Boost Issue Troubleshooting

[Trozzle]

Hey guys,

Just trying to work out if I'm having an actuator issue without being able to test using another actuator...I am currently using a 14psi actuator, which was holding 15psi of boost (showing as a tiny bit above 1 bar on ISC boost gauge). Now when on WOT, the same gauge will show no more than ~0.75bar as well as the stock boost gauge showing around the +7mmHg level. Car also feels very lacking in power, (please ignore the "hoon" thoughts here) and will NOT wheelspin 2nd gear like it would recently when hitting 15psi. This backs up my thoughts that I am certainly not making 15psi.

Here is an image of my engine bay showing my intake piping. I have drawn on 2 circles, the top circle above the valley is where the MAP sensor has been tapped into the intake, and the lower circle is where my boost source is coming from for the actuator.

The actuator rod has adequate preload wound on (3mm/half circle), and I have tried with anywhere up to 6mm or so of preload with same results.

I have ensured that the hose clamps after the boost source (4 clamps) are tight and seated correctly.

Since I am running a MAP sensor, car has been tuned for an overboost fuel and ignition cut at 16psi. Since I have this safety, I have removed the hose for the boost source and run effectively "unlimited boost" as the actuator won't see a thing...car will very quickly hit the overboost cut, which also reflects appropriately as a few notches past 1 bar on my boost gauge.

As far as I can assume, a significant leak anywhere in my piping would not be causing this issue as the turbo would continue to build boost until the intake saw enough pressure to open the actuator. This thought is backed up by my being able to hit overboost. I can only be led to believe that something has gone amiss with the actuator, and it is opening much earlier than it should be.

Are my thoughts correct?

Thanks for reading another wall of text, I have a habit of spouting a lot of information.

[paulr33]

whats changed recently? when did it last work ok?

have you checked for vac lines, splits and loose vac lines?

have you checked actuator vac line and is it tight and not split?

does it wind up 0.75bar instantly and never go above 0.75bar

or

does it wind up 0.75bar slowly and takes ages and is very laggy and never goes above 0.75bar

[Trozzle]

whats changed recently? when did it last work ok?

Nothing, other than removing and refitting turbo. Last worked ok Friday night, AFTER refit.

have you checked for vac lines, splits and loose vac lines?

No, I didn't have much light to work with when I did the hose clamps. Only vac lines that could be split and cause it to read low would be the one coming from the manifold for the gauge reading - which wouldn't explain the notable drop in power

have you checked actuator vac line and is it tight and not split?

Yes. Even if it was, it would increase boost - not lower it. I have completely removed this line and run the car, and it boosts correctly - beyond what it should (as actuator isn't moving at all). Read the paragraph where I mention I'm running MAP sensor and can hit overboost (16psi) easily.

I have also bypassed the factory boost solenoid (controlled via ViPEC ECU - doing NOTHING at this point) by running a single vac line from the intercooler pipe nipple to the actuator, which still did not get me to 15psi.

does it wind up 0.75bar instantly and never go above 0.75bar

or

does it wind up 0.75bar slowly and takes ages and is very laggy and never goes above 0.75bar

Honestly haven't concentrated on spool time, only watched the gauge as I wound out to about 6500rpm to see how high it got. Feels and sounds like it's hitting 0.75bar at roughly 4000rpm, but this is only from memory.

Edited October 12, 2010 by Trozzle

[scotty nm35]

Leaky manifold gasket or a snapped stud?

[Trozzle]

we talking intake manifold or exhaust manifold? Definitely not the exhaust manifold, as that was swapped for a near-new manifold off a NEO motor at the same time as the turbo was installed. Also, no sounds to indicate it (had broken studs and leaking gasket before) as well as it making boost without the actuator receiving boost source.

The only reason I'm strongly leaning against a leak of ANY kind, is the fact that the wastegate is opening, essentially capping my boost at ~10psi as long as the vac line is giving it a boost source.

[EdGTR]

if this started after having the turbo off i would be going over all my vac lines and making sure that 2 arnt mixed. i know that you said it was a 1 bar actuator but did you ever test it by plumbing it straight into the boost source. my hks 1 bars only run 10 psi when hooked straight up.

[gotRICE?]

I dont think its causing you this problem, but as far as im aware, and from every other m MAP car i have ever seen, the MAP sensor is supposed to be plumbed AFTER the throttle body... not before.

