PCM Programming

I read a thread on the Impala SS forum about folks getting their PCM reprogrammed for increased performance. I perused a few websites and it raised some questions. My two 1996 Roadmasters are completely stock. They both have 2.56 rear ends. I am delighted with how they run, shift, etc. I drive like an old lady...slow acceleration, gentle shifts, lots of coasting before stops.

What caught my eye was the "economy tune" claiming up to a 5 mile per gallon mileage increase. That would be very nice as I found a gas station twelve miles away that serves up ethanol free gas. When I go to visit my mother I can't quite do it on one tank of gas. There are no ethanol free providers near her so I end up polluting my system with ethanol. Yuck. A mild increase in mileage efficiency would fix this problem.

I don't know much about how it works. Is it a reasonable thing to do? They mention disabling lots of stuff. Is there a downside to that? Would an economy tune adversely effect the reliability or durability of the engine and drive train?

Thank you,

Russ

+5 mpg is a lot. If it's mostly gentle hiway driving, and your car is already in good shape, I doubt programming your PCM could ever make that happen.

5mpg is certainly no "mild" increase, either.

Thank you,

Russ

Inflate your tires to 50psi,.
run skinny 225-75's

run the car in 3 rd gear going up hills,.2:56's are the worst for fuel mileage UNLESS on relatively flat ground,.


use neutral coming down hills,.

read up on "hypermiling" driving tips and tricks,..

you'll gain a bunch of mileage,.

Now Nick...

when I got my first wagon it was a 94 with 2.56 rear and it was a 1A2 which made it about 70% Police car (lacking suspension bits of a 9c1).

I mention it as I'm sure the tune was different than a normal wagon. back in the ethonal free times of 2007 when I bought it, I got about 425 miles out of two consecutive tanks cruising at 65-70 MPH in overdrive.
This was from Erie, PA back down to flatland where I live so there was up and down in there, but mostly interstate.

The only other time I've come close to that mileage was in a 91 Olds, TBI 305 with a 2.73 rear going North from Georgia in Virginia, where I got about 390 miles out of a tank. Now mind you the TBI tank you can only run about 18 gallons out of before they suck air and you stall.

I've also noticed that there is a big difference in MPG if you keep it under 70.

One of the main differences in the tunes is that they up the spark advance. Often this requires premium fuel to take advantage of it, so any FE gains are offset by more expensive fuel.

talk to the Impala ss folks and see if anybody has real world data.

As a follow on, a good buddy of mine Impalassdude on the Impala forum has a 94 SS. He got a tune and said he gained about 4-5 mpg Highway on it. I'm sure he'll answer a PM over there (he's on here too occasionally as wagondude as he has a 95 wagon, but he's on the ISSF far more frequently)

autoarcheologist wrote:

One of the main differences in the tunes is that they up the spark advance.  Often this requires premium fuel to take advantage of it, so any FE gains are offset by more expensive fuel.

talk to the Impala ss folks and see if anybody has real world data.

There's a lot more to it than that. You can do a mileage tune with 87.

Does anybody know what they actually change to get 5 mpg?

I was a power train engineer for 3 years at Chrysler. We didn't just leave power or FE on the table if we could improve it. Besides fuel and spark timing what do they modify? You are already running at Stoich when you are running closed loop. Unless you want to run lean I don't see where the gains come from.

Power I get, bump spark timing and use 91 fuel.

autoarcheologist wrote:

Does anybody know what they actually change to get 5 mpg?   

They would have to change cars to get that!!

GM LONG ROOF FORUM CONSUMER ALERT

NEVER beleive the words 'UP to" or "AS LOW AS" in any advertising claim.

lakeffect wrote:

GM LONG ROOF FORUM CONSUMER ALERT

NEVER beleive the words 'UP to" or "AS LOW AS" in any advertising claim.

In addition to the above,never believe the phrase "sidepipes are cool on wagons"!

Zing!!!!!

In fact the sidepipes are only cool in the morning, after running they are usually very hot, and thus need guards to protect your legs from bad burns and singed wool. I would know this from the reports that the sheep tell me.

autoarcheologist wrote:

Does anybody know what they actually change to get 5 mpg?  

http://www.lt1pcmtuning.com/tips/

5 mpg is probably a bit of a stretch. There is definitely room for improvement from stock though.

I have often heard of "up to 5 mpg increase" but everyone that I have talked to has said that it will not happen on factory set up.

Everyone that I have talked to about getting an increase in MPG, has made many extra mods along with a tune.

Some sort of CAI, headers, full exhaust will definitely aid in getting "up to 5 mpg". While gaining the extra mpg you will also gain a little extra cabin drone at the same time.

Sometimes i feel like trying to gain those extra few miles is worthless. I understand why you would like to gain the extra few miles, but for most people it is to save a few bucks on gas. By the time you spend the money on the tune, intake, and exhaust you are so far in the hole that it would take you years to see the savings.

On a side note, if you do get an answer from someone at the impala forum please let us know. I would like to look into it a little more. I would like to see some hard proven results, not just from a guy who said so.

jasonlachapelle wrote:

autoarcheologist wrote:

Does anybody know what they actually change to get 5 mpg?  

http://www.lt1pcmtuning.com/tips/

5 mpg is probably a bit of a stretch.  There is definitely room for improvement from stock though.

By the way my favorite part of this article is the "BEFORE YOU BEGIN" section. I wonder how many people have done a tune and fixed many of these issues at the same time and then thinking that the tune actually gained me 5-15 mpg!!!!! Not realizing that the real issue was them not taking care of their car in the first place.

Thanks for posting that.

autoarcheologist wrote:

I was a power train engineer for 3 years at Chrysler.   We didn't just leave power or FE on the table if we could improve it.    

Now thats funny right there,...chrysler,. PFFFfffft,..

rjathon wrote:

Now Nick...

Now Nick what