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mark houghton mark houghton is offline
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Join Date: Jul 2008
Location: Central Washington State
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Originally Posted by b5aar View Post
Hey mark. Here goes I'm like a caveman with a hand grenade with this stuff. I know how to pull the pin but that's about it. Haha.

I believe k Lambda is in open loop until temperature switch (weber book pg 77?)send closed -open? signal to ecu to receive closed-loop control.also comes out of closed-loop with a throttle position sensor.....others commented from various threads.

Probst book also describes where closed-loop goes to open loop
Lambda sensor cool
engine cool
wide open throttle.

I know kinda vague language but paraphrasing

Hey..finallyfound the paragraph.

"because lambda sensor operation depends on high temperature the system operates open loop before the sensor warms up this can cause driveability problems and increased exhaust emissions do too imprecise mixture control. To correct this many cars have a lambda thermal switch located in the coolant or on the cylinder head of air cooled Porsches to give the control unit an additional input and ensure proper fuel metering during engine warm up. When the engine is cold the thermal switch is closed the control unit send a fixed slightly rich duty cycle signal of 60 percent to the lambda control valve. When the thermal switch warm enough to open the control unit sense of fixed middle signal 50 percent duty cycle when the lambda sensor reaches operating temperature so it signals are valid the control unit switches to close the loop operation. Remember in closed loop the duty cycle signals are constantly changing cycling back and forth between about 45 percent and 55 percent so that the air fuel ratio is maintained near the way to metric lambda equals 1.
Very good, you've got "the book" in front of you!! Yes, the throttle position sensor is something I forgot about, which puts everything in open loop when your foot is on the gas and past idle a certain amount. Makes sense, since the lambda system is really meant primarily for at and slightly past idle conditions, and on deceleration. That's where emissions gurus planned to make our cars puke out cleaner exhaust.

I would have to pull out my Bosch K Jetronic manual (which I don't have at the moment, it's being "ozoned" to clean the smoke smell) but I sure don't recall any temperature sensor that feeds info to the computer. But what we do have is a heating element integral with the O2 sensor to get it up to operating temperature quicker. That, of course, will affect how it responds to the presence of oxygen.

This is all fine and dandy, but still doesn't explain why poor connections at the coil caused your symptoms. Maybe the ground is tied to the heating element in your WUR (power for that comes from the rear fuel pump relay); if it doesn't heat up, it will stay in cold warmup status i.e. rich. Again, just brain bouncing here....blah blah blah.....and blah!
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.

Last edited by mark houghton; 02-23-2014 at 06:40 PM..
Old 02-23-2014, 06:38 PM
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