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The OP is expressing concern about the -100 fuel trim.I also did a test at 2000rpm and it only went down to a steady 33kpa also did the same test but watching short term trim and it stayed at a steady -100% I’m not sure at all what’s going on. Thanks.
A simple test that passes no exhaust gas over the O2 was suggested to test that.
To be fair none of us have seen any evidence it's added any meaningful fuel to the short trim no matter what has been tried.
As stated it's hardly turning positive even when an injector is unplugged and that cylinder is just pumping air into the exhaust and over the O2.
Yes it's taken away less, but it's at best evened out the trim with it unplugged.
I would think even a filthy rich engine would throw the trim over more positive if a 1/4 of it's total fueling was suddenly taken away like that.
Just as higher pressure in the intake causes the rich running at idle, a rich running engine will use less air so will cause less vacuum in the intake.
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