yet another gas mileage thread.. this is getting expensive!

[93GTDIN]

Okay, 10 mpg is becomming annoying enough to post this again and hope for some responses.
Here's the scenario.
*I get roughly 10mpg or slightly less, mostly highway.
*vacuum at idle in gear (it's an automatic) is about 9 - 10 in/hg
*vacuum on highway at 70, foot off gas - 20 in/hg
*vacuum under any accelleration is almost always 0 - 3
*my fuel gauge is not full swept so i estimate my fuel pressure to be about 29 - 31 psi under vacuum.
*I use 30 lb/hr injectors with matching mass air sensor
*My tranny is not in the best condition (slips if I take a hard turn)
*Car wont idle well at all (when very cold outside)
*temperature and oil pressure check out--- good
*The car stalls when put into gear when warm unless I apply pedal pressure
*I drive the car nicely, my friends even associate the word *wussy* with how i drive. I never punch it for fear of my engine sucking all the gas out of my fuel tank
*alignment is slightly off, hardly noticable
*I do run the tubes out of my smog pump
*Another thing I will mention is that the automatic is really starting to piss me off. My computer doesn't really understand that my torque curve has been shifted totaly up from the stock curve. THe car shifts really quickly and hardly lets my engine rev up. Sometimes it'll shift into 4th gear at 40 (unless i dont let it) and the car has barely enough torque to accellerate (at 1000 rpm)
*I have an A/F gauge which reads stoichiometric most the time, lean if I go slow up hills, and rich if I let off the gas on the highway
QUESTIONS:
*** Is my slightly lower than normal fuel pressure causing poor gas mileage?
*** Is my transmissions condition severely affecting my mileage?
*** Is my slightly off allignment throwing off my mileage?
*** could my timing be severely affecting my mileage?

One other thing.... what was it... uhh... OH thats right

PLEASE HELP ME


dino

[NotchJohnson]

Did you install a higher rpm torque converter for the larger cam?

[red82gt]

I'll place my bet on the tranny. How do your plugs look?
You'd hate me if I told you what my carbed car can pull for mileage.
How about your O2 sensors?

[red82gt]

I failed to see the longtubes in your signaure, it could be the location of your O2 sensor, some longtubes end up with the O2 sensor only reading from one header tube rather than all 4 and the computer reads lean so it increases the amount of fuel.

[NotchJohnson]

I dont know if the o2 sensors could be the blame. I mean I dont think they would cause you to get 10 mpg. When I put my exhaust on my car a while back, the guy who helped me supposedly knew his **** and said the o2 sensors were useless, and he convinced me that we could just cut them off since they didnt reach the bosses on the longtubes. Big mistake. I never noticed any difference in the way the car performed, and I get 25mpg highway. Regardless, Im still gonna get new ones and hook them back up.

[93GTDIN]

plugs look fine last time i checked. compression is good. Now I am liking the longtubes theory cause I have the worst longtubes on the planet (109 from summit). They were a pain in the *** to install, nothing fit right.... and I had to drill out the holes for 02 sensors. Does anybody else know anything about the longtube theory?

[NotchJohnson]

Did the problem start right after the install of the headers. Just for the hell of it, unplug the o2 sensors and see how it runs with them disconnected. Like I said, mine have been disconnected for 2 years and Ive had no problems and get 25 mpg. Try it and see what happens, if you get some increased gas mileage, then there is a prob with the o2's.

[93GTDIN]

oh, and no new torque converter cause i'm doing the manual sway here in not to long.... another thing i failed to mention

When i'm decellerating to a stop using the brakes after being in 4th gear, when the car hits about 30 miles per hour it wants to downshift into 3rd, but when it does, the engine revs up between the shift. It is very noticable and often annoying. It does it from 3 to 2 but not as noticably. Could this be a sign my tranny is dying?

[93GTDIN]

my o2 sensors were shot when I installed in the headers the first time. i replaced them and saw no difference.

[NotchJohnson]

Unplug the o2 sensors and see how the car drives. There could be a problem with the location of where the o2 sensors are, causing them to be reading too lean, thus telling the computer it needs more fuel.

[Mopar1]

Notch you said diconnect the o2's? This will not effect the comp or performance any? I'm not sharp shooting just asking since urs have been discoonected for a couple of years.

I would not recommend permanently removing or disconnecting your oxygen sensors. They definitely SERVE A PURPOSE! And an important one at that. They measure and adjust your air/fuel mixture and are a crucial part of the Mustang's EEC-IV computer system. If the O2s are not connected or have been removed, your Mustang's computer will just go into a fail safe mode (open loop) with a predtermined air/fuel ratio. You will not acheive optimum performance out of your combination running in this mode.

[NotchJohnson]

I know o2 sensors serve a purpose and never recommended disconnecting them permanently. I suggested this to him because if his are located at an incorrect location in the exhaust, they may be getting a false reading. Disconnecting them will let him know if they are a problem, since the predetermined air/fuel ratio will not amount to 10mpg.

[NotchJohnson]

Oh and Mopar, I never noticed a loss in power either, although Im sure it did take away some. I am going to hook them back up asap though.

[93GTDIN]

well like i said before, the car got 10 mpg before when they were broken, it got 10 mpg after i replaced them.

[jj_jonathon]

im getting 10mpg on my stock 4.6...course thats cuz im doing stop, go, stop, go, stop, go on campus and around town in "2"...lol

i dont think youre stompin' on it, or youd get the gas mileage of a european V12..lol...

[red82gt]

I got the Longtube idea from MM&FF's "Ask Bernie" column in the Feb 2003 (last month's) issue. It's titled, "New Parts, Worse Mileage" He says that if the O2 ensor is in the colector than the computer may be detecting a lean condition. He suggests moving the o2 sensors closer to the stock location, not sure how you'd do that, though.

[NotchJohnson]

Yeah, thats why Im saying to disconect them completely and let the motor run on the factory a/f setting.

[93GTDIN]

notch,
I dont mean to get agitated with you, because you are trying to help, but like i said before, i have already done this. The factory a/f mixture is the same if not worse than what is happening now. I am sure of this. THank you for the advice.


How does everybody feel about the fuel pressure? What should I be running with 30 lbers?

[Mopar1]

Well I'm getting about 18 on the highway, but it is an utter pig in town. 8-9 MPG max. The cam that the guy put in it prior to me buying the car is a big one. Something I would not run on the street. So I will have to stall or change the cam. It makes a lot of power though.

93GTDIN the only thing I would say is ditch the 30lbs injectors. Doesnt seem like the combo in your sig would call for those. If the are used when you put them on get a new set. Maybe 24's or if fuel milage is a concern 19's. Look at the way you drive too.

The more horsepower the more your fuel milage will drop, it is a trade off.