GR Yaris Inconsistent Boost

[JJ.King]

Get the VIM and GTS and check the "Knock Correction Learning Value". If everything is normal, the number should be 24.
If the number is less than 18, boost is limited.
As the knock signal accumulates, the number will drop.
Possible causes include "low octane gasoline," "poorly drained muffler," "carbon buildup in the combustion chamber," "noise in the electrical system," etc.

If the "Knock Correction Learning Value" is 24, but boost is still limited, another cause could be the various temperature corrections.
The surge tank needs to be cooled before launch because higher intake air temperatures will limit boost.

Or, if the various sensor readings are inconsistent, the system may misdiagnose a malfunction and limit boost.
Disturbed airflow signals due to a low-quality intake kit,
or disturbed pressure sensors due to a high quality intercooler.

Disconnecting the battery may not be sufficient to relearn the ECU; a reset by GTS is required.

Sorry for asking a silly question, but what do you mean by get the VIM and GTS? They sound like OBD2 readers?

Where am I able to get these?

Visiting dealership in 2 days, keen on reporting back. After refueling another tank of 98 I’m still having the same issues, so I’m convinced it’s the wastegate.

I have come across something else that may be interesting though: https://www.gr-zoo.com/threads/turbo-oil-pipe-failure.3033/

In this forum they mention turbo oil pipes cracking, from my understanding due to an upgraded exhaust/down pipe not having the OEM bracket. Could this potentially be making the car not hit boost as it’s got to do with the Turbo? Or is this just something that leaks and doesn’t cause any other issues

 

[JJ.King]

Maybe this is the solution?

GR Yaris - ECU Message Codes.

Took my GR for a drive this morning and it was going fine giving it plenty of throttle when suddenly lost all power. At first I thought it was the dreaded " Reduced Engine Power" but this was something else. Pulled to the side of the road and stopped. Engine miss firing badly but only at idle...

www.gr-zoo.com

@Sekred, I’ve read through your comment and what you did to sort out the solution. Seemed like such an easy fix, but a stressful one with the dealership taking as long as they did

I’m not too sure how the wastegate and boost solenoid are related (if someone could explain that’d be great), but this might very well be the issue? I never got a warning or error code about the drop in boost.

Could you link the part number and where you bought the solenoid from Sekred? May take matters into my own hand if Toyota can’t sort it out.

Also how is the car now? Any issues since sorting the solenoid out?

 

[Onehp]

I’m not too sure how the wastegate and boost solenoid are related (if someone could explain that’d be great), but this might very well be the issue? I never got a warning or error code about the drop in boost.

1 Boost is regulated by a bypass valve aka wastegate.
2 Wastegate is default open (no boost, fully closed = max boost (limit approx 1,8 bar)
3 Wastegate is actuated by a vacuum actuated diapraghm (integrated on Turbo) .
4 With vacuum applied it closes the wastegate, creating boost.
5 Vacuum is applied through a solenoid valve that opens/closes the vacuum supply.
6 Solenoid valve is actuated by an electrical current controlled by the ecu.

Possible faults with intermittent/insufficient boost:
- Leaking vacuum line or diaphragm - insufficient to close WG sufficiently. Note that the vacuum system also actuates the bottom flap in the airbox, so a leak there will also affect boost!
- Solenoid not actuating properly, perhaps broken coils
- break in signal to solenoid

All the above are more serious issues then the slight lack of boost sometimes experienced (imho sw issue) and are more about a more consistent loss of boost.

Sekreds fault was about too much boost all of the time due to the solenoid being stuck in the open position.

Solenoid can be fault tested by:
- Measuring resistance should be about 13 ohm
- actuate it with 12v, it should click open
- not possible to blow through when no current applied

Hope it helps...

 

[Michael Knight]

I'd say if you're having mild boost issues its likely ECU related, pulling boost down for some reason, or then mild vacuum leak somewhere as OneHP explained.
More severe, like overboost or no boost at all are likely solenoid related.

 

[Sturesmyg]

1 Boost is regulated by a bypass valve aka wastegate.
2 Wastegate is default open (no boost, fully closed = max boost (limit approx 1,8 bar)
3 Wastegate is actuated by a vacuum actuated diapraghm (integrated on Turbo) .
4 With vacuum applied it closes the wastegate, creating boost.
5 Vacuum is applied through a solenoid valve that opens/closes the vacuum supply.
6 Solenoid valve is actuated by an electrical current controlled by the ecu.

Possible faults with intermittent/insufficient boost:
- Leaking vacuum line or diaphragm - insufficient to close WG sufficiently. Note that the vacuum system also actuates the bottom flap in the airbox, so a leak there will also affect boost!
- Solenoid not actuating properly, perhaps broken coils
- break in signal to solenoid

All the above are more serious issues then the slight lack of boost sometimes experienced (imho sw issue) and are more about a more consistent loss of boost.

