Terrible 5.7L 2500 MPG

[LongTom]

Had an engine code for a P0420. Took out cats and put in anti-fowlers. No engine light so far, but have noticed my fuel economy is absolutely terrible. Was bad before and now seems a little worse. It’s a 2011 Ram 2500 5.7L crew cab longbox 4x4 with 3:73’s and stock tires. I drive it like a grandpa and get 11 mpg on the highway. others seem to atleast get 14 but I just can’t. I’ve gone 150 miles with 35 gallon tank and I’m almost at half. Wondering what could be causing this, or maybe it’s normal and I’m overreacting. Any help would be appreciated!


(What the computer is reading on flat ground)

 

[rzr6-4]

Welcome to the club.

Solution? Let me known when you find it...

Does it run good otherwise?

 

[Jeepwalker]

Just curious, is it stock running gear, or modded. For example, lifted with oversized tires, aftermarket bumper, cold air kit, aftermarket front bumper, winch, etc? One forum member once remarked that every mod he made seemed to knock 1mpg (each) off his original fuel economy.

 

[Jeepwalker]

What do you think the stock mpg should be? You have a pretty good-sized PU.

I guess If it were my truck I would either take it in to a mechanic ...maybe a parts store will do a real good scan for you.....and get a good scan done. Are there any other codes? Is it running in closed loop? Are there any misfire counts (if so, how many?)? There could be a weak or bad coil too. What's the air temp sensor reading (voltage)? What is the coolant temp sensor reading (maybe it drifted). Is the air filter good/free? Maybe a rodent made a nest in the air box..

Have you done anything with the spark plugs? PCV? If I went to change the plugs I would also do a compression test (watch a video how), and record the vacuum.
Autozone rents these tools for free.

Verify no brakes are hanging up. Some tires are as much as 10lbs heavier than other tires ...and 10-ply tires can take off 1-2mpg.

 

[rzr6-4]

Just curious, is it stock running gear, or lifted with oversized tires, aftermarket bumper, cold air kit, winch, etc?

He said stock tires in the post, which is going to be the biggest factor I would think.

 

[LongTom]

Just curious, is it stock running gear, or modded. For example, lifted with oversized tires, aftermarket bumper, cold air kit, aftermarket front bumper, winch, etc? One forum member once remarked that every mod he made seemed to knock 1mpg (each) off his original fuel economy.

Truck looks exactly how it came from the dealership!

 

[Jeepwalker]

Ok. Missed that (tire size). I put some suggestions (above) in another post...

 

[LongTom]

What do you think the stock mpg should be? You have a pretty good-sized PU.

I guess If it were my truck I would either take it in to a mechanic ...maybe a parts store will do a real good scan for you.....and get a good scan done. Are there any other codes? Is it running in closed loop? Are there any misfire counts (if so, how many?)? There could be a weak or bad coil too. What's the air temp sensor reading (voltage)?

Have you done anything with the spark plugs? PCV? If I went to change the plugs I would also do a compression test (watch a video how), and record the vacuum.
Autozone rents these tools for free.

Verify no brakes are hanging up. Some tires are as much as 10lbs heavier than other tires ...and 10-ply tires can take off 1-2mpg.

Welcome to the club.

Solution? Let me known when you find it...

Does it run good otherwise?

Seems like it. Haven’t noticed anything out of the ordinary.

 

[Jeepwalker]

There can be settings which can be on the low side of 'good' and just inside the window ...but cause bad economy. I'll relist them:

-A failing or drifted O2 sensor,
-A slightly drifted coolant temp sensor,
-Low compression in one cylinder,
-Underinflated 10-ply tire/s
-Drifted air charge sensor
-Intake or other air leak
-Weak Ign coil packs
-Draging brake/s
-Other sensors
-Low vacuum
-Bad plugs
-PCV
-Something obstructing the air intake path

Any of the above which is not in spec (but not enough to cause a code) can degrade economy. I had a vehicle where the previous mechanic installed the air tube onto the throttle valve and the rubber was folded under the clamp (throwing off the air metering). Who knows??