Might be something to think about too.

[Trozzle]

Yeah good point (I could also be wrong about that being the MAP sensor. I'm going off what someone told me - not the workshop mind you)

Still, it shouldn't make a difference where it's plumed in my issue, as I'm experiencing the problem while the throttle is open.

[rob82]

Has the boost source for the actuator changed. ie has it changed the from one side of the intercooler to the other? Actuator wasn't rubbing on anything before.

[Trozzle]

Nah, hasn't changed. Same nipple as before.

I'll be trying out an ~18psi actuator that held 17psi without issue on another owner's R34 GT-T with this same turbo - only downside is I'll need to get it retuned a little more extensively than I'd hoped

[EdGTR]

Yes i agree that running the map sensor for the ecu before the throttle is very strange and must be a major pain to tune but if that hasnt changed then it isnt your problem.

You said that the standard boost controller isnt doing anything but it looks like it is still hooked up but from factory they hae a t and they dont work like most people think. If you have it hooked up like a bleed valve then it could be the issue. I think it is your problem. When you had it apart there wasnt a t piece with a short length of hose left over was there?

Iwould try and borrow a bleed valve and see if you can get it to work with that and if you can then i would leave the actuator alone so you can wind it down in the future if you want.

[Trozzle]

I don't know what it's showing in the image, but I've tried it both ways (having T-piece connected; as well as running straight from cooler piping to actuator)

The ViPEC ECU can utilise the factory boost solenoid to bleed boost, acting as an electronic controller. This is why it was originally still hooked up. Even though it was connected, the ECU was not utilising it to control boost.

Unless I am mistaken, as well as a LOT of people before me, you cannot INCREASE pressure between the cooler piping and the actuator with the stock boost solenoid. If the solenoid is my issue, then not only is it doing something it should in no way possible be able to do, but it would have been resolved when I ran a single uninterrupted hose from the nipple on my cooler piping directly to the actuator as it had been completely removed from the system.

I don't mean to sound like I'm ranting, or fishing for the answer I want, but I feel as though I'm a student educating my teacher a little.

If there is any leak at all between the boost source (intercooler piping) and the actuator, be it a split in the hose, bleed valve, or the stock solenoid doing it's job, this will result in an INCREASE IN BOOST. The only way I could decrease my boost below the minimum, would be to plumb in some kind of pump before the actuator.

[Trozzle]

This is my current setup of vac lines. Nothing has changed with this since I last made 15psi. Like I said, even running straight from cooler pipe to actuator nets the same result of ~10psi

There are only 2 logical outcomes: I have a leak in the vac line from the manifold for my boost READING (gauges), or the actuator is faulty. The first possibility would fail to explain the reduction in power though.

[Randon_I_Am]

My money's on the actuator. because when you ran unlimited boost you got to boost cut off... meaning you hit 16 psi very quickly.

and unless you have hooked up some sort of external air compressor into the actuator line it SHOULDN'T open that much with only 10psi

But for some reason the tension of the actuator is tight anough to give you "unlimited boost" (ie. strong enough to hold the gate closed against the force of the exhaust gasses)

But when a small amount of pressure is applied to it, it opens up real easily... Weird

I'll get my high pressure one to ya and give that a hit

[mosquitocoils]

Hey, what was the result of this?

[Harey]

Yeah keen to hear the result as well!

[Trozzle]

Chucked on the actuator with the 18 pound spring and it held the same boost as it did when it was on Pat's (randon_I_am) car. Not sure what happened, but the spring in the original actuator must have gone to shit otherwise it was all good after retune for a bit, then my cat melted and caused a huge restriction. Bashed cat (after taking her for a quick spin down the road with only the front pipe) and she was all sweet!

[Harey]

Ok thanks for the info. My standard hypergear actuator wont hold more than 15.5psi at redline even with a boost controller, so I have purchased an upgraded actuator, just waiting on delivery.

So the 18lb spring from Pat is only making 15.9psi high in the rpm? Or do you have updated dyno figures?

[Randon_I_Am]

Still dropping boost

[Trozzle]

it came up to 17psi then bled down to 15.9psi by red line. This was with NO boost controller at all, just straight to the actuator. No actuator will hold boost flat through the rev range without a controller before it.