Low RPM Pull Stutter and Sputter

[clarkdanimal]

Hey Everyone, (first post woot!)
Got a question for you guys. My 2002 bone stock GT has developed a stutter when asking for hard acceleration in say second or third gear at 1500-3000 RPM. When this first started, I did get a CEL and a Cylinder #3 Misfire code. I swapped the COP from cylinder 3 to cylinder 1 hoping to get a cylinder #1 Misfire but I havent gotten another CEL while the problem persists Here is what I have tried so far........

1) Checked to make sure I didn't over oil my K&N and dirty the MAF (Everything in the intake path looked clean)
2) unplugged each injector (one at a time) while the car was running. (noticable change in idle each time so I know the injectors are at least firing)
3) Replaced the Fuel Filter (55000 miles why not)
4) Fuel pressure was off the scale of the 50 psig tire gauge I was using when revved.

Another note, the car idles fine and seems to run ok at higher RPM, it only happens when under hard acceleration at lower RPM

I have a couple more ideas.... clogged cats or bad gas
Help would be appreciated!
Thanks!

 

[patman0911]

I would check the ignition system - mis-seated COP, moisture in spark plug wells or defective COP boot or bad COP being the most likely causes. Check the plugs and make sure none are loose.

I had the exact same issue a month or two ago and the misfire wasn't present at idle so pulling plug wires and injectors didn't help narrow it down. It was really noticeable under load at low RPMs but seemed to get better as the RPMs rose - it was probably still there but the engine tends too smooth out as RPMs increase making it less noticeable.

 

[eliteJAE]

I have the SAME issue right now, i was going to start mine own thread but I guess ill just post whatever is different on mine and see what responses you get on here.

The big difference in mine is that the misfire started right after replacing the battery and driving it around on 3 week old gas (i left it parked for about 3 weeks without moving it). So i threw in some injector cleaner, ran it and the misfire went away from idle after awhile and now it's only present under load in 3rd or 4th gear. Just replaced oil, oil filter and fuel filter, and misfire came back for a little bit at idle then went away.

-How do I test for bad COP's?

-No CEL's, no coolant loss.

-Plugs/boots were changed about 20,000 miles ago to motorcrafts so I doubt it's that.

-I do NOT pressure wash under the hood (learned that the hard way lol...)

-I have no cats (O/R H pipe).

The only thing I haven't changed on the ignition are the COP's themselves, they are still the original coil packs, and nothing else seems to be wrong. Would bad gas cause this at all?

I almost feel like just ordering a set of accel coil packs, but I dont want to risk that not being the problem and being out $300, which is why I need to find a way to test the COP's.

Could a loose battery terminal cause this? That's about the only problem I can identify.

 

[eliteJAE]

I used the trusty search function and found a thread that explains it all....

http://www.stangnet.com/mustang-forums/675780-99-gt-still-missing.html

hope this helps man, I'm leaning towards new coils if it isn't bad gas

 

[clarkdanimal]

Thanks everyone for the info this forum rocks. Interesting that you say your car sat for a couple of weeks. Mine sat for a while too. I'm going to check for debris in my plug wells. I have heard nightmares about replacing the plugs on na 4.6 but I'm gonna give it a shot once I run the rest of the 1/2 tank of gas.

 

[wmburns]

Clean the MAF

Question? How do you tell by looking that your MAF is clean? Esp. when used in combination with an oiled air filter?

It sure seams to me that a dirty MAF would have similar symptom. Save yourself some possible headaches and clean your MAF with MAF cleaner. This will elimate this as a possible problem source.

Note, the thread referred to also mentioned a dirty MAF.

I seam to recall reading threads with spark problems. Turned out to be damaged insulation on the COP boots. Apparently, you can buy just replacement boots. Saves the $$ verses buying a whole new COP.

 

[eliteJAE]

Yeah you have a point there. Today I did this:

-Oil Change
-Oil Filter Change
-Fuel Filter Change
-Cleaned MAF with MAF cleaner.
-Cleaned and Oiled my K&N

And the problem is getting less and less noticeable, like its going away, which leads me to believe it was bad gas and debris from letting it sit so long and running it dry on that same gas. I still notice some misfire under load in 4th gear, but it's becoming less and less noticeable.

No doubt my COP's are probably crapping out though, doing everything I did today is a ban-aid at best, I'm sure i'll have to change them out, because I looked under the hood today and found that I have 5 OEM COP's and 3 Autozone/Aftermarket COP's (previous owner) which means those three crapped out, so the other 5 are probably doing so as well.

any opinions on the granatelli cop's? accel?

 

[clarkdanimal]

Just won (7) COPs on ebay for $14.00. Gonna swap 'em out one at a time. I'll keep everyone posted.

 

[clarkdanimal]

One bad COP.... I got the CEL #3 Misfire so that's the one I started with. I replaced that one and viola! all better. Thanks everyone for the help