That's why a comprehensive real-time scan by someone who knows what he's looking at (and a print-out) would be good idea. Might not be a bad idea to invest an hour into your local dealer. See if your local dealer has an ace mechanic you can ensure *he* puts his hands on your truck. Find out the tech's name. Get them on your truck. You don't want a newbie, or 2nd rate tech. Talk to the service mgr to make sure you get the "good guy" looking at your truck THAT day you take it in. Stay there and make sure that happens, and he's not sick that day (and you get the new guy who doesn't know crap). If he can't ..reschedule. If there are 10 mechanics at dealers, one of them will be a real ace and know 3x more than the next best tech. You want THAT guy.

I'd probably check/replace the plugs, do a compression test & ohm the coils, before taking it in to the dealer. And show the mechanic the results. The dealer will really nail you just replacing the plugs and performing a compression test. It's kind of time consuming.

.

 

[LongTom]

Ok. Missed that (tire size). I put some suggestions (above) in another post...

Just put the scanner on the truck. Got a P0303 code (misfire in cylinder 3). Truck sounds fine though. Did have an engine code for low catalyst efficiency in bank 1 before I deleted the cats. Wondering if the bad fuel mileage could be the plugs carboned up from the bad cat.

 

[Wild one]

Had an engine code for a P0420. Took out cats and put in anti-fowlers. No engine light so far, but have noticed my fuel economy is absolutely terrible. Was bad before and now seems a little worse. It’s a 2011 Ram 2500 5.7L crew cab longbox 4x4 with 3:73’s and stock tires. I drive it like a grandpa and get 11 mpg on the highway. others seem to atleast get 14 but I just can’t. I’ve gone 150 miles with 35 gallon tank and I’m almost at half. Wondering what could be causing this, or maybe it’s normal and I’m overreacting. Any help would be appreciated!


(What the computer is reading on flat ground)
View attachment 530611

If you just picked it up this morning,there's been a hell'va change in weather since yesterday.Today it's alot colder,and there's a **** pile of snow on the roads,that wasn't there yesterday.Cold tires and driveline also add into the faction today,that wasn't there yesterday Plus if you just filled it up in the last few days,we're on winter fuel now,all those scenerio's add up to kicking the hell out of your gas milege from 1 day to the next day. 11.5 mpg with a 5.7 equipped 2500 isn't all that bad for the weather and road conditions today.I don't think dropping the cats is your issues with milege,it's just the way it is at this time of year.Gotta love Canuckastan in the winter,lol

 

[Wild one]

Just put the scanner on the truck. Got a P0303 code (misfire in cylinder 3). Truck sounds fine though. Did have an engine code for low catalyst efficiency in bank 1 before I deleted the cats. Wondering if the bad fuel mileage could be the plugs carboned up from the bad cat.

When you do the plugs,it wouldn't hurt to do a compression test at the same time. Do not buy plugs off Amazon or Ebay,unless you like doing them over in a months time,lol

 

[Jeepwalker]

Just go down my list.

Check your coolant temp sensor tomorrow morn before you start the truck and after ...to make sure it's good.

 

[LongTom]

When you do the plugs,it wouldn't hurt to do a compression test at the same time. Do not buy plugs off Amazon or Ebay,unless you like doing them over in a months time,lol

Thing is the previously owner replaced all the plugs so they’re fairy new. I can check for a compression test but it seems odd that I’m getting this code right after I’ve deleted cats

 

[Wild one]

Thing is the previously owner replaced all the plugs so they’re fairy new. I can check for a compression test but it seems odd that I’m getting this code right after I’ve deleted cats

Probably more coindence then anything.Dropping the cats won't cause a misfire.I don't want to ruin your day,but you're right in the ballpark for a cam/lifter issue.Hopefully not,and it turns out to be a bad plug/coil or injector,but don't be surprised if it's more serious then that

 

[jws123]

Thing is the previously owner replaced all the plugs so they’re fairy new. I can check for a compression test but it seems odd that I’m getting this code right after I’ve deleted cats

What brand are the plugs? hemis are very picky oem ngk only.

