2003 Ford Taurus losing acceleration when hot

I have a 2003 Ford Taurus, when originally starting the car cold it starts and idles fine. Can drive about a mile or two and nothing seems to be wrong with the car. After that the car loses power and sometimes stalls. Battery light flickers for a second. First it was throwing the O2 sensors code but since then I have changed the fuel filter and fuel pump and the codes have not come back on but still the same problem. Thinking it may be the CAT, but been reading other forums saying it could be coils and plugs. Figured that would be throwing a code though. Any ideas???
Thanks

The battery light is probably flickering due to the drop in engine speed. But it would still be worth making sure the connections to the battery are clean and tight.

Do you have access to a scan tool so you can monitor sensors like the Engine Coolant Temperature (ECT) sensor and the Intake Air Temperature (IAT) sensors, along with the MAF sensor? It sounds like maybe once the engine gets up to temperature some sensor reading may be so far off it's really screwing up the air/fuel ratio. At the time it starts running poorly does the exhaust have a dark color or smell like raw fuel?

-Rod

No, unfortunately I do not have access to any of those scan tools. And yes the gas does smell very raw after a few minutes of driving and after the car starts to heat up...

Are you familiar with what a misfire feels/sounds like? If so, when the car loses power, could it be due to a misfire? If so, plugs, wires, and possibly a coil would be logical places to start, especially since plugs and wires are part of a typical tune up schedule anyway. I wouldn't change the coil right away, I'd start with the plugs and wires. It is possible for a misfire to be present without setting a diagnostic code, especially if the issue is rather intermittent. A spark plug that is not firing would allow unburned fuel to go through the exhaust and could explain the raw fuel smell in the exhaust. But be aware that raw fuel in the exhaust system is quite hard on the catalytic converter, so if you drive it this way for long, you'll also likely damage the converter.

-Rod

Thank you, I have changed the plugs, car seems to be getting worse. I am thinking the converter is clogged. Guess that is the next step, if no one has anymore ideas...

You could try removing the O2 sensor before the converter. If the car runs fine (albeit loud) with the sensor removed, that supports an exhaust restriction. If it doesn't have much effect, then the issue is likely not due to a plugged converter.

-Rod

Thank you, I tried cleaning out the converter just to see if that would help and same problem. Throwing fuel rail pressure sensor and o2 sensor codes now. I'm going to try and change the o2 sensors next. I'll let you know how it goes

It's going to be cheaper to check the fuel rail pressure than to replace the O2 sensors, although new O2 sensors on a properly running engine that you plan to keep awhile won't necessarily be a waste of money in the long run. However, if your engine is not running correctly, putting new O2 sensors in now could damage the new sensors prematurely.

Why not start with the fuel pressure since incorrect fuel pressure at the fuel rail could cause the O2 sensors to report out-of-specification readings? Do you have a list of the specific code numbers that are present?

Also, how did you clean out the converter? I'm not aware of any method for that other than hollowing one out.

-Rod

Sorry, that is what I did, hallowed it out. Also I am getting the correct fuel pressure, even changed the fuel pump to double check myself cause that's what it originally felt like (not getting enough fuel). And codes I am getting is 1132, 1152, and fuel rail pressure sensor. Changed the sensor as well. Running out of options it feels which is why I think the o2 sensors could be the next step. Unless you think it could be something else..

Thank you

Well, unfortunately since you hollowed out the converter, you may never get the O2 codes to go away. Now both sensors will read the same which will likely trigger a catalyst efficiency code since sensor 1 should toggle frequently and sensor 2 should rarely toggle if the converter were working correctly.

-Rod

Yea, I thought that too. May just need to get another converter. I've talked to some of my mechanic friends and most seem to think that is the stem of my problem.

So the codes are for a lack of switching of the sensors, both banks indicating a rich condition. That would suggest you are less likely to have a vacuum leak, but instead a fuel pressure regulator issue or a couple of (or more) fuel injectors that are possibly leaking or not providing a good spray pattern.

-Rod

I going to have someone put it under a more intense scanning tool to see if it can narrow it down or at least cross more things off. Have them coming out later today. I'll let you know what it tells me.

Thanks

Oh, one more thought. I had an issue with my prior '93 SHO fuel economy which took a nose dive over a few weeks, even though it ran fine. That suggested to me it was running rich. I remembered this started shortly after cleaning and re-oiling my K&N air filter. I took out the MAF sensor and noticed the elements were a dull gray. I used electrical parts cleaner (before I knew CRC sells a MAF sensor cleaner) and cleaned the sensor. The elements now had a shiny chrome appearance and my fuel economy returned to normal.

You might want to clean your MAF sensor.

-Rod

Ok I'll give that a try next before anything else. That would be nice if that was the problem.

Ok so I've taken a break from the Taurus as it was driving me nuts lol. So I'm back at it, though I am yet to change the MAF (my next step today) I noticed something I had not before. The car seems to be running fine in the park position, I can rev up to high RPM's and nothing unusual. Soon as the car is out into drive it starts to bog and can't give any gas without it wanting to stall. Once I put the car back into park it will catch itself and I can again rev it up. Any ideas?? Or do you think this could be the MAF doing this?? Ps, all O2 sensors have been changed and so far no lights on dash.

It sounds like the car only has issues when under a load. That could be a lot of things, and without the diagnostic equipment to see what's happening, you're kind of stuck shot-gunning parts and hoping you get lucky.

Normally I'd say it's probably spark plugs or plug wires, but you stated you previously replaced those. Of note though is you said after that it might have even gotten a little worse. Maybe one of the spark plug wires is not making a good connection?

A MAF that doesn't read correctly could cause an issue under load, but again without having datastream data for the MAF, it's just a guess. Fuel pressure could be another cause, but I think you previously said you changed the fuel pump and fuel filter as well, so that reduces the chances that's the issue.

Maybe you have an intake air tube with a crack in one of the accordion folds that opens when the engine shifts under load. Worth checking. Or maybe there is a brittle vacuum line or mis-routed vacuum hose that opens or gets pinched when the engine shifts.

-Rod

Ok I'll see what I can do and start checking things off hoping I get lucky. But yes definitely seems to be only when it's under load. Thank you again. I'll let you know what I come up with if anything. If you think of anything else I'd greatly appreciate the information. Thanks again!

Just for those who have read this post that may have had a similar problem. I never did find out the issue. I believe the transmission just was breaking down so I ended up selling the car.