jz78817

no. Especially not more than one at a time. The only thing I think would cause that is if someone put leaded gas in there, and you have to try really hard to find that.

No. The PCM uses the upstream O2 sensors (the ones before the cats) to monitor the actual engine management functions. Both of yours are throwing "always lean/excess oxygen in exhaust stream" codes which means both cylinder banks are running lean. Your O2 sensors are working correctly by telling the PCM that something isn't right, and the PCM throwing codes because it can't make the engine run right. Like I said, I'd bet real money you have a vacuum leak. Your engine uses mass-airflow (MAF) air metering. The MAF sensor tells the PCM how much air is coming into the engine, and it calculates the fuel delivery based on that. When you have a vacuum leak, extra air is being pulled into the intake. The PCM has no idea about this extra air because it's not passing through the MAF sensor. your engine is now running lean, the O2 sensors tell it so, the PCM can't figure out how much extra fuel it needs to add, and then just says "I give up" and sets codes.

Bobby_Sparks

Ok, so not having a custom tune for the mods probably isn't the culprit here. Possibly a vacuum leak somewhere under the hood. I looked and didn't see anything weird but I'm new..I'm new..I'm new at this so I could easily be over looking something. Could you tell me a few specific places to check for possible vacuum leaks? Would this supposed vacuum leak be come and go? Some times the car runs fine and other times I can't hardly get it down the street without holding the pedal all the way to the floor.

jz78817

- PCV lines
- Check the brake booster hose
- Make sure the brake booster check valve isn't cracked
- check the intake manifold for cracks
- do you hear a hissing noise when you press the brake pedal? if so, the booster diaphragm might be torn

sure, I've seen it before. A hose has a split, or something's cracked, and has to be bent or twisted just so in order for it to start pulling air in.

Bobby_Sparks

I checked for vacuum leaks but no luck. Just noticed something kind of new. When it does let me drive it without bogging down, I push the clutch in to switch gears and it revs up automatically to nearly 3.5 rpms. Is it bad to drive it when it's running like this? Trying to figure out how to take it to the dealership which is 30 miles away.

krazykevin

Did you take the intake apart to clean the TB and MAF ?
if so, make sure the seal is still there and all of the sensors are plugged in.

GCCBrian

At this point you're better off just searching for some good local mechanics and having the car towed to there shop to get the car fixed, codes cleared, and back on the road. Even if you do find it, it's going to have to get fixed, and unless you don't plan on doing it yourself, that car is getting towed regardless. If you do plan on getting it fixed yourself, here is the OEM Service Manuals for the 05-09 v6, GT, and GT500. http://iihs.net/fsm/?dir=1

Bobby_Sparks

Okay so I'm a DIY and trying to figure this out on my own. Will probably end up taking the car back to the dealership tomorrow but I want to try to figure it out also before I take it up there. So just humor me. I'm trying to rule out fuel pressure being the problem. Rented a fuel pressure gauge kit from autozone and not sure where to hook it up to check the fuel pressure. Disconnected the fuel line that connects to the fuel rail but not sure how to get an adapter on there? Can any help?

Bobby_Sparks

Anyone done a fuel pressure test on an '08 GT?

jz78817

honestly I thought fuel rails still had Schrader valves on them (look like tire valve stems) but googling for pictures it doesn't look like the 4.6 mustang has one.

white08gt

the problem most likely is your C&L cai, needs a tune if they reflashed back to stock. put a stock air filter on and will probably clear up. without a tune you are running to lean. worse case if you can't find a stock air filter, someone will swap you theirs for a C&L. one of the best most expensive CAI, did you get a tuner with it.