 

[Jeepwalker]

New plugs can be flaky too... Not common, but I've seen it. When you remove them, look at the tip & electrode and note the color. Put each plug in a certain orientation so you know which one came from which cylinder. Just take one plug out of each cylinder (all cylinders) initially, then do your compression test. If you don't do a compression test you really have no idea what the base compression is. You could have two cylinders with low compression, who knows? Is there a burnt valve? Etc. Watch a couple videos what spark plug color means, and how to do a compression test ...and how to ohm out coil packs. Do all those things. If you don't narrow those down, yer just chasing ghosts and could end up doing a lot of parts replacing only to find out you have a bad coil pack ...after replacing a bunch of other items and 3 months of time wasting fruitless searching. All that is part of competent basic troubleshooting. Autozone has the testors.

Once you've finished the compression test, doing it the proper way, and written the results for each cylinder. Then remove the 2nd set of plugs from each of the 8 cylinders (there's two per cylinder). Again, note the condition of each. Plugs tell a story. Usually the story is good, but you'll know right away if there's an anomoly. then you've found something. Ohm the coils while you have them out and write down the results for each. Ohm the plugs too. Just takes a couple seconds for each one. Check the tips for burnt traces. Watch a video how to check plugs.

It might be after doing all this everything will look good. That's great. That's what you hope to discover. Then you can cross these important basic things off the list of possibilities. Move on to other things.

 

[Wild one]

I pull the starter relay and use a remote starter switch to do compression tests.The truck won't try to start on you,as the key stays off,and you can do the compression test by yourself.Also doesn't hurt to hook a decent battery charger to the battery while you're doing the compression test.Follow Jeepwalkers advice to,he's got some good tips

 

[LongTom]

Probably more coindence then anything.Dropping the cats won't cause a misfire.I don't want to ruin your day,but you're right in the ballpark for a cam/lifter issue.Hopefully not,and it turns out to be a bad plug/coil or injector,but don't be surprised if it's more serious then that

Previous owner actually did replace the hydraulic lifters too! Hoping it’s not that again haha. Code is also pending, might have just been a random instance but I’ll take it for another drive tomorrow and see if the check engine light shows up.

 

[Jeepwalker]

Aaaaahh ....now more critical info come out! There's usually more to the story. LOL.

Well, anytime someone works on an engine, besides the work they did, even if they did a great job, sometimes collateral damage occurs unintentionally and mechanics never know it unless someone lets them know. Connectors can get broken, sensor wires get pinched, Maybe the variable timing isn't working ...headgaskets could leak, pushrods can get bent. Crap in the fuel line to the injectors. Wrong parts got used. Didn't get a good seal on the intake gasket. Coil pack slid off the fender and cracked when it hit the concrete floor (stray spark now). Mechanic wipes off the dust with his shirt, looks around to make sure nobody saw it ....then and installs it . Spark plug fell on floor and cracked the porclean. It opens up all kinds of possibilities. Or, it's entirely possible what you're experiencing has nothing to do with prior work.

That's why I suggest you start with basic troubleshooting. Because right now it could literally be a bunch of things. And there's only one way to rule out the basics. If you could do a leakdown test that would be even better.

The other thing to do would be to remove the valve covers and turn the engine over, watching the rockers move the amount they're supposed to. Or better yet, put a dial indicator on each rocker, turn engine over by breaker bar. Write down the recorded lift for each rocker. Yeah, maybe the new cam there's a problem?? Or they had the head re-done and the 'new summer kid' at the machine shop goofed something up. You MUST ensure the basics are good and work up from there.

If you discovered the rocker lift was off on one or two rockers, then you know what to do next...