PLEASE Help me identify this problem. My 03 GT has about 150,000 miles on it. Last month during long trips (170 miles 1 way) my car would start to stumble around 3,000 rpms (3.73's @ 80mph). I would try to give it gas and it wouldnt go any faster, actually felt like it wanted to quit. I pull over, it idles funny for a second and then when i give it gas it cuts off. I was able to limp it to where i was going and had the spark plugs changed. I havent changed my fuel filter at all. My Superchips said i wasnt getting fire in the #1 and #5 cylinders. Had the plugs changed and it ran ok for about a day or two. It will start the day off fine, great acceleration and what not and after it has been in a constant drive with hanging rpms, if i go to pass a car or something it will rev to about 4500 rpms and then just feel like it is struggling and wont go any faster. What causes this? Spark Plugs, Fuel Filter, Pump????????????????? Anyhelp would be greatly appreciated! Thanks

 

i'd change the fuel filter. could be ignition wires going bad too. compression test?

 

ppl have been telling me that the Fuel Filters go bad/clog easyon the 4.6's. Ill try it. Makes sense like its not getting enough fuel past 4500 rpms.

 

definately get a compression test, but if that shows up ok, i would change fuel filter, throttle position sensor. and lastly fuel pump if still no luck

 

I have the same issue going on. I just changed the filter and it didn't do anything to help it out. So my next guess would be either the TPS or maybe a faulty injector. Let me know if you get it fixed ok. Thanks

 

how many cylinders are misfiring in urs jojo? if its just one, make sure its not clogged and change it with another injector for another cylinder, if it switches to misfiring there, you know its a cylinder, if it stays the same place. u know its not the injector.

 

also, you guys mite be leaking coolant in through the headgasket causing misfire. i just had that happen to me. blown headgaskets are about as common a problem as you can get on the 4.6s

 

I haven't had a scan tool put onto mine yet. It hasn't thrown any coeds, or lights yet. I plan on checking it probably the first week of Jan.

Is there any visual way to see if you are leaking coolant, or if you need to replace the gasket? I do not have any signs of anything leaking, whether it is in my plug wholes or on the outside.

 

I had that probo. After my 4v swap the car seemed to be looseing timeing after 4000 rpm. I put 93 octane in the car and it ran fine and pulled all the way to redline. Just to make sure that I was getting enough fuel though I installed a cobra pump. Havent had too many problems since. Just runs a little rich.