Hunting

[PaulosECR33]

oright car drove more than 200m for first time in 18 months today

i drove from essendon to gisbourne & back and drives great..how ever it idles sh*t..

looked at some threads but could not find anything i have not checked....

problems is>

Hunts between 500 & 1500 & blows heaps of smoke.. runs so rich that gets a miss & takes 15 minutes or so of normal driving before you can get on boost without it spluttering.. however once it has cleared up everything is sweet & goes good. sounds to me like a vac leak.....

I have checked>

For any vacume leaks & found none, checked all hoses & clamps all is ok no audible leaks, sprayed brake cleaner around hoses & plenum to see if revs jumped & found nothing

Blocked of individual vacume hoses & found nothing.

Plugged in a new afm i had lying around & does not change anything..

Disconnected battery for 20 mins just as a hunch to see if anything reset..

Removed idle control valve AGAIN and cleaned out everything seems normal except one thing. there is a port in the aac valve that is not on the plazmaman plenum i have its only very small and is only plumbed back into the main gallery anyway but not sure if it could affect it...

mods are plazmaman plenum, new intercooler piping with front mount, 6boost high mount & gt30 with a turbosmart wastegate and all the other spporting mods, plugs are gapped to .8 & still has AFM on intake side or turbo. does not have a blow off valve of any any sort (so no leaks there) & does not stall at the lights when stopping.

car is on 7psi on stock ecu (i know ill get the old get new ecu & tune which i am saving for at the moment)

i read on one thread about it being an 02 sensor but i can not see how...

any help would be great

Edited October 5, 2011 by PaulosECR33

[PaulosECR33]

also forgot to mention that when you start it it idles fine for about 15 seconds then starts hunting... which did lead me to believe that it was aac but cleaning it did not change anthing ( unless a solinoid has sh*t itself)

[89CAL]

Having an aftermarket plenum, bigger turbo and no bov?

These things could be an issue on the stock ecu

[PaulosECR33]

i thought as much and i understand what u mean.. just hoping to find a bandaid fix for a week or 2 while i get some funds... only thing is that it drive great no issues at all.. just when it idling

[The Mafia]

Factory ECU was meant to have a BOV that is plumb back. This is why it's hunting and running like shit.

[PaulosECR33]

& there is no way around this?

i cant see how a completely mechanical valve that leaks back into the intake anyway would cause an issue if removed and sealed completely... does afm still trip?

i asumed that if there was no blow off valve there would be no leakage @ idle and there for no need for plumb back and no problems.. under boost & with reversion i understand exactly why its good to have a plumb back but i didnt think it would be an issue at idle.

looks like ill have to wait till my vipec gets here to drive it again,,,,

thanks anyways

[The Mafia]

The problem is the factory BOV actually leaks at idle. The ECU is tuned for it.

I blocked mine for the same result.

[PaulosECR33]

i know it leaks at idle.. but like i just said its completely mechanical no sensors or metering of air goes on in the bov system that i can see or have heard of on rb25s

and if its not there its not leaking and how can an ecu meter this when in stock for the bov return is plumbed back in in after the afm anyways so its like this circuit of useless unmetered air that is just there leaking between your boost pipes and your intake duct... how can the ecu be tuned to this?

or does this help equalize inlet pressures at idle or something...

and i dont have any bov, or plumbing or holes or anything so its pretty much like blocking it off anyway

Edited October 5, 2011 by PaulosECR33

[PaulosECR33]

so pretty much what ur saying is if i put a one way valve that leaks from the intercooler piping, into the turbo inlet on idle.. and closes under boost my hunting issue will be solved??

sorry if i come accross rude i just dont see how a bov would be the cause of this.......

Edited October 5, 2011 by PaulosECR33

[Room42]

i know it leaks at idle.. but like i just said its completely mechanical no sensors or metering of air goes on in the bov system that i can see or have heard of on rb25s

and if its not there its not leaking and how can an ecu meter this when in stock for the bov return is plumbed back in in after the afm anyways so its like this circuit of useless unmetered air that is just there leaking between your boost pipes and your intake duct... how can the ecu be tuned to this?

or does this help equalize inlet pressures at idle or something...

and i dont have any bov, or plumbing or holes or anything so its pretty much like blocking it off anyway

Think about it like this. Now that the bov hole isn't there the engine is getting less air at idle. Also the afm is probably reading higher becase its only sucking through it instead of the bov too. I'm sure nissan measured the airflow through the bov at idle and tuned the car around that. Now you have less air the idle is crap. Try disconnecting a vac hose and see if it idles better.

[Hanaldo]

Is this problem only when hot? Or does it do it while it is cold as well?

[rob82]

There is a difference between a BOV (wank valve) and a bypass valve. Nissan from factory use a bypass valve that vents from intake side pre throttle to intake side pre turbo so that if the turbo gernerates more airflow then the engine can consume the valve allows the air to circulate.

There is no provision in the nissan tuning required as the air is always metered.

When you block the bypass valve and the turbo combination can flow more air then the engine can consume at idle then the air will revert back through the intake. I'm not saying this is the issue but it may contribute to the problem.

