Garbage gas mileage, 10mpg

Discussion in 'Fox 5.0 Mustang Tech' started by Grn92LX, Sep 12, 2004.

  1. Well, my gas mileage blows. My speedometer hasn't worked in about a year but it works now so I checked my gas mileage last night and got 10mpg. Thats with around town and highway driving. I guess i'll give the car a code test and see if any sensors come up. I kinda think the problem is since i'm running a 24lb pro m 80mm mass air with 30lb injectors and a pro m remote optimizer that the 'tune' might be off. Im thinking of buying a 30lb mass air. I remember my car used to get around 16mpg with mixed driving and beating on it. My O2 sesnors are about 4 years old.

    One quick thing about the O2 sensors, does it matter which harness they get plugged into? Is there a left and a right for them or it doesnt matter?
  2. You answered your own questions there.

    No it really doesn't matter which O2 plug goes where, it's one system, but I would try to get it on the correct side.
  3. Im not sure what to think. My maf voltage at idle is good, so im not sure how off I have the optimizer dialed in. Its about .6v at idle. I thinks its decent where it is.

    One thing I didnt mention was I extended the wires on my o2 sensors by cutting and splicing. I do electrical work, so I know how to cut/splice, but maybe the added resistance in the wire from cutting is hurting the sensor? Where can I buy new 02 sensors with longer wires?

    Im thinkng about getting new o2's, new coolant temp sensor and while im at it, a new o2 sensor for my saturn (daily driver)
  4. I don't think the longer wires are a problem, you can buy o2 extensions for them so they should be able to handle it. Unless you have a lot more to your combo than listed in the sig, (like a blower?)an 80mm MAF and 30# injectors seem like a bit of an overkill- especially if the MAF is calibrated for 24#'ers. Don't know if that's it, just an observation. Good luck
  5. The pro m remote optimizer is a device that allows you to dial in your maf to make it work with different injectors than its calibrated for.

    I just did a key on/engine off code test and the only thing that came up was 67 which is neutral safety switch I beleive. car was in neutral when I tested it, so thats weird how it came up. I'll probably do an engine running test later and see if anything comes up.

    The 30's are actually ideal for my combination. It was way lean on 24's so the 30's were the best bet.
  6. According to Pro-M, a 70mm MAF is sufficient until almost 400HP, and the 24# injectors, likewise, are good for well over 400 N/A. You can't tell me that your h/c/i is putting out 400 or more, so what do you have that we don't know about? If 24# squirts were lean with that combo, it sounds like something else may not have been up to par. Pump maybe? Don't know, just sounds funny to me :shrug:
  7. C'mon man, internet charts dont mean squat! I have a 255 high pressure pump. Problem was 24lb inectors werent right for my car, I needed to step up. My thread wasn't what people thought about my injector set up, but why I get crap for gas mileage :) Never said im making 400rwhp, but like I said, I dont use internet charts.

    Anyway, back to my question. I tried doing an engine running code test and the POS tester wouldn't let me.

    Stangbear, not to sound rude, but the next thing your gonna tell me is when I swap to a 75mm TB that its "too big" for my combo according to charts?
  8. Grn92 - the data Stangbear is referring to regarding injector size comes from ProM's website - they probably know a thing or two about maf's and injector size. He's trying to help - your car should have run just fine and had plenty of fuel w/24's. So it's likely there may be other issues. Did you buy your maf new or used?

    The system does distinguish the left side O2 sensor from the right side O2 sensor.
  9. Michael, I know what he's trying to do. I just dont use charts to tell me what to use, ya know?

    I tried 2 maf's and both were lean, the pro m might have been a little richer I think but it made less power. The maf's were bought new. 24's did not supply enough fuel and on the nitrous it was 18:1 a/f, a touch lean :)

    Fact is, 30's are ideal for me. What im trying to figure out is why my gas mileage blows? Im thinking I dont have the remote optimizer dialed in perfect, spliced O2 sensor wires or since the car runs too cool at night that it could hurt my mpg. Its still in closed loop though, so I cant see that hurting me too much. I will swap in a hotter stat since fall is near.
  10. Actually, I wasn't going to go there at all. However, since you mentioned it, yes, I would think for your combo (as it is) a 75mm TB would be bigger than necessary. When you're cramming a bar or more of extra atmosphere in there, it would be a different story... and even your 80mm MAF may be justified.
    More relevent- you are running n2o. Didn't know that, and it would definately call for a little more fuel in the mix- when it's on. However, I'm assuming this isn't a track only car. Probably runs great on the spray, right? Ideal, even- but not when the n2o is off (which would be most of the time?) so, I still say they're too big, and still won't commit that it's THE problem, only that it's a fuel related observation, and you have a fuel related problem. I've seen major milage issues before with oversized injectors, so I mentioned it. Just my $.02, take it with a grain of salt.
  11. No, I sold the nitrous. Actually, I could run a 42lb injector now if I wanted and still get good mileage with the proper calibrated maf as long as the eec adapt's. Im sure lightenings and 03 cobra's get good gas mileage :)

