93 Chrysler Concorde 02 sensor fault

[gjbsr19]

1993 Concorde with 3.3l sets code 51 "low fuel pressure" or 21 "voltage from 02 sensor not fluctuating" Both 02 sensors have been replaced and still it fouls the plugs and fuel economy and performance are lost. I love this car and don't want to lose her. Any ideas?

[DanD]

Start looking at mechanical reasons for this as in leaking fuel injectors, restricted air intake, anything that would force the engine to run rich.
The O2 code is likely setting due to the engine being so rich for what ever reason, that the O2 is always sending a rich indication (doing its job), no matter what the computer has tried to do to lean the engine out.
The low fuel pressure code may also be caused by a leaking injector, if the system can’t be sealed it can’t build pressure.
You’ll need to have a fuel pressure gauge connected to the system to begin diagnosing whether or not there is some form of leak.
With the engine running record what the fuel pressure is, shut the engine off you may see a slight increase in pressure until the pump shuts off. This pressure should now hold for at least 15 minutes before it starts to disperse. If fuel pressure starts to drop off as soon as the engine is shut off, you’ve got some form of leak; the trick will be in finding out who or what.
With the engine running rich the way you explain, is why I’m thinking injectors. An external leak wouldn’t cause an engine to run rich.
I would lift the fuel rail and injectors up off the intake as a unit, leaving it connected to the fuel system. Cycle the ignition switch a few times from off to the run position that should allow the pump to run its prime cycle and build fuel pressure. After you have pressure look at the tips of the injectors for leakage, you may get lucky and see one or more dribbling.
There are a number of other things, but that would mean getting a lot deeper involved and it would be time to take the car into someone familiar with the system(s).
Dan.

[gjbsr]

Dan
Thanks, because I have gotten a few leads, and I'm sure this is another viable one. I don't see any leakage from the top of the fuel rail, which doesn't mean the injectors aren't leaking at the intake. I read a TSB which referred to this as being a problem. Another friend says to check the coolant temp sensor which could cause the problem as well.
Gary