MPG and Timing

[Nexuscocker]

Im tyring to increase my MPG, and Im wondering if there is any thing else beside the high octane tables I should be adjusting. And if that’s it can I see and example of someones?

[Stalker L-67]

You could adjust your MAF curve so that at freeway speed/load your running 15.5:1 AFR. This AFR should give you max MPG although your engine will run warmer and test your cooling system a little.

[Eddie-98GTP]

Adjusting the MAF won't work as well as you might think, unless you run in open loop all the time. The PCM will adjust the AFR back to 14.7 using the narrowband O2 sensor and fuel trims. The narrowband isn't very good at anything other 14.7 +/- .5, but it is very good at 14.7.

The first things that come to mind for increasing MPG other then the spark tables are Accel Enrichment, Decel Enleanment, O2 sensor offset (if HPT supported this, you can ask them to add it), and transmission shift points.

[LSChris]

Are there any tips on adjusting DE? I've tried a few things but with no real positive results.

[Eddie-98GTP]

I don't know, I've never really tuned DE. I am running 2005 GTP DE tables, which are leaner then the 98 GTP, but I don't know how big of a difference it made since I imported 2005 AE tables at the same time.

[Nexuscocker]

So if i copy a 2005 GTPs Accel Enrichment and Decel Enleanment tables that should help me out?

[DanGTP]

What about adjusting what the computer considers Stoich? Every tune I've looked at for 3800's has had it stock at 14.70020, but why couldn't we bump it up to 14.9 or 15.0. Is that too far out of the the NB O2's efficency range? I believe we'd still be fine for PE, because that fuels differently.

[murphinator]

What about adjusting what the computer considers Stoich? Every tune I've looked at for 3800's has had it stock at 14.70020, but why couldn't we bump it up to 14.9 or 15.0. Is that too far out of the the NB O2's efficency range? I believe we'd still be fine for PE, because that fuels differently.

before doing that if you run 10% ethanol remember E10 stoich is 14.1

[passingpower]

I have one for you. Reverse the boost bypass "modification" that was once popular. Loosen the nuts and pull the diaphram housing UP. This will delay boost until you really are in WOT. You'll see less airflow (and knock) at part throttle. Less air will need less fuel to maintain stoich. What kind of mileage are you getting now? What kind of driving do you do- city/highway, spirited/sedate? Calculate gas economy using gas pump and trip odometer, not the DIC. It won't be accurate until after you calibrate your IFR table. (I recommend the odometer assuming you're running stock wheels.)

[macca_779]

Since the US models never had lean cruise. What HPT need to impliment is a semi open loop primary fuel table with an RPM axis like what EFI LIVE has in their Custom OS's. Like this you dont even need PE if you so desire.

The way it works is you must disable LTFT's. But anywhere where 14.63 (Or EQ 1.0 if you view in EQ) is commanded you will have STFT's being applied. Anywhere its any other value, you will be running open loop.

[LSChris]

Comparing the few files I've seen, it appears that the 04+ DE tables are the same as in the 03 and older cars.

[Nexuscocker]

I just filled up and im getting 18.8 MPG on this tank it was almost half high way half city. I would also say i drive fairly aggressivie in the city too. Im going to change my DE tables and see what that dose for me.

[Eddie-98GTP]

I just filled up and im getting 18.8 MPG on this tank it was almost half high way half city. I would also say i drive fairly aggressivie in the city too. Im going to change my DE tables and see what that dose for me.

I wouldn't complain too much if you drive fairy aggressivly. I have to drive like a normal person to hit 18.8. All of my driving is in suburbia with VERY little over 60 MPH, normally I'm in the 18 - 17.5 range.

[Nexuscocker]

On this tank im going to drive like a "normal" person to see what I get. And i am happy with 18.8, but if i can get more i want it.