hemi 5.7l poor gas mileage

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

bambinoelchicano

Junior Member
Joined
Nov 26, 2014
Posts
13
Reaction score
0
Location
Tampa,FL
Ram Year
2003
Engine
5.7l
hi im new to this forum and i wanted to ask to make sure, i have a 2003 1500 QC 5.7l 4x4 and im getting 6mpg in the city and about 11 on the interstate. the original engine went kapput and i put in a 2004 durango 5.7l. new plugs, all new gaskets, cleaned throttle body put a cold air intake. it has the 20" rims with falken wildpeak 275/60r20 tires. im not complaining i know its a heavy truck to haul around but i want to see if this is normal gas mileage.
 

HemiLonestar

Senior Member
Military
Joined
Jun 1, 2012
Posts
5,991
Reaction score
2,952
Location
MD
Ram Year
2016
Engine
5.7 hemi
What gears do you have, also where are you measuring fuel consumption, actual calculation or from the trip computer?
 

Rokmonanoff

Senior Member
Joined
Dec 28, 2013
Posts
181
Reaction score
71
Location
Tundra, Alaska
Ram Year
2008 Mega Cab
Engine
5.7 HEMI
Even for a hemi, that's pretty poor mileage. I'm running the mega cab which is heavier. I'm pretty consistently 12-13 for a 50-50 mix of city/highway. I've seen 15-16 on an all highway tank.

As stated before, hand calculate the division problem.

Good luck.

Rok
 
OP
OP
bambinoelchicano

bambinoelchicano

Junior Member
Joined
Nov 26, 2014
Posts
13
Reaction score
0
Location
Tampa,FL
Ram Year
2003
Engine
5.7l
i have hand calculated it. i fill up the tank and i get less than 200 miles to the tank. far as i know it has a 26 gallon tank. i have stock rear end. what is it 3.92 gear ratio posi trac?
 

rabbie303

Member
Joined
May 28, 2014
Posts
57
Reaction score
8
Ram Year
2003
Engine
5.7 Hemi
I have the same truck, 2003 1500 QC with 20's as well, and I cannot get better than 11.4 in the city, and that's being easy on the gas. It's supposed to get 13 or 14 around town, but I cant even get that on Hwy either.

Did you figure out anything more about the problem bambinoelchicano?
 

Redtruck-VA

Senior Member
Joined
Jun 29, 2010
Posts
5,864
Reaction score
984
Location
Virginia
Ram Year
2003 & 1989 D250 RWD
Engine
Hemi-5.7, 5.9 12v & 24v diesel
Are you getting any codes. I would think running that rich your trims are way out of whack. Are you using the 03 PCM with a single O2s? Where is the O2s plugged in on the new engine? 03 uses a 48psi fuel pump 04+ use 58psi, what fuel injectors are you using?
 

StaLL1oN

Senior Member
Joined
Nov 17, 2014
Posts
202
Reaction score
21
Location
Arkansas
Ram Year
2003 1500 Quad cab SLT 4x4
Engine
5.7 Hemi
Red ive got an 03 but I have 2 02's?
 

Trenton

Senior Member
Joined
Dec 28, 2014
Posts
170
Reaction score
49
Ram Year
2006
Engine
5.7
hi im new to this forum and i wanted to ask to make sure, i have a 2003 1500 QC 5.7l 4x4 and im getting 6mpg in the city and about 11 on the interstate. the original engine went kapput and i put in a 2004 durango 5.7l. new plugs, all new gaskets, cleaned throttle body put a cold air intake. it has the 20" rims with falken wildpeak 275/60r20 tires. im not complaining i know its a heavy truck to haul around but i want to see if this is normal gas mileage.

What were you getting before? why did the engine fail? if it blew alot of oil into the exhaust upon failure you could have cooked your cats causing back pressure problem. Did you use 03 intake injectors and all engine sensors? swing by the stealer dealer have them scan it
 

StaLL1oN

Senior Member
Joined
Nov 17, 2014
Posts
202
Reaction score
21
Location
Arkansas
Ram Year
2003 1500 Quad cab SLT 4x4
Engine
5.7 Hemi
I thought this was about a transplanted engine into a 03 with poor mileage.

Ahh got ya, hey what's your opinion on this Red...

Factory setup for the 02's are line setup, front and back same side. With the long tube headers I installed, they have the o2 holes one on each header. What I did was plug the driver side 02 hole and make a **** on passenger to keep it like a stock formation.

Do you think it would've been better to route one over to that driver side hole?
 

Redtruck-VA

Senior Member
Joined
Jun 29, 2010
Posts
5,864
Reaction score
984
Location
Virginia
Ram Year
2003 & 1989 D250 RWD
Engine
Hemi-5.7, 5.9 12v & 24v diesel
The O2s has one in front and one behind the cat. My front sensor is also different than the rear sensor, so don't mix them up. Mounted on either side IMO is good. The passenger side is closer and fits well. I installed dual cats on mine and the rear O2s is mounted on the cross over pipe which technically would be reading the drivers side. I have never gotten a code with this setup. If you still using the original single cat and the rear sensor is behind it then you are good. If you aren't using a cat, then the rear sensor needs to be isolated to keep from throwing a code.
 

