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Horrible fuel mileage runs like garbage when ac on

Discussion in '1994-2004 V6 Mustang Tech' started by Thestigmach1, Jul 22, 2017.

  1. Thestigmach1

    Thestigmach1 Thestigmach1

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    I know there's a thread awhile back about the car running rough while the actual is on. It he had things done to his I have not done to mine that caused the problem. IAC Gasket mod I think is what the problem was. Today I drove 114 miles and used 3/4of a tank. That comes out to 11mpg ish. I've never gotten that bad with the car even when I drove 110 for awhile. The car has always run rough when the ac was on and I assumed that's just the way it is. Lately it's been running really rough and feels like it has no power with the ac on. It blows cold when driving but today I noticed it started blowing warm when sitting in traffic. First thing I thought was that the fan wasn't running. I pulled into a parking lot to check on it and it was running stupid loud like always (is your guys fan really loud to or do I need to look into that as well?) I checked that it was charged when I got home and it had the right pressure. I'm kinda thinking compressor issues but am hoping not. I do currently have the egr unplugged because it was making it stutter and low RPM under load ever since I put the headers and dual exhaust on. It's been like that for awhile now though and never had this problem. Any thoughts on what the deal is? Do you think I need to take it to a shop and have them flush the ac system? Thanks in advance guys
     
  2. Serpent

    Serpent Member

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    if I am not mistaken, with the egr delete, you need a tune. is the car throwing any codes? my guess is the computer is getting all kinds of erroneous information and throwing you fuel maps all wrong. that coupled with the headers and so forth the o2 sensors are probably not providing good info. are the o2's still hooked up? still have cats? lot could be going on to contribute.
     
  3. Thestigmach1

    Thestigmach1 Thestigmach1

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    unplugging the egr was actually a fix for it shaking like a bad miss at low rpms under load after the header install. It ran great for quite some time after that no noticeable change in fuel economy so I just left it alone with plans for a tune in the near future (meaning when the wallet has more than moths) with it plugged in it doesn't throw any codes, obviously with it unplugged it does. I have a thread on here somewhere about the whole mess. all the numbers in the live data added up. I'm going to look into something a read about once where a guy rigged the EGR permanently shut so the confuser didn't freak out but he essentially deleted it. technically the cats are under the car, theres just nothing in them. And I wont put it back either I gained so much power and response after beating the garbage out it isn't even funny. after messing with stuff for awhile and it finally cooling down enough outside to even think about working on stuff I found that the AC compressor is tight as all get out to turn. it almost takes two hands to turn it. also if I rev the engine with the AC on the compressor makes supercharger noises :) I have a feeling that's a bad thing. so the bearings on it must be seizing up. Now I need to figure out if replacing the pulley and clutch on it does anything for that or if I just replace the whole thing. I'm thinking whole thing. And I figure if I'm going to do that I might as well replace the condenser and dryer while I'm at it just to make sure that nothing that might have cannoned out of the compressor is inside of all that
     
  4. Serpent

    Serpent Member

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    got ya. cetainly anything with substantial drag will have an adverse effect on everything. hope it isn't the compressor but sounds like it is. wise to change or at least check the other stuff for fallout.