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Old 04-04-2004, 02:12 PM
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rebuilt 5.0 in a 88 gt mustang. gas hog

i have a 88 gt mustang that had 168k miles on the motor before i rebuilt it. it was bone stock before the rebuild, & the only thing that isn't stock is a set of e6pe heads that i put on it during the rebuild. the e7te heads was going to cost me out the butt to get them rebuilt, so i just used my e6 heads. thats the only difference. before the rebuild i was getting about 18 mpg, now i'm getting about 11 mpg. what the hell is wrong here?

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Old 04-04-2004, 07:33 PM
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check your codes. in theory the E6 heads should give you better fuel economy than E7 heads.
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Old 04-04-2004, 10:15 PM
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You didn't say what all was done in the rebuild or whether it is an auto or a stick. I had an '89 GT 5speed car for many years and it always got in the high 20's bumping 30mpg. So you definetly have something wrong. You didn't give much info but unless the injectors have been replaced there is a good possibility that they are dripping and causing the excess fuel consumption. There are several areas that could do the same.But without codes or further info, it's unlikely you'll get it solved, we'd just be taking stabs in the dark.
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Old 04-05-2004, 03:04 PM
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stock bore, 5 speed, 2.79 gears. now i'm going to ask a dumb question, how do you get the codes on a mustang? the injectors are factory, used the original cam & lifters, & everything else is original accept the heads. i took the old engine out getting decent mileage, rebuilt it, put it back in, & now the mileage sucks *****. o2 censer's wouldn't hurt a thing to be replaced, i've put 50k miles on it & never changed them. but like i said this was a sudden change in mileage. i didn't have a valve job done to the e6 heads, they where low mileage take off's, & they didn't look like the seats or valves were messed up. i put on new valve seals, & bolted them down.
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Old 04-13-2004, 08:12 AM
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My 5.0 89 5spd averages close to 25MPG and that's motoring down the highway at 75 with some stop and go in town. It has the 2.79 axle also.

Unless you have a real heavy foot, you should have been doing better than 18 before the re-build. 13MPG is way off the mark, pull some plugs and see how black they are. I would check to make sure you got the plug wires attached correctly, check for a huge vacuum leak and maybe run a compression test, sounds like something is broken to me.

No check engine light with that economy?
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Old 04-16-2004, 11:46 AM
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I'm having a similar problem with my 5.0 Mine is from an automatic 94 GT though. I just went 204 miles using 10 gallons of gas and that was pretty much all highway. Something isn't right there. I have about 123,000 miles on the car. There aren't any insane mods on the car other than a CAI, and side exhast without mufflers. I have no idea what's causing the gas mileage to be so low. Would a bad wheel bearing cause it? I have a feeling my frront drivers side wheel bearing is shot. If I'm on the highway banking right around a curve, that area gets real lound sounds almost like my rotors are warped, but I know they are fine. Other than that I have no idea why my gas mileage is like that. I figured I'd take it to AutoZone to get the codes checked, but they won't check it because it's the old ECC. Any ideas?
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