JM20

Just had a new cam (236/242 114 LSA), Fast 102 intake, Nick Williams 102 TB and 4.10 gears installed and the DIC’s fuel mileage appears to be reading very inaccurately! Well at least hope so!

A steady cruise on the highway at 65mph…my DIC instant fuel mileage is only reading 17-18 MPG . With easy driving around town it’s like 8MPG . I did reset it and it came back with the same results.

I asked the shop who did the install and they said that the DIC can no longer accurately compute the fuel mileage due to the new 42lb injectors. Is this true?

Now I knew I was going to lose mileage with the addition of the above mods, but could it be that drastic? Can something be adjusted in the tune to compensate for the new injectors so the DIC reads properly? Or maybe it is reading properly????

Thanks in advance for your input!

Deviant LS6

MPGs are calculated out by TPS, rpm and load. Your injectors are still firing the same amount of fuel as your factory injectors except now they pulse less and have more head room to sustain more power. Did you get the car tuned for the mods and injectors? Have you tried calculating your mpgs yet the "regular way"?

JM20

Thanks for the reply!

Yes the car was tuned. And no I have not driven it enough to check it manually.

Basically I'm looking to see what people's DIC said after simular mods.
It appears in reading other threads that they're seeing around 25-28MPG.

sean.b

tinkering with a hand held (predator) tune, i had my MPG drop to ~8 once too. had to reset the computer and re-apply the exact same tune. not sure what went wrong, but it jumped back up to its normal 22+ after that.

barring something being violently mechanically wrong, my money is on a fubar'ed tune.

sfc rick

I know that more power generated = more fuel consumed. Don't be fooled by the belief that more horsepower magically happens without extra fuel be used. Yes you can maximize combustion to a certain extent BUT not to the point that the additonal 120hp you put out by cam/heads/headers all bolt ons come for free and you get 25 mpg!

I used to get 25-27mpg when I was stock, NOW I'm getting 18-22mpg after heads/cam/bolt ons about 410+ whp and maybe 15-16mpg in town and about 10-12mpg when I'm really hauling tail red light to red light.

There is a penalty for power regarding fuel mileage. You can only be sure about yours by checking your mileage the ole fashioned way. Fill up, motor around and check odometer mileage, fill up again, and then divide gallons by miles and THEN YOU KNOW FOR SURE!

Rick

sean.b

i didnt have a wideband/AFR gauge at the time, but my car was legitimately drowning itself in fuel when the tune just randomly (months after the last time the hood was up) decided to lose its mind.

unless he's running an .800 lift cam, turbos, and shifting at 9000 rpm, i dont think a H/C car is gonna get 8mpg unless he's beating it like he's being paid for it.

baxsom

wow my 72 454 with the holley 850 4bbl carb gets better mileage than that (although not by much)

sean.b

my 383 with a 750 holley 4bbl doesnt get but about the same thing. you must have a better setup

ZZOOM06

I really think something is screwed up with your tuning. When I had H/C, Fast 90 etc. on my stock shortblock, I consistently got 26-28mpg on highway trips and 18+ in stop and go traffic. And yes I did verify it the old fashioned way and the DIC reading was very close, +/- 3%.
The way the car sits now with the 416 stroker and 42# injectors I consistently get 24+ on the highway and 15-16 around town. Of course that all goes to hell if I start hammering on he car.
I'm sure your tuner knows about injector scaling and I know there is a simple provision for it in HPTuners, but maybe he forgot to use it,
Just a thought for you to look into. Your car, even with the 4.10 gears should be getting way better mileage.

Jimbo

JM20

That's what I'm affraid of...something F'd up in the tune. But the place is saying it's due to new fuel injectors.

Full Cam Specs: 236/242 114 LSA .601/.610.

Not beating on it at all! and driving like a grandpa! Getting 18mpg at 1600-1700 RPM's crusing at 65mph on teh highway. According to the DIC anyway.

JM20

LOL...that's whay my DIC #'s are reminding me of. The good old days!

JM20

Yeah I hear ya Rick! I'll try the old fashion way and see. Thanks!

JM20

Jim! Now yours is a perfect example! I'm not looking for Toyota Prius numbers, but would think the DIC would read better than 18mpg.

I guess I'll check the old fashion way and if need be get a re-tune by another shop. Since this shop is saying the new fuel injectors are causing the reading.

baxsom

full roller cam conversion

racetchr

I'm having the same issue. I had ECS do a tune for change in injectors, went from stock to 38# and lost 10mpg. Others have said with proper tune no loss whatsoever. I'm going to send the PCM back to Doug @ ECS and see if he can straighten it out. Bad time for gas to be $4 a gallon.

DOUG @ ECS

Incorrect MPG readings can be shown on the DIC because of injector scaling being off in the tune, or improperly flowing injectors. That does not mean the tune is necessarily that far off so you should do a manual check of the fuel economy.
The green top 42's have been known in my experience to not have that nice of a spray pattern which also hurts fuel economy too.

Keep in mind that the car will correct your A/F ratio as you drive, if it is too far out of range for it to correct it will make a CEL appear on the dash.

DOUG @ ECS

This is why we only say our mail order tunes are for stock or bolt on cars, otherwise they are considered "start up tune files". We do not know the flow characteristics of your injectors, and are those rated at 3 bar? four bar? and so on.
I'll be happy to make a change for you at any time, but I will only be taking another shot in the dark without data logging information since there are variables with unknowns in the equation.