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Discussion Starter #1
Ive been having some problems with my '93 LX 5.0L. It idles good but when i drive it after a while (mostly at higher rpms) it seems to miss. timing is correct. Does anyone know what might be the problem?
 

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plugs, wires neeed replacing...run 93 octane...add Kenne Bell Boost a spark...good luck
 

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I'm guessing by your timing is correct means it's stock. You don't need higher octane gas unless you advance the timing in most applications. Check the plugs and wires first since it'd be the easiest. Then check if you're getting proper fuel pressure. The regulator on these year stangs are known to have issues with failing. By miss you do mean heavier vibrations at those higher rpms right?

I'm betting fuel on this one just because I'm having the same problem. At idle my fuel pressure is close to correct, but when I give it throttle it drops more and more as I give it more.
 

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one more Q ... did you check out any leaks ? from intake? headers? ... etc.
 

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Discussion Starter #5
at times it backfires a little like the fuel isnt being ignited from one or more cylinders. the exhaust smells very rich as well. i checked the plug wires and i didnt see anything wrong with them that might make them arc off the headers maybe, left it running and watched to see. didnt see anything. they are new spark plugs also. only started happening after i put the GT40P heads on. wasnt as bad as it id now though. come to think of it i changed my injectors when i swapped the heads.. maybe theres something up with the injectors? they arent new but they are off the explorer i got the heads from. '98 was the year.
 

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Discussion Starter #6
ive checked and havent found any vacuum leaks.
 

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Discussion Starter #7
timing is set as it would come from the factory. also there are times when the car runs perfect even at higher rpms. sometimes it starts at 2.5k sometimes its 4k.
 

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just a thought

This is probably unrelated but something to think about. Did you upgrade the valve springs on those P heads before install? As I understand it the stock springs that came on the P heads couldn't even handle the stock Mustang cam and would coil bind.
 

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Did you buy used or new injectors
 

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he said used injectors, and did you have the heads checked before installing them? might have a valve hanging open if its firing back through the intake
 

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he said used injectors, and did you have the heads checked before installing them? might have a valve hanging open if its firing back through the intake
Aye good call missed that lol. Could be a plugged injector(s) not being able to allow enough fuel through at higher RPMs. I think if it was though you'd feel it at least a little bit at all times.
 

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Discussion Starter #12
thank you guys, im not using the stock cam though. i have an E303 and no all i have done is cleaned up the heads before i put them on. i had asked a couple people and they told me that would be fine. Hoping i wont have to pull them off and do that lol. about to go swap my injectors so we will see what happens :p ill let you know. thank again
 

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Well that is your problem right there as the stock springs are weak and not even enough to support a stock mustang cam.
 

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Discussion Starter #14
i still have the stock heads in the garage. what if i were to just swap the springs? can i do that?
 

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Discussion Starter #16
ok, so im going to change the valve springs. any suggestions on brand or what ones?
 
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