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Huge MPG drop after intake gasket change - 2006 6.1L SRT8

6K views 19 replies 12 participants last post by  CUUDA 
#1 ·
Hi all

A leaky intake gasket was causing a vacuum leak (and code P2173) in my 2006 Magnum SRT. After it was replaced, the leak is fixed and code is gone, but the fuel economy dropped from 16-17 to 11-12 mpg... I know, I know - fuel economy in an SRT8? LOL

But seriously, what could be the issue here? Besides an oil change while the car was at the shop, nothing else was done or upgraded... On a related note - the shop did idle the car for nearly two hours, as i later discovered from my dashcam video.

I did the "reset" and "reset all" options in EVIC menu, but it's still hovering at 11-12, not going back up.

Any ideas what could be causing this major mpg drop?? Thanks in advance!
 
#2 ·
did you have a bunch of highway miles before you brought it in? If I take a long trip my mpg is around 14. With my normal routine driving, the evic shows 10.
 
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#6 ·
Thanks gents! Feels good not to have the P2173 pop up every 20 miles. I tried everything, MAP sensor, throttle body, PCV valve, etc... All to find out that the gasket was shot.

I did not have highway miles on the car... Mostly local driving for the last year, year and a half... I will try to take it on the highway for a bit, I think those two hours of idling at the shop is what killed the gas millage. I used to get 17/21 routinely, that's with Corsa exhaust, AFE stage 2 CAI, Frank's Tomahawk cam, and a few other small things done.
 
#8 ·
Jeeezus! I get 10-11 around the hood. 23 @ 70 on the highway!

EVIC is just a estimate. I actually used real life fuel consumption to determine that.
 
#11 ·
Agree with this post. Resetting your Pcms adaptive memory will help the car re-learn how to drive and learn for better fuel economy since it basically learned how to fuel the engine with a big vacuum leak. Disconnect the battery and take the cable ends and connect then for about 5 minutes. Then reconnect and drive drive drive. Let the PCM relearn.

Sent from my iPhone using Tapatalk
 
#14 · (Edited)
Thanks all for the advice and chiming in in this thread! I appreciate it

I did pull fuse 11 and later also disconnected the battery, just in case. It went up to 20 mpg for a short period, hovered around 18 for some local highway drives, and now settling on 16-17 for the everyday short drives. "Seems" back to normal, i think i need another 100 miles on it before i can tell though.

Never heard of the Short and Long Term fuel trims (i did find a few threads on LTFT/STFTs here and other forums)... what's the procedure for checking it in LX vehicles? Is this an EVIC menu? or do i need to fire up my blue tooth ODBC module with an app to read that somehow? Edit: based on my research - looks like i need an ODBC/app to see the LTFT/STFT. Hopefully Torque on Android has that, will check.
 
#16 ·
Thanks all for the advice and chiming in in this thread! I appreciate it

I did pull fuse 11 and later also disconnected the battery, just in case. It went up to 20 mpg for a short period, hovered around 18 for some local highway drives, and now settling on 16-17 for the everyday short drives. "Seems" back to normal, i think i need another 100 miles on it before i can tell though.

Never heard of the Short and Long Term fuel trims (i did find a few threads on LTFT/STFTs here and other forums)... what's the procedure for checking it in LX vehicles? Is this an EVIC menu? or do i need to fire up my blue tooth ODBC module with an app to read that somehow? Edit: based on my research - looks like i need an ODBC/app to see the LTFT/STFT. Hopefully Torque on Android has that, will check.
Yes, you can pick up an ODBII dongle for ~$20 from Amazon and download Torque (Android) for the interface monitoring. I don't believe Torque on iOS would work with Bluetooth

If you have a handheld tuner, that will work too. Anyway, the fuel trims are corrections the PCM is making for fueling. LTFT = Learned fuel trims over a period of time,.
 
#15 ·
Around 16 city/mixed, 18~19 highway sounds normal for a stock/near-stock first gen SRT8. That's what I've been seeing on 3 of them over the years.

On a somewhat unrelated note, my 2006 Silverado SS (06 model is RWD, not AWD by the way, but turns over a heavier rear axle) had been getting dead at 13.1 forever. I switched to synthetic oil, same grade as the conventional indicated in the manual, and picked up over 1mpg which ain't a lot but it's noticeable! Hundreds of miles later of mixed driving and it's still hovering around 14.3 or so.

We don't buy these vehicles with mpg in mind but it's nice when it's not atrociously bad. :)

Richard
 
#18 ·
This little $8 gem from eBay works on every foreign and domestic vehicle I have plugged it into!

 
#19 ·
Thanks guys. yep got a couple of those, one is that same blue ELM327 module, been using them with Torque on a variety of cars. Will check out the LTFT/STFT with it. Good tips!

On a side note, the mpg after the reset/fuse pull is dropping down to 13 now. No stuttering, no codes, seems as strong as ever.... funny that with the leaky gasket i was pretty consistently getting 16 mpg overall.
 
#20 ·
Thanks guys. yep got a couple of those, one is that same blue ELM327 module, been using them with Torque on a variety of cars. Will check out the LTFT/STFT with it. Good tips!

On a side note, the mpg after the reset/fuse pull is dropping down to 13 now. No stuttering, no codes, seems as strong as ever.... funny that with the leaky gasket i was pretty consistently getting 16 mpg overall.
Running leaner with that leak! More air, less fuel.
 
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