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Sadly, no progress at all on avg. fuel economy.
Even though it is now possible to maintain the speed as low as 6-7l/100km momentary fuel consumption @ 100km/h.
This is mostly because I retarted intake cam as much as possible (120 centerline, instead of around 106-110).. vvt (vanos) is great, when it works. I did service both; intake and exhaust vanos. New seals and rings.
And did try as lean as lambda=1.30 at 60-70km/h and up to 1.40-1.45 at 100km/h accidently, when I tested my alpha-n maps (maf not connected) .
- lambda=1.30, no missfiring but lacking power -> maybe could try more advance or intake cam advancing?
- lambda=1.40 still no missfiring, but even less power, so no benefits.. also could try different ignition advance and intake cam advancing
- lambda=1.45, missfiring, but there is that possibility the bank 2 (4-5-6 cyl) is running even leaner so not saying the lambda=1.45 is the limit as for missfiring.
Did try, and currently running the NGK BKR6EQUP spark plugs which are platinum plugs.
Platinum should work as a catalyst for ethanol, but I'm quite sure I don't have enough compression and/or heat to cause pre-ignition because of platinum.
I did notice the engine not being as sensitive for random missfiring, but that may be because of their different design versus Bosch FR7LDC+
Main problem is the engine being a bit unstable on power output.
It can maintain sometimes speed (100km/h) as low as 6l/100km momentary fuel consumption and starts accelerating when more throttle given, so the momentary fuel consomption is 8l/100km.
I haven't yet figured out what is causing that. If I had possibiliy to record in-cylinder temperatures and pressures, maybe that would help me.. but not possible on my budget and limited time.
Anyways, I'm quite sure I've hit the limit where I need to start doing mechanical changes to improve my fuel economy which isn't too bad.
Increasing engine tempereture did not improve fuel economy 'at all', which is actually quite odd. And I haven't been able to reach higher than 96C at 100km/h or even at lower speeds because the engine doesn't seem to build heat at lean burn mode as much (cruising at low/moderate load).
It should be very interesting to test with high compression ratio and faster squish velocity, if I it would be possible to run the engine succesfully with leaner than lambda=1.40
But I do need a standalone ecu and two wideband lambda sensors, because:
1) no safety features, what may already be fooling me and limiting fuel economy gains because fuel trims are limited to +5%, and running the engine fuel trims maxed out to achieve lean burn (not possible to adjust target afr on Siemens MS42)
2) both banks require logging, since the engine will be near missfiring when going very lean mixture, and only standalone ecu can work at that (to keep the mixtures stable enough)
Luckily there is cheap standalone ecu available which is near 'plug and play': speeduino for m52tu/m54.
Other benefit is I can throw away the MDK throttle body and go mechanical (which isn't good for FE tho but reliability: yes), which has caused some problems earlier and not really trusting it.. if the MDK fails = goes limp home mode 2: the car won't move faster than 10km/h if at all.
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