fluctuating boost needle
Turbo Mini Forums

Hi guys,

My boost needle doest hold steady when its on full boost. It likes to fluctuate, almost like a rev gauge would when a car is running on the limiter.
Its smooth all the way up however. And ive tried it with different amounts of boost and it still happens.
Its a 2.5bar racetech gauge.
Could it be a leek in the system somewhere?

Cheers,
Al

Could it be a weak spring in the actuator?

If something is worth doing, it's worth doing half of.

As above, or possibly if you're using a bleed valve for boost control, these do cause spikes and fluctuations - they don't control boost very well.

I wouldny have thought so,

Its an avonbar T3 hi boost actuator that will boost from 6-over20PSI Actuator bought from Avonbar about a year ago. Its only been running 0.5bar and only done about 800miles.

It may be the bleed valve. Im running it off a solenoid so I can get high and low boost and ive just started using it.

where is the actuator getting it's boost signal from? before or after the intercooler?, I'd try taking it from the plenum

Team Racing

The actuator is getting its boost sigal before the charge cooler. It has a 'T' piece which fits to the air intake side of the turbo. one side runs straight to the actuator and the other runs to a switch controlled solenoid then to a bleed valve so that when the switch is flicked the pressure is bled off meaning the turbo has to produce more pressue (say 10psi) to create the amount needed to open the wastegate (7psi).

I'm guessing that is your problem, try running it's own boost signal from plenum chamber.

You should have your boost gauge plumbed into the manifold, but the wastegate signal should come before your carb / throttle body

Team Racing

i thought you shouldnt use the manifold for the actuator, when the throttles closed it wont reflect the true boost level

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

joey, what does it matter what the actuator is doing when the throttle is closed? that only thing it can do is hold the wastegate shut to bring in more boost

Would also expose the wastegate diaphram to fuel. Not sure if they are the correct material to cope with that.

might you not risk stalling the turbo if no dump valve is fitted?

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

Thats why I run my actuator signal from before the throttle body or carb

Team Racing

sorry guys,

did you mean where is the boost gauge connected?

if so its connedt via a 't' peice that connects to the inlet manifold and a dumpvalve.

your boost gauge, dump valve and actuator should all be on seperate hoses taking there own signal independently

Team Racing

As standard the actuator takes its signal from the tee ontop of the compressor housing why move it? Mine fluctuates some of the time but i'll put it down to the turbo being old. Plus i do ru the ecu at times and that can cause the needle to flick about.

Edited by Mr Joshua on 3rd Sep, 2009.

Own the day

on the standard metro turbo engine there is no intercooler for pressure to drop accross. You really want the pressure to be contant at the car mouth.

Why would an old engine cause boost fluctuation?

Team Racing

All to do with the blade condition but to simply put it imperfections in the blade and internal surfaces can cause wave formations that affect the actual flow of air. Plus factor in worn bearings and movement in the turbine shaft.

Own the day

ahh right, you've edited your post now, as you said old ENGINE and not old Turbo

Team Racing

AlexF

nothing special but you can really see it in the fuel pressure gauge. At low boost the fuel pressure is smooth, rises and falls very evenly but at the upper end it becomes very erratic

Own the day