Sekreds fault was about too much boost all of the time due to the solenoid being stuck in the open position.

Solenoid can be fault tested by:
- Measuring resistance should be about 13 ohm
- actuate it with 12v, it should click open
- not possible to blow through when no current applied

Hope it helps...

It’s off topic, but I just want to say: I’m a fan of @Onehp

 

[Yahonza]

Agree with the above.
However, one of the highlights for me is the slightly inconsistent boost. Keeps you guessing.

 

[Sekred]

Maybe this is the solution?

GR Yaris - ECU Message Codes.

Took my GR for a drive this morning and it was going fine giving it plenty of throttle when suddenly lost all power. At first I thought it was the dreaded " Reduced Engine Power" but this was something else. Pulled to the side of the road and stopped. Engine miss firing badly but only at idle...

www.gr-zoo.com

@Sekred, I’ve read through your comment and what you did to sort out the solution. Seemed like such an easy fix, but a stressful one with the dealership taking as long as they did

I’m not too sure how the wastegate and boost solenoid are related (if someone could explain that’d be great), but this might very well be the issue? I never got a warning or error code about the drop in boost.

Could you link the part number and where you bought the solenoid from Sekred? May take matters into my own hand if Toyota can’t sort it out.

Also how is the car now? Any issues since sorting the solenoid out?

I think Onehp and Michael Knight have covered it pretty well meaning its likely an ECU issue causing the inconsistent boost.

Saying that the hertz for a boost control solenoid is around 20-30 times a second so if the solenoid is sticking slightly the boost can certainly vary.

The other issue is where its mounted at the rear of the engine. Subject to a lot of heat and stuck under an insulated engine cover is not going to help.

The part number for the solenoid is 25819-0W010. I brough mind from Japan, cheaper than Toyota Australia by about half. The solenoid is not made by Toyota/Denso it actually made by a German company called Pierburg. I know they make solenoids for Subaru and Nissan as well.

I have recently fit a Motec M1 ECU. Its so recent I have yet to get it tuned. Once its tuned I expect little variation in target peak boost pressure and I mean accurate to 0.1psi.

The other thing I may done is replace the OEM boost control solenoid with MAC 3 port solenoid. I have already purchase what I want and its just a matter of fitting it if I decide to go that way. See below.

 

[nikoel]

Get the VIM and GTS and check the "Knock Correction Learning Value". If everything is normal, the number should be 24.
If the number is less than 18, boost is limited.
As the knock signal accumulates, the number will drop.
Possible causes include "low octane gasoline," "poorly drained muffler," "carbon buildup in the combustion chamber," "noise in the electrical system," etc.

If the "Knock Correction Learning Value" is 24, but boost is still limited, another cause could be the various temperature corrections.
The surge tank needs to be cooled before launch because higher intake air temperatures will limit boost.

Or, if the various sensor readings are inconsistent, the system may misdiagnose a malfunction and limit boost.
Disturbed airflow signals due to a low-quality intake kit,
or disturbed pressure sensors due to a high quality intercooler.

Disconnecting the battery may not be sufficient to relearn the ECU; a reset by GTS is required.

So I did a test run. And this value is variable. For me under normal driving conditions it’s at 20.5. But when giving her the berries she instantly goes to 21.3

 

[JJ.King]

I’m back with an update from the dealership. They told me they pulled some data off from the car and sent it in for Toyota to look through. When they got back ti me, they basically said the car was operating at normal parameters?! In fact they told me my car was making more boost than stock.

They took it for a test drive and found that ‘nothing’ was wrong with it. I asked if they could check any hardware issues as the software (ecu) seemed to be all good - told me they wouldn’t know what to check because the ecu says everything running as it should.

So maybe it is the solenoid? Or perhaps it’s my intake that’s somehow unclamping again under boost pressure? Idk.

Anyone got any ideas?

 

[Michael Knight]

I’m back with an update from the dealership. They told me they pulled some data off from the car and sent it in for Toyota to look through. When they got back ti me, they basically said the car was operating at normal parameters?! In fact they told me my car was making more boost than stock.

They took it for a test drive and found that ‘nothing’ was wrong with it. I asked if they could check any hardware issues as the software (ecu) seemed to be all good - told me they wouldn’t know what to check because the ecu says everything running as it should.

So maybe it is the solenoid? Or perhaps it’s my intake that’s somehow unclamping again under boost pressure? Idk.

Anyone got any ideas?

hole in intake messes up AFR and would assume engine would run more poorly.
Likely just software acting randomly. but just guesses.

