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Old 10-08-2008, 10:45 PM   #1
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Question Getting hestation af 5000 rmp

Hey guys i got a problem I have a 91 GT. When i'm driving normal my 5.0 doesn't hesitate, but when i start to floor her and hit 5 grand i get back fires and hesitation. I noticed it on first and second gear and then I stopped. Oh and my car is manual. I have no clue2:
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Old 10-10-2008, 10:05 PM   #2
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Re: Getting hestation af 5000 rmp

is it throwing any codes?

how many miles?
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Old 10-11-2008, 12:26 PM   #3
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Re: Getting hestation af 5000 rmp

Sounds like a spark issue but it's hard to diagnose a care over the internet. Like silverstang said, are there any codes, any other things it's doing? Is your car modded at all?
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Old 10-13-2008, 12:27 PM   #4
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Re: Getting hestation af 5000 rmp

how do I find out if it's throwing any codes? I know the check engine light will come on every now and then but then it shuts off. It's wasting a lot a gas too. It has cams but that's all i know.
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Old 12-13-2008, 04:53 PM   #5
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Re: Getting hestation af 5000 rmp

try to clean the mass air flow sencor
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Old 12-19-2008, 02:49 PM   #6
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Re: Getting hestation af 5000 rmp

Had the same prob. Its worth tryin to replace the ignition module & stator in the distributor,that fix my 93. The parts are cheap enough & the labor is simple you wouldnt be out much if it didnt take care of it, but i think it will!... what mods do you have, your not floating valves are you?.. may need stiffer springs to close the valves at high revs!
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Old 12-22-2008, 12:46 PM   #7
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Re: Getting hestation af 5000 rmp

what are floating valves?
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Old 12-22-2008, 09:26 PM   #8
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Re: Getting hestation af 5000 rmp

Valve float is happens at high RPM's. If your valve springs are not strong enough, the valve will stay open (aka float) when it should be closing. It really is a bad thing, haha. You also don't want to go with too strong of a spring for the cam as well, this also produces bad things.
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Old 12-23-2008, 12:09 PM   #9
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Re: Getting hestation af 5000 rmp

Wow i really don't know cuz i'm a newbie with the 5.0 and only had it for 3 months. i noticed that it doesn't do it all the time sometimes it runs smooth. But just the past few days when somebody was trying to race it started up at 3 rpm. How do i find that out.
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Old 12-23-2008, 01:03 PM   #10
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Re: Getting hestation af 5000 rmp

If it's happening around 3000 rpm it's most likely not valve float. The valve springs would have to be so weak that they would barely function to be doing it at that low an rpm. To figure out if your springs are bad you need to remove them and use a valve spring pressure tester to see what kind of numbers they put out. Whether you're taking the heads off the car or doing it in car, it's a pain. You also need to have the little tester, the specs for the springs, and the know how on how to use the tester/calibrating it. If not, you need to take the whole head to the machine shop and have them do it. Also, if you do it on the car, you need to use air to keep the valves from falling down into the cylinder when you remove the springs. I would look into the more obvious systems first. Check for fuel, spark, and compression/leak down and see what kinds of numbers you get.
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