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]

What WB do you have?
How old is the lambda? 4.2 or 4.9 LSU?
Have you been running the engine with no power to the lambda? (bad)
What are you using for a TB? dual TBs have similar sync issues as carbs.
How much advance on the timing?
Are you 100% sure of your wiring connections and grounding?
How far is the bung from the head?

The WB usually only has 4 wires but some have more, the WB signal is a just number between say 0.60 to 1.40 and the gauge does the math, I'd assume MS has a setting for type of fuel, 14.7 for gas and does the math as well.
BTW it's very simple math, a reading of 1.0 X 14.7 = 14.7 AFR that you see.

The two different readings are odd.
The fast swings of the meter Vs ecu may be normal, my SDS O2 ecu reading seems to dampen the swings compared to the meter, but they're the same reading.
I'd expect even if the meter had an error the same number would be showing on both the meter and ecu.

[Mark Henry]

dp-

[wndsrfr]

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

First step is to replace and properly calibrate the O2 sensor....

[Mark Henry]

First step is to replace and properly calibrate the O2 sensor....

That's why I'm asking which WB meter, older unit's need calibrating, new one's are self calibrating.
I have a new 4.2 that I'll likely never use if you need one.

[VaccaRabite]

The O2 bung is in the pipe between the cans on my Triad muffler. I’ll have to find my build thread to see what WB I’m using, but I have serious doubts that’s the issue. I’m camping right now so I’ll update this with more info on my setup when I have a moment.

[VaccaRabite]

The Wideband is an AEM 30-2310
The wiring was done by @McMark as part of the injection system I bought from him.

I don’t have a separate AFR gauge on my car. The gauge I was looking at was one on my tuning laptop, getting it’s info from the ECU.

Zach

Zach

[VaccaRabite]

I recalibrated the AFR EGO, burned it to the ECU and did a little logging.
The engine is still showing a lean condition in the AFR, despite fuel table calling for a slightly rich condition. And the car is still acting overly rich. Bogging on throttle etc, while the gauge reads lean.

Trying to find a way to share the log file. Okay, here is the log file:
https://www.dropbox.com/s/lsn1hl75a2rc609/2....04.15.msl?dl=0



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

[ChrisFoley]

Are you sure the system is running closed loop when it's showing lean?

[Mark Henry]

Are you sure the system is running closed loop when it's showing lean?

(IMG:style_emoticons/default/agree.gif) good catch, check to see if you're running open or closed loop.

[VaccaRabite]

Are you sure the system is running closed loop when it's showing lean?

No. And if the ECU isn't set to use the AFR to add or pull fuel my theory is blown. I should have checked that last night while I had the tuning laptop up. I've been working on the assumption that its.

Zach

[crash914]

I have a spare AEM and controller along with a couple sensors if you need them.

[VaccaRabite]

Well, my theory was somewhat dashed yesterday afternoon, but also somewhat supported.

In the ECU, the AFR EGO was set to adjust fuel only under kPa 0 - it was turned off. I set it to activate under kPa 85 which means it will be active everywhere (after warmup) except WOT.

However. Two missing bolts... One on each side. When the hell did this happen?
(IMG:http://www.914world.com/bbs2/uploads_offsite/live.staticflickr.com-1435-1560863682.1.jpg)
(IMG:http://www.914world.com/bbs2/uploads_offsite/live.staticflickr.com-1435-1560863684.2.jpg)

So, before I go to texas next week I need to replace and test to see if there is an improvement.

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

[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