StaLL1oN

Senior Member
Joined
Nov 17, 2014
Posts
202
Reaction score
21
Location
Arkansas
Ram Year
2003 1500 Quad cab SLT 4x4
Engine
5.7 Hemi
Yea I'm running cat delete. Have front sensor in front and made a **** for the rear sensor about a foot behind it in part of the y pipe...still throwing a code but I think its because I havent done the defouler trick
 

Redtruck-VA

Senior Member
Joined
Jun 29, 2010
Posts
5,864
Reaction score
984
Location
Virginia
Ram Year
2003 & 1989 D250 RWD
Engine
Hemi-5.7, 5.9 12v & 24v diesel
If the rear sensor isn't isolated from the front sensor it'll throw a code. The short version is the sensors count voltage changes (flips) if the count is same you get a code. With the rear sensor isolated, it's count is lower than the front and you won't get a code.
 

StaLL1oN

Senior Member
Joined
Nov 17, 2014
Posts
202
Reaction score
21
Location
Arkansas
Ram Year
2003 1500 Quad cab SLT 4x4
Engine
5.7 Hemi
Here's a pic of what I did

20150218_093053_zpsm70bmgxo.jpg
 

Redtruck-VA

Senior Member
Joined
Jun 29, 2010
Posts
5,864
Reaction score
984
Location
Virginia
Ram Year
2003 & 1989 D250 RWD
Engine
Hemi-5.7, 5.9 12v & 24v diesel
Here's a picture of mine. You can see one of the cats and the rear O2s on the cross over pipe.

img2013050100074.jpg
 

StaLL1oN

Senior Member
Joined
Nov 17, 2014
Posts
202
Reaction score
21
Location
Arkansas
Ram Year
2003 1500 Quad cab SLT 4x4
Engine
5.7 Hemi
Hm, do you think maybe I should moving rear to the cross over as well? Or is mine ok just run the defouler trick?
 

Redtruck-VA

Senior Member
Joined
Jun 29, 2010
Posts
5,864
Reaction score
984
Location
Virginia
Ram Year
2003 & 1989 D250 RWD
Engine
Hemi-5.7, 5.9 12v & 24v diesel
Hm, do you think maybe I should moving rear to the cross over as well? Or is mine ok just run the defouler trick?

Without using cats it would serve no purpose to move it. Just isolate the rear sensor.
 
OP
OP
bambinoelchicano

bambinoelchicano

Junior Member
Joined
Nov 26, 2014
Posts
13
Reaction score
0
Location
Tampa,FL
Ram Year
2003
Engine
5.7l
the 03 ram that has the 04 hemi in it, i used the 04 intake only to realize after that the 03 and 04 use different injectors. the previous engine failed from a spun rod bearing. The 04 engine also had egr system but the 03 ram did not therefore i deleted it. ive checked it for stored codes but nothing shows up on the genysis scanner im using. The truck has all stock exhaust 02 sensors on each pipe coming down from manifold
 

xb1230

Hobby Mechanic
Joined
Aug 22, 2014
Posts
960
Reaction score
226
Location
South Shore of Montreal, QC, Canada
Ram Year
2020
Engine
5.7 HEMI
What Spark Plugs did you put in ?

Were the '02 sensors replaced ? Even if the O2's are good or not throwing a code does not mean they are providing an efficient and accurate reading. I was not getting any codes, but still went ahead and replaced them for good measure and it did a small difference in the MPG's.

My next step is to take the injectors out of the intake and make a DIY rig to get them through a cleaning routine and also check the spray pattern as well as if they are leaking.

Does the truck produces any odors (strong unburned gas smells) when running (cold or at operating temp) ? this could be indicative of a poorly working O2 or PCM or Injector making the engine running with a richer air/fuel mix than actually required.

You could also check your IAT to make sure it sends the proper values to the PCM. A degraded IAT can lead the PCM to believe the engine is running with colder air than it actually is, generating a too rich air/fuel mix.

Just throwing a few ideas on the table of things to look for.

Hope this helps
 
OP
OP
bambinoelchicano

bambinoelchicano

Junior Member
Joined
Nov 26, 2014
Posts
13
Reaction score
0
Location
Tampa,FL
Ram Year
2003
Engine
5.7l
The only time i smell unburned fuel is in the morning, which i believe is normal. I smell burned cat when i get on the throttle heavily. But i believe that is normal too. THe only thing that i think is causing this problem is the different injectors. 03 injectors only fit 03 hemis and the 04 and up are all the same.
 

Latest posts

Forum statistics

Threads
194,927
Posts
2,864,183
Members
155,296
Latest member
VLG6963
Top