Working on some various bits & pieces for my car, I had a few questions that I could use some information on.

How does the ECU detect that the brake light has failed? I assume that's what the "brake light" indicator is - for a burned out bulb. I'm planning to try converting my brake lights over to LED based ones for faster response & such, but I'm suspecting that will trip the sensor if it's amperage based.

Also, how would one detect the duty cycle on the injectors? I'm planning to tap into the ECU output going to the injectors, but I'm not sure exactly what the output is - does it go to 12v when the injector is open, or go to ground, or what?

Finally, what is the voltage range on the TPS sensor? I can find this without a problem if I want, but if anyone knew, it would be helpful. I'm planning to wire an alarm to an A/F meter to alert on a lean condition at open throttle settings.

Thanks!

-=Russ=-

 

Well, I found the answer to the brake light question (it's current based, so LED tail lights would cause problems - though some people have worked around it).

Anyone care to give me info on the other stuff? I can figure out the TPS by myself, but information on the injector driver would be quite helpful.

If I get these things working, I'll probably be selling modules and have the schematics online.

-=Russ=-

 

It doesn't, the CPU does. The warning is triggered by insufficient current.
It will.
You need a DMM that can measure frequency and calculate duty cycle from that. Most mid-range DMM's can do this. Easiest is to tap into the injector wires at the ECU.
0-5V. Note the the S4 TPS only measure the first quarter (approximately) of the throttle travel, i.e. closed throttle = 0V, 1/8 throttle = 2.5V, 1/4 throttle (and above) = 5.0V. This won't be much good for your planned warning system.

 

At what point of throttle opening does the ECU switch from closed loop mode to using maps? Given that I can cruise down the highway doing 85mph at maybe 1/8th throttle, I'm hoping that 1/4 throttle and beyond would be open loop mode, since the S4 ECU has no way to measure throttle position beyond that point (other than indirect airflow/RPM calculations). One way to find out, I suppose (unless anyone knows for sure).

Anyone with an A/F meter installed want to help me out here?

-=Russ=-