OK...here's the latest. So far, replaced on the GP were the following:

2 Oxygen sensors (sensor 2 and 3)
2 Coil Caps (servicing bank 1)
PCV
MAF Sensor

I had shop diagnostics done, and the only thing they stated was fuel pressure was too low:42-44 psi where as it should be 48-55 psi. Of course they want me to replace the fuel pump for ~$500 all inclusive.

I also purchased a fuel regulator, but have not installed that yet.

One guy stated that if the fuel pump was bad, I would know it. Another stated that the injectors need to be properly cleaned. Any ideas before I sink more bucks w/o positive results...???


Argh....

Well clogged injectors will not make the fuel pressure low that i know of... If you have the regulator, put it on, if that doesn't work, could just be a weak fuel pump... maybe try a different shop?

What I probably do is get the injectors done anyway. There's a special at Pep Boys here. Don't want to drop the regulator. That's another $60 buck part on top of all the other $60 buck parts spent already.

Part of my question is my need to understand the OBD-II logic a bit. If the fuel pump was pushing low, wouldn't there be a code more reflective of that And wouldn't it report low on bank 2 as well??

Not necasarily.

You say they tested the pressure and it was low. That's a definate problem. Cleaning injectors won't cure it but might help a little. My guess is the fuel pump it's self is going. It's not all that bad of a DIY job. There is an access panel in the trunk.

I have had a fuel pump go on me on another car, just before it died out completely, it started with stuttering, hard to start, dying, and sometimes it just ran fine...

OK guys (and gals)....here's the latest of this never-ending saga. I took the GP to a qualified mechanic and had them change the fuel pump. Pressure is now up to ~55 PSI. Yippie. But the P0171 error is still present. . They will keep the car overnight with battery disconnected with the hopes that several hours of cap discharge will correct the problem. If it doesn't, they mentioned something about re-flashing the computer. This problem has them stumped...not to mentioned me pissed. Has anyone experienced the need for computer flashing??? And the costs..?????

Wow... got me stumpped on that one too... glad to hear about the preasure back tho!

reflash should be cheap. But doubt it'll help

Herc....OK...if no help then you talking about a complete replacement..?????

Geli,
It's possible that replacing the fuel pump may have fixed the problem. The PCM will only turn off the SES light after three consecutive trips in which the self diagnostic has been run and passed.
After reconnecting the battery, the car needs to be driven several times to make sure the code doesn't return. If the code comes back, I'd check for vacuum leaks and exhaust leaks; even bad injector O-rings could be the culprit(vacuum leak). Good Luck!

Arrow,

Fuel pressure was measured as being low, which made them believe that was causing the 0171. After replacing pump, the error still appeared. The mechanics then put something which is to identify vacuum leaks (something which emits yellow vapor). I cannot be specific right now as to what that was, but nothing was found to identify any breach of vacuum failure. Even they are baffled. Car is sitting now with battery disconnected, and I will retrieve tomorrow morning. Close to $700 has been spent in trying to correct this problem, which should get me a free pass for inspection here in NC. I love this car..I hate this car....

FWIW..... The Grand Prix only has one bank "Bank 1". There are 2 sensors in that bank "Sensor 1 and Sensor 2" These are the O2 sensors pre cat and post cat. Sensor 2 will not indicate a lean condition as it is only there to monitor the cats performance.

I'm wondering if your shop has the capability of scanning the car while it's running? It's possible there is a loose connection going to the O2 sensor. Getting the injectors cleaned, and checking for vacuum leaks sounds like you may be on the right path, but won't solve your problem if you've got electrical issues.

Clint,

Both sensors have been replaced. I did have a P0142 failure which indicates a faulty sensor, and replacing sensor 1 rectified that. 171 and 142. Only 171 is left. I can understand computer system hiccups (I work servicing Dell systems), but part of me is seeing simplicity, as in poor injector injecting.

Having them cleaned if condition continues in the AM is my next logical step...

Just to recap, here's a checklist of things that can set Code PO171:

1. Misrouted Oxygen sensor wiring contacting the exhaust system
2. Poor PCM to engine block grounds
3. Low fuel pressure or injector problems
4. Vacuum leaks at the throttle body, EGR valve, and intake manifold. Damaged or disconnected hoses, improperly installed or bad PCV Valve
5. Exhaust leaks in system, cracked or leaking exhaust manifold etc.
6. Mass Air Flow Sensor
7. Fuel Contamination by water or alcohol
8. Poor connections at the PCM or damaged wiring harness.

I wasn't implying that you need to change the sensors, only pointing out that you only have one bank w/ 2 sensors and what thier purpose is.

If you re-read my post you may understand the direction I was going.... IE the bad connection theory.