Author Topic: Overboosting  (Read 2552 times)

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Offline fez200

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Overboosting
« on: Aug 18, 2006, 02:23PM »
I started a previous thread on my car misfiring but have now found that its due to it overboosting and the fuel cut stepping in.

ive got the standard turbo, apexi twin chamber BOV, upgraded intercooler etc.

i have tremoved the manually adjustable boost control and sealed it up.  yet i am still seeing a spike in boost.

any ideas.
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Offline noss

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Re: Overboosting
« Reply #1 on: Aug 18, 2006, 02:44PM »
there is a boost limiter on nissan ecu's for stock boosted motors, you'll need to have that removed (via a modified chip) or you could probably buy one of those fuel cut defender things.

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Offline Impakt

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Re: Overboosting
« Reply #2 on: Aug 18, 2006, 02:46PM »
AFAIK the ECU doesn't have a fuel cut. The closest thing to a fuel cut on the ECU is perhaps not putting in enough fuel when the AFM outputs 5.1v. I doubt that a stock turbo would ever be able to get the afm to this point too, unless the boost was high (15psi +) and revs were very high (5500+ rpm). Even then i don't think it will reach it...

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Offline omad

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Re: Overboosting
« Reply #3 on: Aug 18, 2006, 03:01PM »
is it overboosting or spiking? ie: does it just keep boosting beyond what it should be set to, or does it hold at std boost but spike in some gears/rpm?

If it's just rising past the set boost level, your waste gate isn't opening like it should. It could be stuck, or the waste gate actuator could be forked or your vac/boost line running to the wastegate actuator could be perished or leaking.

so you removed the manual boost control and put the stock one back in the loop? If there's no boost controller, or your wategate actuator is not hooked up to the boost/vac lines at all, it won't open and the turbo will just boost as much as it physically can.
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Offline fez200

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Re: Overboosting
« Reply #4 on: Aug 18, 2006, 05:19PM »
at first with the controller in place it spiked in some gears.

when i removed the boost control. ie. had no control or standard..your right i had no control over boost.

the boost control i had was crap anyway.. at its minimum setting it was reading 14psi.

so you think that the wastage is sticking? ..sounds like a reasonable answer to me.
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Offline Craazy

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Re: Overboosting
« Reply #5 on: Aug 18, 2006, 06:32PM »
if you were running 14 psi then yes you were hitting the boost cut. and since this is a part of the ecu settings that as soon as the afm reads 5v's then your fuel is cut momentarily and it will feel like it is misfiring.

did you reconnect the standard boost controller back up or seal it up completly?? also without the valve in the hose will cause a problem standard and raise the boost a little aswell


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Offline omad

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Re: Overboosting
« Reply #6 on: Aug 18, 2006, 07:38PM »
at first with the controller in place it spiked in some gears.

when i removed the boost control. ie. had no control or standard..your right i had no control over boost.

the boost control i had was crap anyway.. at its minimum setting it was reading 14psi.

so you think that the wastage is sticking? ..sounds like a reasonable answer to me.

Either that, or your lines are crap, your boost controller is, as you said, crap or the actuator is broken.

Process of elimination now :P

First thing I'd try is borrowing a half decent manual boost tap off a mate and see how that goes.
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Offline Impakt

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Re: Overboosting
« Reply #7 on: Aug 18, 2006, 10:48PM »
Are you sure the ECU cuts when the AFM reaches 5v? I have never seen this happen on a dyno and seen plenty of Nissans hit 5v on there.


Also, I'd be *very* surprised to see the stock turbo get 5v out of the stock AFM on the road..

Offline Jono

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Re: Overboosting
« Reply #8 on: Aug 18, 2006, 11:34PM »
I've seen a 180sx with an SR misfiring when it hits 5v. This was with a fast-responding DMM hooked up to the AFM during a road test.
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Offline omad

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Re: Overboosting
« Reply #9 on: Aug 19, 2006, 02:13AM »
Are you sure the ECU cuts when the AFM reaches 5v? I have never seen this happen on a dyno and seen plenty of Nissans hit 5v on there.


Also, I'd be *very* surprised to see the stock turbo get 5v out of the stock AFM on the road..

When the waste gate isn't working properly, it's not hard to imagine. The turbo may not be efficient, useful or even safe at those boost levels, but it doesn't mean it's not possible.
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Offline Craazy

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Re: Overboosting
« Reply #10 on: Aug 19, 2006, 06:11PM »
my car has the stock t25 but high flowed and running 12psi, with a 3 inch intake and it max's it out at 6500rpm, i know this coz i have a consult

so yes it is not hard to imagine that it does happen. and if the wastegate is stuffing up then your boost will be uncontrollable. i have also suffered this when the wastegate hose fell off and i got 20 odd psi, wasnt pleasant thats for sure. and it wont necessarily cut all the time but it may cause it to run like shit and also cut if it feels like it, generally as a rule of thumb on SR20's the fuel cut is at 14-15psi


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Offline fez200

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Re: Overboosting
« Reply #11 on: Aug 20, 2006, 03:37AM »
its overboosting with the standard and non standard boooost controller.
thats why im gettin it checked by my mech. he thinks its the wastegate/actuactor sticking from first check.



id love to see an SR booosted at 20psi safely, it would be a bloody screamer..!!!

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Offline Impakt

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Re: Overboosting
« Reply #12 on: Aug 20, 2006, 11:56AM »
Mine was tuned to run at 20psi. The first thing you'll notice when running this on my car is that the turbo sounds completely different, bloody unreal too  :)
I run 15 everyday though, so it very rarely hits 20 these days...

Offline Craazy

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Re: Overboosting
« Reply #13 on: Aug 20, 2006, 12:39PM »
20psi is very fun, i wasnt expecting it at the time so i was like "does my car have more power??"


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