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Thread: new to me TJ issues

  1. #1
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    Default new to me TJ issues

    alright just picked up a 03 TJ, 4.0, 5 speed, 2.5" lift, 68k miles, blah blah blah.

    i hate post like this but I'm gonna ask.

    first there's a vacuum issue I'm assuming somewhere. at idle at random times i will get an unbelievably loud whistle from the intake, with the loss or addition of any vacuum the whistle will stop. its not a vacuum line or leak that i can find. I'm almost thinking the TB is leaking air somewhere internally, a brake clean/throttle body spray around it shows no change though.

    secondly I'm getting schitty mileage, like 10 in town and 12-14 on the highway. put a new catback, home brew CAI, and no change. i don't have smog and am thinking bout gutting the cat/cats next to see if thats the issue. it warms up super fast like 2-3 minutes even on a cold day so I'm leaning that way. i also read that the heads have issues with cracking on these casting but have no tell tale signs of that yet.

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    Land Squid Jeffb_79's Avatar
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    check your vacuum line on the driver side coming out of the intake manifold.... it branches off to the master cylinder, then circles around to the passenger side, enters a black box and splits off into the passenger side firewall. The rubber fittings where these lines split off have a tendency to crack/brake. You'll get that noise from them when this happens.

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    Member Hamr25's Avatar
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    really the only thing to truly improve mpg is driver discipline. i can make a toyota prius get 5 mpg, i can make my jeep get 30. if your worried about gas, get your foot of the skinny pedal. you may gave gained a few mpg from your cai and cat back. i would keep your cat, well a cat in there. 4.0l needs some good back pressure in order to scavenge properly. and since you said you made a home brew cai, if you just got rid of the corrugated tubing to smooth flow and a cone filter, but retained the stock location. all i can say is fail. in order to get a colder air intake charge, your must first move the filter to where it is in a stream of cold air, and your engine bay is not really one of those places. get creative, find some ways to route some tubing for your intake. experiment a little, find out what works best for your set up.
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    Quote Originally Posted by Jeffb_79 View Post
    check your vacuum line on the driver side coming out of the intake manifold.... it branches off to the master cylinder, then circles around to the passenger side, enters a black box and splits off into the passenger side firewall. The rubber fittings where these lines split off have a tendency to crack/brake. You'll get that noise from them when this happens.

    didnt check the evap bs stuff yet. ill check it out tomorrow. brake booster lines are fine though.

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    Quote Originally Posted by Sentry87 View Post
    really the only thing to truly improve mpg is driver discipline. i can make a toyota prius get 5 mpg, i can make my jeep get 30. if your worried about gas, get your foot of the skinny pedal. you may gave gained a few mpg from your cai and cat back. i would keep your cat, well a cat in there. 4.0l needs some good back pressure in order to scavenge properly. and since you said you made a home brew cai, if you just got rid of the corrugated tubing to smooth flow and a cone filter, but retained the stock location. all i can say is fail. in order to get a colder air intake charge, your must first move the filter to where it is in a stream of cold air, and your engine bay is not really one of those places. get creative, find some ways to route some tubing for your intake. experiment a little, find out what works best for your set up.
    having built numerous 4.0 and variants 4.0 i have never ran a cat on any of them. CAI is a overused general term. its a 3" AFE prodry 7 to a reducer at the TB. intake charge temps have been argued to death, the 10 degrees difference on a NA engine is miniscule, i will agree every little bit helps.

    as for mileage im not driving it hard at all, under 2k rpm's all day. easy on acceleration. my 4.7 turbo stroker with 60lb siemens got twice the mileage im getting now, and that was raping it a every light. im planning on swapping over to a 0721 head and working on the VE with this motor to try and help it breath alot better. the exhaust currently is at about 80% of the intake flow so im fine with scavenging power for what im doing.

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