Lesson #3 – What is turbo overboost and underboost

Lesson Overview: Lesson #3 – What is turbo overboost and underboost:

ECU Remapping and tuning can be great but their may be times or situations when you shouldn’t remap or tune a vehicle. In this lesson I will cover what is UNDER / OVER BOOST, the potentially dangerous P0234 fault code. I will also cover the commonly mistaken confusion between bad overboost and manufacturers designed overboost. The aim of this lesson is that you learn and understand why and when you should avoid remapping a car or when to insist on a disclaimer to be signed from your customer.

I have attached the lesson as an audio clip and a few video clips as reference to limit the amount of reading for you 😉

↓↓Please PLAY the BELOW audio clip 1st↓↓

↓↓Please SCROLL down for more information, after playing the above audio clip↓↓

Why use turbochargers?

The move towards smaller engines fitted with turbochargers has come about as a result of car manufacturers seeking to increase fuel economy and lower emissions from their engines without sacrificing power.

Turbochargers work by forcing extra air inside the cylinders of an engine so that more fuel can be burnt than would otherwise be possible, which generates more power. Since turbochargers are powered by exhaust gases from the engine, rather than fuel, and are usually used to make smaller, lighter engines more powerful, their application normally results in improved efficiency compared with a non-turbocharged engine producing the same power.

Turbocharging has downsides as well as benefits. One of them is that forcing air into the engine raises the pressure and temperature inside of it, which puts more stress on the engine’s components. Engineers have to take this into account when deciding exactly how much air the turbocharger should force into the engine at once; too much and the engine is likely to wear unacceptably quickly, or even fail completely. Too little pressure and you miss out on power that the turbocharger and engine have the potential to produce together.

Should you tune a car with a overboost fault or RTO:

The short answer is NO. Don’t tune a car with an overboost fault without either diagnosing what the issue is and explaining the potential risks to your customer (disclaimer will need to be signed by your customer).

We recommend fixing the issue first. In the above audio clip I have covered the potential risks of tuning a car that has an overboost fault.

If a car that you have already tuned and it starts to develop an overboost fault then follow the advise in the above audio clip and return the car back to stock.

How to diagnose a boost leak:

We recommend not getting involved with the fixing of the vehicle unless you are a trained experienced mechanic but below are two useful videos to give you an insight. We recommend a good smoke machine to look for boost leaks.

In the follow video there is some useful knowledge on what your car will try to do to counteract a boost leak problem and the symptoms it’ll cause.

What fault code will come up when I have an overboost fault:

P0234 code definition

Engine Overboost Condition

What the P0234 code means

P0234 is a generic OBD-II code that is triggered when the Engine Control Module (ECM) detects that the intake boost pressure sensor input signals intake pressure above the maximum specified pressure by 4 psi for more than 5 seconds.

What causes the P0234 code?

• The turbocharger/supercharger wastegate is damaged or sticking
• The wastegate control valve solenoid is sticking
• The wastegate control hose is getting blocked and the boost pressure cannot be relieved quickly enough

What are the symptoms of the P0234 code?

• The Check Engine Light will be illuminated and the P0234 code will be set in ECM memory.
• The engine overboost condition may cause gaskets or seals to the intake or heads to fail.
• The engine may run normally until the excessive overboost pressure blows out a gasket or seal.

How does a mechanic diagnose the P0234 code?

• Scans codes and documents the freeze frame data in order to verify the problem
• Clears the codes to verify whether the concern comes back
• Checks the operation of the boost pressure solenoid for proper operation of the wastegate
• Checks the wastegate for sticking or binding
• Check the wastegate relief hose for kinks, blockage or damages

Common mistakes when diagnosing the P0234 code

Follow these simple guidelines to prevent misdiagnosis:

• Check the boost pressure sensor hose for obstructions or kinks
• Verify that the overboost pressure condition is not from boost pressure sensor incorrect input voltage

How serious is the P0234 code?

• The boost pressure in the intake can give you a lot of power, but an overboost condition when the engine is not designed to handle it may cause catastrophic engine failure, like a blown engine or blown head gaskets.

What repairs can fix the P0234 code?

• Replacing the boost sensor if it is not giving the correct input pressure reading to the ECM
• Replacing the wastegate control solenoid if it is sticking
• Replacing the wastegate valve if it is sticking or binding
• Repairing or replacing wastegate hoses due to kinks or blockage of the wastegate lines

Additional comments for consideration regarding the P0234 code

Code P0234 is triggered by the intake boost sensor indicating an overboost condition and the most common failure is the wastegate binding or sticking intermittently.

In the below video you will see a blocked turbo causing a under / over boost fault:

For more information on Datalogging and the stages of remapping please checkout our knowledgeable on the TRC website below:

http://www.theremappingcompany.co.uk/can-i-offer-stage-2-or-stage-3-remapping-and-what-is-datalogging/

https://www.ziptuning.com/tuning-file/file-development/datalogging/