Rear Wheel Drive Newsletter - February 2009

Air Fuel Ratio Meter

When making engine modifications to your Volvo you can make fine-tuning safer by monitoring the air fuel ratio.

Most people don’t realize there is an analysis tool already on their car and all you need is a way to read and interpret the information - the oxygen sensor. You can check your modification and know what adjustments are needed for the most reliable power. The oxygen sensor constantly monitors the lean or rich condition of the engine. The most power is had at slightly rich mixture. This air fuel ratio meter is easily installed in line to the oxygen sensor and gives easily interpreted mixture ratio information with LED lights which flash from lean to rich. If you have a turbo and are tempted to up the boost this is a must have so that you don’t melt the pistons. Great for monitoring fuel economy as well.

Boost Actuator

ipd’s boost actuator endows the factory turbo with a more solid boost response while ensuring boost is maintained at a preset level, resulting in increased torque and hp. Where the factory actuator drops boost as the revs rise, the ipd actuator delivers constant boost all the way to redline. An extremely safe, reliable and effective means of raising your boost level. Fits Garrett series turbos for 200/700/900 intercooled models.

Timing is Everything

By Scott Hart

Ignition timing is an often misunderstood function of a good running engine. A properly functioning system must provide a good, strong spark to the spark plug at the precise time. The system must also advance the delivery of spark along a predetermined curve as the engine RPMs increase to keep up with the rapid pace of events required for proper combustion. The ignition system is a complex combination of rather simple processes. We’ll go into the basics of ignition timing and explore some common distributor faults.

Initial Timing & Spark Advance

Initial timing is what you’re setting when you use a timing light to set the timing at idle. For most Volvo models, this is around 10-12 degrees before top dead center (BTDC) at idle (750-900 RPMs) with the vacuum retard disconnected and plugged if equipped. Spark advance is controlled by mechanical advance weights in 200 series Volvos up to 1988 and 700 series Volvos up to 1985. Spark advance is electronically controlled on newer models. Full advance of 28-32 degrees BTDC should be achieved at around 2500-3000 RPMs. This can be easily confirmed with your timing light.

To make the job easier, take a few minutes to clean the timing mark on the crank pulley. Mark it with white paint or scribe it to make it stand out. Also, if the timing degree range is dirty, be sure to clean it for better visibility. Models up to 1975 have the timing mark on the timing gear cover and the degree range on the crankshaft pulley. Newer models are the opposite, with the timing mark on the pulley and the degree range on the timing cover.

Rev the motor to 2500-3000 RPMs and you should see the timing advance to approximately 28-32 degrees plus or minus a few degrees. If the timing mark seems to bounce around quite a bit, then you’ve probably got broken advance springs in the distributor for models so equipped. Electronically controlled systems should no vary much. If you do notice an unstable timing mark on an electronically controlled system, you’ll have to consult a good workshop manual for your model. There are several electronic ignition systems used over the years and many possible causes including a worn rotor shaft retaining pin, broken vacuum diaphragm or possibly a control unit malfunction.

Most models 1983 and newer (excluding 240 turbos) incorporate electronic knock sensing to retard the ignition whenever engine knock is detected. A faulty or loose knock sensor can also cause erratic timing fluctuations. The ignition timing became completely computer controlled in 1988 and is no longer manually adjustable.

Be aware that beginning on the B230 engines (1985 and newer 4 cylinder engines) the crankshaft pulley is also a vibration damper. The outer part of the pulley is vulcanized to the inner part of the pulley. If the vulcanization fails, the timing mark will appear to rotate around the pulley when viewed with a timing light. The pulley should be replaced if this occurs for two reasons: 1)To ensure that the timing is set to specs and 2) If the damper shifts it will create damaging vibrations and very expensive damage if it comes off.

Power Timing

As engines age, lots of things can change internally. The compression can drop due to worn rings or camshaft wear. It can go up due to repairs to the head or a build-up of carbon. Fuel delivery can also change significantly and the ignition system may be weak. All these variables can affect the ideal timing setting. One way to deal with this is to “power tune” the car. Start at the factory recommended base setting and then gradually increase or decrease the timing in 2 degree increments until the car no longer knocks under hard acceleration from 20 mph to 50 mph in 3rd gear or drive. The idea is to run as much base timing as possible without knock under high loads.