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Stock Turbo Overboosting with No Bleeder...

strutto

By strutto,
in Engines & Forced Induction

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strutto Grand Master

strutto

Posted
Posted

Riddle me this...

33 GTS25t

3" Trust Catback Exhaust

3" Unknown Front Pipe

Stock Dump Pipe

Stock Turbo

K&N Pod in Cold Air Box

Until recently I had the stock intercooler and a DIY in cabin bleed using a ball valve, a needle valve and some t-pieces... Boost control was perfect... I installed a Hybrid FMIC and Piping kit and ever since then I have had overboosting problems... I have removed the in cabin bleed completly in an attempt to eliminate this problem... I am currently running a vacuum line directly from the post FMIC piping to the factory wastegate actuator... The turbo still overboosts :)

The symptoms: Half throttle 3rd gear the turbo spools to 5psi and stays reasonably stable... If I use full throttle, the boost just keeps on rising past 5psi until the AFM maxes out (or the exhaust turbine delaminates)... Not cool...

My theory: The stock dump pipe is causing too much backpressure around the wastegate causing the excess exhaust gas to go through the turbine instead of out the wastegate -OR- I have a sticky wastegate -OR- I have NFI and need your help... :headspin:

Comments? Ideas?

TIA!

strutto Grand Master

strutto

Posted
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Have you got any leaks in your tube from the intercooler pipe to the wasteguate??

 

 I installed the Hybrid FMIC kit too and hardly got any different boost pressures.

Nope... Brand spanking new hose... Clamped up nice and tight...

What boost pressures are you talking about?

When it overboosts? I've seen it get to 13psi+ before I backed off...

predator Grand Master

predator

Posted
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in fact.. if you are running straight from post fmic to wastegate it should just boost to around 8psi (done this in the past)...so something else *must* be going on.

So either you have some sort of boost leak in your FMIC setup or piping, meaning post-fmic its not building up enough pressure to open the gate at the right point...or the wastegate itself..

seems logical(?) but could be wrong..

strutto Grand Master

strutto

Posted
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The hose to the actuator isn't hasn't got a slight crack in it?
Nope...  Brand spanking new hose...  Clamped up nice and tight...

Some more testing tonight has revealed that the problem doesn't seem to be dependent on throttle position, rather RPM... :Oops:

As my car is auto, at low speeds, going full throttle results in the auto kicking down and the revs jumping to 5000 or so pretty quick, and the overboost problem occuring immediately... Tonight I had the chance to put the car under heavy load / full throttle whilst keeping it in 3rd gear (read high speeds :headspin: )...

Full throttle at anything below 4500 RPM and the boost stays solid at 5psi (bear in mind that the auto 33 actuators have a lower pressure rating than the manual ones)... After 4500 RPM, the boost just rises, and rises, until I chicken out... I'd be content with a little bit of creep up high in the revs, but by 6000 RPM, it's at 11psi+ and still rising awfully fast...

Thanks for all the advice so far guys... Much appreciated... Keep it up! :)

Doctor Mentor

Doctor

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Check your boost guage just incase.

*Try tapping your boost guage directly into the line that runs to the wastegate. Will give you the exact psi out of the turbo.

*Pull off your turbo cover and slide off the wastegate arm and check and see if the wastegate is sticking.

*Or plug the wastegate back into its normal position directly from the turbo to the wastegate acuator instead of going post intercooler.

*There may be a blockage in the wastegate actuator.

*There may be a leak in the wategate actuator casing.

Give that ago, until then I will have to think some more. Strange problem.

Do all the simple checks fist before anything.

Ben

strutto Grand Master

strutto

Posted
  • Author
Posted
Check your boost guage just incase.

*Try tapping your boost guage directly into the line that runs to the wastegate. Will give you the exact psi out of the turbo.

*Pull off your turbo cover and slide off the wastegate arm and check and see if the wastegate is sticking.

*Or plug the wastegate back into its normal position directly from the turbo to the wastegate acuator instead of going post intercooler.

*There may be a blockage in the wastegate actuator.

*There may be a leak in the wategate actuator casing.

Give that ago, until then I will have to think some more. Strange problem.

Do all the simple checks fist before anything.

Ben

Thanks for the advice Doctor... I'll run through your suggestions and see how it goes...

- Boost gauge was working perfectly pre FMIC install...

- I'll try tapping the boost guage into the WG line... Bear in mind that it IS overboosting, the AFM cut confirms this...

- I'm yet to check the actual wastegate actuator... It's been a busy week / weekend... Plan on getting to it this week...

- 32's have the wastegate line directly fed from the compressor housing... 33's are fed post IC out of the factory...

- A leak / blockage in the wastegate actuator casing you say... Interesting... Hadn't thought of that... Definately worth a look...

Thanks! :D

  • 3 weeks later...
  • 1 month later...
strutto Grand Master

strutto

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/sigh... This really sux...

I can't for the life of me solve this problem... ;)

I wired the wastegate open this weekend... Result: Bugger all boost (and power) until about 4500rpm... After 4500rpm, boost rises fairly quickly up to 12psi+

So open wastegate - 12psi+... I don't get it... :)

That rules out any piping to actuator leaks, actuator problems, wastegate stickyness, hose problems... The boost gauge is working perfectly and the AFM is maxing out up high in the revs... So the boost pressures are correct...

I plan on dropping the exhaust after the front pipe sometime soon... Not sure what this will achieve but I'm stumped ATM...

Any other suggestions guys?

Stock BOV should still be OK at this level of tune correct? Would a leak somewhere else in the system cause these problems? Could the wastegate be somehow "clogged" up?

BHDave Grand Master

BHDave

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So the boost is spiking and then dropping back to somewhere around 10-12psi or so?

I would recommend having the actuator running off a point as close to the compressor outlet as possible, particularly if you aren't running any type of comtroller. I've found the shorter the lines when running boost controllers the better the control and reduced spiking.

It's also the way it gets done on most factory turbo cars that dont use a boost control solenoid

strutto Grand Master

strutto

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  • Author
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So the boost is spiking and then dropping back to somewhere around 10-12psi or so?

I would recommend having the actuator running off a point as close to the compressor outlet as possible, particularly if you aren't running any type of comtroller. I've found the shorter the lines when running boost controllers the better the control and reduced spiking.

It's also the way it gets done on most factory turbo cars that dont use a boost control solenoid

Nope the boost is not spiking and then dropping back...

With a short hose from the FMIC piping to the actuator (no controller), the boost sits on 5psi till about 4500rpm, and then rises, and rises, and rises, to 12psi+...

But it's not an actuator problem... This happens with the actuator disabled and the wastegate wired open...

Just let a mechanic check it out, dont wanna rip apart the whole engine and after finding that its something completely different.

Thanks for the advice...

cameron Mentor

cameron

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Sounds like oil in the actuator, I've seen it happen to a R33 recently. Boost will keep rising under accelleration intil you back off. This was using avc-r and it wasent that solinoid because we swaped it into another and it worked fine.

If its wired open it shouldnt make any boost at all. :uh-huh:

:D

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