    Fyi, Ed Curtis recomended a 75mm TB for my car. It will not slow me down. This im not getting into as I wanna keep my thread on point or at least try to :)

    I listed 3 possibly causes, I guess I can try them 1 by 1 as I have time.
  12. Get a MAF calibrated for your injectors...and see what that does...

    And yes a 75mm TB is to big :D and get the same driving qualities that I would like...

    Yeah the o2 sensors are side oriented...

    My gas mileage has suffered also...dang 30lb injectors :nonono:
  13. Lightnings and 03/04 Cobras are tuned from the factory for those... :nice:

    A tune does wonders...
  14. I would try finding a stock maf and 19's # injectors and put them back in to see what happens to mileage/drivability under normal driving conditions. If it significantly improves, then the issues lies with maf/injector size/transfer function/ecu compatibility. If it doesn't improve, then it's likely simply the fact that the combo makes its power high enough in the band that low rpm torque is crappy - hence the poor street mileage.

    "I just dont use charts to tell me what to use, ya know?" No - don't know why you wouldn't take advantage of companies like Pro-M's expertise, ya know?

  15. Because the real world and internet charts are 2 completely different things.

    My car makes good low end torque and its not as high rpm monster, it peaks about 5400rpm. Im considering a new maf and keeping the optimizer to help dial everything in better. I just dont wanna chance buying a new maf and having to deal with surging. The optimizer will help fix surging. How much does a pro m recal cost? Usually the car see's under 3k rpm when I drive it, except when I wanna have fun and it see's around 6k here n there.

    How would I know which O2 goes to which side? Reason I ask is I had a guy put my tremec in and he had to pull my longtubes to bolt the scattershield in and I'd like to be sure the O2's are in the right harness. Im considering buying new ones. Where can I get longer wire ones?
  16. I'm going to have to say also that you have an overkill combo and a tune that is , well, not in tune. You have a hell of a lot of turbulant air flowing around in there and your MAF is telling your ecu a different story and it is trying to combust a wrong mixture of air/fuel. The stuff you have on your car is easily capable of probably 450 horses if not more. It seems however though without the bottle and assuming from what you have stated and all, you aren't even past the 300 barrier - overkill. Your car is way out of tune by what you have done to it which is why what everyone is telling you IS relevant to your post. Making a great engine run great is a science of mix and matching the appropriate components to make them all work well together. When someone does what you did and go big on everything they can, nothing will run its best because of mismatched components. These "internet charts" are a guide and are pretty dead on. But like I said they are a guide most people follow them for a reason - but they are by no means 100 hp off like what your setup is for your engine output.
    As for not enough power, did you mess with your fuel pressure and turn it up a little to try and get the performance your car needed first? Your fuel pump sure as hell will support it, so i'm sure that if your engine was being starved of fuel that you turned the fuel pressure up a bit to help increase fuel flow........
  17. I find it hard that your stang performs well at 6k revs, but if you have aftermaket valve springs, then I suppose you don't have valve float that all stock 5.0's horrendously suffer from around 5k rpm.
    But anyway, they actually make o2 estension harnesses which are direct plug in and are made because of long tube users - so here you go:
    BBK o2 sensor extensions
  18. He doesnt have a stock 5.0......
  19. Thanks, but what I was wondering was where I could buy new o2 sensors with a longer wire?

    My car revs to 6k just fine, I have trickflow TW heads and upgraded valve springs from ed curtis :) 30's are NOT overkill for my combo man. If they are (which their not) then why did ed curtis recommend 30's for 5spdGT's car, my friends car and many many other h/c/i 302's making under 320hp??? Im going to see what happens with this tank of gas and report back when I refill. If it sucks, then I might send my pro m back to get re-cal for 30's.
  20. pep boys and stuf usually sells them. Ive gotten them by mistake. They were probably twice as long as the regular sizes. YOu should be able to move the harness around and get them to reach though. Mine reached without a problem