AFR reading lean, AFR table showing rich..., guessing an exhaust leak? Other options? Options

[VaccaRabite]

As I get closer to Dyno Day for my 914 (July 22), I have a theory about some of my drivability issues.
This car has modern EFI, not carbs or Djet/Ljet. It’s running MS2 through a Microsquirt controller.

The car is clearly very rich. It bogs heavily coming off idle, to the point that it will sometime stall out if you don't dance the accelerator pedal just right at a stop sign or a traffic light. Last oil change I could also smell gas in the oil. And while Bob Hill ( @saigon71 )was driving my car the other night I occasionally saw puffs coming out of the muffler on overrun. Kinda cool, in a way, but not great.... lol.

I hooked up my trusty ancient tuning laptop and opened up the AFR table while looking at the AFR meter. Where the table is showing ~13, the gauge was swinging ~15.5, especially just off idle, when the car got hot.

So my theory is that the ECU is reacting to a false LEAN condition and dumping huge amount of gas into an already rich environment.

So, my possibilities are:

1. Exhaust leak at a joint
2. cracked SSI exchanger (UGH)
3. incorrect values for the AFR entered into the ECU (I doubt this one, given that the issue gets worse as the engine gets hot)
4. Some issue I have not thought of yet...

@mcmark
@Eric_Shea
@Mark_Henry
@chrisfoley

Thoughts?

Zach

[Mark Henry]

C&P from 14point7

The normal operating temperature of the Bosch LSU 4.9 is 780[C]. Lambda Accuracy is heavily dependent on sensor temperature, only when the sensor is at proper temperature is Lambda accurate, -/+ 25C from normal operating temperatures is considered acceptable. If the Lambda sensor is too cool; readings will tend to look “leaner”, if the sensor is too hot; readings will tend to look “richer”.

If your lambda is too cool you will get a false lean condition, therefore you will actually be richer than the sensor is reading.
Just because you may have a "heated lambda" this is only a warm up function that turns off. You have to have proper heat from the exhaust to operate correctly.

[VaccaRabite]

C&P from 14point7

The normal operating temperature of the Bosch LSU 4.9 is 780[C]. Lambda Accuracy is heavily dependent on sensor temperature, only when the sensor is at proper temperature is Lambda accurate, -/+ 25C from normal operating temperatures is considered acceptable. If the Lambda sensor is too cool; readings will tend to look “leaner”, if the sensor is too hot; readings will tend to look “richer”.

If your lambda is too cool you will get a false lean condition, therefore you will actually be richer than the sensor is reading.
Just because you may have a "heated lambda" this is only a warm up function that turns off. You have to have proper heat from the exhaust to operate correctly.

So where are people putting their sensors that gets more then one cylinder but also meets the requirements for hot exhaust? Unless I move back to a header with a 4-1 collector I can't see how this is possible. And I give up heat, which I'm trying to put back into my car - at least enough to keep my windshield defogged on humid MidA days (seems to be theo nly kind of day we have anymore...)

Are people using dual sensors and only measuring two cylinders? Several people have used AFR meters in their cars and gotten more or less accurate responses, where are the bungs going?

Zach