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My 2000 insight almost always runs closed loop fuel system(oxygen sensor is being used to control mixture) However when engine is warm and under low load as in going down a long downgrade it goes to open loop. Is this the controller going into lean burn mode? Anyone know the logic or control system pathway. No error codes. Good mpg.
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Open loop :arrow: Closed loop

Simply refers to whether or not the ECM (Engine Control Module, engine computer) is using data from the O2 sensor to calculate injector on time. On a downhill (or deceleration) your in fuel cutoff mode (injectors are turned off) so therefore by definition your in open loop.

I can't imagine that lean burn is an open loop function as evidenced by the necessity for an LAF type O2 sensor ("reads" the lean burn range).

The loop part of the term refers to the circular nature of the system. O2 sensor data "reads" combustion efficiency (rich / lean) and the ECM then adjusts the fuel injectors on time (amount of fuel delivered) in response.

Of course there are other sensors that have injector on time input too, but their not in the loop. ;)

HTH! :)
 

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I agree with Trekker. Off throttle, there's no fuel going into the engine so the engine is pumping air. The Insight's wideband O2's are much better than other cars allowing it to stay in closed loop at all time (including lean burn). In shortband cars (like my MINI), whenever your floored, it goes into open loop as the A/F drops down into the 10-11:1 range :( . This means it's reading injector values off a pre-programmed chart in the ECU.
 

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kapps said:
This means it's reading injector values off a pre-programmed chart in the ECU.
Not to nit pick, and I'm not 100% sure how a Mini's fuel system works, but many OBDII MAP (Manifold Absolute Pressure) MAF, Mass Air Flow systems are different)) systems are similar.

I'd suspect the RPM, ECT (Engine Coolant Temperature), TA (Throttle Angle) and MAP sensors become the primary inputs for injector timing in open loop.
 

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gisnar said:
However when engine is warm and under low load as in going down a long downgrade it goes to open loop. Is this the controller going into lean burn mode?
Like most modern fuel injected cars, when the throttle is closed, fuel flow it totally cut off. The Insight is a little more aggressive about this and will cut fuel under many zero load conditions.

kapps said:
I agree with Trekker. Off throttle, there's no fuel going into the engine so the engine is pumping air. The Insight's wideband O2's are much better than other cars allowing it to stay in closed loop at all time (including lean burn). In shortband cars (like my MINI), whenever your floored, it goes into open loop as the A/F drops down into the 10-11:1 range :( . This means it's reading injector values off a pre-programmed chart in the ECU.
If your Mini is falling to 10:1 under accell, then there is something drastically wrong. 10:1 will result in a plume of black smoke from the exhaust, quickly foul plugs and wash the oil film from the cylinders. Your oil will be as thin as water and REEK like fuel at oil changes. Even 11:1 is very rich in any naturally aspirated car and still kind of rich in forced induction applications unless you are talking high boost setups.

Your Mini is also ALWAYS reading injector times off of a preprogrammed chart (generally based on MAP vs. RPM). The O2 sensor is just used to correct these times based on current and past A/F ratio. :)
 

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Yeah, I know the ECU takes values from a lot of sensors but when in open loop, the O2 is not one of them. The MINI runs very rich over 4k rpm and when floored, I'm in open loop. There are dyno's of stock Cooper S's in the 11:1 A/F range and John Cooper Works models (still a stock option) close to 10:1. It's supercharged (~10 psi stock) so 12-12.5:1 is what tuners shoot for. The tailpipes are pretty black after a week of driving.[/u]
 

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kapps said:
Yeah, I know the ECU takes values from a lot of sensors but when in open loop, the O2 is not one of them. The MINI runs very rich over 4k rpm and when floored, I'm in open loop. There are dyno's of stock Cooper S's in the 11:1 A/F range and John Cooper Works models (still a stock option) close to 10:1. It's supercharged (~10 psi stock) so 12-12.5:1 is what tuners shoot for. The tailpipes are pretty black after a week of driving.
I can't believe that a car from what should be a competent tuner is into the 10:1 range at only 10 PSI of boost. If cars I built where that badly tuned, I'd cut myself. :)
 
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