Hi Everyone.


I'm putting this up because I'm pretty stumped.

My spool-up wideband measurements have always been totally whack. It doesn't matter if I'm (trying to) tune my AFRs with lean-spool off, or reviewing street/track logs with lean-spool on. At spool-up, there is always a significant delay in the real AFR compared to the logged ECU AFRMAP.


Here's a great example that really highlights the issue. Black line is wideband reading (LC-1, positioned near front o2 between t/c and cat, analogue sampling). Purple line is logged AFRMAP.







Things of particular note here...

• There is barely any lag when the ECU gets off stoich and drops AFR straight to the 12s.
• There is no lag at the top of second gear, when AFR heads south again.
• There is no lag at the throttle-off point at the end, where AFR heads north.

But what's with the spool-up readings?


Side note: I don't care about the "Y" axis difference between AFRMAP and wbo2 reading. Just thought I'd say that out loud.


I care a lot about the huge apparent "X" axis variance between AFRMAP and wbo2 reading during spool-up. This weird behaviour is the source of all pain and suffering in my attempts to get to grips with my 4B11's fuelling.


I do have some ideas rattling around my brain (honest). Feel free to exclude them, ridicule, or suggest new ones!...

1. There's some sadistic ECU behaviour I don't know about, where it decides to delay its fuelling changes.
2. My LC-1 is hopeless at measuring AFR during spool-up.
3. Turbos do crazy things to airflow during spool-up.
4. My fuel pump relay is sluggish, and always takes half a second to kick in, resulting in low fuel pressure at initial WOT.
5. My fuel pressure regulator is sluggish, and is slow to react to its reference boost and raise fuel pressure.
6. It's sunspot activity. Venus shining through marsh gas. A weather balloon.

Regarding 4, I'm going to replace the relay and see. Next week. But honestly, the AFR is clearly offset on the X axis compared to AFRMAP... whereas I'd have expected a short-term lean condition to just offset things on the Y axis. This "feature" has also been way too consistent in my logs - summer, winter, first WOT, last WOT.


Input will be greatly appreciated... coz I'm probably not gonna figure this out all on my own!


Rich

 

point #3 would be my guess..

 

So, stuff like progressively richer exhaust gases following earlier, leaner air... being "mixed" in a blender?

And/or having two very different pathways for the exhaust gas to take once the wastegate opens?

 

It looks like you start off-throttle, so in this particular log its also possible that you are going from mid to high LTFT causing a slight, temporary change.

I've generally had similar problems and notice some tuners make the spool up area more blocky and similar to the WOT area... which I think is in direct response to this.

EDIT: having an open dump is also a possible cause... there may not be enough exhaust gas flow over the sensor temporarily.

 

It could be your enrichment tables aren't adding as much gas as they should.

I wouldn't really worry about it. Your afr drops right when you hit peak boost.

 

Yeah, but I do worry. My last attempt at tidy "lean spool off" fuel tuning was in March - I was well on the way to having it run nicely in the mid-11s. But it all went badly off the rails when working on WOT spool-up around the 4000rpm mark. Two audible pings and a knocksum spike of 26 is as big a slap in the face as it is nasty to your engine.

It's taken me three months to work up the guts to even contemplate a fresh attempt.

If I can get a working understanding of when wbo2 reading are reliable, and when they are unreliable, I'll be able to approach any tricky areas with confidence.

Put simply, this feels like a dangerous gap in my knowledge - hence the query.


And look, I've visited the old "knocksum confessional" here too - "Forgive me, Father, for I have pinged."

Rich

 

I have had that before.. Its really scarey..

AFR's looked good too, search for a thread by me, called something like 'really bad knock all of a sudden'

I really don't know what solved it, heck I dont even know if it was real, it sounded real to me...

 

I put mine 100% down to inexperience - not an unreasonable assumption. I've spent the last three months revisiting everything from scratch.


Here's what happens if I take the WOT spool-up AFR readings at face value, and tune "to" them directly. I end up with a ludicrous fuel map like this...



With lean spool OFF, the rich areas bog the car down horribly at spool-up on the street.

So I just reverted to Bryan's RA base map fuelling, which uses stock lean-spool offsets. That map richens up to 10:1 after a lap on-track, but feels very peppy on the street.



I found your thread - working slowly through it! You were asking the same sorts of questions...


