MPG updates

[06JeepXKHEMI]

Just checking with other HEMI owners out there.. Before I installed the CAI I was avg 10-11mpg, all city driving. After the intake I was at 12.2-13 all city and was for awhile.. Now Im avg 10.5 at best, Im thinking its the heat but curious to see what others are getting. I do have a heavy foot but to drop that much with the same driving????? No codes, new OEM plugs, any ideas or is everyone else close to this during the summer

[pjmjr508]

I avg 10 - 11 98% city Kinda heavy foot

[Matt]

I get 12-13 with a relatively light foot for my city driving. Sometimes I'll see mid to high 13s when cruising 50-60 mph on some back roads.

I don't see 10 unless im towing or offroading...

[07JeepXK]

My friend Bob who just got the 06 HEMI XK a few weeks ago called me last night. A few days ago he swapped out the spark plugs with oem champions purchased from the dealer. He said that the plugs he pulled out were the same part number as the ones he put in and that they looked like they were original from the factory. His XK has 72,000 miles and the plugs that came out were shot with a gap of .060+. The new plugs were gapped according to the sticker under the hood and he said his Hemi runs so much stronger now but at the same time his MPG has dropped down significantly. The only change was the new plugs.

Now im not an expert on this but is it possible that the engine learned the gap of the old plugs and is now dumping more fuel to make up for the new plugs and better spark? Maybe the PCM just needs to relearn everything now with the new plugs.

[06JeepXKHEMI]

Not sure, but I was talking with my Dad this weekend about our computers and what not.. Although they need to "relearn" at times, they are sensitive to the driver itself. For instance, when I accelerate even if not WOT it will accelerate almost like WOT per my driving habits its learned. Its possible it reads a better spark and cause of his driving habits its dumping more fuel in to accommodate the better spark, but Im trying to figure out why mine as dropped with no change to the XK at all. Im guessing just how heavy my foot is but Ive been nursing her around and my mpg is going down! Maybe a good question is what fuel type are people using and which gas station?? I wish there was a race trac around here I always got waaay better mpg with their fuel..

[07JeepXK]

What octane are you using? I wouldnt go over 91. Thats what I run and have flashpaq tuned to 91 performance. Bob uses the same octane on same tune.

[06JeepXKHEMI]

I dont have a tune and Ive been doing 87 or 89 and saw real no difference. Next fill up I will do 91, best mpg came from Sunoco which is what Im running now 87 so I will go up to 91 or 93.

[07JeepXK]

I thought that its recommended to run a minimum of 89 octane in the Hemi's??

[06JeepXKHEMI]

I thought so but it doesnt say anywhere on gas cap or owners manual. I think only the str8 HEMI's require minimum octane

[Matt]

My 07 owners manual recommends 89 octane. It says 87 can be run if no knock s experienced and that 91+ is not recommended for use.

After any mod or engine maintenance like spark plugs its a good idea to disconnect the battery. The computers do "learn", but disconnecting the battery puts it directly into an accelerated learn mode. After a period of driving time the algorithm slows so it takes changes to the system longer to propagate.