vacumm/02 sensor

[BJazzy759]

hello i have changed nearly every sensor on my 91 explorer. from map sensor to just recentlly my 02 sensor. my check engine light was on,hooked up to machine.it read o2 sensor,so i changed it. the check engine light still comes on and trucks rpms drop really low almost shutting off then revs up again and repeats. also started hearing whining from fuel pump?thank you for any help

 

[arco777]

Throwing parts at your problem is killing you. Just because the computer says an O2 sensor is reading an unexpected value, does not mean that sensor is at fault. There could be an actual lean or rich condition caused by something else. The PCM tries to compensate for abnormal conditions but it can very easily be confused by situations it does not fully understand. For example, a computer would not know that a vacuum leak is what is causing a lean mixture, and since the MAF is reporting normal values it would simply say "O2 sensor reports bank 1 (and/or 2) lean". It is indicating a reported value outside of normal operating ranges, and does not know why. It may dump extra fuel into the engine to try to compensate, which can compound the problem.

Start with the basics of fuel (check fuel pressure with a gauge, and while driving), air (check for vacuum leaks, clogged air filter), spark (check for misfires, arcing from damaged wires), and compression (compression tester).

 

[BJazzy759]

I have checked vacuum lines all seems to look ok,truck has new air filter. It has been burning gas like crazy. Could it be fuel pressure regulator? The other night my fuel pump wss whining? Thank you

 

[arco777]

Pumps do whine normally to some extent but shouldn't be too loud. Some models make more noise than others. If it's making unusual noises, the fuel filter could be clogged or the pump could be going bad.

The FPR can be checked by using a fuel pressure test gauge. If you do a search on the forum you can find a how-to guide.