Boost Drops

[irie]

Good day everyone,
Been getting boost drops when under load. Usually peaks at 20PSI and drops to 15 before slowly climbing back in the higher rev range. I have attached a picture showing two separate incidents I managed to capture.
When the boost drops off I have noticed a bit of smoke coming out the exhaust.
I have changed the boost solenoid, SCV and MAF not that long ago.
Been struggling with this for a bit now.
Any help would be greatly appreciated

 

[Old.Tony]

Check all the vacuum lines and make sure they're not only tightly fitted, but won't turn on the joint and there's no cracking of the hoses.

How's braking performance? Still good, or do you have to press the pedal much harder to make the vehicle slow down?

 

[irie]

Check all the vacuum lines and make sure they're not only tightly fitted, but won't turn on the joint and there's no cracking of the hoses.

How's braking performance? Still good, or do you have to press the pedal much harder to make the vehicle slow down?

Thank you for the reply!
I have replaced all of the vacuum lines not too long ago. Including all of the hidden ones on the side of the engine.
The brakes are perfect except for one issue. I do sometimes get a hissing sound that goes away when the brakes are pressed. This only happens occasionally on mornings and goes away after using it a few times.

 

[Old.Tony]

Let's hope the hissing sound isn't a snake that has made its home near your brake pedal!

The next thing to try is removing the charge hose from the baffle on the side of the engine and check inside for metal flakes. It's easy to do: wipe your finger on the inside of the hose, then look at your finger under a bright light. Metallic flakes at this point indicate wear on the turbocharger. Gold flakes = bearing, silver flakes = impeller.

 

[irie]

Ok will do and report back. Thanks again!

 

[TCN]

MAP Sensor on the intercooler

 

[irie]

MAP Sensor on the intercooler

The boost reading on my diagnostics tool match the readings on my boost gauge. Am I missing something or would this rule out the MAP sensor being faulty?

 

[TCN]

dunno..........like old tony said you obviosly got some kind of leak if you hear a hissing noise

 

[irie]

Let's hope the hissing sound isn't a snake that has made its home near your brake pedal!

The next thing to try is removing the charge hose from the baffle on the side of the engine and check inside for metal flakes. It's easy to do: wipe your finger on the inside of the hose, then look at your finger under a bright light. Metallic flakes at this point indicate wear on the turbocharger. Gold flakes = bearing, silver flakes = impeller.

Hey again. Sorry for the delayed reply life is a bit busy at the moment. But there’s no flakes at all.
All out of ideas at this point. I have also recognised that the boost is also varying wildly at higher rpm. I have attached a video showing it.

 

[Old.Tony]

I wonder if there's a boost leak - one of the large hoses that connect to the intercooler, perhaps, or even the intercooler itself?

 

[irie]

I suspected this and attached the vacuum hose directly to the boost actuator. The truck boosts to 20 psi and holds no problem. No fluctuations.
Could it be something in the software limiting the boost?

 

[Old.Tony]

I suspected this and attached the vacuum hose directly to the boost actuator. The truck boosts to 20 psi and holds no problem. No fluctuations.
Could it be something in the software limiting the boost?

Absolutely. It could also be the BCS is a little dodgy - and that may just be the electrical connection.

 

[irie]

Absolutely. It could also be the BCS is a little dodgy - and that may just be the electrical connection.

I suspected the solenoid and purchased a new one but with no luck. I even tried a friends own, but with no luck.
What does the ECU look for when calculating the correct boost?

 

[Old.Tony]

I suspected the solenoid and purchased a new one but with no luck. I even tried a friends own, but with no luck.
What does the ECU look for when calculating the correct boost?

There are numerous things it pays attention to. The MAFS for one, to see the amount and temperature of the incoming air. The boost pressure sensor is another. Then there's engine load, RPM, gearbox state, brake and clutch state.

Here's something to check: go over the brake and clutch switches, but more importantly the neutral position switch on the gearbox. If the NPS is a little flaky the ECU will think you're dropping into neutral and will try to limit boost pressure. The easiest test for the NPS is to unplug it and drive the car.

