OK, I am going to try and answer a MILLION questions all at one time and through in a VERY GENERAL explanation to go along with it.

Regarding Computer Controlled Vehicles:
Since the late seventies and early eighties, the factories have been selling vehicles with different degrees of computer controls. The first systems were just controls for the ignition and timing, but the systems soon were controlling fuel flow, cooling fans, air conditioning, brake systems, air bag system, even stereos and more. The point is, NONE OF THESE THINGS CAN BE PROPERLY REPAIRED IN A BACK YARD USING AN ADJUSTABLE WRENCH. Computer systems used on modern vehicles are more complex than the systems first used to put a man into space and they require a Technician with an equal amount of ability and knowledge in order to be able to repair them PROPERLY.

Let me give you a little GENERAL information. A internal combustion engine requires different fuel flow for: Idle, Cruising under light load, acceleration, full throttle and different engine and air temperatures, plus starting warm or cold. For many years a Carburetor was used to control fuel flow for these different stages, but very few Mechanics ever took the time to learn the different systems or the requirements. Engine timing also had to change with different engine requirements, Cold starting, warm starting, Idle, acceleration, and different engine loads and speed. This used to be handled by a distributor that again, few Mechanics ever took the time to figure out. Now, a computer system gets information regarding: how cold the engine is, how cold the air is, how much throttle is being applied, how much load the engine is under and supplies fuel accordingly. Plus the system is helped with a sensor in the exhaust that measures how much UNBURNT oxygen is present and also uses that information to maintain a PROPER fuel mixture. The computer system controls when each cylinder is fired and adjusts that firing to different engine loads, vehicle speed, temperature, throttle and even what gear the vehicle is in. Each vehicle computer has a different PROGRAM, depending on engine size, transmission type, gear ratio, tire size and even accessories.

Are you starting to understand?

And now a few facts about engines: A cold engine requires more fuel to start and run than a warm engine. An engine under full load requires less timing than a engine under light load. A rich mixture requires less timing than a lean mixture and a engine requires more fuel at full throttle full load, than it does at full throttle no load. Some computer-controlled vehicles have a warning light system that is usually ORANGE and it comes on when the computer detects a problem in one of the systems that it monitors. This light was made ORANGE because it is a WARNING that there is something WRONG and it MUST be repaired AS SOON AS POSSIBLE. Many vehicles DID NOT have a warning light system and the only way a driver would find out there was a problem was when it was TOO LATE. (Except OBD 2, ANOTHER STORY.) In order to repair these vehicles, a Mechanic or Owner MUST know what is causing the problem before any repairs are made and the only way to KNOW what is wrong is by TESTING THE SYSTEM AND COMPONENTS. Many Companies make special tools called SCANNERS, that can give information out of the computer system, but there are many vehicles that WILL NOT give out information. In these case, manual testing of EACH component may be required, involving a lot of time and money, just to diagnose the system PROPERLY. If you have a vehicle that stalls, it is a problem in the system that is designed to KEEP IT FROM STALLING. (And you MUST be able to check out the SYSTEM in order to find out what is wrong.) If you have a vehicle that uses too much gas, it is a problem if the SYSTEM that controls fuel flow and timing. (And again, you MUST be able to check out THE SYSTEM before repairs are made.)

There are only TWO ways to repair Computer Controlled Vehicles.
1, Have PROPER testing Equipment that is very expensive.
2, Manual testing that can be very time consuming and using the TRIAL AND ERROR METHOD, where you just keep replacing parts until the vehicle gets fixed, or the owner runs out of money and TRADES THE VEHICLE OFF. (And someone else BUYS this problem that the previous owner gave up on!!!!)

"TOOT" Rick "The Wrench" - May 31,1999
Copyright of Rick The Wrench, 1999