one thing after another....

May be your o2 sensors went out, When my car's o2 went out, it ran like crap and threw all kinds of cel #'s

Not sure about your fuel issue, May be you should clean out the fuel system. May be send out your injectors to get it cleaned etc etc

Good luck man

Was the car up to temp when you ran codes the first time? If not, you can toss the ECT code (the EEC expects the coolant to be at 170+ when you run codes).

You could swap the O2's and see if the code follows that particular O2.

Is it still running rough?

When the O2s fail, they indicate lean. Actually, from a design standpoint, this makes sense because the computer response to a lean condition is to add fuel, and you would rather the computer add fuel when it didn't need to (in response to a failing O2 indicating lean) than pull fuel. Better to run rich than lean, right?

I am starting to think this is EGR valve related issue, may be others can get in here and figure this out

So was it EGR? What was/is the problem? Also if you have off-road X/H pipe, It will burn your o2 lot faster, IT seems like i am replacing mine every year or year and a half...

Any chance of a wiring harness issue? Seems like you change one thing another pops up some where else. I knew someone who stored a camaro for a bit a critter got in at the harness.
Just a thought

May be your ccrm is going out, Did you change the fuel pump and fuel filter lately? how old is your pump?

I hope you get this fixed soon

Hey, guys, new here, but not new to Mustangs (86 GT and 94 GT engine in a Ranger). Seems I'm in a very similar situation. I'm going to keep an eye on this thread to see where it leads. I'm going to throw my similar situation out there, which may or may not be of help. It's going to be long, but thorough.

I have a 94 Mustang 5.0 in my Ranger. I have been having an issue that has continually gotten worse and I'm at my wits end to figure out what is going on. The engine is a stock engine with wiring harness, computer, etc from the Mustang. When cold the engine starts up and idles well. Going down the quarter mile driveway it seems fine and then upon acceleration it acts like I just pulled the choke on. It bogs down, has no power, occasionally backfires out of the intake. Then, for no reason it will just start running great with full power. I initially pulled an O2 sensor code and a 542 (fuel pump circuit). I'm not sure what the fuel pump circuit is supposed to mean. I have a low pressure and a high pressure pump and both are working well. I can check fuel pressure even during the low power issue while accelerating going down the driveway and it stays around 40 psi. So, I would like to think that I could rule out the fuel system. Now, the thing I don't understand is that when initially trying to pull codes I could not get the code scanner to work. When I plugged it in and turned the key on it would just beep in the hold position. When flipped to test it would do nothing but continue to beep. I ended up messing with the wires at the connection to the computer and found that if I wiggled a certain wire it would stop beeping, but if I touched another wire it would start back up. That certain wire was for the O2 sensor. So, I disconnected the O2 sensor harness from the injector harness and I could now use the tester. Figuring there was a problem with the O2 sensor harness, which I made myself 6 years ago (solder/heat shrink high quality job), I pulled it out and tested for continuity through all the wires (along with a visual inspection). I could not find anything causing a short. So, with the O2 sensors disconnected I reconnected the O2 harness to the injector harness and again could not pull codes. Figuring there was something wrong with the connection there I eliminated it and hard wired the O2 harness to the injector harness. Well, that just made things worse because I can not pull codes at all now.

Similar to the situation above it will occasionally go into self test mode without the scanner (idles between 1400 and 1800 on its own for a short period of time before going back to normal).

When this problem started I could let the truck warm up and then it would run fine. Now, it seems that it will barely allow me to drive it even with it warm.

I have already swapped the computer to verify that's not the problem.

Any ideas on this would be great. I hope we can solve both our problems.

Brian

I'd say wait for Hissin or Richter to chime in, they're pretty much the gurus in this dept. I'm pretty sure you'll get that code if the fuel pressure drops out of good range, so it might be your fuel pump is going out on you, that wouldn't be surprising as the car has sat for a while. Smell your gas for one, but just cause it's good, doesn't mean that your pump is still fine.... If you have access to a tool, test your fuel pressure. I have a full sweep autometer gauge on my car because I've had such horrible luck with pumps for some reason.