Poor Fuel Economy after tuning (updated)

[LucasZ]

2009 Dodge Challenger SRT8 M6
U7135
Release 9r29
Only current mod is K&N "off-road" CAI part 63-1114

Prior to the the CAI, I was getting 25mpg highway at 75mph in 6th gear on flat land. After the CAI, I was getting 26mpg in the same situation.
I then got a predator rev2, updated to 9r29. I updated the callibration files and did a 91 octane + CAI performance tune. MPG dropped.

I just tested back to back to compare different tunes. Counting myself and some heavy stuff in the trunk, about 250lbs in the car. Nearly full tank of 91 octane. 72 degrees outside (Compared to high 90s when I first installed the CAI). Flat highway, 65-70MPH in 6th gear.

Tuned for 91 octane and CAI = 23.5MPG
Tuned for MPG Booster = 24.5MPG
Stock tune = 26.5MPG

Needless to say, I'll be sticking with the stock tune. I bought this thing because it's advertised as more HP and better fuel economy assuming you don't have a lead foot. Even if it's putting out as much HP as advertised, it's not worth the 13% extra fuel consumption.

Yes, I'm sad.

[brandy16]

2009 Dodge Challenger SRT8 M6
U7135
Release 9r29
Only current mod is K&N "off-road" CAI part 63-1114

Prior to the the CAI, I was getting 25mpg highway at 75mph in 6th gear on flat land. After the CAI, I was getting 26mpg in the same situation.
I then got a predator rev2, updated to 9r29. I updated the callibration files and did a 91 octane + CAI performance tune. MPG dropped.

I just tested back to back to compare different tunes. Counting myself and some heavy stuff in the trunk, about 250lbs in the car. Nearly full tank of 91 octane. 72 degrees outside (Compared to high 90s when I first installed the CAI). Flat highway, 65-70MPH in 6th gear.

Tuned for 91 octane and CAI = 23.5MPG
Tuned for MPG Booster = 24.5MPG
Stock tune = 26.5MPG

Needless to say, I'll be sticking with the stock tune. I bought this thing because it's advertised as more HP and better fuel economy assuming you don't have a lead foot. Even if it's putting out as much HP as advertised, it's not worth the 13% extra fuel consumption.

Yes, I'm sad.

You are very lucky to have that car. The EPA is 22 hiway and you are getting 26.5 stock. Some thing wrong here. Your getting 4.5 miles per gallon better than you should. I think you should keep it stock and never sell it. http://www.fueleconomy.gov/feg/bymodel/ ... nger.shtml

[LucasZ]

bump

[mikel]

Yeah, how about doing the math and not relying on the DIC?

[LucasZ]

I assumed it wouldn't be accurate, but the difference between the tunes should still show which ones get better fuel economy, right? Seems logical.

I guess I can do some testing on my next road trip and also use the predator to watch and log data to double check the DIC.

[srt8-monster]

What's happening is that the tune is adding fuel to compensate for the CAI. Try the 91 octane tune w/out CAI and you'll probably get the 4mpg you've lost. Never heard of anyone buying an SRT8 that was concerned about gas mileage. Trade it in for the 3.5L if you want better MPG.

[LucasZ]

How are people completely missing the point that DiabloSport advertises their tuners as increasing fuel economy?

From the DiabloSport Predator product description:

"The increase in MPG is a byproduct of maximized engine efficiency, the improved timing curve and air/fuel ratio creates a more complete combustion, i.e. the engine extracts more power from each molecule of gasoline."

Most of the time I'm not racing the car. If I only wanted to go fast, I would have started with the Mustang. Over the 10 years I had my 93 Camaro Z28, I made several mods that increased power and fuel economy at the same time through increased efficiency. That is how I choose to mod my DD street cars. I bought the Predator with an understanding from the DiabloSport product description. It claimed that the car would get HP on demand at WOT and better fuel economy the rest of the time.

[LucasZ]

@srt8-monster, the MPG booster/saver tune provided worse fuel economy than stock tune. That right there should tell you something is goofy.

[cruiserdan]

Lucas I gotta ask......

Have you computed the mileage by filling up the tank and recording the actual miles traveled and then doing the math?

If you have done so in all cases then your issue is valid. If you are relying on the EVIC or some other electronic measurement you are not getting accurate information.

[LucasZ]

I just got home from a road trip. 93 octane plus CAI tune took me down to the 1/2 mark. Stock tune coming home took me down to the 5/8 mark. The mpg readout may not be accurate, but this shows that the difference between tunes can be trusted to make comparisons. Stock tune gets better mileage than all the predator tunes. I also logged data a few weeks ago on the 93 octane plus CAI tune. No significant KR.

[oilslick]

I just got home from a road trip. 93 octane plus CAI tune took me down to the 1/2 mark. Stock tune coming home took me down to the 5/8 mark. The mpg readout may not be accurate, but this shows that the difference between tunes can be trusted to make comparisons. Stock tune gets better mileage than all the predator tunes. I also logged data a few weeks ago on the 93 octane plus CAI tune. No significant KR.

But which tune is giving you more power?????

[LucasZ]

I took my car to a local performance shop to get a custom tune. CAI + custom tune provided 450hp at the flywheel. On highway, I appear to be getting the same fuel economy as stock. I haven't had a chance to 100% verify with a long road trip yet, but initial testing was performed the same way as I did initial testing using stock tune and the canned tunes. The car also feels way smoother with the custom tune. Difference is like between night and day.

The custom tune will pay for itself in preserved fuel economy in 2-3 years over the DiabloSport canned tunes.

[Hemi1014]

Lucas, I have an 09 Challenger RT auto (I know you have a different motor) and check every tank. I usually get 22-23 mpg with my stock tune going to work on a 32 mile one way drive 80% hwy. My best was 30mpg on a 180 mile trip. I put the Predator 91 tune on the first time and got 18 mpg. The next tank I was up to 22 mpg again driving conservatively. I then tried the MPG booster tune and my mileage dropped to 20mpg. After the next tank I got 23.5 mpg all hand calculated with the MPG booster tune.

In short, my theory is that the computer needs some time to adjust in order to get optimum efficency. I am also 100% conviced through my tests that Shell gas gives me better mileage and BP gives me the least mileage. I live in a Chicago suburb and was wondering if anyone else noticed this. I know gas is forumulated a bit differently in certain areas. The Chicago winter blend gas is terrible by the way...

[Mike_Levy]

Shell gas also knocks the most. Their additives have a very low anti- knock index. Thats why Exxon/Mobil and BP are the ones that are recommended. Their AKI is the highest.

[Hemi1014]

I guess I should give Exon or Mobile a try...