2000GT-JR

Hi gang,

I have a 2000 GT Mustang with the 4.6L V8. It has about 88,000 miles on it and original everything except tires and the IAC valve (of course).

Just in the last month it has started running rough. It has some miss at idle though not a whole lot worse than it was when new. It is most noticeable at low RPM from say 700 up to 2000. After that it smooths out enough that it doesn't buck the car anymore (the bucks are very small - not big). I have no MIL illumination and no codes are returned by the OBD-II tool (nor freeze frames).

I have been through multiple tanks of gas and it seems like it is getting fuel though I suppose I could change the fuel filter to be safe.

I have checked for vacuum leaks but haven't found anything definitive. The plugs and coils are all factory original.

The problem seems a bit worse after the engine warms up. When it is very cold, it is hard to detect but once it is good and warm, any demand on the accelerator at low RPM will result in intermittent power delivery. There is usually a very small buck then a period of decent power delivery but there may be other hick-ups along the way as I accelerate until into the better running 2000+ rpm range.

I must say I'm pretty disappointed in the OBD-II codes system. Does anyone know just how bad a misfire has to be before it can register in the OBD-II system? I was hopeful it would tell me the exact cylinder with the problem (can't imagine this is more than one or the problem would be a lot worse). However, the OBD-II tool returns NO codes.

I probably need to replace plugs by now I'm sure but I've always taken a leave it alone if it ain't broke attitude up til now. Also, I have not removed the coils/plugs before. Are there any special considerations to be taken in doing so? Is it hard to do? Any online recommendations for instructions? I'm ok with vehicle maintenance - just haven't worked on these before and don't want to goof them up due to ignorance.

Thanks for any tips/comments!
Jerry

reznap

Before you do anything, with the car running jiggle the injector and coil harness plugs... make sure your problem isn't something simple like a bad connection. I had a miss due to a loose injector harness plug that I knocked loose when changing coils/spark plugs.

Seems like a good place to start, the plugs at least. It's not bad, you only have to remove the intake tube from the throttle body and air box and move it out of the way. The coil packs are held down with a single fastener, twist and pull them out right around the fuel rails, piece of cake. You'll need an extension and universal joint for plugs, I used a 3/8" drive. Be careful removing the plugs, they can break in half if you're too hard on them (you don't want that). I think the reverse torque limit for taking them out is 17 ft-lbs... could be a little off on the number, so squirt them with some penetrating oil or wd-40 before attempting to remove and use a torque wrench if you can in order to not exceed the 17 ft lbs. Also don't remove them when the engine is hot.

If I'm not right on the 17 ft lbs, I'm sure someone here will correct me.
Also be careful not to get dirt or debris into the plug holes, and if there is anti-freeze/water or anything around the plugs, clean it up and make sure it's dry before removing them.

I'd replace with whatever Ford puts in there... motorcrafts I think. No need to get fancy, same with the coils if you replace those. I know I have aftermarket brand stuff - but most will agree there's no reason to stray from the OEM stuff. Gap for the motorcrafts is 0.054" I believe.

Torque specs on the plugs going back in is 13 ft lbs (I think - double check that somewhere). Seems low to me. You can use a drop of anti-sieze but that will increase resistance to turn so it's ok to bump it up a few ft lbs (edit: I know some people here will disagree with me though and I think the specs call for 13 ft lbs even with anti-sieze). In either case, you really have to be careful doing plugs on these cars though, between the aluminum heads and the lack of threads the plugs have to hold on to it's easy to F it up royally and have a plug back out on you.

devongarver

read my sticky in my sig

2000GT-JR

Thanks very much guys. This is some great information. I will give thought to what you have said and let you know what I find out. Thanks for taking the time to share this info with me. I am hopeful it is simple.

Do you have any opinions on why I can have a fairly significant mis-fire like this and yet it doesn't get captured by the engine computer (doesn't show up in OBD-II codes)? Seems like it must have to be really bad before it gets logged there then.

BTW Reznap - your stang looks a lot like mine - Red! :O) (Mine's the convertible!).

Thanks again to both of you!

Jerry

reznap

Mine was only missing for 30 mins or so and it never left my garage while it was happening, but I also never got a code. And it was a VERY significant miss. Basically if I just went out to my car and unplugged an injector from the harness... wasn't squirting at all in the rear cylinder on the right (driver's side) bank. The car sounded like it was cam'd almost and the idle was rough.

I pretty much got lucky while trying to isolate the problem by unplugging each cylinder's coil pack, one by one... then moving to injectors (this might not be the best idea, but I didn't imagine it would hurt anything). It was the last one I tried, unplugged it, engine didn't react so I knew that was my issue. Cleaned the plug up with wd-40 and it's been good since.

I've told this story like 3 times here so I'm sure people are sick of hearing it. Gotta start with the basics before you throw expensive parts at it though.

Enjoy the 'vert!

gunpig0313

Alot of times when you have a missfire it wont throw a code especially if the miss doesn't happen that often. It's often enough to be felt, but doesn't pose a problem to the computer so to speak. You can take the car out for a long drive and see if it will throw a code, but reznap has some good suggestions to pinpoint the problem also.

2000GT-JR

Ok, thanks again guys. I will give those things a check and see what I find.

I noticed driving home from work tonight that it is indeed much worse once it warms up. I have maybe 5 minutes after starting it cold before the hickups start. However, mine does it pretty much any time I demand power at low RPM once it's warm. (By that I mean, all the way home from work). That's why I figured it would throw a code but apparently not.

Well, after 88000 miles, I wouldn't be surprised if a plug or coil (or two) were going south. It's been a fantastically faithful vehicle and I've not babied it over the last 10 years either! Ford earned their "Ford tough" claim on this car; that's for sure!

Happy motoring and thanks again,

Jerry

devongarver

I'd put money on a failing COP if it gets worse as it warms up. Resistance changes with heat, making it harder to fire the plug. i.e., as your engine comes up to normal temp, the bad coil is only getting worse. Try the method mentioned above, unplug COP one at a time and listen for a change in idle. If it changes, its not that one, if it doesnt, theres your source. I know Im repeating, I just dont want you to waste your time looking elsewhere first.

Eagle2000GT

At about the same mileage I had a miss that didn't throw a code (at first). It finally got bad enough that it did. It was a COP.

2000GT-JR

Ok, thanks again Devon and Eagle for sharing your thoughts on this too. Great suggestions all around (nice sticky article too Devon!).

Man it is such a fantastic thing to be able to meet nice folks such as you and get this kind of advice! Just super! I am really pleased I found this forum.

I can't thank you enough and I'll let you know what I find as soon as I can get some time under the hood.

Thanks again so much!

Jerry