Baldy

1. Ok, so an aftermarket ECU lets you control your injectors and timing and stuff, right?

2. What else does it let you do?

3. What do the CAS and trigger wheel do?

4. What's the difference between them?

5. How do they work?

6. What is the significance of maps, and what is the purpose of different maps?



Like I said, I'm just trying to get a grasp on this stuff, just so I can understand the stuff I read, and possibly putting it to use later.

j9fd3s

1. yes

2. its up to you and how many outputs you have. for example on the microtech you have 1 output, you can run the fans, or the bac valve. on some of the others they give you more and you can pretty much run everything (i'm running the electric metering pump, the fans, tach, bac valve, boost control, and i have room for more)



3. the cas tells the ecu where the engine is rotationally, so it can deliver the spark at the right time, and the fuel too. ie the ecu needs to know when the engine passes tdc so it can fire the #1 rotor at 5degress atdc



4. basically a trigger wheel is a wheel with teeth machined into it, and it is mounted on the crankshaft (can be on the cam too) and sensor(s) are mounted so as the crank turns the ecu counts the teeth, usually there is a "home" tooth, and thats like 0 and it will count up until it hits home again. the cas actually has 2 sensors in it, its got a fine tooth wheel, and a home wheel. the big differece in the cas is that its mounted remotely vs directly on the crankpulley



5. its either read by a magnet, or a hall effect sensor, breakers points etc



6. basically since you control the air, the ecu needs to be able to supply the right amount of fuel and spark for any given situation.

every ecu has load sensor(s) (like an afm, or a map sensor, or tps), that it uses to determine the engine load or airflow. it will also use the other sensors (coolant temp, air temp, barometer, etc) to make corrections to the basic load amount as air varies in density with temp/humidity/altitude. "maps" are how the ecu determines what to output. what the ecu will do is look at the rpm and the load input (afm, for example) and it will either calculate an injection time (like the stock ecu) or it will go to a "table" or a "map" where a number is stored, this is the injection time (or ignition), and then it will look at the corrections (usually in %) and fire the injectors.



the actual map values vary with each motor. as they all vary, in things like porting, exhaust setup, intake etc etc. in addition the factory is looking for emissions, drivability, it cant explode on regular gas, and its gotta last for 100k miles, power is way down the list, while drag racers are looking for power, it doesnt have to do anything else, road racers are looking for drivability, and usually durability etc etc. so maps are usually a compromise between a few different things

Baldy

neat, that explains a lot. So a map is like a formula, different formulas with different variables.



so if you ditch your AFM (or other stock sensors), how does the new computer comensate for this data? Does it just derive it using another combination of input sources, and referring to the map?

Sinful7

The computer needs input from all your sensors to function accurately. Some ECU's may default to a ultra-rich setting if some sensors are bad. On many cars, sensor failure causes the vehicle to enter 'limp home mode'.

Baldy

so how does switching to an aftermarket ecu let you get rid of your afm, as I've heard so many times?

j9fd3s

well the stock ecu is setup to run primarily from the afm. the aftermarket ones are setup usually to use a map sensor, although you can keep the afm if you want to



an interesting thing about the stock ecu is that is has a lot more features than any aftermarket one, ie it runs the smog system, it knows what gear its in etc. the flip side of the added features is that they needs to be plugged in/working.

rmaiersg

Well any that are available...

CypherNinja

Here's a good link to a presentation on FAST's site which talks about all the different kinds of fuel injection/sensors/calculation methods/air metering methods/etc......



http://www.fuelairspark.com/common/informa...files/frame.htm



Its not all directly relevent to the RX-7, but VERY informative to someone who doesn't know anything about it.

j9fd3s

not bad, its laid out very nicely.

Baldy

Neat, I think I understand the basics of it, but that article was a little over my head.