legacycentral bbs

a bad misfire would show up at the O2 sensor as a huge rich condition,. off-the-charts rich. That would certainly cause the ECU to cut back on fuel, but totally off, maybe and maybe not

true fuel cut should be pretty rare unless overboost is detected, so I wonder if a lot of what is thoguht to be fuel cut is really some other malfeasance.

the interesting thing is, if it were a misfire, it would take a couple seconds for the fuel to be cut back, just like you are describing. I'm liking that heat off the intercooler thoery, it does seem to fit

We actually see the injectors shut off right when I get the FC and before that event there is no noticeable misfire or anything.

I agree that the hot ignitor theory is very interesting, it's just that apon reflection I'm unsure that it could cause the fc.

professor wrote:a bad misfire would show up at the O2 sensor as a huge rich condition,. off-the-charts rich.

Off-the-charts lean. The sensor measures oxygen, not hydrocarbons, so a bad misfire is read as lots of unburnt oxygen.

true fuel cut should be pretty rare unless overboost is detected, so I wonder if a lot of what is thoguht to be fuel cut is really some other malfeasance.

It's apparently not rare at all. Matt's seen it a bazillion times.

it would take a couple seconds for the fuel to be cut back, just like you are describing.

This definitely isn't some closed loop correction gone awry. For one thing, he's not in closed loop at WOT. For another, I don't recall any fuel trims when this was happening. And anyway, fuel trims can't reduce pulse widths that much.

But if the ECU does see a momentary lean reading from the oxygen sensor while the MAF sensor is railed and the TPS indicates WOT, that might upset it enough to trigger fuel cut.

So maybe.

>>>Off-the-charts lean

oops, yes, I stand corrected

what would really likely happen with misfire is a real crappy and oscillating O2 sensor reading, but it definitely would tend toward lean