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Misfire In 3Rd & 4Th 4000+Rpm


oplock27

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  • Member For: 12y 2m 11d
  • Gender: Male

Hi Guys,

Did a search but not having much luck. Car recently started spluttering/backfiring under wide open throttle in 3rd and 4th gear from about 4000rpm onwards. Havent gone quick enough to see if same thing in 5th and 6th but would assume so. Funny thing is it pulls strong in 1st & 2nd through full rev range. Could it be starving for fuel? Replaced plugs and igniters about 20000km ago and fuel filter about 5000km ago. Specs as follows:

'03 BA xr6t sedan 6spd man

12psi off the shelf tune

K&N filter in stock box

Additional snorkel

Always 98 pulp (bp ultimate usually)

Edited by oplock27
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  • Member For: 11y 9m 28d
  • Gender: Male
  • Location: Liverpool

Low fuel? Mine does this when around the 1/4 tank. But once it has more in it it's fine.

Otherwise could be coils? Plug gap?

Does it only do it at certain times?

Edited by Peppy_t92
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  • Member For: 12y 2m 11d
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Had 3qtr tank so plenty of fuel.. Will check plug gaps. I've been reading that maybe over boost is cause so might look at replacing actuator. Mainly just under load in 3rd and 4th. It was fairly noticeable tonight and it was a fair bit cooler tonight.. Car was fully warmed up though. 160000km on clock. Do dodgy valve springs have this effect or do they cause or a more sudden failure?

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  • Member For: 13y 9m 9d
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  • Location: Sydney

Wat do u mean by off the shelf tune?

You gotta regap your plugs when tuning time comes.. more boost blows em out.

This cold weather will see a fair few cars overboosting.

If its a generic tune at 12lbs I think your nuts lol

Edited by Kroozin
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  • Member For: 11y 9m 28d
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I forgot to mention valve springs, but yes that is very possible, ba's have the weakest springs as far as I know.

You would of been told to gap the plugs to 0.75 when the tune was sent to you.

Boost spike is possible especially with this cool air and a generic tune doesn't help either.

I run an e-boost soo I control the boost as needed

Edited by Peppy_t92
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  • Member For: 12y 2m 11d
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I forgot to mention valve springs, but yes that is very possible, ba's have the weakest springs as far as I know.

You would of been told to gap the plugs to 0.75 when the tune was sent to you.

Boost spike is possible especially with this cool air and a generic tune doesn't help either.

I run an e-boost soo I control the boost as needed

Just out of interest is the e-boost easy enough to wire/plumb up yourself? Might put one in

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  • Member For: 11y 9m 28d
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  • Location: Liverpool

It's pretty easy to install, and you will need a tach driver to pickup the rpm signal. But I definitely suggest some kind of data logger and sone mechanical knowledge to tune it right.

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