I have an '05 QC 1500 Hemi 4x4. I have had it from 89,000 km, and I now have 133,000 KM. Mileage has never been great on the trucks I know, but on the over head display on the highway I used to get around 17, tops 18 mpg. City was usually 15 or so.


As of late my mileage has became worse and worse. Typically on the highway, flat, cruise on at 100 KM/hr (60 MPH) I am getting 14. It's pitiful.


I had a buddy scan the truck this morning, no codes popped up.


I also have another issue that has happened for some time, every once and awhile If I start the truck, it idles fine, but as soon as I throw it in reverse to back out of the garage it runs rough for about 2 seconds like its about to stall, then the RPM's pick back up and its good to go. It doesnt happen all the time.


So first off, I should be getting better than what I am right? City most of the time is around 10. I have already done the transfer case, diff and tranmission fluides about 5,000 KM ago.


My thoughts on tackling this are below.


1.) Plugs, not sure when or if they were ever changed. Could this be a big cause of poor mileage? I have read its best to go with the standard Champion #570 Copper Cores.


2.) Plug Wires, same as above, not sure if they were ever done. worthwhile to replace? I am trying to keep costs down here.


3.) EGR and PCV Valves. I have read they have caused a lot of issues for guys, wondering if this would be a source as well?


4.) Throttle Body cleaning. Again, looksl like they build up with oily crud pretty quickly. Was thinking of pulling it off since it looks fairly simple to clean with some iso propyl alcohol.


5.) 02 Sensor, no codes were thrown, so not sure if its worthwhile to switch out.


6.) fuel filter? How hard to repalce these things, would it be a cause?

 

I do not know where you are located, but here in the northeast, the winter blend of gasoline reduces my gas mileage 1 to 1 1/2 mpgs. That combind with the richer setting until the motor warms up. Your city mileage is higher than I normally get, about 13 to 13.5 in warm weather, 12 during the winter. The highway mileage is close to mine. Do not rely on the overhead for true mpgs, but for purposes of comparision it is ok.

Responces to your thoughts.

1.) If the plugs are the orignals, you are more than twice the manufactors recomendation of 30,000 miles. Unless you have a fouled plug, I do not think this would account for 3 mpgs. Picking a brand of plugs is personal, but the basic copper cores are best. The most popular are the Champs and the NGKs. I use the Champions with no issues. Since you need 16, paying less than $2 each is bearable.

2.) My truck a is year older and slightly more miles. My wires look and feel ok, but if you have the money, it would not hurt to swap them out.

3.) Normally if your EGR fails, it would trigger a CEL.

4.) Throttle body does "crud up". Infact, TSB 18-016-05 describes this for 2004 and 2005 Hemis. Use only brake cleaner (stated in the TSB) and make sure you protect the electrical components. On all the forums, there has been much discussion on the benefits of grounding the TB. Use the search option. For less than ten bucks, I will likely try it.

5.) Many thoughts about swapping out the o2 sensors, you got three. I go long with the thought, if it ain't broke (no codes) leave it alone.

6.) I would love to change the fuel filter, but it is part of the fuel pump in the gas tank and not meant to be changed separately. It's either time consuming or an expensive chore.

Best advise is to go back to the basics. Check the air pressure in the tires, make sure the filters are clean and follow through on routine maintance. I found going 100% synethic fluids of the proper weight (5W-20 motor oil) makes a measurable difference.

The rough running could be caused by a low transmission fluid, seriously.

Good Luck

 

I think the previous post is bang on. Some of the Hemi's really seem to burn down the plugs. By 80,000km they are usually worn out. My 07 certainly did. Idle and engine smoothness improved a fair bit with fresh plugs. Since mine is coil on plug there isn't any plug wires to change. Not sure if yours has them or not, can't recall when it changed. Make sure the coil packs and wiring are in decent shape. Mileage didn't really change much, and mine is worse than yours. Mind you I am a 2500 megacab with 4.10 gearing. 10.5 city, and 15 hwy at best is all I have seen.