 

[JJ.King]

hole in intake messes up AFR and would assume engine would run more poorly.
Likely just software acting randomly. but just guesses.

I’ve got an MST intake on mine, but usually you mean the hole in the stock intake?

Anyway to reset software myself without potentially voiding warranty?

 

[Michael Knight]

I’ve got an MST intake on mine, but usually you mean the hole in the stock intake?

Anyway to reset software myself without potentially voiding warranty?

no just any air leak after the MAF sensor would mess up the engine AFR and cause less optimal engine operation.
If Toyota mech tested your car and its boosting fine maybe there is no actual issue, more or less a feature from the ecu / car.

 

[nikoel]

I’ve got an MST intake on mine, but usually you mean the hole in the stock intake?

Anyway to reset software myself without potentially voiding warranty?

Disconnect the negative terminal from the battery, but make sure not to close the trunk. Wait for a certain amount of time—some suggest 20 minutes—before reconnecting the terminal.

For a more thorough reset, consider purchasing an MX+ or a similar OBDII dongle to reset the ECU via its associated app or software.

In most cases, if nothing is severely wrong with your vehicle, the issue often lies with the ECU. Tuning experts, particularly those at Motive, highlight how inconsistent run-to-run performance can be. The ECU aims for a specific power output and utilizes the throttle butterfly valve to achieve that goal.

I initially thought that perhaps oil was seeping into the intake through blow-by and the PCV system. However, many, including Andrew from Motive, have debunked this theory.

Moreover, the benefits of air intakes are often overstated by aftermarket manufacturers and promotional videos. A video is circulating that shows MST achieving more power than Eventuri, pointing again to the inconsistency in run-to-run performance. I won't go as far as accusing manufacturers of falsifying power output numbers, but it's certainly possible to cherry-pick the test runs. One deceptive way to increase power is by altering the piping diameter to trick the ECU into supplying more fuel.

Many vehicles, including ours, experience these issues to some degree. For example, after cleaning, straightening, and degreasing my intercooler, I experienced a significant one-time acceleration boost, followed by the car reverting to its restrictive "nanny mode" until I reset the ECU. To completely resolve this, a comprehensive re-tuning is necessary, ideally using specialized software like ECUTEK to modify throttle behavior under boost conditions properly.

There's also the possibility of simpler issues, such as over-oiling the intake cone, leading to an airflow sensor coated in oil.

Lastly, don't expect much help from Toyota or its technicians, no matter how well-intentioned they may be. They have consistently failed to address this issue, as evidenced by more than 50 combined pages of discussion on this and neighboring forums, as well as the Australian GR Facebook Page. According to them, it's a non-issue.

 

[Sekred]

Data logging is probably the only way to get an idea of what is really happening. Unfortunately Logging using the OBDII port is so slow its next to useless.
My previous vehicle a Fiesta ST was notorious for closing the throttle to control torque. Tunners eventually got around this but it took some time. The advantage with the Ford was the fact it used a Bosch ECU, considerably easier to "Tune" than the Denso fitted to our GRs I think.

 

[JJ.King]

no just any air leak after the MAF sensor would mess up the engine AFR and cause less optimal engine operation.
If Toyota mech tested your car and its boosting fine maybe there is no actual issue, more or less a feature from the ecu / car.

That’s the strange thing though, the car feeling the way it does would make sense if it was like this from day one.

However I know it’s definitely slower, from getting pushed backed in 1st and 2nd WOT to now feeling nothing + no orange around the boost gushed dial tells me something’s definitely up

 

[JJ.King]

Disconnect the negative terminal from the battery, but make sure not to close the trunk. Wait for a certain amount of time—some suggest 20 minutes—before reconnecting the terminal.

For a more thorough reset, consider purchasing an MX+ or a similar OBDII dongle to reset the ECU via its associated app or software.

In most cases, if nothing is severely wrong with your vehicle, the issue often lies with the ECU. Tuning experts, particularly those at Motive, highlight how inconsistent run-to-run performance can be. The ECU aims for a specific power output and utilizes the throttle butterfly valve to achieve that goal.

I initially thought that perhaps oil was seeping into the intake through blow-by and the PCV system. However, many, including Andrew from Motive, have debunked this theory.

Moreover, the benefits of air intakes are often overstated by aftermarket manufacturers and promotional videos. A video is circulating that shows MST achieving more power than Eventuri, pointing again to the inconsistency in run-to-run performance. I won't go as far as accusing manufacturers of falsifying power output numbers, but it's certainly possible to cherry-pick the test runs. One deceptive way to increase power is by altering the piping diameter to trick the ECU into supplying more fuel.

