Boost Fluctuation

[Omurru]

I have noticed this a bit it the past with my car but it became more of an apparent problem today going up a long steep hill. When at full boost or accelerating I have no probs, but when sitting at a constant speed on boost (not full obviously) say going up a hill the boost level will start bouncing up and down and you hear a bov type noise (I presume it's the bov's opening a closing), it's almost like the controller or the bov's won't hold low amounts of boost for a long time. Anybody experienced this problem before or have any ideas what it could be due to?

Sorry about the poor explination, I can't think of a better way to explain it

[Guest 40th-edition]

AFM?? they can do cause that.. but not sure about under load

[Omurru]

It has fairly new z32 AFM's, It's fine at idle and general driving, it's just at long periods at say 4000rpm and 50% boost. It sounds like the bov's suddnley starts opening and closing.....

[R31 POWER]

What turbo/s?

[Omurru]

There high flowed stockers with steel wheels. Running about 0.9bar normally.

[paulr33]

sounds like compressor surge

have a read up on what compressor surge is

where is the hiflow from

[700HP-GTR33]

I have noticed this a bit it the past with my car but it became more of an apparent problem today going up a long steep hill. When at full boost or accelerating I have no probs, but when sitting at a constant speed on boost (not full obviously) say going up a hill the boost level will start bouncing up and down and you hear a bov type noise (I presume it's the bov's opening a closing), it's almost like the controller or the bov's won't hold low amounts of boost for a long time. Anybody experienced this problem before or have any ideas what it could be due to?

Sorry about the poor explination, I can't think of a better way to explain it

Hello Kyle,

Could you have a faulty blow off valve?

Have you done any work on the intercooler or exhaust lately?

Sound like a block of some-sort.

Is your petrol pump making funny noises on start up and shut down?

This can be caused by fuel delivery also.Less fuel for motor to keep turbo's spooling.

Does it feel like it wants to stop and go...stop and go when the turbos play up?

The other thing it could be is boost controller ,do you run one?

But then again could be compressor surge...as Paul has said.

Good luck.

Hope I have been some help

[Omurru]

paulr33 - I though it may be compressor surge or flutter(dunno what that is, is it the same as comp surge ) just been waiting for someone to say it to see if it's a possiability.

700HP-GTR33 - Haven't done any work on any of the intake stuff since i had the car but then again it has also been doing it most of the time i have had the car so may be worth a look, is there anyway to check the bov's off the car to make sure they are working properley?

Pump only makes funny noises when it's at high rpm/boost I know that thats the pump surging though cos it can't supply enough fuel to the engine, car despratley needs injectors, pump, fpr, and a new tune, it's the next thing I need to do on the car. Though could this same thing be causing this problem at low rev's injector duty is only about 30% ish when it does it?

Does it feel like it wants to stop and go...stop and go when the turbos play up?

Yep thats exactly what it feels like.....

Car has a Blitz Dual SBC and a Power FC.

Thanks heaps for the help no doubt I will have a million more questions

Edited August 29, 2006 by Omurru

[Omurru]

where is the hiflow from

Woops forgot to answer this one, no idea on where they are from I don't even really know the specs of them, the turbos were done by the first aussie owner of the car who had it before the guy I bought it of had it. When I bought it I was told they are 'custom turbos capable of running 2bar and holding 1.5 all day and they have upgraded steel wheels'. I bought the car for the engine not for the turbos though...there the cheap part.

[paulr33]

hiflows sometimes can be associated with compressor surge.

this is commonly seen as fluttering whilst ramping up or coming boost.

compressor surge is actually boost past the compressor wheel is higher than what the compressor map can supply. ie the compressor map says the max flow in the ideal scenario is 19psi but when its ramping on boost it actaully peaks past 22psi so the compressor wheel surge's

[The Dan]

start by checking the basics : fuel flow, fuel pressure, check spark plugs, intake etc.

Then move on to check BOV after you are sure everything else is fine. If you don't know how to test the above things then you will waste a lot of time trying to solve your problem.

[The Dan]

hiflows sometimes can be associated with compressor surge.

this is commonly seen as fluttering whilst ramping up or coming boost.

compressor surge is actually boost past the compressor wheel is higher than what the compressor map can supply. ie the compressor map says the max flow in the ideal scenario is 19psi but when its ramping on boost it actaully peaks past 22psi so the compressor wheel surge's

Didn't he say it only does it at around half boost (~0.4 bar)

I doubt the turbo would be surging at this level.

[paulr33]

no he said its fine on 0.50 bar but no ok on 0.90bar

[Omurru]

no he said its fine on 0.50 bar but no ok on 0.90bar

nah it is the other way round when at max (0.9) it's fine (i think i haven't really checked it when not accelerating) but when not accelerating and sitting at say 0.5 the problem occurs....

[paulr33]

now thats wierd

check the bov

[Omurru]

now thats wierd

yup....theoretically could you check the bov's of the car? ie. supply pressure to them and then cut it of somehow to see if they were holding??? I work at for Qantas so I should be able to rig something up to test them, just wanna know if it's a waste of time or not....as not really sure exactly how they work, never looked into it.....

other than that might do some research on compressor stall....thanks for the help as well guys!

[FOG35]

I have exactly the same problem however mine is in a rb20det with rb25 highflow turbo. Goin up long hills on the highway if i build boost slowly, at about 5psi boost gauge will bounce up and down (max boost is 10psi atm). But once it it hits 10psi everything is fine. Mine usually only does it between 3000 and 4000rpm and more often in high gears, eg 4 and 5. For the moment i have been putting up with it but would love to find the solution.

[700HP-GTR33]

AFM?? they can do cause that.. but not sure about under load

Hello again,

AFM's.....give them a clean and check connections.

Sensor's O2 might also cause this problem.

When have you last checked your spark plugsand coils?

Last car I had Mazda 929 had corrossion on the leads, it would play up when I was at low revs.

At high revs the car would run fine.

You really need a tune....get one before it causes bigger problems for you.

The tuner will identify your problem.....it should be apparant under low load conditions.

Cheers

[Omurru]

Will give the AFM's a clean and a check, I know one of them is wired up pretty dodgely....Spark plugs were changed about 300k's ago there BKR7E's gapped to 0.7mm, coil packs are about 5000K old.

Might be a good time to get that new pump and injectors and get a tune. It was tuned by Godzilla Motorsports just before I bough the car but am unsure of any details of the tune appart from what the dyno graph shows me....