I'm considering getting a PCM tune done to my otherwise essentially bone stock truck. It'll probably get a Magnaflow catback in a few months, but at the moment the performance mods list consists solely of a K&N drop-in (pretty hard-core, eh? ).

Anyway, I'm just a bit confused about how a tune is supposed to improve my mileage? I keep hearing reports of 2-3mpg, which sounds "unbelievable" to me both literally and figuratively. If this really is possible though I'd be a fool not to buy a tune.

I fully understand how these things can make more power (and provide an additional acceleration improvement through transmission reprogramming), but what in the heck are these folks doing with computer software to increase mileage by 3mpg? And if this is possible, why didn't GM do it in the first place...given that a 3mpg improvement could add BILLIONS of dollars to GM's bottom line.

My truck gets 14mpg in my 70% around town 30% California highway driving (which is probably equivalent to 100% city driving anywhere else). Right not it runs on Chevron 87 at $2.29/gallon. My only real concern with buying a PCM is increasing the already way-too-high $/mile cost, but if a 91 tune can bring the mileage up by 1MPG the cost is a wash.

And while we're on the topic of tunes... does anyone know anything wrong with going the Jesse Bubb route? He's getting glowing review over on FSC and the price is right.

Thanks for any help/info!

 

And one more question, how are you all measuring the mileage improvement? Are you actually dividing miles driven by gallons purchased, or relying on your DICs? Just curious if the DIC's mileage numbers could be skewed by a tune.

 

I got jesse's tune. I havent checked it yet for milage, but I do at every tank. I've just made a few changes lately, so I want to give it a fair shot. I can tell I am going futher a given gas level than I was, but have no numbers yet.
As far as how I am not sure. Possibly because its easier to move the bricks we drive (big heavy bricks) with more power, so that makes the engines more efficient. Or because something other than the amount of fuel burned is making the power. Ie. air/ spark (timing).
I did gain between 2-3 MPG when I installed my LS1 fans, and that was with 2 trips to the track, so it may be slightly more, but I think its consistantly about 2.5 mpg more.
As far as the more expensive gas. In La, the gas is .10 more per grade. So premiun (93 oct) is .20 more than 87 oct. .20x26gal=$5.2 per fill up from an EMPTY tank, so about $4-$5 per fill up. For the extra power, I'll gladly spend $5 per 300 or so miles. 300 more enjoyable miles

 

Endo,
From the factory, cars (and trucks in this case) are designed to work in many varying climates and varying qualities of fuel and additives.

Because of these variables, engineers tune the vehicles on the conservative side. They also build into the engines computer settings that will prevent premature wear on parts like your transmission.

What some of the respected tuners have done is to look at these engine parameters and saw where the computer is adding too much fuel, and they leaned out the mixture. They looked at the timing map and where they couldn't pull out fuel, they advanced the ignition timing. Where there was sloppy or slow shifting, they looked for ways to up the line pressure to improve shifting performance.

So all the tuners have done is get more agressive with the tune for what your goals are with the vehicle. You say your only going to run 91/92 octane in your vehicle and not 87 at all ever, they will tune for a more advance timing, and possibly a more lean (hotter) mixture.

In my last car, at WOT, my car would be in the 10:1 A/R range. After tuning, I was runing around 11.8:1-12:1 at WOT, and gained about 30HP This is a ratio of air to fuel. The higher the number, the leaner the mixture. Too lean, and you detonate. This is where the A/F mixture will ignite prior to the power stroke.

So can you gain MPG, yes. Can you pick up some more power, yes. Will it pay for it self in a few years, yes?

GM did nothing wrong here, just wanted the best all around tune for the mass market.

 

 

Fully agree with unredeemed, perfectly put!

 

I have also been planning a tune for my truck when I get my new tires. I have been talking to Jeff Creech @ CAM in North Carolina and he tells me that he can get me ~30hp and ~3mpg through his dyno tuning (on my 6 liter). He also told me that just changing the shifting on the truck and adjusting torque management is well worth the tune. I will be finding out in the very near future (after my new tires get here) .

 

Also with I believe 2001 and new trucks, he has the cabability to enable Lean Cruise mode. I've just been doing some research on it and came back with some good results.

I just finished making another custom tune for mine with Lean Cruise turned on and I'm going to test it out after work today.

Will post back with results.

 

I just purchased one of Jesse's tune for my truck and it really woke it up.. I have had it for only 2days, so I am still on the playing mode (flooring it every chance I get!!).. whenever I am ready to test the mpg gains I'll let ya'll know... but I think it is way worth it!!

 

I have one of Jesse's tunes also. I'm going to try to dyno it tomorow. I also want to take the stock PCM with me, so I can compare. I'll post numbers when I can. Probably start a new thread though.