Belgian1979 wrote:It hunts severely when running stoich or leaner and even constantly starts missing. Some cams just don't let you do that
Get rid of closed-loop autotune, if you have problems with stoich AFR closed-loop is not usable either. Even with very mild stock cams std engines have almost zero ignition advance at light load to keep EGT high enough to keep lambdas alive. With high-overlap cam EGT recirculation with rich afr will certainly lower egt to point where false lean happens, and ecu corrects to very rich afr, which ruins engine incredibly fast.
0° advance at light load ? Seems counterintuitive to me. Engine will tend to run hot under those conditions as well.
Are you now referring to a NB O2 sensor or a WB O2. An WBO2 has it's own sensor heating.
Belgian1979 wrote:It hunts severely when running stoich or leaner and even constantly starts missing. Some cams just don't let you do that
Since we're touching on this topic, how much total spark advance is programmed in during light throttle cruise? Too little will cause surging; it needs as much as 50°+. Some mid-eighties GM vacuum cans were 30°...
Belgian1979 wrote:
0° advance at light load ? Seems counterintuitive to me. Engine will tend to run hot under those conditions as well.
Are you now referring to a NB O2 sensor or a WB O2. An WBO2 has it's own sensor heating.
Stock NB sensors have heating too, but even with heating they are not accurate at very light loads if engine is tuned to best power. Stock ignition maps call for near zero load ~10 degreee timing which increases way over 40 degree when load increases. There is no way that WBO is accurate at richer than stoich, normal ignition timing and near zero load, it will show lean condition and ecu will richen up, and if ecu autotune has not sane limits if will go pig rich - and in such conditions it's not uncommon to stick oils rings in piston with a few thousand miles. And the result is smoking engine in decel.
Coming back to this old thread of mine. I just recently acquired a smoke machine and connected it up to the engine. I see smoke coming out of each individual intake channel (ITB manifold). As said before I have a vacuum chamber underneath each runner connected with a small hole to the runners themselves. I couldn't quite see the source as the runner got filled up with smoke but due to fact that each and every runner smokes, I assume that at least this is not caused by an openstanding valve and smoke migrating up from the crankcase through the ring gaps and such.
The vacuum chamber (underneath the cross ram runners forming a 'v' have a SS plate that closes it towards the lifter valley. It is sealed up with blue silicone. I assume that it has failed. Would it be possible that oil migrates up into the lifter valley to create the issue ?
Absolutely!
A manifold vacuum even in your vacuum chamber under the manifold if it is leaking under vacuum will pull oil up from the lifter valley area and send it through those individual ports into the ITB inlet runners and burn it. When you are decelerating you will have maximum vacuum and thats when it would happen the strongest.
Is there a way to plug temporarily 7 of the 8 holes and then put some slight air pressure into that chamber with a hose and just pressure when you blow on it to see if it holds any pressure. If it has a leak into the valley it should bleed of and you might even hear the leak if its quiet enough.
