open loop on coasting?

454cid · Post by **454cid** » 03 Sep 2022, 16:21

Last night, I decided to take a look at live data on the way home from work. I had smelled exhaust when sitting idling, much like I had when my O2 sensor was bad. I think it was just exhaust from the many other cars leaving the parking lot, as the O2 seemed to be functioning fine. I did notice that when I closed the throttle for a few seconds, such as when making an exit from freeway speeds, the car would switch to open loop for a second or two. Is this normal, or indication of a problem? I thought maybe it's the equivalent of a carb systems dashpot?

454cid · Post by **454cid** » 04 Sep 2022, 17:33

No one has noticed this or has any insight?

Post by **volvolugnut** » 04 Sep 2022, 17:43

Holiday weekend. Many regulars are not posting. I have no insight for you.
volvolugnut

Post by **Sveedy** » 04 Sep 2022, 19:17

I saw this, but the only thing I know about it is that the car should be in closed loop when coasting. Maybe it has something to do with the ECU noticing the leaning out because your suddenly not demanding fuel, and it's figuring out what to do. I just installed a AFR gauge, and when I take my foot off the throttle and coast, the gauge will sometimes spike briefly off the chart. This is normal, so maybe your seeing something similar. All I got...

Post by **abscate** » 05 Sep 2022, 05:47

I seem to remember short term fuel trim drops to 0 on over run which is probably telling upu it’s going open loop temporarily. I would have thought doesn’t set the open loop flag, but that’s why I don’t think too much anymore…

454cid · Post by **454cid** » 05 Sep 2022, 15:59

abscate wrote: ↑05 Sep 2022, 05:47 I seem to remember short term fuel trim drops to 0 on over run which is probably telling upu it’s going open loop temporarily. I would have thought doesn’t set the open loop flag, but that’s why I don’t think too much anymore…

Yes, I did see stft going to zero.

I'm about ready to fill up with gas again, so I'll check mileage again..... it's been hanging right around 24.x-25.x mpg with mostly highway driving anywhere from 55mph-80mph.

Post by **abscate** » 05 Sep 2022, 18:01

Good mpg for a turbo. Bit low for an NA.

454cid · Post by **454cid** » 06 Sep 2022, 02:48

abscate wrote: ↑05 Sep 2022, 18:01 Good mpg for a turbo. Bit low for an NA.

Hmm, it's only rated for 26highway. What's normal for an NA? Any ideas on what I should look at? I've got the tires aired up to 36psi, per the alternate air pressure printed on the gas door. O2 sensor got replaced with a new Bosch when the original pooped out, as did the TPS. Ignition has been done.... well original coil. LTFT hangs right around 3%.

I should replace the fuel filter, as I haven't done that yet.

I also have noticed that my miles traveled may be a little off.... no not because of tire diameter, but It seems the 850obd2 app only reports mileage to the nearest 10 miles.

Post by **abscate** » 06 Sep 2022, 04:45

Our two NA p80s get 30 mpg highway, my p2 34mpg

In dead of winter , they might drop to 28 mpg highway

My Evita log….

Hot test run to Boston at 65-70 mph
Returned 29.9 mpg on 91 octane

Post by **volvolugnut** » 06 Sep 2022, 06:34

Compare the MPH when these MPGs are reported. I suspect 454 may have faster highway speeds with A/C than Abs on cooler New England highways.

Fresh Volvo coils have been reported to improve mileage.

Your mileage may vary.

volvolugnut