I think this is very interesting.

I've been running a 87 octane tune for a month or so now. (consume a little more than one tank per week)
Well, at the same time I switched octane.. I went with these larger 32" tires which threw off my tune, odometer, speedometer, and scanguage. It took me a few days to get those lined out and now they match my GPS.

Well... my 87 octane tune/fuel is now running in the 17mpg area. I'm thinking it's not just the tires causing this drop in milage. The air temps are much cooler (30-40s) and I'm guessing by now we are into the full mix of winter fuel (lower stoich btw)

IMO that's horrible because I was running 20-21 avg during the summer and on shorter tires too.

Yesterday, I put in some speedway 92 octane. (tank was nearly dry - 19.4gallons to fill ) I then flashed my 93 octane tune into the trucks PCM, and dis-connected the battery to reset the KAM. Did the idle re-learn and then gave it a good 50 miles of stop/start/drive learn time before I started to accept the instant MPG numbers as factual.

Summary:
My instant mpg went from 16-19 to 23-25! Timing running down the road at 70mph was 23-ish on the 87 tune (very very close to the OEM tunes timing)

My 93 octane tune is running in the 34-41 degree area depending on climb/flats/declining.

I can clearly see that when timing gets up over 35 the "load" goes down, the TPS is more closed (to maintain same speed), and the instant MPG is significantly higher. The sweet spot seems to be in the 36-41degrees area of timing. (The closer to 41degrees the better the milage)

The down side with this 92 octane fuel from speedway is that I'm hitting the knock sensor at heavy throttle. So I either need 93oct fuel, or I need to make a 92tune with reduced heavy throttle timing. (I get a decent discount at speedway that's why I'm trying it)


This kind of stuff is just interesting to me.



Rich

 

Hmmm that is pretty interesting that you are pushing that.. what if you just run 91 or 93 Oct on a stock PCM tune?

 

Your wallet will get lighter...

Running premium fuel on a stock tune is a waste.

 

ha where i live.. the reg grade is 85 oct.. thats our low grade..

 

The timing on a stock tune is very low IMO. Running anything higher than 87 would be a waste... other than any cleaners they might put in it. (like shell "v-power" is supposed to have)

Increasing the timing just the proper amounts for a given octane should allow me to get the most "value" for it. If gas is 20cents more for high octane.. I'll just have to see if the mpg improvement is able to make up that cost as well as save even more. I think it's possible that running a 93 octane with the proper timing curves just might be more economical than the stock tune with 87 octane. Besides... it's got a WHOLE LOT MORE punch with the timing increased.

Rich

 

How does one have the timing increased?

Obviously i know little about timing and all that so am i to buy a tuner with the tunes in it already?

 

I have tuning software. So I can go in and adjust a specific timing number for a specific throttle/load/rpm/fuel situation.

If you buy a x-cal flash device... your "tuner" should have addressed these sorts of things already. (note they "should have" )

Rich

 

Who do you recommend to go to for the tuner?

 

ya im listening here too, i just put on some 32's (265/75/16's) and my truck is a total dog now compared to the stock tires.

Id really like to fix this.

 

I noticed with 87 reg. my timing on the highway cruising is around 37, never watched it go higher, I think you should come to Wisconsin and tune my truck for me...Yeah I like the sound of that!..lol

 

I experienced something very similar to this on my truck recently, its just a little more old school way of learning. I have finally figured out that funny noise I would hear at WOT was pinging.... so I check the timing on my truck. 10* advanced is stock, and I was at 30*! so I reset it to about 14* to 16* advance and go figure the pinging stopped. But was interesting to me is my mileage decreased as well. I was pulling a solid 17.5 to 18 mpg every tank of mixed driving. With the lowered timing i'm only getting 16 to 16.5 mpg. Now on my truck I can't read out the instant mpg, but i check at the end of every pump, and I know how many miles I should have on the trip at each of the fuel gauge marks. Now i'm thinking I might go increase my timing some more to say about 20 to 22* and see if I can run it there without pinging on 87 octane.

 

my truck actually ran better and mpg increased when i was running 85 when i drove cross country.