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post #1 of 21 (permalink) Old 12-18-2010, 11:06 PM Thread Starter
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only getting 8-9 mpg wtf help!

seriously, i dont even know what else i can do to help my mpg, since this happened i have replaced fuel filter,air filter, cleaned maf,changed oil/filter,put fuel injector cleaner in my gas tank, fixed a vacuum leak, new spark plugs,switch different gas brands,flushed radiator and put in new antifreeze,started driving like a grandma.

doesnt have any visual leaking of gas.

like today alone i put 3.3 gallons in and ran out of gas at 29 miles.

what else could cause that bad of a mpg dump? bad cats? this things got me stump.

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post #2 of 21 (permalink) Old 12-18-2010, 11:51 PM
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A little more info would be helpful. Do you smell gas? Is the car running rough? Is it smoking?

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post #3 of 21 (permalink) Old 12-19-2010, 12:56 AM
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Is there fuel dripping from exhaust? You may need to have idle for a few minutes and then have someone watch for it as you pull away.

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post #4 of 21 (permalink) Old 12-19-2010, 09:41 AM
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Well number one..... if you are going to calculate gas milage do it right. Fill the tank, set the trip odo to zero, then run it for a little bit. Then fill back up and divide milage to gallons to fill back up. Then you can get a much better idea of what your true milage is.

Is the CEL on? As said before, do you smell gas? Are you sure you have the fuel filter on there with zero leaks? Does it run rough? When was the last time the O2 sensors were changed? Have you checked the fuel rail for leaks? What octane are you running(different parts of teh country have different octane ratings for regular, plus and premium)? There's a lot that can be wrong............... IF the actual gas milage is correct.

With this 'Winter blend' **** they pump in your tank, my bird gets about 21-23mpg highway and 14-15 local. And I run Shell 87 octane.

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post #5 of 21 (permalink) Old 12-19-2010, 10:50 AM Thread Starter
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i also run shell regular, i dont see any visual leaks around fuel filter or fuel rail, i dont smell gas either. so having my gas tank being empty then putting in gas and running till its empty again isnt my true mpg? not smoking any different then when i first got it, it may be running a little rich.

i did get a code saying my idle control valve isnt working and my car idles higher than normal, but its always been like that,the engine does run a lil bit rough at times,again it has always done that. i normally get about 17-22 mpg.

i never changed the 02 sensors,could they cause that? im going out now to double check everything tho.

air silencer removed, dorman intake manifold,clear corner lights,psp with psp windshield mount,blue led moded gauge cluster.
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post #6 of 21 (permalink) Old 12-19-2010, 11:17 AM
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Originally Posted by lozer81 View Post
i also run shell regular, i dont see any visual leaks around fuel filter or fuel rail, i dont smell gas either. so having my gas tank being empty then putting in gas and running till its empty again isnt my true mpg? not smoking any different then when i first got it, it may be running a little rich.

i did get a code saying my idle control valve isnt working and my car idles higher than normal, but its always been like that,the engine does run a lil bit rough at times,again it has always done that. i normally get about 17-22 mpg.

i never changed the 02 sensors,could they cause that? im going out now to double check everything tho.
Don't run the car dry, ever if you can help it. Sludge will collect in the bottom of the tank and get pulled in the filter. If the car is having trouble sucking the gas through the line, it could account for some of the issue. A "little" rich shouldn't be that bad... but get that tank full, run some various driving, down the road to the store, on the freeway for a few miles, around town a little, put about 50 or so miles on it and fill it back up at the exact same station, and same pump if you can. When you fill it, fill it till it hits the autostop, and don't put any extra in... then when you top it back off, also let it fill to the autostop... makes your calculation more accurate by removing variables.

Bad gas can account for issues as well. I recently filled up at a local station that offers non-oxygenated gas and it was bad gas. Mileage in town went from 18mpg to 13mpg with no change in driving, warm up, etc. Took me two tanks at my usual station (BP with 93Premium) to get back to "normal". So for comparison sakes, try a different station or grade of fuel once you have a good baseline reading.

Also... have you made any modifications to the car such as rear end gears, different sized tires, cold air intake, etc?
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post #7 of 21 (permalink) Old 12-19-2010, 11:24 AM
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I Have The Same Thing Happen

RUNS RICH, SMELLED GAS CHANGED PLUGS, CHECKED FUEL REGULATOR CHANGED EEU, STILL NO CHANGE WOULD IT BE THE O/2 SENSORS ??? DON,T KNOW TO DO NEXT ,,,TO COLD TO PLAY AROUND
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post #8 of 21 (permalink) Old 12-19-2010, 12:36 PM
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I'd run some seafoam in the gas tank just to clear out what may or may not be there, Cant hurt right? Then maybe check your shoes for lead lol.

