Tuning + MPG issue

[WA 2 FST]

Question for you guys (Terry, if he's out there)... so, you may recall awhile back I found a pristine '00 L with 33k miles on it in Baton Rouge. Purchased it with the sole intent of letting my daughter buy it from me. Vehicle was reportedly stock except for C&L elbow, 90mm MAF and CAI (all parts are confirmed to be installed, as I can verify visually). The owner gave me the OEM equipment and an SCT handheld. I just _assumed_ the SCT program was installed/flashed, since the 90mm MAF was installed.

When I got it home, I changed the fuel filter, trans fluid, verified I/C pump working, changed oil, etc.

So here we are several years later (she drove it for a year with her learner's permit, and just turned 16 in late Dec. '13). I really have never tracked the MPG in it b/c we were always driving it short distances, and it wasn't being driven _that_ much, even when she had her permit. We just weren't putting a lot of miles on it, and fill-ups were rare. I thought it was interesting that with the SCT tune it still shifted into OD like factory (way late, even with the 3.55 gears) and the shift quality seemed OEM, too. Fast forward... now that she's driving it a lot, seems like fill-ups are very frequent. I had her check the mileage this last time... whopping 10mpg, and I can _promise_ she drives it easy. Granted, its almost ALL in town, to school and church and home, to friend's houses.

So, I decided to see if indeed the SCT program was installed. Flashed the PCM and took it for a drive. The answer is obvious... the guy must've flashed it back to stock before selling it. Idle rpm is lower than stock (600... but I turned on all accessories, came to multiple standing stops, and it doesn't die or shudder... seems ok). Shift quality is significantly better/firmer, but not horrible when under light load (which is how she drives it), and viola!! ... it shifts into OD at ~40mph instead of 50mph. I think this alone will net an increase in MPG, as 90% of her commute is 40-45mph.

Here is my question... given it has he 90mm MAF installed, and has been running the OEM tune, could this have had a negative effect on fuel economy??

Bottom line... if it doesn't help, or she doesn't like the way it drives (she's happy with the earlier shift into OD under light load), I will install the OEM MAF, inlet elbow, and airbox, change the plugs (which may have never been changed) and have the dealer flash it to stock, so I know for sure what we have.

[L8 APEX]

You may want to get a tune emailed to you from JDM or whoever you deal with these days. Make sure there is not a chip on the PCM. Lower idle and lockup sounds like a stock tune. A 90mm on 2000 should net a lean burn and more timing. The PCM uses the MAF to calculate air, but it also factors in to engine load. It will register less load so it will run higher timing in the lower load tables. Most tuners raise the idle to 750 in neutral and in gear for smoother operation. Stock is 688 I believe. Stock tune locks up ASAP and idles as low as possible for best fuel economy. Usually the easiest way to spot a tune is the removal or torque reduction or the lay 5 cylinder shift at WOT between 1-2. It tends to make a farting noise and the truck noses down for a minute.

[WA 2 FST]

Thanks for the feedback, Terry. I must have it all backwards. Whatever the case, the thing drives like it should with whatever tune I just loaded into it. If it had the performance tune in it, it wasn't very good, IMHO. I don't remember it laying down on the 1-2 upshift yesterday when I nailed it, but I don't think she's ever had the thing WOT, so that doesn't even matter in reality. But I remember what you're talking about... my '99 did that. I will check MPG for the next several tanks and see if it improves. I'd be happy with 13. It probably needs plugs, but if I go that route, then I'm just returning it all to stock... which is really fine.

[WA 2 FST]

Terry... you nailed it. About a week after putting the other program (which I will now assume as you stated... was the stock program) back in, but leaving the C&L elbow and 90mm MAF... I got a P171 lean bank code. Gas mileage had improved a little on her last tank of gas (most likely due to shifting into OD at 40mph, instead of 50mph). So, I put the stock elbow and MAF back on. All is well. Truck runs good, and I'll wait and see what the mpg shows after this next tank of gas. I am guessing it will be 13-14mpg, which would be such a vast improvement over 9.xx. If it doesn't improve, I'll change the plugs. They are probably the original ones... only 35k miles, but 14yrs old.