Q—My ‘76 912 E just does not have the power that I expect…I had another one that ran better. Some smart-Alec said “put a six in it.” But I like the car, it is well-balanced, inexpensive and here I go again, defending my choice of Porsches. Brad
A –I sympathize with you Brad, for more than 50 years people have asked if my Hudson was a Mercury. Fools!…but back to your 912. The basic theory of engine power revolves around three things: air, fuel and spark, all in the proper proportions and at the right time. When you say it is not running well, trust your intuition. If you drive it far enough when it’s running poorly you can damage the engine.
To get the proper volume of air into the engine involves the air filter, air flow meter, engine valves and their proper adjustment. Once the air enters the engine, it has to be compressed. To verify this, you need to have the compression and cylinder leakage tested to determine the basic soundness of the engine. This also gives you the opportunity to inspect the spark plug coloration and condition. If you find one plug that looks different than the others, you might need to take a closer look at that one cylinder.
The next step in diagnosing and verifying performance issues is to perform an under hood inspection paying special attention to the electrical component wiring and connections. This inspection will also visually inform you of rubber hose connections, fuel lines, etc.
Spark to fire the fuel air mixture is another critical factor to making power. Common distributor problems include ignition points which burn or wear out, advance mechanisms that get sticky due to lack of lubricant, internal springs can be broken, weak, or fall off. Engine ignition timing and advance can be tested using a timing light with an advance dial. Old-timers have tools like these. Having a well functioning ignition system before attempting any advanced diagnosis is a must to avoid wasting time and money.
Your fuel injection system relies on sensors, wiring, voltage, injectors and the computer. Common issues include voltage losses due to old wiring or loose terminals, sensors that have gone out of range and that electro-mechanical device known as the “air flow meter” (AFM). Over a period of time, the AFM wears and it can send erroneous signals to the computer leading to an overly rich (too much fuel) or lean (too little fuel) mixture.
After the electrical system is put in order and rubber parts are corrected, then I get out the smoke generator. With smoke under low pressure, the intake system can be tested for leaks in the under hood components that lead from the AFM to the cylinders themselves. This is done to ensure that ALL the air entering the engine flows through the AFM. Air bypassing the AFM through leakage will upset the fuel mixture and cause the mixture to go lean (too little fuel).
So let’s say you have gotten to the point where the compression, cylinder leakage, ignition, electrical, breather, and vacuum systems all pass muster. Next step is fuel pressure. Your fuel pressure MUST be within specification or the engine will not produce power. The fuel pressure regulator on many models also has a vacuum hose attached to it which will increase fuel pressure during acceleration for more power. If that component were to fail you could get too much or too little fuel.
So with every component tested and verified while the car is stationary, how can you test it dynamically? On the road! For validation of the fuel injection system, I suggest a wide band air fuel ratio monitor gauge. In basic terms, this component “sniffs” the air fuel ratio at the tail pipe (or in the exhaust) and displays the results in real time. With this gauge, you can drive the car under various conditions to find out whether the engine is running rich, lean, or right on the money. This gauge works with fuel injection or carburetors and with it the fuel curve can be modified as needed to produce the maximum power your engine is capable of…even if it is a classic like yours. I like this method better than dyno testing since it is done under actual road conditions compared to simulated conditions.
Gone the way of the dodo bird, air flow meters, points, distributors and routine adjustments have been rendered extinct by the modern “engine management system”. Your classic cannot adjust it’s own ignition timing or fuel mixture but if you have the patience and budget to follow this process to the end, you can have another great running 912 E. The best part is once it is properly sorted out and tuned, it should rarely need to be done again. –MC