Timing Bump = Decrease in Gas Mileage?

[cary]

Well about a month ago, I bumped my timing from 3 degrees so 7 degrees to see what would happen. The results for me, better throttle response, off idle pinging, more power, and strangely lower gas mileage. At first I thought it was me driving harder, but I have monitored it carefully over the past several tanks and noted about a 10% drop in mileage. The confirming fact for me was I drove 150 miles this weekend of freeway driving. I would normally get 14.5-15mpg in this type of driving. This tank 13.4mpg. I have noted similar drops for in town mileage (consistantly 12-12.8 mpg, 11.5 last few tanks). As a result I have dialed the timing back to 4degrees bdc. Anyone noticed this?

Cary

 

[cruiserman]

More lead on the pedal.

 

[cary]

After the first tank I have been very careful in how I am driving it. I would think heavier pedal but the freeway trip was done carefully with fuel economy in mind.

Cary

 

[IdahoDoug]

Cary,

Interesting. I have felt/wondered this same thing. My mpg figures are almost exactly what yours are and I've also had my timing at 7 deg and noted about a drop of 2. My truck is totally stock except for the tires, which are a traction tread that reduces fuel economy so I've attributed it to the tires. Hmm. Maybe it's time to go back to stock timing to see what happens.....

In addition, my bro in law's 80 has stock timing and the exact tires as my 97 (also at 7 deg) and on a recent trip together he got almost 2mpg better. hmmmm again....


DougM

 

[landtank]

off idle pinging

Doesn't this automatically mean the truck will retard the timing when it sees this giving you poor gas mileage.

 

[cary]

Doesn't this automatically mean the truck will retard the timing when it sees this giving you poor gas mileage.

Not necessarly. Many vehicles now have a bit of pinging off idle at very light throttle settings as manufactures continue to try and optimize mileage/power. My wife's 525i has the same pinging with no chip or anything and running 91 octane (the best we can get here in the PRK). After you get through the trace ping, the timing should advance (assuming it ever retarded) as the computer will continue to advance according to the map only pulling back if there is more pinging. The computer will continue to do this and check to keep the timing as advanced as the map design allows.

 

[7P's]

I bumped mine 8* (from 3* to 11* on a '95) several months ago with no ill effects. It feels stronger from a stop. No ping. Mileage was a bit better for the first tank of highway driving but then settled back into the normal range, which is 16.2 to 16.8 at 65 mph. I have 35's with 4:88 gears. On the last trip to Moab (May '06) I averaged 16.4 going out at 65. Increasing the speed to 70 and above the mileage goes to hell in a handbasket. Around town the mileage is nothing to talk about but didn't decrease any with the timing change.

 

[Rainy Day FZJ]

Anyone with a supercharger bump the timing? a couple degrees.

 

[sdbrassfield]

advanced timing = poorer mileage, chance of knocking, runs a tad hotter. You sacrifice something for the extra response and power...

 

[flintknapper]

I haven't noticed any change in mileage (still about 15 mpg). Off idle performance was noticeably improved (not stark by any means). No pinging.

I went from 3 degrees to 8 and am satisfied thus far.

 

[haulin79]

Just a guess, when the timing is advanced perhaps the computer is adding extra fuel at specific times to reduce the occurance of pinging, thus the mpg reduction.

 

[MTBGUY]

Summer VS Winter?

I was about to advance mine this weekend but now wonder about it after reading this thread. One question I have for those of you that DID lose MPG. What were the temperatures like in the areas you live before and after the timing change?

I know there is a relationship between cold weather MPG and Summer (regardless of gas blends). I just can't remember which way it works in theory.