Need help if any of you could...when i accelerate from zero it's fine until it gets to 2000rpm, then it starts to misfire and struggles to go faster than 40mph. so i run the code and it says cylinder 1 misfire and the lean code comes on as well. and just everybody knows, i installed a new cop on that cylinder so it can't be that. i'm guessing it might be a vacuum hose leak, but im not too sure. and also this happens when the engine is warmed up, when it's cold theres no problem. so if anybody can give some insight, it would be greatly appriciated.

03 Expedition 5.4L

 

So nothing changed with the new COP ? and you had just those codes , which lean code? What bank? , that could be important ? - How did #1 plug look , or diidn't you check that yet ? I would pull the plug at this point - see how it looks.

What kind of plugs are you runnin?

 

I had the same problem on a 5.0L, would not rev over 3000rpm sputtering and running like crap. I went through the entire ignition system, fuel system etc, so before you go and spend a bunch of money throwing parts at it, pull your mass air meter and clean it gently. Its free.

 

i changed them with the motorcrafts and cylinder 1 looks good. and the leand code came up as P0172. the problem was happening before i changed the plugs then i put in the new motorcraft plugs and the engine runs better but until i rev the engine to 2000rpm, the it goes to **** after that. I'm guess the miss fire is from the lack of air or fuel, becaue the COP is brand new and so is the plug and the fuel injector is spray fine, because everthing is fine at idle and at low revs, it only kicks when i accelerate past 2000rpm (which opens the throttle body to let air in.) so i'm hoping its the vacuume hoses... but i want to be sure.

 

ohh yeah and when i changed the plugs i cleaned out the mass flow like crazy with that CRS mass flow cleaner. so i'm pretty sure it's not that.

 

Yea , you have a low grade misfire. Usually after replacing just one COP - you end up replacing the others soon after.

The Misfire monitor will not pickup "low grade" miscue's.

To save youself some time and to keep you from pulling your hair out on trhis one , just replace ALL ignition COP's with 8 fresh ones .

Keep the one that you just bought for a spare and hit up Global Automotive for a set.

Total Price = $96 for the complete set.

This is the quick way out of your probelm , Heres Globals Link -

http://cgi.ebay.com/ebaymotors/NEW-I...mZ160111254456

 

so jbrew... you don't think it would be a vacuum leak...i really have to get all new COP's?