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

[rhodyguy]

What do the plugs look like? Do each of the throats read the same with regards to flow? The same at idle and with the arms off of the stops at a higher idle?

[VaccaRabite]

What do the plugs look like? Do each of the throats read the same with regards to flow? The same at idle and with the arms off of the stops at a higher idle?

Not running ITBs. Using a 1.8 manifold and throttle body and a modern IAC valve to control idle air. The idle bypass screw on the TB is closed.

The problem seems to go away under throttle. The car runs great with the throttle open and under load. The head temp are prefect (360 climbing long hills on the freeway at speed in 5th, cruising on the freeway heads are about 325).

Plugs. When I had the NKG b5es plugs in they were showing rich. I changed to NKGB6es (one range hotter) and the plugs are now normal, which is expected as the plugs are hotter and get into self cleaning mode easier.

Zach