General questions about engine parameters - : The site for all your Ford Mazda and Volvo needs
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post #1 of 2 (permalink) Old 10-11-2006, 09:15 PM Thread Starter
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General questions about engine parameters

I am posting this because a friend of mine has had some issues with engine timing, I know every car is set differently but the should be some rules of thumb that I can go by to help him out before he goes to get raped by a stealership. I have the software on my laptop to look most all the numbers the ECU puts out. Any answers would be very helpful.

NOTE: The questions below are NOT specific to the Mazda series of engines.

1. What would be a good fuel / air mix be
2. Should the timing be advanced or retarded at idle / high revs
3. About how long should it take for the ECU / TCM to "re-learn" after being reset

And if anyone in here is a former / current Focus drivers here is a link to a post I made on another site [url][]


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post #2 of 2 (permalink) Old 10-12-2006, 09:09 AM
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Re: General questions about engine parameters

Proper air fuel mixture when warmed up (coolant up to temperature and O2 sensor readings varying instead of holding constant) is in the range of 14.4-14.9:1, it should be in that range except under high throttle. Small blips of richer or leaner are not a problem.

Under warmup situations or under high throttle air fuel is likely to be in the range of 11.5-13:1 and is normal.

Timing advance should allow full combustion of the mixture around 20 degrees after top dead center. The spark has to occur before this as it takes some amount of time for the flame front to travel through the cylinder. Generally the base timing should be in the range of 8-14 degrees BTDC (before top dead center)...this allows the flame front to tavel sufficiently to strike the piston when it has reached 20 degrees after top dead center (ATDC). This timing is the BASE timing, it will vary depending on engine speed on all motors, and most it will vary based on throttle positition, engine knock, etc. I have seen numbers as steep as 40ish degrees BTDC under very light load and 3000-4000rpms cruise.

It should maybe 15 seconds to a minute after the engine reachs fully warmed running condition to relearn all settings, in a few cases it might take a few seconds to a minute after returning to idle for the first time after reaching warmed up condition to manage this. However, the ECU is constantly relearning and adapting to running conditions, but the above should cover its ability to reach a proper air fuel mixture and timing under most conditions.
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