Fuel shut off during coast down

[Matt B]

*sorry, typo in the headline - it's fuel SHUT off* (can't change the headline)

I found in the shop manual that the LT-5 shuts off fuel delivery completely during extended coast down to protect the catalytic converters.
I observed my instant fuel consumption today and even in long downhills it never reads less then 2L/100km (sorry, metric...). My Audis drop to "0" reading in such situations. What is expected behavior for my 91 Z? Should it also display "0" fuel consumption at a point?

Sent from my SM-G991B using ZR-1 Net Registry mobile app

[XfireZ51]

Most calibrations from tuners disable DFCO. Is urs completely stock?

[Mikey]

That's equivalent to 120mpg so I wouldn't worry about it. Could just be the minimum sensor reading or computer calculations. As mentioned though there is maybe a possibility of a tuner changing something. Does your car crackle and pop like a Harley motorcycle if you are aggressively on throttle and suddenly let off while leaving it in gear at higher rpm's?

[Matt B]

Originally Posted by Mikey

That's equivalent to 120mpg so I wouldn't worry about it. Could just be the minimum sensor reading or computer calculations. As mentioned though there is maybe a possibility of a tuner changing something. Does your car crackle and pop like a Harley motorcycle if you are aggressively on throttle and suddenly let off while leaving it in gear at higher rpm's?

No, no noises like that at all. Calibration is stock at the moment.
I was just wondering if the reading (though being very low) might be an indication of anything going wrong.
My Z had a crumbled catalytic converter core when she arrived (driver side) and I was wondering how this could have happened on an 18.5kmls car. I mean this ceramic body looked really bad.
However she had her injectors replaced at around 17kmls so I suppose this was the result of one or more bad injectors. But as I don't actually KNOW I thought there might be another issue.

Sent from my SM-G991B using ZR-1 Net Registry mobile app

[1991 Corvette ZR-1]

Originally Posted by Mikey

That's equivalent to 120mpg so I wouldn't worry about it. Could just be the minimum sensor reading or computer calculations. As mentioned though there is maybe a possibility of a tuner changing something. Does your car crackle and pop like a Harley motorcycle if you are aggressively on throttle and suddenly let off while leaving it in gear at higher rpm's?

Mine does this. Although I am running headers without cats into a Corsa. If I run the revs up past 3K rpm and if I am off the throttle just coasting, I get the loud pops. Once the rpms get below 2500, the pops turn into the desired crackles and surges of louder burbles. If I really run it up to say 5500-6K and off the throttle completely to coast down, it is very loud bangs. The kind of bangs I can feel thump the bottom of my feet through the floor board.

The chip was updated to work with headers. I chalked this up to an air leak somewhere in the exhaust system but I have not found any black stripes or marks anywhere exhaust could puff out from the headers to heads and headers connection to the Corsa. The only remedies I have are to keep on throttle and slowly ease off to let the revs drop with less and less throttle or put the car in neutral. I feel like it is a tuning issue but unfortunately, no one around here wants to touch LT5 software for a dyno tune. I feel like those with well sorted cars running no cats and headers do not have this issue and can coast down from 7K with no issues.

Spins rpms and makes great noise all rpm range but once the coast down happens, depending on where the needle is on the tach, you get pops or loud bangs.