Misfire issue only in 4th gear.
06-02-2009, 05:02 AM
#1
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Misfire issue only in 4th gear. Got a missfire with my tt iron block 402. just had the hot side replaced from a log setup to a stainless header setup with tial 44mm wastegates. the turbo's are garrett gt35r's with .63 exhaust housings.
it has a slight misfire when the turbo's come on but only in 4th gear. every other gear it revs perfectly clean in 1st, 2nd and 3rd.
the shop have tried changing the ignition timing, and running it rich, and leaning it out. we've swapped plugs, wires, coils. but no matter what we do it still does it.
i'm getting the car back tomorrow because they aren't getting anywhere with it, and are of the opinion it might be the valve springs. but they're not sure.
I'm going to pull the covers off and have a look for a broken spring, check the spark gaps and close them down to .025" and give that a try.
it has tr6 plugs and comp 921 springs in it. so far it's only been to 13psi boost.
has anyone else had this? what are some other things i can try while i have the car back?
it has a slight misfire when the turbo's come on but only in 4th gear. every other gear it revs perfectly clean in 1st, 2nd and 3rd.
the shop have tried changing the ignition timing, and running it rich, and leaning it out. we've swapped plugs, wires, coils. but no matter what we do it still does it.
i'm getting the car back tomorrow because they aren't getting anywhere with it, and are of the opinion it might be the valve springs. but they're not sure.
I'm going to pull the covers off and have a look for a broken spring, check the spark gaps and close them down to .025" and give that a try.
it has tr6 plugs and comp 921 springs in it. so far it's only been to 13psi boost.
has anyone else had this? what are some other things i can try while i have the car back?
Last edited by joffa; 06-02-2009 at 08:38 AM.
06-02-2009, 07:07 PM
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changing the timing doesn't have much effect. It's got ngk tr6's in it. I'm not sure what they've gapped them at. I'll find that out today.
My cam has .580 lift and the springs are rated to .620, would shimming them up 30 thou make much difference if it's a valve issue. The springs are about 2 years old but have not even done 10,000 miles.
My cam has .580 lift and the springs are rated to .620, would shimming them up 30 thou make much difference if it's a valve issue. The springs are about 2 years old but have not even done 10,000 miles.
