96 T-birds Check engine light chronic 4 years

Code 171 and 174 on both of my T-birds, with mileage being drastically different. 126k to 77k. On the 126k one it all started 4 years ago. I changed all 4 O2 sensors. Still on. I changed the MAF, still back on. I had a vacuum leak fixed, still on. Plugs, wires, TPS, PVC, etc. Still back on. Always comes back on, after reset upon excellerating onto highway speeds, at about 50+ mph timeframe. I have not even begun to pay to fix the other bird. LOL
Anyone really found the root of this Ford money pit problem? : )
Michele

Check for a dirty fuel filter and proper fuel pressure

Basically, the car is running lean, so check as peppermrj said fuel filter and fuel pressure. Also look at the injectors, ensure the wiring is good and a bottle of fuel injector cleaner might do you good. That will be a good start for diagnosing why theyre throwing those codes.

Hey, thanks to you both for trying, but I forgot to mention that we even dropped the gas tank and changed the fuel pump in our dispair of this persistant problem. Its like the achilles heal of all check engine lights.

Code 171 and 174 on both of my T-birds, with mileage being drastically different. 126k to 77k. On the 126k one it all started 4 years ago. I changed all 4 O2 sensors. Still on. I changed the MAF, still back on. I had a vacuum leak fixed, still on. Plugs, wires, TPS, PVC, etc. Still back on. Always comes back on, after reset upon excellerating onto highway speeds, at about 50+ mph timeframe. I have not even begun to pay to fix the other bird. LOL
Anyone really found the root of this Ford money pit problem? : )
Michele

So the 96 TBirds do have 4 oxygen sensors? That's going to be expensive for me to change because my check engine light came on a few days ago that read, "system running too rich"

I think it was four. I was pregnant under the care 4 years ago and I know of one on each side and one further back from the exhaust which was harder to spot. I think I bought four of them. LOL
I have spent a lot on too lean. I also changed my Idle air controller, still same problem, and now the 50.00 for the EGR valve. I will see if that fixes the problem now. But I have soaked like 500.00 into this code problem, and I hope you find an easy fix. : )