New Mustang, unknown problems

PapaSmorzy

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I recently came into possession of of a 2004 Base Model 3.8 V6 Mustang. During my test drive I experienced no problems and of course the guy I got it from said it had no problems but, here I am so apparently not. My current most concerning problems are:

1. At some point in every drive, I have a problem where the car won't pass over 2000rpms and it pops and rattles but no power. If I leave a red light and this problem is happening, I can't go over 25 miles an hour until it "fixes" and I regain power. It doesn't happen all the time but probably about 75 percent of the time it's having this issue.

2. It's misfiring on cylinder 4, I'm not sure if this is part of the previous problem, but when I pulled the spark plug for cylinder 4 it was wet, and all of the contacts were gone, so I swapped a new one into it but I believe it is still misfiring. The other codes it throws has to do with oxygen sensors I think, I'll get a printout later today.

3. When I let off the gas pedal while driving the car slightly decelerates like it's rolling backwards or something.

Some evidence I've found of potentially concerning things:

The plastic antifreeze reservoir is cracked at the top.
The exhaust manifold is broken right before the donut gasket, I ordered and have received a new exhaust manifold, I just need to find a plug for it because it has an extra fitting on it.

A guy at oreillys said that these cars rely heavily on the o2 sensors to control the timing? Is this true?
 

96blak54

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1st off welcome to the forums

2nd go looking for stupid aftermarket add ons like ebay purchased performance enhaners or fuel mileage improvers that plug in between sensors, piggy back on the computer or plug into the obd2 port. These things simply dont work and create over looked headaches.

If their are any noticeable aftermarket parts they should be in question. Rule these out 1st. Then we can diagnose possible problems from there
 
OP
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PapaSmorzy

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Aa far as I know it's pretty much stock performance wise, it has an aftermarket air filter on because it got hit. And it has e3 plugs and pipes but other than that it's bone stock. The guy said maybe it has a tune on it, but he can't remember if it was before or after motor swap.
 

cobrajeff96

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Go to all factory ignition components, because almost every aftermarket coil/wire is garbage.

You fixed the spark plug, might as well replace all plugs and all coils or coil packs, whichever you have. Because they could all have a hundred thousand miles on them for all you know. Hopefully that will fix any misfiring, but if it was running like crap for a long time then chance the O2 sensors could be heavy with soot or oil residue etc. Might as well replace them too as they're not super expensive and they're easy to replace. I'd do that after replacing the ignition components though because you may not have to replace the O2 sensors if the problem is fixed beforehand.

Fix the coolant reservoir, don't want her overheating. Make sure to burp the air out of the system after filling it back up.

Clean the MAF sensor with either MAF cleaner. And be extremely gentle.
 

OpalFrostGT

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Welcome! These guys offer you the benefit of their experiences. Listen to them. Save your time and money by following their advice. Can't have better people helping you.
 

Adfalenski

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Change the fuel filter. No telling how much crap has built up in it. A clogged fuel filter restricts fuel flow which restricts fuel pressure which restricts engine speed. Also relieve fuel tank pressure before changing the fuel filter. Do this by opening the gas cap and then putting it back on.
 

mrwrong33

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Hi , first post , I,m in uk with 3.8 new edge , had all sorts of misfires , 4 and 5 , some times 1 and 6 as well , p 1309 etc , new cam sync and crank sensor didnt fix , cleared pcm did a new crank/ cam relearn , fixed every thing , as battery had been off for shipping to uk
 

Monday

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Wet plug??

Head gasket. Might even be a crack.
 

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