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Boost pressure cannot be controlled even with wastegate forced in open position.

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Hi, I have a problem with my boost pressure going out of controll, by that I mean rises higher than it is suposed to, I have a gt2860rs that I ran for 2 years with the stock wastegate acturator wich will give me a boost pressure at 0,8bar/11,6psi

But last year my turbopressure sudenly starting to go way higher, I removed my boost controller so that the actuator is connected directly to the plenum but the boost still rises until the fuel cut is triggered a 1,5 bar/21,75psi (will go even higher if the ecu allows it)

I checked the hose for cracks and holes.

Checked the actuator for movement when pressurised

After that I bought a Kinugawa adjustable actuator and put in a 0,5 bar spring, makes no difference.

After that I proceeded to lock the wastegate swingarm it the open position and ran the car with the wastegateflap fully open and the car will still overboost only this time it takes spool is slighly slower.

Then I proceeded to take a snake eyecam and checked the wastegate hole for objects blocking the wastegate hole but found none.

Now I was about to go insane so I unbolted the turbo and took it apart and inspected the turbine housing thoroughly and yes nothing there that could be blocking the wastegate.

I got a litle sick of the car and abandoned it for a while, now I bought a Gtx2867 wich I bolted back in to the turbine housing, I just took the car for a testdrive and guess what the car will still overshoot the boost pressure.

Can somebody please help? The next thing I will consider is to fit an external wastegate and hope that will work.

This problem will almost leave me sleepless at night if I cant find the problem, remember it was working fine before and now even with the wastegate in a fully open position the turbo will stilll boost until fuel cut occurs.

Note: I haven't tried runing with the wastegate forced open with the new turbo only the old one.

What would you do if you had this problem?

I just saw this incredebly usefull thread: https://www.hpacademy.com/forum/general-tuning-discussion/show/crazy-boost-due-to-retarded-timing

I would say that this coul be what is causing my problems, as the problems first apeard after I replaced the stock ecu with a standalone ems

I know that I have retarted the timing in the base map by a lot as I'm really worried about knock.

I can see that my ignition i set to -12 deg. at 60kpa and 7 at 100kpa@ 4000-600rpm

Attached Files

Has anything changed in the tune before all of this happened?

If not I'd check the exhaust for collapsed silencers and perform a quick compression test but from your user name I'm guessing your running a rotary?

usually from what I've seen that boost pressure that cannot be controlled is from poor wastedgate placement so the majoirty of the air\pressure\heat\energy gets directed out of the turbine and contiunes to produce turbo revs and the wastegate has very little control.

It can be poor wastegate placement

or in the case of the internal wastegate the flap is opening enough or there is no direction for the energy to go out the wastegate hole as well the hole being to small

Try to replace the vacuum hose with new one. Last year I had she same problem with MAP vacuum hose, it got oily mud inside.

I would als check the intercooler and other mechanical things for restiction. If less air can go trough intercooler or exhaust, it will produce more boost. Where do you have placed the boost source for your gauge? Have you tried a different boostgauge at different locations?

In my experience its very very unlikely to see boost creap on a gt28 turbo.

You've got avery strange problem there. I'm a little lost since you said that originally you had no problem with boost control. If I'm chasing a boost control problem I'll usually start by connecting the wastegate directly to a boost source with a fresh piece of vacuum, hose. It sounds like you have dealt with this in a round about way by forcing the wastegate open. The only other issue I can think of is that something is mechanically limiting the travel of the actuator. I've had at one point an exhaust housing that distorted through heat and jammed the actuator.

If the flexi coupling in the exhaust fails and becomes blocked this actually results in less boost due to high back pressure.

I would be trying to think very hard about anything (no matter how insignificant) that has changed since the last time the car had good boost control. It's possible that massively retarded timing could cause some of what you're seeing but that would typically show up in other ways too - Low power for instance.

"I would say that this coul be what is causing my problems, as the problems first apeard after I replaced the stock ecu with a standalone ems "

This seems to be the causal factor in his problems starting.

Why not get the timing tuned when the ECU was installed?

Thanks for some incredible usefull sugestions and answears.

But it looks as if the problem was due to massively retarded igniton, I datalogged the a 3. gear pull with the car overboosting and reaching the fuel cut limit.

Then I advanced the ignition timing by something like 6 degrees maybe more and tried again. (maybe seems much but I know that I have retarded the basemap ignition by a lot)

This time the boost went from 1,5bar where it was limited by the fuel cut, to a maximum of 0,90 bar so I guess that the wastegate is working as it should.

It is was only me that exaggerated my ignition settings in the boost area, as I said before I got this problem a while after I installed a standalone system wich I had a basemap for.

Then I got hooked on the tuning part and wanted to learn more about it and try tuning it myself a least the fuel side of it before having it done by professionals on a dyno.

This way I could also use the car while gathering the rest of the parts that I want to change before tuning it like camshafts manifold etc.

