Bucking in 5th gear

[jaboy_x01]

Hello,

I was referred here by a friend who thought you might be able to help me. I have a 2003 Mustang GT. Yesterday, on the way home from work, I was coasting down a hill in 5th gear @ about 50 mph. When I got to the bottom of the hill, I gave it very little gas just to keep going. About 10 seconds later, it started bucking pretty bad. I let off the gas and it stopped. I tried to reproduce the problem, but it doesnt happen in any other gear except 5th. When I am at lower RPMs, below 1500 and just give very little gas, it just starts bucking. The oil pressure didnt jump or anything. Since my car is out of warranty, I wanted some input on what it might be before I spend a ton of money with Ford for them to tell me it was a 30 second fix. As for mods on my car, they are minimal. I have a CAI, steeda springs, bilstein shocks. Most everything is still stock, including clutch, and I have 62,000 miles on it. Any input would be a great help. Thanks.

 

[jaboy_x01]

I tested it again on the way home today. It does it in all gears at low RPMs, between 1000-1500. I guess I shouldnt say bucking, bucking would be more like a clutch issue. This is more like it is running outof gas. It is also idling quite rough. I forgot to add a mod earlier of SLP exhuast. When idling it make a very distinct blurping noise that is also visible on the tach. With each blurp, the RPMs drop for a split second then right back up. Last week I used seafoam, just to make sure that it wasnt just buildup or anything. Almost a week later, I am still getting black soot from the exhaust, but only from the drivers side. At WOT, there are no problems, it seems fine, but when you try to go WOT, there is a delay from when the power kicks in. The Check Engine Light is not on. Anyone know what could be the problem?

 

[Mustang5L5]

Sounds like misfire under load.


See if you can have the codes read at autozone or somewhere. Check the plugs and COP and make sure they look good and the plugs are not overly worn. Maybe even replace the plugs.

 

[SRMobile]

How did you go about using the seafoam ?

How much millage is on the car ?

 

[silver4.6]

With the black smoke on one side, it sounds like your running rich in that one bank. Maybe you've got a fouled plug, sticky injector or even a bad cop. Change your plugs, it's a cheap and easy way to narrow it down a little.

 

[jaboy_x01]

How did you go about using the seafoam ?

How much millage is on the car ?

I just put it through the pipe to the intake man. It pretty much sucked it out of the can. I did it by myself so I had to stick a rag on the TB stopper so it would stay running. It smoked more than I do, and that is quite a bit.

As for milage, I am just over 65k.

I guess all of this crap started, the rough idle, after I took it to a local shop to get some normal maintenance done, plugs lube etc. Apparently, they didnt have a clue what they were doing and attached the vent from the other valve cover to the PCV valve and the PCV intake man port was plugged into the CAI. It ran like **** on the way home, when I looked under the hood I found their screw-up and fixed it. It seemed like it ran so much better after that, maybe cuz it was running like **** when I took it home. Pretty soon after that was when the rough idling started. It has been getting worse ever since. The other day when I noticed the bucking/jerking, I had noticed that the idle is even worse now. It pretty much sounds like the 68 cam'd out GT 390 I had, with the loping and all.

I just picked up some new plugs on the way home today, I am about to go change those and see if that helps.

 

[DBMSTNG]

Sounds like misfire under load.

it's not a load issue if he's coasting down a hill and has momentum and barely gives it gas.

 

[DBMSTNG]

when the car idles, does it run fine for a few seconds, burble and drop rpm, then run fine again for a few seconds? if so, it may be an intermittent COP problem. it won't show up in the check engine codes unless it happens more than 2% of the time.

 

[jaboy_x01]

when the car idles, does it run fine for a few seconds, burble and drop rpm, then run fine again for a few seconds?

That is exactly it.

I just got done changing the plugs, and I about died after starting it. After they were changed, I was going to let it idle to see how it did. I started it up, lit up a smoke and walked around behind the car to hear it better. As soon as I got back there, I was almost K.O. by the smell of gas. I put the smoke out quick (yes, I still have my eyebrows), and killed the car. The plugs didnt look bad at all.

Now that it may be a COP problem, how do I figure out which one is actually having the problem? Is there something that you can plug into the COP to test it, or do I need to replace all of them.

Here is one set I found:

http://www.mustangsunlimited.com/itemdy00.asp?T1=AB101+01

Or should I just buy the Motorcraft version that is like $70 each.