I have to run premium gas in thsi engine its got a more agressive ignition timing then the 5.9s in your trucks

 

Please explain.




Serious, I'm not knocking you, I seriously want to know about this. Jeeps apparently have some interesting little stuff going on...

 

The Jeep grand cherokee's in 98 had one production year of the 5.9 engine only 14k ever made.. They had 2 versions.. One had a slightetly different camshaft and more agressive ignition timing and thus the HP/Torque are slightly higher then the numbers in your trucks this is the one i have.. Thats why on my gas cap, in the manual and the dash it says premium only more specificly 91 octane.. They also had a second version with the same cam.. but with a performance PCM that required 92 octane... The dodge trucks that did get this camshaft were the later model ones i believe the 2000-2001 models

I dont know the details 100% but this info i told you is true.. Look it up yourself.


Anyway I disconnected the catch can reset the pcm drove around town for 35-40 minutes and my overhead is now reading 12.7mpg and its only climbing higher... This is the gas mileage i remember.. prior to this it was struggling to pass 9.9mpg..

Why does my oil catch can lower my mpg so much ?? That doesnt make any sense to me anyway. Its cought a ton of oil since i installed it right after my intake.. but if my gas mileage was being hurt by it i guess those 1-2-3 tablespoons of oil in the intake every 1k miles wont hurt it.

 

Interesting.


How long are your hoses for your PCV? I'm using a total of 4 feet and so far I haven't noticed a drop in mpg.

 

They were about 2-3 feet. And im using this can its an air compressor filter from lowes.. I removed the stone filter and put the copper scrubby thing in instead.. and then just hooked it all up.. and it worked great too.. see below

 

That's the exact setup I have on mine.
However, I cut the copper scrubber in half and used teflon tape on the barbed ends. You DO have it pointed in the right direction, right?

 

Yes I made sure of it

 

That shouldn't make any difference at all..... Unless your PCV valve is the wrong flow rate? What brand valve ya got?

 

Maybe your overhead isn't all that accurate, also your other method of guessing by how many miles you go on half a tank could throw off true mpg. To get real mileage divide miles driven by number of gallons used.
Use a small propane torch, unlit of course,with small piece of flexible hose and direct it at suspected vacuum leak areas.

 

I did do the real method by going on how many gallons i filled up and how many miles i drove... I got 10.6mpg... and trust me from half a tank to full is always around 13 gallons of gas.. For Jeep its a known fact that half to empty always goes quicker then full to half because of this.. But i wasnt saying i used that to calculate mileage... I filled the tank up completetly.. drove about 120 miles and my tank was at half... then i filled it back up and divided that to the miles i drove and it came to 10.6

But anyway, i still seem to be getting low gas mileage.. I dunno, today i drove around. The car idles for a few minutes at home because i was filling my a/c up ect.. Drove around town and the overhead is now at 11.4mpg.. My PCV valve and grommet are newish and they are Mopar.

I dunno, i just dont see why it is getting such poor mileage after my plenum fix... My pinging is deff gone and i havent lost a drop of oil since but damn my mileage sucks... What the hell could I have done wrong installing the intake to cause this ?? I used a felpro gasket.. the intake went on fine bolted down to 144 inch lbs.. and drives great... Its just like i go from burning oil and pinging and getting 12-13mpg to not pinging and not burning oil and getting 10-11mpg. Im starting to not want to drive this thing anymore.. Go to my 4.0 Grand cherokee.. that thing has no power but at least it gets 16mpg in the city and 21 highway.

A propane torch isnt going to blow up my engine or set it on fire like the brake cleaner did will it ?