So just to make sure that I wouldn't have any knock, I retarded the whole ignition map a litle and then some more in the boost area.

And when I'm thinking about it now that is when I started having this boost problem for the first time.

I bet I could advance the ignition even more and the boost would probably decrease more.

I bought a link knockblock (tuning tool) but are finding it hard to set it up correctly, and for a novice it is tough to distinguish between engine noise and knock especially light knock,

I tried seting it up at the recomended settings for a 3sgte that I found in the Link instructions, but the odd thing is that the led indicator is allerting me of knock allmost all the time after reaching 3000rpm no matter how much I retard the ignition, but I cannot hear any knock trough the headset.

So I guess I can't trust the led indicator, any thought on this Andre? as I know you used the knockblock sytem before you switched to the Plex system.

I will have the car tuned by proffesionals later after I'm done with the build as I have no dyno, I'm finding it really fascinating and interesting the whole concept behind tuning an engine and would have loved to tune it myself but a dyno is just to expensive for me.

At least I have the all the HP academy courses to watch.

I'm happy to hear that you got your boost problem under control. Often if retarding the timing has such a dramatic impact on the boost, it also points to the wastegate being marginal in terms of size. This is an issue I've struck a few times on setups where the wastegate is marginal and I've started tuning by retarding the timing for safety. Of course on the dyno it's a lot easier to spot.

Unless I missed it I'm not sure you've said what you're tuning? Your username suggests a rotary (although I hope you haven't put a 2860 on a 13B :) You also mention a 3SGTE so I'm not sure. The reason I ask is that if you are in fact tuning a rotary, I'd be very careful using a knock block or any other knock device. Generally a rotary won't tolerate almost any amount of knock - Particularly with factory seals. This means you can damage the engine while finding the knock threshold. Caution and a conservative approach are the name of the game when dialling in the ignition on a rotary.

If you're tuning a 3SGTE (or almost any piston engine for that matter), then the engine will be much more tolerant of light detonation. I rely solely on the audio aspect of the knockblock as I have found that to be incredibly reliable. The best idea to get your ear accustomed to what knock sounds like on your engine is to purposely advance the timing at low rpm to induce a small amount of knock. You will then be able to distinguish between background noise and knock. From what you're explaining, the knock light is being triggered off engine noise alone.

Thanks, I realise that I my username may sugest rotary but it actually has nothing to do with rotary, no I'm a piston guy and yes the engine I'm tuning is a 3sgte in an old Celica.

I found examples of what knocking sound like in the EFI tuning fundamentals course and on youtube.

I think I've encountered light knock a few times and when I did it was a verry sharp/crisp sound wich differs from the engine noise, and when I retarded the ignition a few degrees and that particular sound would be gone.

Would you say that the Plex system is so superior that it is worth switching from the Link knockblock to Plex even when it is just for hobby use?

For hobby use I'd just stick to the Knock Block, unless you have money to be throwing around, I used mine successfully for years.it's good to know that it's a 3S-GTE your dealing with, it helps us help you.

If you now know what light knock sounds like there's no reason not to invest in a good AFR gauge and do some basic tuning on the car yourself, there's enough information in the courses not get you well on your way, fundamentals, understanding AFR and road tuning will give you a fantastic grounding

The Plex unit is definitely superior to the knockblock, but I agree with Chris, the knockblock is more than adequate for hobbyist or professional use. I relied on one for many years and had no complaints.

Mr FDFX3, out of interest, where did you mount your knock sensor on your 3SGTE?

I've been mounting to the top of the cam cover for my headphones, but it does pick up a lot of noise there. I have a Phormula KS4 which I managed to mount on my permanent car in the original knock sensor position, but it's very difficult to get down there when doing other cars.

Interested if you found anywhere better?

I am also interested in extra knock sensor position on 3S-GTE - I have a knock took waiting to be installed and I've had a quick look and can't find an appropriate place (easily)

Hey, c'mon guys !

If you are serious about detecting knock you know that there is no shortcut. If the correct mounting points are hard to reach, you just have to find a way to mount hem there, period. The rocker cover, intake manifold etc. are obviously not where the sensors belong, otherwise even OEM sensors would sit there.

I've tuned numerous 3SGTEs of various generations and while I can't tell you off hand where I fitted the knock sensor, I don't recall ever having too much trouble finding a spot. One tip that can widen your options is to drill out the centre of the Bosch knock sensor carefully with a 10mm drill bit. I know it sounds dangerous but I've done this with every knock sensor I've used and it does not affect the sensor's ability to detect knock. This opens up options to use an M10 or 3/8" threaded boss in engine blocks which seem to be more common than M6/M8.


backside of the engine block, below the intake manifold a bit towards the passenger side (driven on the correct side of course - LEFT :) ) is a 10mm Boss you can use.

You don't even need a lift to reach there, can be done from the top.

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