 

[irie]

There are numerous things it pays attention to. The MAFS for one, to see the amount and temperature of the incoming air. The boost pressure sensor is another. Then there's engine load, RPM, gearbox state, brake and clutch state.

Here's something to check: go over the brake and clutch switches, but more importantly the neutral position switch on the gearbox. If the NPS is a little flaky the ECU will think you're dropping into neutral and will try to limit boost pressure. The easiest test for the NPS is to unplug it and drive the car.

Thanks for the help!
So I should probably say that I have changed the MAFS and the NPS pretty recently. The NPS was faulty. I observed the inconsistency on my diagnostics tool.

Do you have any idea what values I should be seeing coming from the MAFS and engine load?

 

[Old.Tony]

Thanks for the help!
So I should probably say that I have changed the MAFS and the NPS pretty recently. The NPS was faulty. I observed the inconsistency on my diagnostics tool.

Do you have any idea what values I should be seeing coming from the MAFS and engine load?

I could chart those figures from my own car, but I won't be able to do that for at least a day. I've just got my bike back on the road (new tyre, who'd have thought it was so damn hard to get one) and tomorrow is a ride day!

Although I should note that the MAFS is really measuring what the engine is breathing (but it's in grams not litres). I could probably calculate what the MAFS will tell you at a given ambient temperature and a given RPM, because the YD25 drinks 2,488 litres of air every minute at the nominal cruise RPM of 2,000rpm. At 25 degrees celcius, air weighs 1.18grams per litre so the MAFS should read 1.18 * 2488 = 2935g/min or 49 grams per second (assuming zero boost - boost will change this dramatically).

Okay let's do around 20psi of boost at 25C ambient 2000rpm. That's 2,488 litres of air weighing about 2.8 grams per litre = 6966g/min or 116 grams per second.

Engine load is up to you - 100% is achievable with a caravan and a hill to go up. It can also be achieved with a Hilux at the lights next to you - it's all personal choice.

There's a valid reason for the sign on the Alpine Way "Not suitable for caravans". Then again, I've pulled our 2.5T caravan up Kurrajong hill, Thunderbolts Way (numerous times for both), Cunninghams Gap (once), Mt Ousley (twice) and Victoria Pass (once). It's achievable, but she no like it much. I try to find other ways!

 

[irie]

Hello again. So not sure how to interpret this data as the tool I have is not telling me whether it is per second or per minute. This picture was taken with the car stationary. What is odd is that the intake air volume when the truck is shut off says 281.69mg/
The accelerator pedal ranges from 0.76v to 4.5v. The graph is smooth and has no drops.
The accelerator sensor 2(I’m not sure what this is) ranges from 0.38v too 2.24v
The brake switch seems consistent will have to do further testing while driving to see if the state changes
Same with the p/n sensor and the vehicle speed sensor.
The boost reading on the diagnostic tool seems to match my aftermarket boost gauge.

Kinda stumped what else this could be

 

[Old.Tony]

It should be reading milligrams per second. At full noise (5000rpm with moderate boost and ambient air at 25C) = (2500 * 2.488/1000) * 2.186 / 60 = 226.6 grams per second.

Air weighs 2.186kg/1000 litres at moderate (1 BAR) boost (assuming intercooled to 50 degrees Celcius).

The figure you're seeing with engine stopped is likely to be an error due to not catering for that condition in the ECU (mostly because it doesn't matter what the airflow rate is when the engine isn't running, the injectors aren't being opened anyway).

 

[irie]

Ok the numbers seem to check out on my end. Any idea where else I should check for a solution?

 

[Old.Tony]

It's possibly the brake booster. It's also vacuum-controlled and the hissing sound near it may be a clue there. The diaphragm in the booster fails (rarely, but it has been reported here a few times). You can usually tell by the brakes not performing like they used to - it takes more effort on the pedal to make the car stop.