Huge mpg boost after filling up

[diamondlarry]

When I filled up for the tank prior to the one I'm about to finish now, I found that it was extremely easy to keep the FCD maxed out at 150+ on the 8+ mile trip home from the station; sometimes even under light acceleration. In fact, when I got home, I switched the display to metric and did the conversion math and it figured out to 158.8 mpg. I'm assuming it is due to the vapors present from the fill procedure being burned off. This has me wondering if there is some practical/safe way to duplicate this. I have seen some awesome feats attempted and most of them accomplished by some very brilliant members here and am wondering if somebody could put together some kind of a vapor chamber that could operate automatically or even manually?

[ackattacker]

Originally Posted by diamondlarry

When I filled up for the tank prior to the one I'm about to finish now, I found that it was extremely easy to keep the FCD maxed out at 150+ on the 8+ mile trip home from the station; sometimes even under light acceleration. In fact, when I got home, I switched the display to metric and did the conversion math and it figured out to 158.8 mpg. I'm assuming it is due to the vapors present from the fill procedure being burned off. This has me wondering if there is some practical/safe way to duplicate this. I have seen some awesome feats attempted and most of them accomplished by some very brilliant members here and am wondering if somebody could put together some kind of a vapor chamber that could operate automatically or even manually?

There's no such thing as free lunch. I'm not sure if what you describe is possible but *if* you're burning "vapors" off the charcoal canister then that's still gasoline, just gasoline that hasn't been accounted for by the fuel computer since it hasn't gone through the injectors. In that case your true fuel economy is not actually improved so there's no reason to try to rig a "vapor system" just to fool yourself by getting an incorrect MPG display.

[hybriddancer]

Originally Posted by diamondlarry

When I filled up for the tank prior to the one I'm about to finish now, I found that it was extremely easy to keep the FCD maxed out at 150+ on the 8+ mile trip home from the station; sometimes even under light acceleration. In fact, when I got home, I switched the display to metric and did the conversion math and it figured out to 158.8 mpg. I'm assuming it is due to the vapors present from the fill procedure being burned off. This has me wondering if there is some practical/safe way to duplicate this. I have seen some awesome feats attempted and most of them accomplished by some very brilliant members here and am wondering if somebody could put together some kind of a vapor chamber that could operate automatically or even manually?

I observed this glitch once and it happened like this: Ignition was completely off, headlights were on (and running on the backup 12v battery), turned on the ignition and started driving. The FCD display stayed at 150+ for the entire trip (about 10 miles). Knowing this mpg was impossible, I stopped, shut everything down, restarted, then turned on the headlights and it returned to normal operation. I haven't seen this glitch since. This is probably what you observed as well.

[Eli]

Originally Posted by hybriddancer

I observed this glitch once and it happened like this: Ignition was completely off, headlights were on (and running on the backup 12v battery), turned on the ignition and started driving. The FCD display stayed at 150+ for the entire trip (about 10 miles). Knowing this mpg was impossible, I stopped, shut everything down, restarted, then turned on the headlights and it returned to normal operation. I haven't seen this glitch since. This is probably what you observed as well.

I have also had this happen once. Freaked me out, thought my dash display broke!

[diamondlarry]

I have had that happen several times where the display sticks like that and it is always after I have bump started after a forced auto-stop (keying off while gliding). What I was describing was immediately after a fill up and the display would work fairly normally as far as going down when accelerating and up when letting off. It's just much easier to stay at 125+ even with a TPS on the Scangauge of 16-18. After just under 10 miles, the FCD starts acting normally and goes to the 100-125 range if I keep TPS well under 18.

[Mikeyy]

I've gotten this too on my first two refills. not the fcd sticking though. Just like larry said it's was so easy to stay at 150+ on the fcd at 41-42 mph. after 2-3 mile trip home pulled into my driveway with 117 mpg showing. your still using gas, but not from your fuel tank.

[Eli]

Interesting. I've never noticed this. I'll have to keep an eye out.

[kennysmith]

Originally Posted by diamondlarry

I have had that happen several times where the display sticks like that and it is always after I have bump started after a forced auto-stop (keying off while gliding). What I was describing was immediately after a fill up and the display would work fairly normally as far as going down when accelerating and up when letting off. It's just much easier to stay at 125+ even with a TPS on the Scangauge of 16-18. After just under 10 miles, the FCD starts acting normally and goes to the 100-125 range if I keep TPS well under 18.

I've experienced this a few times, too. Always after keying off as you describe and bump starting. I have had to turn off and restart to get the FCD to operate properly, One time I just left it alone to see what would happen. I was surprised to see it stay pegged regardless of how I drove and that I was racking up amazing mileage on the trip mileage. I had not just filled up. I don't know how much fuel I had on board. I think my car may have been pretty cold because I think it was near home each time.

[diamondlarry]

Originally Posted by kennysmith

I've experienced this a few times, too. Always after keying off as you describe and bump starting. I have had to turn off and restart to get the FCD to operate properly, One time I just left it alone to see what would happen. I was surprised to see it stay pegged regardless of how I drove and that I was racking up amazing mileage on the trip mileage. I had not just filled up. I don't know how much fuel I had on board. I think my car may have been pretty cold because I think it was near home each time.

Sean Welch showed me how to fix the sticking FCD on the fly: Just do a very quick cycle of the ignition key from run to accessory and back to run. By very quick, I mean so quick that the engine barely loses any rpm. The FCD will return to normal as soon as the key is turned back to run.

[02insight]

i think two different things are being discussed here,

one is the glitch where the FCD sticks to 150mpg no matter what (i've experienced this regardless of fuel fillup time)

the other is the tendency to stick to 150mpg (but can be brought down), that occurs right after a fill-up

neither one is desirable, because we are simply fooling ourselves into high mpg happiness.