Mazda 2008 MazdaSpeed3 Wartungshandbuch PDF herunterladen (Seite 5)

COBB TUNING

Issues you will likely run into while modifying your vehicle.

This section has been put together to help explain what mechanical issues you may run

into as you continue to modify your vehicle from stock. The stock components were designed with

specific applications in mind. When you increase the power output, efficiency, and other functional

aspects of the engine several stock components will no longer be up to the job of supporting the

increased power output.

Rapidly wearing spark plugs.

Most DISI engines have special piston designs that direct the incoming air and fuel charge

towards the spark plug for a more complete combustion. We've found that this and other DISI

features wear spark plugs more rapidly than a normal port-injected engines would. Depending on

the level of performance modifications, the standard port-injection engine would be able to run the

same spark plug set for around 15,000-50,000 miles. Although, with the L3T DISI engine, we've

found that this engine wears spark plugs more rapidly. You should budget on changing the L3T

spark plugs at shorter intervals, something along the 5,000-15,000 mile rage.

A wearing spark plug initially exhibits higher boost miss-fires, poor power production, or

stumbles under WOT conditions. If you then run a calibration that runs lower boost and the miss-

fires go away, this is an indication of wearing plugs. Some very worn plugs will also create idle and

part-throttle miss-fires on various cylinders which the ECU may detect and then report as a

recorded miss-fire. The first Service Bulletin Update will give you the information you need to order

the correct replacement spark plugs.

Inability for the stock BOV to hold turbo boost pressure above 17-18psi.

The L3T DISI engine has a turbocharger that is capable of safely generating more boost

pressure once the supporting Stage2+ modifications have been added to the car. Although, we've

found that the stock BOV cannot hold the increased turbo boost pressures above 17-18psi. Around

these pressure levels the stock BOV (or By-Pass Valve [BPV]) simply opens and allows the charged

air to recirculate back into the intake. This BOV leak pushes the turbo to work much harder to re-

compress the purging intake charge.

If you plan on running over 17psi of boost pressure on a Stage1 or Stage2+ hardware

combination or if you are running an after market turbo, we highly suggest that you replace the

stock BOV with an quality aftermarket one like the COBB XLE BPV.

Excessive crankcase pressures due to poor Positive Crankcase Ventilation

(PCV) design – Burning oil at idle.

Some L3T DISI engines (in completely stock form) burn oil through the engine and oil smoke

pours from the tailpipe while at idle. This is due to several issues that we've found with this

platform. First, the PCV source where the crankcase pressures are pulled (or sucked) comes from

the engine block itself, not from the head or valve cover as is on almost all other vehicles. Pulling

the crankcase ventilation from the top of the engine assembly, rather than the lower crankcase

assembly as is done on the Mazda L3T DISI engine, is done to avoid pulling in atomized, liquid oil,

or further contaminated crankcase gases from the crankcase housing. The crankshaft is spinning

through pressurized, hot engine oil at several hundred RPM while at idle and mixes combustion

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Mazda 2008 MazdaSpeed3 Wartungshandbuch Seite 5