Just something i was pondering.........

in a mpfi car without a crank angle sensor (like my ea81t), i presume the ignition module tells the computer round about when to fire an injector. This won't tell it which injector to fire though (will it?), so how does it know?

I have no clue what the EA81T setup is, however heres a little knowledge of port fuel injection.

 

You can either have:

 

Gang Fire: This is where all the injectors fire at once, and the fuel/air is carried into the combustion chamber whenever the valve opens. For this setup, a crank sensor is mainly used for RPM, and an angle sensor (and or cam sensor) is not REQUIRED, but can be used. This setup is very similar to TBI. (when using only an RPM sensor, all the injectors would deliver half the fuel needed for that rotation, and the next rotation the other half would be delivered)

 

Bank Fire/Group Fire: Back in the 80s the gas quality wasnt that great and so having the fuel resting there on a closed hot valve caused carbon deposits to collect on the valve, restricting air after a while, also causing that cylinder to run lean, etc etc... SO what was developed was bank fire, where half the injectors would fire in one rotation, and the other half would fire in the other rotation, reducing the time the atomized gas loitered above the closed valve. ALSO on larger V8 engines firing 8 injectors at once dropped the fuel pressure considerably momentarily, to reduce this jolt of pressure loss, firing only 4 injectors at a time was more feasable. An RPM sensor and a cam sensor is required for this operation, but not necesarily an angle (position) sensor.

 

Sequential Fire: By far the most superior and effecient system was sequential, cause each injector is able to fire right at the moment the intake valve is opening, with minimum carbon buildup, and more precise fuel control. This requires mainly two things which can be achieved from several combinations of sensors, the computer needs to know the angle of the crank, and when cylinder #1 is. on late model optical destributor ea82's this is acheived with having a circle of slits, but one slit is wider. (its been a while since I have looked at one, does that sound about right?). It can also be achieved with having a sensor ring on the crank, with different numbers of pulses for different angles, and a single pulse on the cam for cylinder #1.

 

Anyway. I believe early model 85-86 EA82 MPFI systems were gang fire, and in 87 they switched to sequential. Unfortunately I dont know about the EA81T's I believe I have talked enough, anyone feel free to make any corrections

 

-Mike

Yeah, that explains it. The injection system for the ea81t is the same as the early ea82, so far as i know. Cheers.