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Discussion Starter #1
I have a problem i cant figure out please help.My 03 Mach1 loses power when its been running for a while.Check engine light comes on when sitting in heavy traffic after running on highway.It is beast and performs awesome when its cold.When hot it loses power after 3500rpm.Runs great up to 3500rpm but really loses power after 3500rpm.Its seems like it is running to hot or something but fan comes on and temp gage is never over halfway.On the hills on highway it starts popping and very sluggish after 3500?I have changed plugs coil packs still nothing?I had the codes pulled and there was a misfire cylinder 5 so i replaced plugs and coil packs.Oh yea when it is doing that the pedal feels kinda spongy? And ther is only 45,000 miles on it car has never been abused and all maintenance done religously
 

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I knew you'd end up here bud. Hopefully someone can chime in and help. Welcome to the forum. I'll call you tomorrow.:bigthumbsup
 

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Discussion Starter #6
If the cats were plugged wouldnt it do it all the time or only when its hot? One more thing i forgot to add is when the coil packs were replaced with ACCELL"s it seemed to run worse.I replaced the old ones back in it run way better but still acts the same when hot..
 

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yeah, you need to check and see what code its sending, is the electric fan working, check the fuses for the fan, the cats could be stopped upp
 

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Discussion Starter #8
Hey man its sent a misfire code in cylinder 5,Fan comes on in sitting in traffic cant tell if its on while driving on highway though.And it seems the hotter the day the worse it runs?I will check the fuses and its getting the coolant flushed and system checked monday..If it were the cats would it throw out a code.One more thing the CEL hasnt been on in a couple days but still runs rough when hot.It loses power but rpms still climb.
 

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Discussion Starter #10
Thanks my friend would it only do it when its hot,It seems like it is running hotter would it throw a code it it was running to hot
 

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mine had the exact same problem and it was indeed misfires. there have been bad stories about those accel coil packs (and actually most poeple dont like aftermarket coils in general. they always like the ford motorcraft ones). i purchased a set of summit racing coil packs and havnt had a misfire yet. i would have gone with ford motorcraft but my dealer was trying to charge me $110 a pop.
 

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Discussion Starter #12
With the new ones it ran worse,Did your car do it only after sitting in traffic?Or on the highway.And it runs great and tons of power when its cold,the hotter the engine gets the worse it is.The temp needle is never over halfway?And it hasnt thrown a misfire code out since the code was cleared but the engine light comes and goes.
 

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I think the first [lace to look is the furl filter, that popping sound you hear under load is detonation, usually caused by a lean fuel mixture. You may have gotten a bad batch of gas, that can trash a filter in a hurry. Also check and make sure your air filter is in good shape and not being restricted or blocked.
 

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Discussion Starter #14
Thanks racin366,air cleaner MAF sensor all clean,But if it was the fuel filter wouldnt it do it all the time.Not just when its hot?When the car is cold it makes incredible power all through the rpm range.When its hot stops making power around 3000rpm when you floor it? and then no power but rpms still climb it just stops pullingI am quite certain pushing the throttle slowly it will still pull hard {NOT LIKE WHEN ITS COLD THOUGH} just not if you floor it.It feels to me like its chokin for air or starving for fuel..And yes acts like the air filter is plugged or starving for fuel when its hot.But if you pull over it revs great just not when :headscratch: under a load
 

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did i already mention the cats?:headscratch:and yes when they are starting to fail you first notice after they warm up:so
 

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and yes before i changed the coils it ran strong as hell when cold and after it warmed up it would missfire and like lurch under acceleration. it almost felt like i was running over some bumps
 

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Yeah, it could be the coils as well, it being dependent on temp is a bit unusual, most of the ideas so far are plausible, the cats, fuel filter, coils... I would probably start by going through the simpler stuff like the air and fuel filters, me I'd replace the fuel filter, its cheap and easy.
 

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Discussion Starter #18
Thanks gilomach,I had it in at ford today and they say its probably the fuel pump.I had them replace fuel filter today and it seems to be running better,drove it for an hour or so engine light came back on but still ran great!But it is cool outside today and usually runs great in the cold i will have to wait until a hotter day to see if its fixed.Ford told me when its hot out the fuel pump has to work harder and deal with more pressure in the tank.If its just the filter i got lucky if not its a $900.00 bill for fuel pump!!
 

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You can find pumps for a lot less than that if its necessary to change it. See if the problem comes back first, you may be set, otherwise I would go somewhere other than the stealership for a pump replacement, thats retarded to pay almost $1000 for a pump.
 

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Discussion Starter #20
Yea thats what i thought to LOL.Thanks for all your help!!I will keep my fingers crossed.The filter was hard to blow through and a bunch of black **** came out of it..
 
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