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Old 08-07-2012, 07:33 AM   #1
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Default Help! Engine suddenly Revving at 4-6000..

Need some advice / suggestions please.

This has me stumped, did a full track day 3 days ago (saturday) without missing a beat, then drove it back home 50min trip.

Went to move the car out of the garage tonight to help my nephew on his car and the car backfired in the intake on turning on ignition, ran on 3 cylinders for about 2 mins and then settled evenly on 3-4000rpm idle.

I gently drove around the street thinking that would sort it out and it hasn't.

Left it for 2 hours, started it again, idles straight up around 4000rpm...

Anyone have any ideas where to start?
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Old 08-07-2012, 08:48 AM   #2
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Vac leak after the throttle body. Check for vac hoses not connected, broken or cracked. If you dont see anything bust out the carb cleaner and start spraying around while the car is idling, when the car bogs you sprayed near the leak.
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Old 08-07-2012, 09:45 AM   #3
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Agree with leafy. Backfire may have blown off the hose cap on the back of the manifold or one of the seals on the injectors.
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Old 08-07-2012, 04:39 PM   #4
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Thanks, will check that out!
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Old 08-07-2012, 07:20 PM   #5
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Okay no obvious hoses off or holes I can find...BUT there is a strange mist or steam coming from the engine bay...

Is that likely to be injector related...? Atomised fuel (though it doesn't smell like fuel...)
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Old 08-07-2012, 09:31 PM   #6
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Sounds like some sort of intake leak, intake gasket,Hoes. Backfire caused something pop off
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Old 08-08-2012, 06:42 AM   #7
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Okay, so it looks like I may beed to pull IM and check some ---- out. As such I have some questions...

- Are there any mods I should do while IM is off?

- There is a mod to the fuel rail soemwhere around here, at 6, soon to be 8-9 psi is it worth doing?

- Car frequently backfires on ignition, is that likely a leaking injector?

- Is the IM gasket reuseable or do I need a new one?

- Are the supports for the IM required, was there any concensus on the butterfly shaft screws breaking being related to IM support removal (can the 1600 IM even remove the runners..?)

- Is there any point in port matching or flowing the IM while it is off?
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Old 08-08-2012, 09:35 AM   #8
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Pull the intake first to make sure the butterfly is seating well and there isn't a POS holding it open. Yes a leaking injector can cause the backfiring. The support, in my mind is superfluous, I have about a dozen of them if people want to re-install.
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Old 08-08-2012, 09:40 AM   #9
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The support, is necessary if you race, IMO. You will break a tb shaft if you take it out and actually race hard. I mean you've got to be running faster than SM.
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Old 08-08-2012, 09:46 AM   #10
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Quote:
Originally Posted by Leafy View Post
The support, is necessary if you race, IMO. You will break a tb shaft if you take it out and actually race hard. I mean you've got to be running faster than SM.
Not arguing with you, but what forces are thought to break the tb shaft? Harmonics?

I can understand a severe bounce affecting the structure of the IM with no support, as can a severe bounce affect a starter with removed support, but the throttle body shaft eludes me.
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Old 08-08-2012, 09:51 AM   #11
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I'm going to go with harmonics. Because it seems like cars that must keep the brace on to be legal almost never break shafts but ones that take it off break them. The intake vibrates, its cantilevered off the vibrating engine and it vibrates from the air inside it, so the extra stiffness and weight provided by the brace changes the natural frequency of the manifold and tb.
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Old 08-08-2012, 09:23 PM   #12
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Thanks guys.

Older guy, the harmonic thing was a theory develping in the thread re broken throttle shaft/screw issue, which was why I asked. I don't know if it was ever proven or disproven but wanted tosee current reaction...1 for and 1 agaisnt is a bit inconclusve though!

anyway, leaves a couple of questions if people could jump in.....

- There is a mod to the fuel rail somewhere around here, at 6, soon to be 8-9 psi is it worth doing? (my search capability on this site is terrible, any links welcomed!)

- Is the IM gasket reuseable or do I need a new one?

- Is the result worth the effort, in port matching or flowing the IM while it is off?
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Old 08-08-2012, 09:26 PM   #13
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You could reuse the IM gasket, but why take the risk and have to pull it all apart again. Course your might break it taking it off the first time. What mod do you want to do to the fuel rail? The stock one is more than plenty for what you want to do.
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Old 08-09-2012, 02:14 AM   #14
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Thanks Leafy. Some gaskets are reuseable I just wasn't sure if it was or not, sounds like not. Will order one. I'm going to pull the injectors this weekend, I presume that can be done without much associated dismantling...

SO much info here, hard to know whats relevant or not...The fuel rail thing (from memory) was opening up the closed end and looping it around to even fuel flow/pressure across all cylnders ....I may have that totally wrong...?

But while everythings apart I was just trying to do what should/could be done to improve.

If it's not required I won't waste my time. Ideally I would be running 12 psi boost but i'm doing it in slow planned stages..8-9 is next and will be it for the next year or so at least. (famous last words...)

Cheers.

Last edited by mx5-kiwi; 08-09-2012 at 07:57 AM.
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