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Car Stalling On Decel

Hanaldo

By Hanaldo,
in Engines & Forced Induction

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Hanaldo Grand Master

Hanaldo

Posted
Posted

Hey all,

Sorry to start another one of these threads, but I've done a search and didn't find anything that quite matches my symptoms, so I was hoping someone here may be able to point me in the right direction. To cut to the chase, here is what my engine is doing:

http://youtu.be/-g0nValrfZY

Basically it struggles to return to idle after a quick blip of the throttle, and under higher load (longer rev or while driving) it stalls as soon as it comes off throttle. Now normally I would say this is pretty symptomatic of a vacuum leak, however my car is running on a MAP sensor. I really don't have any experience with how an engine functions on MAP sensors, but I was under the impression that air leaks would not cause the car to stall, is that correct? Is this more likely to be something like the IAC valve? If I turn the air con on and give it a quick blip, the engine will stall; so that leads me to believe it is the IAC?

A bit more of a background, I have JUST finished putting the engine back together following a full cylinder head recondition. The only things that have changed since I last drove the car are Tomei Type-B poncams (possible timing issue??), valve springs/retainers, and bronze valve guides. I have checked for air leaks, but everything seems tight and as previously mentioned, the car is on MAP. My external wastegate is also a leak at the moment as it seems to be stuck permanently open, but I didn't think this would cause the stalling issues?

Thanks for any help,

Martin.

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Gunzla Contributor

Gunzla

Posted
Posted

Probably need to get computer tune touched up. Maybe because of the new cams and flow rates of your head. Could have put

your ignition out of wack. Used to happen to my GTR, got it retuned and now I dont have any problems. But, then again it really could be something to do with getting your head put back on.

Hanaldo Grand Master

Hanaldo

Posted
  • Author
Posted

Yeh, that's what I'm worried about. If it's an issue with the tune then that's fine, I can get it to the tuners and they can do their thing. But I'm HIGHLY reluctant to give my car to the tuner when it's got issues, lest they then be stuck trying to sort out my shit :/

msports180 Mentor

msports180

Posted
Posted

If your wastegate is stuck open this would mean it has no vac/boost signal? So maybe the vac line you have hooked up to it is leaking through the wastegate straight to atmo? Causing both issues?

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted

Try raising the idle screw on IAC. Make sure its plugged in.

Be sure ignition timing is correct. But it sounds as tho its just in the tune.

Did u have cams last time it was tuned?

Not being experienced with MAP tunes, but does it utilise a deceleration fuel cut like AFM based ECUs?

I had a mate fully ulleh BOV and increasing the deceleration fuel cut rpm stopped it stalling off throttle blips or hey cruising.

Hanaldo Grand Master

Hanaldo

Posted
  • Author
Posted

Unfortunately with the Plazmaman, adjusting the idle screw on the IAC is impossible. But I guess if it's quite possible it's an issue with the tune being out then I'll sort out the wastegate and just get it to the tuners.

Hanaldo Grand Master

Hanaldo

Posted
  • Author
Posted

No not at all, it was perfect. But it's had some pretty major work done since it's been driving, and it's the first time I've removed/reinstalled a cylinder head. With the car running on MAP, I wasn't sure what I should be looking for; didn't want to take it to my tuner with potential leaks or other problems all over the place.

Problems like this:

560354_10151017032802541_1906570586_n.jpg

Anyone else seen a bent valve on a Turbosmart wastegate before, or know whether replacement parts can be had? I'm confused about how it happened, but I have a suspicion. The car backfired on start-up the other day, found a massive patch of soot directly under the screamer pipe afterwards, so it's clearly backfired through the wastegate. No idea why, or if it would cause this damage.

Hanaldo Grand Master

Hanaldo

Posted
  • Author
Posted

Ahhh true, I just had a look at the Turbosmart product info, and yes I'm missing the valve seat! I don't even remember it at all... Now I wonder where that could have got too :unsure:

That's a relief though, thanks Scotty! :D

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