95 850: opposite mpg effect with gas pedal Topic is solved

Post by **CIK7** » 13 Mar 2026, 19:38

Instead of getting better gas mileage by letting off the gas pedal, it actually plummets from maybe 20 or so down to 4 or 5 mpg. If I'm averaging about 20 or so with a constant pedal pressure and I suddenly stomp the gas down, the gas mileage will skyrocket to 30-40 miles per gallon. Bonkers like Yonkers.

Post by **hausmeister** » 14 Mar 2026, 15:17

Just stomp that pedal then!

Post by **abscate** » 15 Mar 2026, 02:58

Somewhere buried in these pages Jimmy57 went through how this algorithm works and how it can get fooled. I seem to remember it samples at about 1 Hz and uses the average fuel spritz time divided by the speed sensor reading or something like that.

I’m channeling my late father, regarding computed values, who once watched a technical presentation of a guy using the an IBM mainframe for a complex Space shuttle engineering calculation, saying “ your first two eigenvectors are right, but you made a mistake on your third. Go find your code error”

Post by **CIK7** » 15 Mar 2026, 07:40

abscate wrote: 15 Mar 2026, 02:58 Somewhere buried in these pages Jimmy57 went through how this algorithm works and how it can get fooled. I seem to remember it samples at about 1 Hz and uses the average fuel spritz time divided by the speed sensor reading or something like that.

I’m channeling my late father, regarding computed values, who once watched a technical presentation of a guy using the an IBM mainframe for a complex Space shuttle engineering calculation, saying “ your first two eigenvectors are right, but you made a mistake on your third. Go find your code error”

Sounds mathematically complicated to my mathematically incorrect brain.

Post by **volvolugnut** » 15 Mar 2026, 13:44

I doubt the software is wrong or failed since it worked for decades. Likely a sensor is failing. With luck it will only impact your MPG display.
volvolugnut

Post by **hausmeister** » 22 Mar 2026, 02:57

I mean, if you are concerned something is wrong, get an emissions test done and see if it passes that.
The only time I had extreme consumption the o2 sensor was bad. but that was not a display issue, it displayed and used a lot.

Post by **CIK7** » 22 Mar 2026, 09:13

Ill be installing a new ignition switch on Monday and doing a tune up on Tuesday. Ill let yall know if the switch does anything. That has been causing cluster related bugs.

Post by **CIK7** » 26 Mar 2026, 18:56

Okay, so I installed a new ignition switch yesterday and did a tune up today. I did not test the ignition switch before I did the tune-up, so I don't know if that is what fixed the sporadic mpg thing. However, it is working perfectly now. I would lean towards the ignition switch being the fix because all a bad electrical ignition parts system (sp, sp wires, dist cap&r, etc) does is cause MPG to be worse.