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]

Where is the Lambda mounted?
I've measured a huge temp drop from one side of the flange (header/exchanger side) to the other side (muffler side), the lambda needs heat to give correct readings.

So what I'm saying is the lambda has to be in the header/exchanger to give a correct readings.

http://www.914world.com/bbs2/index.php?showtopic=338730

But this still doesn't explain to me why the ecu/meter have different readings.

[VaccaRabite]

Where is the Lambda mounted?
I've measured a huge temp drop from one side of the flange (header/exchanger side) to the other side (muffler side), the lambda needs heat to give correct readings.

So what I'm saying is the lambda has to be in the header/exchanger to give a correct readings.

But this still doesn't explain to me why the ecu/meter have different readings.

The lambda is in the muffler in the collector pipe where it can sniff all the cylinders (in theory). If I put it on the exchanger it would only be able to sniff one cylinder. The EGO probe has a heater element and is up to operational temps in a few seconds. In the below pic you can see where the bung is, in the pipe leading from the exchanger flanges to the main muffler.
(IMG:http://www.914world.com/bbs2/uploads_offsite/live.staticflickr.com-1435-1560875365.1.jpg)

The ECU is the meter. I don't have a separate dash gauge in the car for the AFR. While I'm watching the AFR, I'm looking at the virtual meter on my tuning laptop (driven off the ECU) and looking at the AFR map table to see what the AFR is supposed to be at that given engine speed. The table projects a dot in the location where the table is reading at that point in time, that moves around as the engine changes.

The map is the target AFR (what the ECU is supposed to be providing) and the lambda is sensing what actually happened.

An air leak in the exhaust would explain some of it. But since the lambda was not set to adjust fuel, my theory about adding too much fuel kinda went to shit.

Which means that it actually could be really really lean at and off idle, causing my low speed drivability issues. It just starts nicely with the warmup enrichment.

I think that when I fix the two missing bolts (and test), I'm also going to turn up the fuel pressure a little and see if that does anything.

Its a mystery though (or I'm straight up not up enough of the tuning learning curve yet). If I am lean after warmup, I should be able to close up the IAC more without changing idle speed since the engine is already burning all the fuel and has leftover air. But if I close the IAC any more then it is, idle starts to stumble. And my head temps... I could not much ask for nicer head temps (measured at the number 3 spark plug which should be the hottest place on the engine).

Maybe I should just step away from the whole thing until the pros can look at it in July.

Zach