Peek at MembersPage/MarcellGal/EngineSwap/AirFeed (idle air section)
The bipolar stepper has 2 coils, that is 4 pins together. Measure resistance between each pair of pins, and document it. Usually 40 Ohm. This rover (?) had 64 Ohm stepper widings.
It is possible to connect the 2 coils in 2 ways regarding the stepper outputs:
- A-B, C-D recommended, (iac_step_seq=0xC9 or 0xD8)
- A-C, B-D
- A-D, B-C this engine was connected this way (iac_step_seq=(0x1E = 30) or (0x2D = 45)
The ends of the same coil must be driven a half period away from each other, and A,B,C,D are encoded as 0,1,2,3 respectively.
However, if you reverse one coil, you get reverse stepping sequence. Easy to notice this: engine gets less air as you bump up the mdi.. (forced iac position) during the tests.
This is not easy to measure beforehand, so you have 50% to get it right first. Easy to change config. So 2 config "directions" possible for each wiring (one is good, the other is reverse):
- 0 2 1 3 (0x27 = 39) or 0 3 1 2 (0x36 = 54), but historically written as (effectively same):
- 3 0 2 1 (0xC9 = 210) or 3 1 2 0 (0xD8 = 216) so this is what you likely find on cavewalls
- 0 1 2 3 (0x1B = 27) or 0 3 2 1 (0x39 = 57)
- 0 1 3 2 (0x1E = 30) or 0 2 3 1 (0x2D = 45)
History and LESSON
Unfortunately installer forgot to document this (it would have taken 2 mins when he made the install (when car-back was off), while it took half day to investigate with the car-back on. The car owner apparently doesn't have proper drawings or connect-lists of his engines's, VEMS installers should make sure to leave this info at the owner.
- we searched for a similar connector to connect to IAC
- made a test-fixture (connector with cable) to connect to iac
- that can be controlled from a spare-VEMS controller (this turned out to be unnecessary, but it was made the same time with the fixture to avoid a short drive back-n-forth)
- swapped to the test-fixture and found how it is in fact connected
- controlled from the spare VEMS