I, too, am curious. I see consistent "delayed enrichment". If it's real, it needs tracking down. If it's due to "measurement accuracy" limitations, it needs an alternative tuning approach (eg. steady-state AFR tuning at load points 140, 160, 180, 200...).

If I just guess and pick one, then I'm flipping a coin and betting my engine.


What if some fuel pressure regulators don't/can't respond quickly enough to reference boost with a corresponding fuel rail pressure increase? Once you're at peak boost, it'll be totally fine... and at light boost you'll be fine... but at very rapid boost increases it isn't up to the job? It would surely look exactly like this...?

Rich

 

your pic is broken..

like I said its been a long time..

I think I fixed the lean spool issue (not related to LeanSpool)... My fuel map is very rich at that point now...

 

Weird... I can see the pic. Don't worry, it's not that exciting anyway.


Yes, I guess that enriching the spool-up area is the sensible thing to do. Guess I'm going to import the "ludicrous" map as a base!

With it that rich and lean-spool OFF, part-throttle driving is sluggish through those load areas. Reckon I'll give it a shot with lean-spool ON, set the table to enlean between 0.3 and 0.5 AFR, adjust the max-load mixtures to suit, etc. Time to get back on that horse.


Thanks for the input, and the thread reference.

As I recall, that big knock incident of mine occurred after 3 or 4 WOT tests, each starting between 3500rpm and 4000rpm... each test not pushing past 5000rpm. It makes sense - if it was really, truly lean (as opposed to a measuring issue), things got hotter in there each time, until all hell broke loose on the 4th test.

As I said, inexperience on my part. What I thought was all wideband lag was in reality a bit more complex. Bryan's RA GST Base Maps use lots of MIVEC mojo... MIVEC gets a lot of coverage in your "sudden knock" thread.


It was the only time I've seen knocksum anything like that. Hope it's the last - it doesn't do the nerves much good at all!


Rich

 

knock up top doesn't matter as much as knock down low IMHO.

I just cringe when I hear knock down low because I know the engine is already under a lot of stress

 

Rich, have you tried tweaking the map load tables around the spool areas to see if that helps the situation any (as in upping the load values a bit in those areas)?

Also see if you can log injector pulse width on one of those delayed fueling pulls.

 

Okay, so I've brought over a "super-rich-on-spool" test map I had from some earlier work, dropped it into my latest ROM, kept lean-spool enabled - with 0.5 AFR offset. And tried it out on a wee drive (or four).

Here's real-AFR versus AFRMAP...



Spool-up AFR no longer looks like a "horizontal offset" lag or delay from AFRMAP.

But it really shows the variance between AFRMAP and real AFR during t/c spool. After reading all 10,000 pages of your knock thread, I gather this is to do with aggressive MIVEC tuning. No worries there at all... as long as I know the logged AFR is "real" and accurately timed, I can manipulate it.


That drive was a relaxed affair before nailing the throttle that time, so the above AFRs are enleaned 0.5 by lean-spool. AFR crosses "through" 13.0:1 at 10psi, on its way down to 11.8:1.

On the track after a enough corner exits, lean-spool will have dialled itself out of the picture. I expect it will then cross through 12.5:1 at 10psi, on its way down to 11.3:1. I'll see how she likes that.


I also noticed that part-throttle mixtures are hovering around 11.3:1 after spool-up, but I can live with that - there's no sluggish pick-up, thanks to lean-spool doing its job.

Here's an example - 50% throttle...




Can't wait to get back into fine-tuning this on the street and track!

Thanks for the support. A few demons exorcised today. Also, some previous tuning work extracted out of "cold storage" and put back into service.

Cheers.

Rich

 

Yeah, I'm actually running smoothed 3xMAP tables now! Bryan sent me a set he smoothed for me while he was working on something entirely unrelated. I don't know if anyone's noticed yet, but he's a little bit of a perfectionist.


I was logging that for a while. It helped me spot the massive comms lag when my LC-1 readings were coming across serial link. Since then, it hasn't really told me anything useful - simply because I'm not experienced enough to "read" stuff into that particular data.

I eventually sacrificed IPW to get my standalone logging speed up to 13-14 cycles per second. More data is always nice, but sometimes you've gotta be ruthless!

Rich

 

Also make sure to check your Open Loop Load tables as they can mess with you at spool up.