I love my V8, but I'd love it more if all 8 cylinders worked. (they do now)

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post #9 of 21 (permalink) Old 12-19-2010, 12:51 PM
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Quote:
Originally Posted by lozer81 View Post
i also run shell regular, i dont see any visual leaks around fuel filter or fuel rail, i dont smell gas either. so having my gas tank being empty then putting in gas and running till its empty again isnt my true mpg? not smoking any different then when i first got it, it may be running a little rich.

i did get a code saying my idle control valve isnt working and my car idles higher than normal, but its always been like that,the engine does run a lil bit rough at times,again it has always done that. i normally get about 17-22 mpg.

i never changed the 02 sensors,could they cause that? im going out now to double check everything tho.
The O2 sensors are responsible for fine-tuning the air:fuel ratio, so there is a possibility if they are failing but within spec. Without putting a scanner on it and watching the STFT/LTFTs, you wont know unless you start replacing parts. Have you checked your fuel pressure at the rail?
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post #10 of 21 (permalink) Old 12-19-2010, 12:54 PM
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Another thing is the fact that it's cold out now so those morning startups and idle to warm the car will kill your milage now as well. You'll NEVER get the same milage in the winter as you do in the summer. I dont even care to start calculating gas milage in the winter cause it's not what the car will 'normally' do.

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post #11 of 21 (permalink) Old 12-19-2010, 01:04 PM Thread Starter
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Don't run the car dry, ever if you can help it. Sludge will collect in the bottom of the tank and get pulled in the filter. If the car is having trouble sucking the gas through the line, it could account for some of the issue. A "little" rich shouldn't be that bad... but get that tank full, run some various driving, down the road to the store, on the freeway for a few miles, around town a little, put about 50 or so miles on it and fill it back up at the exact same station, and same pump if you can. When you fill it, fill it till it hits the autostop, and don't put any extra in... then when you top it back off, also let it fill to the autostop... makes your calculation more accurate by removing variables.

Bad gas can account for issues as well. I recently filled up at a local station that offers non-oxygenated gas and it was bad gas. Mileage in town went from 18mpg to 13mpg with no change in driving, warm up, etc. Took me two tanks at my usual station (BP with 93Premium) to get back to "normal". So for comparison sakes, try a different station or grade of fuel once you have a good baseline reading.

Also... have you made any modifications to the car such as rear end gears, different sized tires, cold air intake, etc?
no i havent done any real mods i have a hard time just keeping this thing on the road,its pretty much stock,

i did just recently switch from BP to shell gas,because i've heard that shell was better.

air silencer removed, dorman intake manifold,clear corner lights,psp with psp windshield mount,blue led moded gauge cluster.
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post #12 of 21 (permalink) Old 12-19-2010, 03:29 PM
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My .02

1) If it fast idles, it 99.9% has vacuum leaks. Check all vac lines (there is a T in back of motor on passenger side that ALWAYS goes bad). The ones to the fume canister also goes bad, as does the pcv hoses (small and big) and the valve cover grommet.

2) Like GM said, bad O2 sensors will cause bad mileage, but nowhere near what you are experiencing (ECM would run open-loop first).

3) Plugged cats you would definately know. Wouldn't be able to rev up engine, and it would be really low on power.

4) sousa632 is right. Are you ACCURATELY measuring this mileage you claim? You don't have to run it empty, just fill it completely up, keep track of at least 100 miles of driving, then fill it up again. Divide the 100 (or however many miles you went) by the number of gallons used (NOT the dollar amount). Simple biscuit.

5) Bad gas causing seriously bad mileage would also cause engine to run badly enough that you should notice it.

6) ThunderRoad has good suggestions, too. Pull a plug out to see what it looks like. Is it black from running so rich? My guess is the plugs will be almost white from the vac leaks (mine was); I've seen it a few times. As for checking fuel regulator, just pull the vac line off and see if there is any fuel in the air side (that's how they go bad).

7) The reason I asked if it's running rough or smoking is because if an injector was hanging open, that's what should be happening.

8) I know this is a long shot, but could someone be syphoning fuel from your vehicle when you have it parked somewhere? It's happened to me before, so it is possible.

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post #13 of 21 (permalink) Old 12-19-2010, 10:46 PM
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1) If it fast idles, it 99.9% has vacuum leaks. Check all vac lines (there is a T in back of motor on passenger side that ALWAYS goes bad). The ones to the fume canister also goes bad, as does the pcv hoses (small and big) and the valve cover grommet.
96-97 4.6L engines don't have this T, and the OP's profile says 97. There are always other locations that could be leaking though.

