Hello, im new. normaly dont do forums, have seemed to be able to fix anything i touch, except this car. and im really tired of thinking all day on it and getting no where.
Vehicle is a 1990 mustang lx 5.0 with auto/aod. dead stock engine, with no mufflers.

parts i have replaced: egr valve, maf, cap-rotor-wires-plugs, all intake gasgets. (all parts still look new)

problem: the car is running incredibly lean. has other quirky issues as well. maybe related.

heres the story: car runs good, not great. starts every time hot or cold, doesnt matter, starts right up. idles smooth, no tach jump, no miss. spark plugs are only white on the ground prong, the rest of the plug doesnt looked touched. the ceramic around the electrode is clean like i just put them in. electrode is clean with no wear. the plugs have been in for over 6 months, and this car is a daily driver, so they are well used with plenty of dohnuts and high speed hard driving on them.

the car is incredibly quiet as well. WAY quiet, even with out mufflers.

fuel pressure with key on engine off is emidiate 40lbs then down to 38lbs and holds. fuel pressure with engine running and vacuum plugged is 46lbs. at idle, does not move when throttle is opened. with vacuum hooked up it is 36lbs. at idle, and will jump almost to 50lbs. when throttle is opened. returning engine to idle brings pressure back down to 36lbs. shut down engine, key off, fuel pressure rises to 41lbs over a period of 2 minutes. "have not done a driving pressure test yet"

fuel pump is loud and changes with electrical load on vehicle, but drivability stays the same.

Drivability: The car in my opinion is gutless for what it should be. 1st gear is lagy off the line, builds power above 2600rpm then starts 'popping' out the exhaust as it gains rpm. 2nd gear has even less power with the same 'popping'. 3rd gear has the most power, very reponsive, and just flat gets it at 60mph or higher, but still 'pops' at high speeds. all the above under "drivability" is a WOT issue. cruising speeds the engine is flawless. very slow speeds that require just the weight of your shoe to go makes the car stumble almost like it had a cam, but not so nice.

i have disconnected o2's and drove it, no difference except for the check engine light DID NOT come on saying its "always lean". i have disconnected fuel pressure regulator and drove it, no change. its like a dryer vent out my exhaust, very hot, no fuel smell at all.

something extra. the car passed california emission tests just fine. all my friends have the same car, theirs is loud like it should be. aggresive sounding if you will. and wont pass smog. (and ha ha, i know its gutless cause it passes smog)

i apologize for the long post, but i need to be pointed in some direction i havent thought of. thank you for reading this.

 

Have you ran a koer to see what the computer throws at you ?

http://www.dfwmustangs.net/forums/showthread.php?t=7908

Key on engine running will give you a glimpse at what the computer sees when its running.

Also do the koeo to see if any codes are stored in memory.

The ecu doesn't always turn the cel on when it sets a dtc.

 

Definitely need to read codes, most of the auto parts stores will read them for you if you don't have a code reader, though the readers are cheap. Hopefully the codes will point you in a direction.

 

no i have not ran a koer test. nor have i ever done it. only koeo tests. my friend has my code reader at the moment, but thank you "dawson1112" for the link. ill get on that when the car returns from its daily rutine. any other suggestions from the info listed? did my post have enough information?

 

What is your timing set at?

The fact that you think it sounds quiet with no mufflers makes me believe your timing is way off.

Also Im assuming you still have the cats in place, possibly partially plugged .

 

Timing is 10.5 btdc with spout disconnected. All 4 cats in place. It seems to breath fine. I've had it over 120. I don't think clogged cats would allow that would they?

 

I would lean (no pun intended) to your o2(s) being faulty. Have you checked/replaced them? Didn't see them in your list of replaced parts. Idk if the Fox is the same as the SN cars, but have you reset the computer? They usually run pretty rich after a base idle reset.

 

No I have not replaced the o2's yet. I'm battling between replacing them, or the tps. But at the moment my parts fund is going into another car I'm still making payments on. As for resetting the ecu, disconnecting the battery is as far as that goes. Is there a better way reset it? I'm a smog exempt or obd2 guy. So this car is a learning experience. It seems partially dependent on all sensors at different times. Not like a full monitored obd2 like my Toyota s runner.

 

You just unplug the battery for about 20 minutes. This will eventually drain the capacitors in the computer = no power. This resets the computer.

I would definitely check your o2's

 

I have reset it then multiple times.