My girlfriends V6 Mustang is running lean and stuttering when it is at load. I changed the O2 censors, plugs, fuel filter, and air filter. I know it is lean because I had autozone check the check engine light. She wants a new car but I think we can fix this one. How should I go about fixing this problem?
Thanks,
Chad

 

Seems like you are checking all the right things. Problem is that you probably need to have had a complete computer diagnostics run on the car. The stupid Autozone ones are great for checking codes and clearing them, but they can send you on wild goose chases. A mechanic or a dealer will have the ability to check all of your sensors to see if they are making sense.

You can have a bad sensor and not have a code.

Running too lean means too much air, right? Or, not enough fuel. So, think about those sensors that are involved. I might suspect the TPS (throttle position sensor). If it is off and not showing the correct voltage, the car might not add the right amount of fuel. Also, if the MAF is dirty (Mass Air Flow Meter), the car will think that less air is moving and then not add enough fuel.

She could also have an exhaust leak. Leaks are common ways of showing a lean condition, BUT actually make the car run rich...not lean. That is because the O2 sensor sees too much air because of the leak, but tries to compensate by adding more fuel.

You may also want to pull a few spark plugs to see how they look. If the straps are white, then the car has been indeed running lean.

Hope this helps.

 

Thanks, first I'll pull some plugs and check it out and look under the car for a leak. The Mass Air may well be dirty. I had just metioned that to her right after I had posted the thread.
Thanks,
Chad

 

Does the car have a K&N Filter??? Had it recently been re-oiled? Sometimes oil can get on the wires inside the MAF. Be VERY careful cleaning the MAF. Screw up and the MAF is toast.

A Ford tech showed me how to clean one and I have done it several times. I am not sure how a V-6 MAF looks, but on a V-8, there are two screws that you need to loosen on the top of the MAF. They, you pul the sensor out from the housing. Yu will see two wire loops. They are very small. Pour some rubbing alcohol over the sensors. You can even clean them carefully with a cue tip, but don't break them or you are hosed.

 

A mass air meter isnt going to cause the car to run like that unless its fried which is the reason for the code, or you have the sensors completly covered to receive no accurate signal. If they are simply dirty, you would probably just get pinging on acceleration and no codes being thrown. Do you know the code that was thrown because we have a code database here where you can look the code up to get an idea of what the problem is. If you have access to alldata or have a friend whos a mechanic (who probably does) they can look up your code and tell you however many problems are attributed with that code and what to do to fix the problem (usually...)

 

clogged fuel filter. change that before you go much further. very often the cause of lean conditions under heavy load.

 

Hey redneck....welcome to the show. Read his first post.

 

thats the first thing to check...

but he said he changed that...

try running some fuel injector cleaner...

you may also want to check the timing, and distributor cap and rotor(if you have one)

 

So the only code was lean banks one and two thats it?

I had a similar problem on my f150. I have blown the intake manifold gasket out and it was leaking in alot of air and causing that problem. I am willing ot bet its some sort of vaccum leak. If it drives fine idles fine just tosses that code then i would be more then willing to guess its vaccum related. You might want to go rent a vaccum guage from auto zone and see what kind of vaccum the motor is pulling. Tell us and i can tell you if its high or low.

 

my bad... didn't even see that. go on...

 

How low does she let the gas get? If she drives on empty very often she could have very well overheated her fuel pump. I had this problem and replaced plugs, cops, tps, iac, and injectors before I realized it was the fuel pump.

 

Isn't there a "sock" on the pick-up? If so, that may be clogged...

 

might not be a bad idea to ohm out injectors? couldn't hurt imo just another thing to cross off the list

 

She says that she ran it on empty a long time ago. She got this car brand new and it has never been run hard at all. It's crazy how things just go bad on a car. No mods at all done to it. One day it just started acting up and not quite hesitating but almost like really quick pulses almost made me think the automatic trannie was going bad. I always thought it would be an good idea to have the fuel injectors cleaned. I think I'll try that next. That's kind of cheap. A shop near here does it for $30. I am sure they are disgusting. Do you guys think that would make it run lean as the computer is displaying?
Thanks,
Chad

 

yes.

 

Thanks, I'll try that and post an update.