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Old 07-16-2010, 07:31 PM   #1
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Exclamation check engine light misfire code

hi everyone i just joined this sight and i need a little help. i have a 1998 mustang gt with 90k miles on it and i just swapped the intake manifold because the stock one had a crack on the coolent runner right next to the alternator and it was spraying everywhere and the coolent would get into the spark plug holes and cause them to short out. after i swapped the manifold it is now giving me a P0303 code and thats a misfire code on cylinder 3 i have replaced the plug and the wire and it still gives me this code. now it seems to miss randomly sometimes it runs great and others it has a terrible miss is it possible that the injector is failing? i have unpluged the injector while the car is running and it didnt make any difference in in idle but could that just be because the cylinder isnt firing at all? i am a really capable machanic i do it for a living but this problem has me stumped so any help would be greatly appreciated thanks.

ps the new manifold in an oem manifold it isn't an aftermarket one
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Old 07-16-2010, 10:50 PM   #2
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Re: check engine light misfire code

With the 98 I believe you still have the two front mounted coils on the 4.6L. Try swapping them and see if the misfire jumps to another cylinder. Also, and I'm not trying to belittle you, pull the plug wire on the cylinder and install it again with some dielectric grease and push it back on until you hear and feel it snap. I went for months with a misfire that I couldnt figure out until the third time I reseated the plug wire, it snapped into place and its been running great ever since. Sometimes its the weird things that get you. Inspect the injector harness as well, maybe there is some residual moisture in it thats causing an intermittent short.
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Old 07-16-2010, 11:30 PM   #3
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Re: check engine light misfire code

hey thanks for the fast reply ya i never thought to switch the coil packs thats why i love hearing other peoples opinions most of the time they think of something you over looked i will look into this tomarrow and post back with the results
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Old 07-16-2010, 11:41 PM   #4
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Re: check engine light misfire code

Sweet, good luck. That trick helped me in the past.
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Old 07-17-2010, 11:54 AM   #5
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Re: check engine light misfire code

ok i checked spark and i have spark at all cylinders i used a noid light on the injector wiring all the wires are working and i used a stethascope on the injectors and they are all firing i have no clue whats happening now and it through another engine light but this time its a cylinder 4 misfire any ideas now?
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Old 07-17-2010, 12:04 PM   #6
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Re: check engine light misfire code

Was this after swapping coils?
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Old 07-27-2010, 09:27 AM   #7
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Re: check engine light misfire code

no i replaced the sparkplug in cylinder 3and then it started misfiring on cyl 4 so i wiggled the plug boot on 4 and it stopped misfiring so i replaced the plugs and wires and havent had problem with it yet

it turns out that the coolent got into all the plug wires on the passenger side and corroded the clip that grabs the plug and i guess this car has never had new plugs in it because the electrodes were gone! so with the new plugs and wires it feals like it has a lot more power than it did before

thanks for all your help
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