ok, but I realized that If I gave it any kind of hard acceleration, it stuttered and slowed down. Eventually it put the MIL on with the codes P0131 and P0151 (both upstream O2 sensors low voltage). I've had some trouble for a while with system too lean codes (both sides) when it is cold as well, which leads me to believe the O2 sensors aren't at fault, especially given they are both showing issues, not just one side.

I tried checking for a vacuum leak with carb cleaner, couldn't find anything, but I may not be looking in the right place. Where should I be checking?

On another note, the truck will not start when gas is below 1/4 tank and it is left overnight. it will run down to nothing fine, and will start if only left for a few hours, but refuses to turn over if left longer. I'm not sure this is related, but I thought I would mention it just in case. Any guidance is welcome.

 

[lkrasner]

Tested the fuel pressure this morning. about 48 PSI with key on, engine off, 42PSI with the engine running. This seems low to me. Could a bad fuel pump be causing all these issues?

If it does need replacement, I currently have a full tank of gas that is about 1/4 E85. would that be safe to put in a non-flex fuel vehicle. I don't exactly have 26 gallons of gas cans sitting around.

 

[JennaBear]

Bad fuel pump could certainly be the issue. 1/4 E85 wouldn't be a huge deal, just don't beat on it. Fuel pressure might be correct the 2002 flex fuels have a different fuel pressure regulator in some cases.

 

[OR VietVet]

Hopefully the fuel pump is all it is. I agree with JennaBear. I would still make sure that the codes go away and stay away and not just assume that they will with a new fuel pump. Use AC Delco pump. Replace the fuel filter at same time if has an in line filter. Might want to have back pressure checked also for possible clogged exhaust but likely not a problem.

 

[Marv02]

I just replaced Fuel pump and screen filters I picked my off E Bay OEM DELCO kit for $30.00.

Mine was hard to start in the mornings or after sitting a couple hours.

And I had a O2 Code also thinking about it.

 

[andrewg29]

I have an 02 z71 with the 5.3 flex and these are the normal fuel pressure specs key on engine off However 42 with engine running does seem low. I had the same problem when it would get below a quater tank it would not start.. replaced the fuel pump and works pefect now. The reason i decided to check the fuel pressure was because i was having a stalling problem as well but at low speeds..

 

[lkrasner]

Fuel pump seems to have done it! Kind of a tough job though. Maneuvering the tank out was a pain, and removing the stupid fuel lines was damn near impossible. I accidentally broke the nipple off the vapor canister and had to replace that. Every auto parts store AND GM matched the part wrong which I found out once I got mine off. Almost the same, but a different mounting system.

The car no longer stalls or hesitates, and there are no codes after about 100 miles, I will report back about the low tank not starting problem when I run it low again. Thanks for the advice!

An additional note that could help others: my fuel pressure gauge has a release button to bleed the pressure off. If I pressed it while the engine was running with the old pump, it quickly stalled from lack of fuel getting to the engine (all coming out the Guage). With the new pump, it shot fuel out the drain tube and ran the engine no problem.

---------- Post added at 09:05 PM ---------- Previous post was at 08:55 PM ----------

Also, I'm getting about the same pressure as before. Maybe a touch higher while running. Does anyone have a good source of the specs for the flex fuel 5.3?