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-   -   High RPM and fuel consumption while driving (http://www.jeepgarage.org/f80/high-rpm-and-fuel-consumption-while-driving-50447.html)

K_SRT8 11-18-2012 03:04 PM

High RPM and fuel consumption while driving
 
Hi
I'm a new member in this great forum and I hope to be an active member here.
First I have to say that English is not my mother language so please excuse me if you find some mistakes in my grammar.


I bought a second hand 2010 GC SRT8 3 months ago, when I went to see the car I noticed the check engine sign apeared, when I asked the owner what is the reason he said becaise of the exhausts system but son't worry the car is under warrenty so the dealer will fix it for you, then I said ok no problem.
After I bought the car I found that the RPM is too high while driving and it is abnormal. At 110 kmh (68.3 mph) the RPM is at 2500 and at 140 kmh (87 mph) the RPM is at 3050 and because of that the fuel consumption is very high it is just like the fuel is draining from the tank! (at 87 mph the average is 17.5 L/100km)
I took the car to the dealer and told them please fix the check engine sign and also do something for the fuel consumption. Next day they called me and told me that the check engine sign is because the previous owner removed the catalytic converter or to be mor specific he removed the filter inside the catalytic converter as the dealer told me to gain more power and noise and this caused the engine to drink more fuel.
The guy was so nice that he told even it is not a factory defect but becaus you did not know about this problem we will order a new exhaust system for you under warranty.

The question is: If I replace the exhaust system with a new one will it fix the fuel consumption problem? If not then what should I do because I'm planing to sell the car and buy a 2012 GC SRT8

Scottina06 11-18-2012 03:26 PM

Re: High RPM and fuel consumption while driving
 
you shouldve just replaced the cat converter...but it sounds like the exhaust will improve the problems

SvenskaJeepGuy 11-18-2012 04:35 PM

Re: High RPM and fuel consumption while driving
 
That should fix the problem, the sensors were tricking the computer into adjusting the fuel consumption

viking757 11-18-2012 06:54 PM

Re: High RPM and fuel consumption while driving
 
Quote:

Originally Posted by SvenskaJeepGuy (Post 712636)
That should fix the problem, the sensors were tricking the computer into adjusting the fuel consumption

What sensors tricking what?:confused:


Fuel trims are not calculated by the rear 02's they just monitor the cats(That's what triggers a CEL for cat inefficiency hence his check engine light). So with that said while removing the cats may have increased exhaust flow thus increasing the engines ability to breath causing AFR to change and the PC compensates by adding more fuel (to achieve lambda 1) I don't think it will be drastic. The OP has to understand the SRT's are geared low(3.73) so yes at highway speeds your rpm will be a bit higher than what you are normally use to.

17l/100km = ~13.84mpg That's in the ball park of what I average

K_SRT8 11-19-2012 04:23 AM

Re: High RPM and fuel consumption while driving
 
Thank you for sharing your opinions.

So does that mean if I replace the cats the fuel consumption will return to normal?

viking757 11-19-2012 09:12 AM

Re: High RPM and fuel consumption while driving
 
Quote:

Originally Posted by K_SRT8 (Post 712873)
Thank you for sharing your opinions.

So does that mean if I replace the cats the fuel consumption will return to normal?

Your fuel consumption is right around normal. You may see a very small increase as your computer can only make small changes in fuel trims but don't expect anything drastic.

Relwarc 11-19-2012 10:13 AM

Re: High RPM and fuel consumption while driving
 
..... I get 13 MPG MAX on the highway..... it's an SRT thing bud.... Maybe going 87 MPH all day is pushing it too. My best MPG is usually 65 or 70.

ekaz 11-19-2012 11:01 AM

Re: High RPM and fuel consumption while driving
 
I would've loved a 14mpg average in my SRT, I was around 10, but that was with a 426 and heavy foot. :D

Relwarc 11-19-2012 11:04 AM

Re: High RPM and fuel consumption while driving
 
wanna trade? My "fuel saver" modern blue SRT for your 426? LOL

K_SRT8 11-19-2012 01:23 PM

Re: High RPM and fuel consumption while driving
 
No I'm sure the fuel consumption is abnormal because I used to own a 300C SRT and it consumed waay less fuel than the jeep (almost 25%) with same engine and tranny. You may think it is normal but if you drive my car you will know there is something wrong here.
Any way thank you all for your help. I will try to replace the cats and I hope this will fix everything here.

ekaz 11-19-2012 01:40 PM

Re: High RPM and fuel consumption while driving
 
You have to remember that the 300 is way more aerodynamic than the Jeep. The equivalent of 14MPG isn't really that bad for these. You also have to remember that theses are AWD too. Same engine and trans yes, but everything else is different.
Hopefully the new exhaust will fix it for you but I wouldn't expect too much.

viking757 11-19-2012 07:13 PM

Re: High RPM and fuel consumption while driving
 
Quote:

Originally Posted by K_SRT8 (Post 713012)
No I'm sure the fuel consumption is abnormal because I used to own a 300C SRT and it consumed waay less fuel than the jeep (almost 25%) with same engine and tranny. You may think it is normal but if you drive my car you will know there is something wrong here.
Any way thank you all for your help. I will try to replace the cats and I hope this will fix everything here.


Yes same engine and trans but final drive ratio is different..ours are geared lower thus higher rpm at the same speed compared to your 300c which in turn causes more fuel consumption.

Jeep final drive 3.73 + jeeps weighs more so it takes more energy(fuel) to get it moving
300c final drive -3.06


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