A common problem with turbocharged engines is a sudden spike in boost pressure when the turbo initially spools. This is known as boost spike. Some boost spiking should be expected with every turbo application due to the turbo pressure equalizing under sudden acceleration. However, excessive boost spike, which is most common on modified turbo engines, can damage the turbocharger and other engine components. For this reason, boost spike should be diagnosed as soon as possible.
A damaged turbocharger unit is one cause to boost spikes. If the turbo shaft or bearings are worn, the turbo wheel will spool inconsistently. This can cause sudden boost spikes, as well as an inconsistent peak boost pressure. Another issue that causes boost spikes is a malfunctioning turbo wastegate. The wastegate allows excess exhaust gas to bypass the turbocharger under acceleration. If the wastegate spring or actuator malfunctions, it may allow for inconsistent exhaust flow into the turbocharger. This will cause boost spikes and/or low peak boost pressure.
The pressurized air from the turbocharger is circulated through the intercooler system and piping before it enters the engine. A loose intercooler pipe or other leak will allow a substantial amount of boost pressure to escape the system. Since the turbo pressure is constantly monitored, the turbocharger will try to compensate for this leak by producing increased boost pressure. The inconsistency in boost pressure inherent when a boost leak is present will cause the boost pressure to spike and hold inconsistently.
Just as with an intercooler leak, a boost or vacuum leak in any other part of the turbocharger system will cause boost leaks to occur. The turbo system features various vacuum lines connected throughout various components in order to monitor and equalize boost pressure. If these lines are damaged or detached, boost leaks and spiking will occur. Boost leaks at other locations will likewise lead to boost spikes. Common places for boost leaks to develop are any components that feature rubber gaskets or fittings, such as the engine throttle body and intake manifold.
On the upper intercooler pipe is a blow-off valve, which releases excess boost pressure from the turbo system when the engine throttle is lifted. Blow-off valves feature an actuator so that the unit opens and closes properly under boost pressure. If this actuator is damaged or improperly set, boost leaks and boost spikes may occur. If you have an aftermarket boost controller installed on your system, it may be the source of boost spiking. An improperly installed or leaking boost controller will lead to boost spikes.
