My lil sister bought a 98 Z28 auto with about 95k on it. It seems to run fine but every time I hit it full throttle these codes come up. P0131, P0151, P0137 and P0157. I was done some little changes in the pcm like fan setting and some other little things so I first though maybe I done something. So I flashed it back to stock and these codes still come up at the first wide open run I do. She just bought the car yesterday and drove it 140 miles home and got no codes but she also drove it really easy. I drove it today and if ya don't floor it the codes don't seem to show up.. Some guys on another forum are telling me it's the fuel pump crapping out on the wide open rune but I don't know. Thanks

All 3 DTC codes are related to the 2 rear 02 sensors.

Check to see if the past owners removed them.
If they did and you do not intend to put them back in then those DTCs will have to be turned off via the tune.

If they are installed check for bad wiring, or problems with the CATs, they also might have been taken off.

So these codes have nothing to do with the fuel pressure?

I see the P0131 is Heated Oxygen Sensor (HO2S) Circuit Low Voltage Bank 1 Sensor 1.

The P0151 is Heated Oxygen Sensor (HO2S) Circuit Low Voltage Bank 2 Sensor 1. The other two I see are for the rear O2s so yes I think your correct about a cat problem but the first two are for the fronts. Everybody is telling me it's running out of fuel but honestly it doesn't run like it is. It does stay in open loop when it sets this code.

Without seeing scanner data or knowing what mods it might have is hard to pinpoint the exact cause but the car has 95,000 miles on it and O2s SHOULD be replaced every 30,000 miles

So it can be o2s are just too old, they got corrupted from cheap gas, wiring for them have got burned, exhaust leaks, not installed ( like the rears) or even the fuse for O2 heaters is blown

If the fuel was too rich or lean then the PCM would be tripping DTC error codes for that and not O2 DTCs which are pointing to O2 failures.

Yes it would cause loop issues as PCM seeing all 4 O2s with problems.

You have to get under car and look to see if all 4 are installed, is there any wires fried, is there any exhaust leak from flange at heads all the way back to rear O2s.

If CATs are installed they could be clogged up, taken out, or leaking.

Fuel pressure, either dirty gas filter or worse would cause engine to run like crap and most likely trigger lots of engine knock.
Simple check as to test valve at end of fuel rail allows a pressure gage plugged in and then rail pressure should be 58 PSI.

Of course past owner when selling car took some mods off and the tune they have in it now is crap to engine makeup now.

Ok thanks JR. I'll check the filter first and then check the fuel pressure. The car is stock other than a lid and a catback. The tune is stock also because I compared it to a tune that I know is stock. Like you say I may also get a couple sensors for the front and see if that helps also. The funny thing is that the car runs perfect, no rough idle or bogging or anything.

If the 02s are the orginal or your not sure how old they are for the cheap cost I would replace both fronts but again I'd check the fuse for the 02 heaters and assure there is no exhaust leaks or wiring problems.

With scanner I would do the I/M and 02 tests and see if they pass.
If the scanner supports the mode 6 tests I also would run it and look at the results

Ok, I'll get a couple new sensors tomarrow and put them in and check all the wires. While I'm under there I'm gunna change the fuel filter. Will my EFI Live scanner be able to scan what needs to be checked?

I do not use that scanner but I have a V7.3
Click View,
then click on On-Board Information window

They have tests there but I do not know if they work and how well. It does not seem to have the $06 mode tests but I see the 02 and I/M tests

well JR I put two new O2s in and just deleted the rears and also checked the fuel filter and it was plugged so bad I couldn't even blow through it. I changed that also. I drove it for quite a while with several WOT runs and NO CODES!!! The only thing I noticed was that it still has some knock retard. I though maybe it was doing it at first because I just flashed the tune in to it. It did seem the longer I drove it the less knock it had. The tune is stock other than the fans and O delete and egr. I also hear that 98 had false knock so maybe that's my problem