[PaulosECR33]

Is this problem only when hot? Or does it do it while it is cold as well?

only when hot

There is a difference between a BOV (wank valve) and a bypass valve. Nissan from factory use a bypass valve that vents from intake side pre throttle to intake side pre turbo so that if the turbo gernerates more airflow then the engine can consume the valve allows the air to circulate.

There is no provision in the nissan tuning required as the air is always metered.

When you block the bypass valve and the turbo combination can flow more air then the engine can consume at idle then the air will revert back through the intake. I'm not saying this is the issue but it may contribute to the problem.

that is what i was thinking ill have to hook up some kind of relief valve to see if it helps

so i asume the running rich and looking like its in RnR is all due to to much air & system trying to correct this?

also noticed today having another close look that the solinoid for idle control vavle energises at the highest rpm when hunting so i think your onto something its getting to much air and not needing it

but why does this only happen when its hot and why dont all the other cars with wank valves such as ssqv (whhich apparently doesntt leak) have hunting problems

thanks for your help

Edited October 6, 2011 by PaulosECR33

[PaulosECR33]

Think about it like this. Now that the bov hole isn't there the engine is getting less air at idle. Also the afm is probably reading higher becase its only sucking through it instead of the bov too. I'm sure nissan measured the airflow through the bov at idle and tuned the car around that. Now you have less air the idle is crap. Try disconnecting a vac hose and see if it idles better.

dude that makes no sence i have more air now as the there is no leakage back to the intake which may be causing my hunt... and like rob82 said there is no metering cos its all after the afm. your probably right about disconnecting a vac hose in the intercooler piping before the throttle body to relieve pressure but then this "leak" is not controlled and i will have another problem

Edited October 6, 2011 by PaulosECR33

[PaulosECR33]

ok new question is there an aftermarket "BYPASS VALVE" which i can weld or have plumped into my intercooler piping that WILL leak back into my intake when hooked up to recirculate?

standard one's flange is huge.. hopefully the turbosmart kompact recirc series will be sufficient they some in a 34mm barbed fitting inlet & outlet and would be the best fit for my engine bay......

[Hanaldo]

Is this what it does??

I don't think it's the bov, my money is on the cold idle control valve. Not the same as the AAC valve just by the way, but it's near it. The cold idle control valve is much like a thermostat, it's a piece of thin coiled wire that expands when it gets hot to block the vacuum line. It's very easy to break, and if it get's stuck open then the vacuum line will be constantly open and act like a vacuum leak when the car is hot.

The valve is on a vacuum line coming off the AAC, so try blocking these lines to see if it changes anything. Also try running the car with the AFM unplugged. Try things to change it's symptoms so you can narrow it down.

[PaulosECR33]

Is this what it does??

I don't think it's the bov, my money is on the cold idle control valve. Not the same as the AAC valve just by the way, but it's near it. The cold idle control valve is much like a thermostat, it's a piece of thin coiled wire that expands when it gets hot to block the vacuum line. It's very easy to break, and if it get's stuck open then the vacuum line will be constantly open and act like a vacuum leak when the car is hot.

The valve is on a vacuum line coming off the AAC, so try blocking these lines to see if it changes anything. Also try running the car with the AFM unplugged. Try things to change it's symptoms so you can narrow it down.

this is what it does exactly. where is the valve located on an r33 and where does the vac hose go after this cold idle control valve coil.. do u have a pic by any chance as i have replaced heaps of vac lines and must have missed this..

have not had a chance to look at bov yet so ill try this first.. am still a little skeptical on bov as there are heaps of cars out there that dont have a bov and also dont have this problems

[PaulosECR33]

so picked it up tonights and did what hanaldo said and it does not hunt any more but still over fuels like crazy on idle..

what i have noticed is that this happens at all temperatures unlike the hunting. start the car and its fine. but as soon as you touch the throttle once the revs settle the engine idles at about 550 and then starts pumping fuel and black some out the exhaust...

i am starting to think that i will be able to sort this with the new ecu but i would really like to sort everything else out before plugging a new ecu & fitting big injectors and then have to set everything up properly.. would be nice to kno it was running sweet before i did this..

any ideas on what this could be its not bov so plz no more on that im thinking more along the lines of sensors but not really sure.. i kno its stanard ecu so if no1 has experianced this i wil just put the new one in and tune around this problem...

thanks

[The Mafia]

have you put the factory bypass valve back on to confirm that it is not the BOV?

If you haven't tried it then you are wasting our time and your own time.

[PaulosECR33]

i dont kno how it could be the BOV cos i dont have one. i havent put the bypass valve on as i said in a previous post its flange is to large to mount in a spot where it will actually work unless i put standard plenum + intake pipes, exhaust manifold ( and studs as they are shorter......) etc...

i also asked if anyone knew if turbosmart compact plumbacks act as a bypass valve on idle cos i can fit one of them and i got no answer and i cannot find much other info other than.. "superior flow, oem fitment, handles more pressure and so on"..

so im going to keep looking for those answers and not jump into reversing half of the stuff i have changed until i kno there is no other alternative.. if im wasting your time then dont reply im still just trying to figure out all my optiions