Many vehicles, including ours, experience these issues to some degree. For example, after cleaning, straightening, and degreasing my intercooler, I experienced a significant one-time acceleration boost, followed by the car reverting to its restrictive "nanny mode" until I reset the ECU. To completely resolve this, a comprehensive re-tuning is necessary, ideally using specialized software like ECUTEK to modify throttle behavior under boost conditions properly.

There's also the possibility of simpler issues, such as over-oiling the intake cone, leading to an airflow sensor coated in oil.

Lastly, don't expect much help from Toyota or its technicians, no matter how well-intentioned they may be. They have consistently failed to address this issue, as evidenced by more than 50 combined pages of discussion on this and neighboring forums, as well as the Australian GR Facebook Page. According to them, it's a non-issue.

Thank you so much for the explanation for resetting the car.

Hmm, I’ll give the MAFS a clean/order a new one to see if that potentially solves any issues @Michael Knight.

The intake is still oiled from when I got it out of the box, so definitely can’t be that, but good to keep in mind when re-oiling

“Tuning experts, particularly those at Motive, highlight how inconsistent run-to-run performance can Be” - can you lead me to where I can read/watch about this?

 

[JJ.King]

Data logging is probably the only way to get an idea of what is really happening. Unfortunately Logging using the OBDII port is so slow its next to useless.
My previous vehicle a Fiesta ST was notorious for closing the throttle to control torque. Tunners eventually got around this but it took some time. The advantage with the Ford was the fact it used a Bosch ECU, considerably easier to "Tune" than the Denso fitted to our GRs I think.

Yeah it would be good to get some live data to see what’s going on and where the issue maybe coming from…

It’s strange the cars apparently over boosting my a considerable amount as seen on my attachment on toyota live data - definitely don’t feel it lol

 

[nikoel]

Thank you so much for the explanation for resetting the car.

Hmm, I’ll give the MAFS a clean/order a new one to see if that potentially solves any issues @Michael Knight.

The intake is still oiled from when I got it out of the box, so definitely can’t be that, but good to keep in mind when re-oiling

“Tuning experts, particularly those at Motive, highlight how inconsistent run-to-run performance can Be” - can you lead me to where I can read/watch about this?

Stock ECU with identical conditions, back to back variations of 30HP - watch the entire series, it's very, very good!

Save your money and get a proper tune. You will end up doing this anyway - you may'swell buy your partner a bouqet of flowers every month for the next year and at least you will make someone happy than just going BRRRRRT with the parts canon

 

[Onehp]

Yeah it would be good to get some live data to see what’s going on and where the issue maybe coming from…

I log very often with JB4. Far from everything but you can see ignition, boost request and real boost pre-throttle and at the manifold, AFR and throttle which are the most relevant here. If it were timing pull due to e.g. contaminated fuel causing knock, I would expect the boost request to drop together with the timing. But it doesn't, it's just the boost not making the request. And sometimes boost is obviously overshooting, WG is pulled open, too much, closed again and you sometimes see a wavy boost curve, ignition following in oppsite to try to smoothen out the torque. And sometimes boost shoots over massively (0,3bar easily at times) and for some reason the WG isn't opened more (firing the solenoid less) and instead the throttle steps in and reduces the manifold pressure. As far as I can tell this is all 'normal' ecu behaviour.... and the WG actuation control is pretty shitty compared to an electrically servoed one that can actually tell the WG position.

I think it might also be that in this car you simply feel the variations much more than on your typical heavy isolated modern car. All cars vary, NA and old school turbo with ambients, modern turbos compensate boost for ambients but feel more boosty then, electric cars throttle power when batteries are too cold or too hot etc.

 

[Duke]

I log very often with JB4. Far from everything but you can see ignition, boost request and real boost pre-throttle and at the manifold, AFR and throttle which are the most relevant here. If it were timing pull due to e.g. contaminated fuel causing knock, I would expect the boost request to drop together with the timing. But it doesn't, it's just the boost not making the request. And sometimes boost is obviously overshooting, WG is pulled open, too much, closed again and you sometimes see a wavy boost curve, ignition following in oppsite to try to smoothen out the torque. And sometimes boost shoots over massively (0,3bar easily at times) and for some reason the WG isn't opened more (firing the solenoid less) and instead the throttle steps in and reduces the manifold pressure. As far as I can tell this is all 'normal' ecu behaviour.... and the WG actuation control is pretty shitty compared to an electrically servoed one that can actually tell the WG position.

I think it might also be that in this car you simply feel the variations much more than on your typical heavy isolated modern car. All cars vary, NA and old school turbo with ambients, modern turbos compensate boost for ambients but feel more boosty then, electric cars throttle power when batteries are too cold or too hot etc.

Is a servo wastegate possible without going to an aftermarket ECU?