Fuel cut signal at around 3000rpm in logging

[spacejunkiehsv]

I did some logging the other day with TARI. Since I was getting fuel cut on an earlier (bad) tank of gas, I decided to monitor that signal. As it turns out, the fuel cut signal went from a 0 value to a 1 value a few times, just for one line at a time in the log file. It did not happen at high rpm's like I expected it to. It actually happened at around 3000 rpm. I don't have the log files here at work, but I could share them tonight if anyone wants to see them.

 

My KC values were never negative. I'm running Cobb Stage 1 for 91 octane and actually burning 93 octane fuel, due to my "bad fuel" problems last week.

 

Also, I never felt anything either. Maybe it would have to be a 1 for a certain time span before fuel was actually cut or it was cut long enough to be noticed by a driver.

 

I'm just sharing my information.

[RochNY91TSI]

Interesting... Did you stay on the gas during the whole time that the fuel cut signal showed in the log? And were you at WOT?

[spacejunkiehsv]

Interesting... Did you stay on the gas during the whole time that the fuel cut signal showed in the log? And were you at WOT?

I was on the gas the whole time. I never lifted the throttle. I didn't have a clue about the fuel cut signal until I was looking at the data last night. Last week when my fuel cut happened (at WOT right after a redline automatic shift from 1st to 2nd) I had to let off the gas then mash it again to resume acceleration. Like I said, I wasn't aware of any fuel cut while driving.

 

I was not at WOT. I'm pretty sure it happened while I had cruise control set. I may have had cruise control not set and been at partial throttle though. It was on the drive home yesterday during moderate, but fairly smooth flowing interstate traffic.

 

I plan on looking at my data again tonight. I could post snippits from the log, right around the times the fuel cut signal toggled.

[lookslikeanevo]

log it at WOT... it maybe the 93 oct on a 91 tune\

[spacejunkiehsv]

log it at WOT... it maybe the 93 oct on a 91 tune\

It was about a 20 or 30 minute log, whatever the timeout is on the defogger switch. I will have to look at the logs again, but I think the fuel cut signal level changed just for an instant at WOT at around redline too.

 

I hope I'm remembering all this right. I'll post some of the data tonight, when I have the spreadsheet in front of me.

[lookslikeanevo]

do a wot in 3rd gear from 2000-7000k...and that will pretty much cover what everyone needs to see

[spacejunkiehsv]

Here is one, at WOT.

http://i9.photobucket.com/albums/a76/jason_w_carter/fuel-cut-3-wot.jpg

 

Here is another, not at WOT.

http://i9.photobucket.com/albums/a76/jason_w_carter/fuel-cut-2.jpg

 

Here is yet another, not at WOT.

http://i9.photobucket.com/albums/a76/jason_w_carter/fuel-cut-1.jpg

[RochNY91TSI]

Does the KC column represent knock count? It looks like the fuel cut signal appears mostly after an increase in knock. Maybe that's what the ecu does in addition to pulling timing (cut fuel)? In most of the cases above, the knock count had just --or recently-- went up and timing went down...

[Jon in CT]

Your automatic transmission's Transmission Control Module (TCM) has signaled the ECU that it wants a brief fuel cut in order to reduce torque while it shifts gears.

[RochNY91TSI]

^^That makes sense at the points not at WOT, but in the WOT chart, the rpms increase even beyond where the FC signal is. Also on line 258 of the second graph and line 164 of the third, there is a decrease in rpm, consistent with shifting, but no fc signal

 

And may I ask how you know that the tcu is able to send a fc signal to the ecu?

[TSiWRX]

Does the KC column represent knock count? It looks like the fuel cut signal appears mostly after an increase in knock. Maybe that's what the ecu does in addition to pulling timing (cut fuel)? In most of the cases above, the knock count had just --or recently-- went up and timing went down...

 

^ Positive knock correction (KC) indicates no noted knock in that area, unless I'm totally wrong.....

[lookslikeanevo]

^ Positive knock correction (KC) indicates no noted knock in that area, unless I'm totally wrong.....

 

i believe you are correct

[RochNY91TSI]

So with regard to kc, does a higher number indicate that there hasn't been knock detected in a longer period of time? It appears to me that timing is being pulled at or around each point where the KC value has increased

[Jon in CT]

^^That makes sense at the points not at WOT, but in the WOT chart, the rpms increase even beyond where the FC signal is. Also on line 258 of the second graph and line 164 of the third, there is a decrease in rpm, consistent with shifting, but no fc signal

 

And may I ask how you know that the tcu is able to send a fc signal to the ecu?

The TCM could also request a brief fuel cut when it decides to lock the torque converter. These TCM-directed fuel cuts are fairly brief so it's very possible to miss some if you're logging a lot a variables. Alternatively, if there were indeed an upshift without logging an AT fuel cut, the TCM could have, instead, requested a brief retard of the spark advance because only a slight torque dip was needed.

 

On a Subaru Select Monitor, the fuel cut variable is reported as "Fuel Cut Signal from AT" and the retard variable is reported as "Retard Signal from AT."

[RochNY91TSI]

Good call on missing the signals if they're brief, since the logs show that there are some gaps in the time from line to line (not sure what the logging interval was, but it wasn't real time).

 

Thanks for the information; interesting stuff...