When you have the throttle body open for cleaning, and while changing pcv etc, be sure to clean out any vacuum lines and hoses. Making sure there isn't excess oil and build up there is a good idea. Shouldn't be much there, but every bit helps to keep those sensors clean. Also make sure all the clamps connect up tight and seal. Vacuum leaks are not a good thing either.

Has anything changed recently? Cold air intake, muffler, tires, wheels? Added extra weight or change the wind profile (canopy, tool box, Lift)? Those things can all affect mileage to some degree. Especially if you get to liking the new sound of a muffler and then drive it more aggressive.

what grade of fuel are you running? Manual calls for 89 octane preferred. Many use 87, but there is some reports on the web that those guys end up with more engine problems (plugs burning out quicker, valves and piston wear etc).
As part of govt. initiatives, many fuel stations now add ethanol to almost all grades of fuel. Ethanol in my experience seems to make my mileage worse. Since it now exists almost everywhere, that could be a factor as well. Many stations premium do not have it, but the extra cost is not worth it to go to 91 or 93 octane. 87 and 89 more often than not contain ethanol from what I have seen. In the next couple years, all motor fuel sold in Canada is supposed to contain at least 10% "renewable" content (ethanol in gas, bio-diesel).

Good luck. Making the most of your gasoline $ is tough on these beasts.

 

I checked the fluid, its totally fine. I'll probably look at doing plugs soon myself or have my shop do them. He's pretty cheap, $270 to change them all. I hear it can be a tough job.

Nothing has changed recently other thant he diff/tranny service and a new set of tires. Tires are the exact same size and make only one model newer. I had 265/75R17 Bridgestone Dueler AT REVO on before, and I replaced with same size REVO II's.

My mileage last night in down was like 9.2, never used to be that bad. Only thing I can think of right now that would cause that would be winter gas, or possibly plugs. I am also thinking the TB probably needs a cleaning. Going to try find a used CAI somewhere to save a few bucks on a new one if I can unless you guys have any recommened suggestions. It sounds like they are 350-400 new.

 

Minor addition to the brake cleaner for the TB----- non-chlorinated, use an old toothbrush for gunk removal behind the throttle plate, the plug wires should be changed every three years, and the crossover layout of the wires DOES MATTER
You can get the FSM for the truck from WEED, it in his profile I believe--free download.

 

You could try some fuel injector cleaner as well. Maybe the injectors are obstructed a bit affecting the spray pattern/fuel atomization.

 

Sounds like plugs and tb to me. Take the time to pull the tb all the way off. Its only 4 bolts. Use Maf sensor cleaner as it isn't as abrasive as brake parts cleaner. You can take off the egr valve and spray/clean that with Maf sensor cleaner as well. If your not comfortable doing plugs then pay your shop, but it's about $40 to DIY. Not too bad really except the back four. Totally worth a little bit of struggle to save a couple hundred bucks IMO. Good luck.

 

As far as cai is concerned, the biggest problem with the stock set up is the "hemi hat" it contains a 3" 90* with a few noise restricting chambers which makes it inefficient but quiet. I took that out and put a sch 40 90* in its place. Opened it up nicely. When it came time to replace my factory air filter I decided to use my old k&n cone filter inside the factory filter box. A 2 1/2" sch 40 bell end fits perfectly inside with no modification. I heated the stick to bend it so my filter would sit in the box nicely. For a $5 stick of pipe I have a true cai with a factory look and it's cool to be a little different than every one else.

 

could also reset the PCM to make it relearn.

What about your air filter and tire air pressure?

 

Im gonna go out on limb and say clean ur TB first. I had some same symptoms and that was the sole problem. Do it once or twice a year. I changed my plugs at 70000 miles just because it was over time not because I was having problems, way too long, the gaps werent terrible but they were bad. Change them. I didnt do wires but I should have.

And as Weedahoe stated; tire pressure, airfilter and reset pcm.