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post #14 of 21 (permalink) Old 12-20-2010, 11:28 AM Thread Starter
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okay guys i just checked some things, i started the car and watched the exhaust and it appears to have steady dripping from both ends,and also dripping from the front of the mufflers.... smoke out the exhaust does smell like gas although i tried smelling the liquid to see if its just water but i cant tell, i do have black soot all inside the pipes. it hasnt been raining or anything so i doubt it is water coming from the pipes.

i havent check fuel pressure or anything because i dont have a pressure gauge.i did double check for vacuum leaks but from what i can see they're good i replaced a couple of them a while back

air silencer removed, dorman intake manifold,clear corner lights,psp with psp windshield mount,blue led moded gauge cluster.

Last edited by lozer81; 12-20-2010 at 11:34 AM.
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post #15 of 21 (permalink) Old 12-20-2010, 12:27 PM
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you got injectors stuck open ????? how about fuel in your oil ??? if you do have fuel in your oil don't drive it till you fix it as for some reason , bad injector , whatever , it's washing the cylinder down with fuel and it's getting past the rings and eventually you could have catastrophic failure . black soot in my oldies and i'd imagine even these suggests it's running pretty rich to me , and all of them will have water / condensation dripping from the tailpipes so make sure it's not that before you think it's fuel . just took the wifey's gm piece 'o' crap mini to the dealer { i will not work on the blasted thing !!!! } as it lost / had two injectors get stuck open for some odd reason on an 08 with only 45,000 on it with an extremely rigorous maintenance schedule by the dealership . so it can happen ............. p.s. 8-9 ain't bad that's what my flattie 53 pick 'em up gets on a good day ..................

i used to think i knew a lot , now with the trials and tribulations with the old and the modern i have i realize .... I DON'T KNOW JACK SH-- !!!!!!!!!!!!!!!!!!!!!!!!!!
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post #16 of 21 (permalink) Old 12-20-2010, 12:59 PM Thread Starter
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after watching my car idle the liquid or whatever it is is coming out fast! so fast and so much it actually makes a puddle underneath in four spots,two out the front of the muffler and two out the end of the pipes.

could it be the injectors? ive never replaced them and i dont think they ever have been.

air silencer removed, dorman intake manifold,clear corner lights,psp with psp windshield mount,blue led moded gauge cluster.
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post #17 of 21 (permalink) Old 12-20-2010, 03:35 PM
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In your sig you state that you have a dorman intake manifold. I would suspect that a fuel injector or 2 may have been damaged during the install unless the manifold has always been on the car.

Your ECU could be causing an injector to hang open but that's not a common issue with the '96+ comapred to the '94/5.

Last but not least if one or more spark plugs isn't firing it too could cause the unburnt fuel to make its way through the valves and into the exhaust.

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post #18 of 21 (permalink) Old 12-20-2010, 03:41 PM
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it could be the injectors, but it also could be the fuel pressure regulator leaking threw the vacume line into the intake, it was sudjested to check it, pull the vacume line off the fuel pressure regulator and start the car to check for fuel, did you do it?
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post #19 of 21 (permalink) Old 12-20-2010, 06:31 PM
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In your sig you state that you have a dorman intake manifold. I would suspect that a fuel injector or 2 may have been damaged during the install unless the manifold has always been on the car.

Your ECU could be causing an injector to hang open but that's not a common issue with the '96+ comapred to the '94/5.

Last but not least if one or more spark plugs isn't firing it too could cause the unburnt fuel to make its way through the valves and into the exhaust.
A lot of people here have had 97 eecs go bad; especially in the past couple of years. Too bad no one has posted their catch codes, so we could figure out whether or not it was limited to one group.

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post #20 of 21 (permalink) Old 12-20-2010, 06:41 PM
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A lot of people here have had 97 eecs go bad; especially in the past couple of years. Too bad no one has posted their catch codes, so we could figure out whether or not it was limited to one group.
Well, I'll start by posted the two I've go bad in the last couple of years. They were both 1995 Thunderbird 4.6L Std. Emissions F5SF-CA catch code A5W0. The computer I have in it now is a 1994 Thunderbird 4.6L Std. Emissions F4WF-AC catch code E4A3 and so far, so good (except for the lock-up schedule being crappier on the '94 ECM). People gotta understand, these computers are approaching 20 years old; of course they're going bad! Reality is, they weren't designed to last 100 years out on a spacecraft or something...

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post #21 of 21 (permalink) Old 12-20-2010, 08:17 PM
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my 96 was a MBE3 code pcm and the heater circuit was malfunctioning(power to everything and was energizing the circuit but the PCM didnt recognize it and threw all 4 o2 heater circuit malfunction codes). I now have a MBE2 in it and it's working fine.


But that's all off topic.



You will get condensation out of the tailpipes, ESPECIALLY in the winter. If it's smelling like raw fuel out of the exhaust, I would suspect a leaky injector, or bad FPR...... both of which would make the gas mile to down the toilet. The tailpipes will always look a little black from normal use. Excess and black soot means it's running rich, which takes me back to what I just said before, IF you ruled out a vacuum leak.

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