Hi, I'm new to this so trying to figure it out. But I bought a 2003 3.8L mustang with the auto tranny. It was fine when I test drove it but now (once I brought it home my luck lol) if you go up a steep hill(which is alot where I live I'm in Pa) or stomp the car hard(like to pass someone) it falls on its face and will load up some and has no power. When this started it threw code for misfire on cyl. 4 and 5 but the pcv valve was loose. We checked it, its fine(works correctly and tube to intake isn't plugged)and pushed it back in. Car has/had very old bad gas in it. Put new gas in and cleaners. Sometimes car will go like it should be most of time(others) it will do this no power thing. Looked on other threads on here for help. Tried most of what it said, we changed coil, didn't help. My husband did the fuel filter, helped a little but its still messed up, doing same thing. Checked wires plugs gap thats all correct. Like I said pcv is good, haven't noticed any vacuum leaks/bad lines anywhere. Car has 25000 on it with headers and 2 converters. Don't think convert. are plugged because car doesn't stink, sound like plugged convert. don't think any exhaust leaks don't see, smell, hear any. we had code cleared it only comes on when car messes up and stays misfire on cyl. 4 now only. don't think its head gasket, anything bad, no leaking/using oil/antifreeze, no white smoke, blue or black even when car messes up coming out of exhaust(so don't see how its a big prob. thing). not timing car only messes up at high rpm up hills idles, goes easy perfect. heard on here it could be the camshaft synchronizer but not sure. we were thinking since fuel is bad the sock on fuel pump is plugged or fuel pump is weak not pos. if we should try that next. also when he changed fuel filter the next day it was really bad car wouldn't run at all towed home. (luckily i was 1 mi from home). he pulled a line(vacuum) off fuel rail area(he used to have 85 tbird with 3.8 in it so he knows about engine and is mechanic in mine so my hubby does got idea whats going on about troubleshooting)and took small straight screwdriver pushed in when car was idling bunch of air came out of it with fuel but instead of fuel spraying it did some but some dripped so we were also thinking that maybe fuel inj. on 4 is bad/plugged. so i think that explains it all if anyone has any idea what to do/fix PLEASE tell me I didn't buy the car so it could sit in driveway! lol thanks and I appreciate help!!

 

Could be several things but the old gas stands out to me, more so because it is an intermittent problem. When gas gets old it varnishes and is no good. You can not just add new good gas and hope it all mixes up well. Easy way to pump out all the gas is too disconnect the fuel filter and put on an extension hose from the filter to jugs. You can turn the key on and the pump should energize, letting you drain the whole tank. If the EPA isn't around, use the gas as a fire starter, or to drop beetles into, it is not good for engines at this point. I grew up in PA! I miss that great state!

 

okay great thats what my hubby kept saying about fuel but he just kept trying to add cleaners/94 octane from sunoco to get the old fuel out. i said about draining it and he said he was thinking about that too(he thinks fuel varnished like you said too) because even though its running like krap we been driving it some to try to get old fuel out of tank(unfortunately the car was almost full when i brought it home). So we'll try that and take it from there thanks so much!

 

I agree. Pump out the old gas and start fresh. No need to run anything other than 87 oct in it. Higher won't do anything helpful.

 

Welcome to the forums, we will try to help as best we can.

Here is one area to look at after you get that old gas out.

Remove the coil pack and inspect for cracks.

My 01' had a similar problem and it was the coil pack.

If you dont see any cracks that does not mean that it is not bad.
Buy a new one and test it, return it if it didnt work.

Also make sure that the spark plug wire is in good shape, swap wires with another cyl and see if the missfire changes to that cyl.

Can you tell us what other codes you are throwing, if at all possible let us have the code numbers.

 

The car sounds like it could use a good tune-up.
STOP POURING ADDITIVES IN YOUR GAS, it's not good to use often if at all. It WILL damage your emissions equipment and rot out your cats.

Run a couple tanks of quality gas, not discount no name gas, then do a good seafoam treatment, then perform a propper tune-up.

 

hey thanks to all the help/replies i received about the car not running right! well we drained the old gas then (i'm glad we did this too) dropped tank and removed fuel pump. the sock on the f.p. was almost completely plugged with rust and junk. so we changed it(it was so bad i dunno how the car ever started let alone ran)and put everything back in/together, got some new gas put a thing of seafoam in and the car runs excellent! yay! i'm really happy so thanks for the advice and now i can have some fun

 

Glad it was this simple! Don't be a stranger on the forums now. Every bit of wisdom is wisdom someone else will be in need of down the road (or stuck in their driveway) =-D