I bought a 91 RS with a 305TBI in February and since day one I was only getting a best of 17MPG. And if that wasn't bad enough it just got worse and worse. After my last fill up I checked my mileage and I only got 11MPG! What could be the problem? I dont get on it too hard too often or anything. My 88 GTA is getting 23 to 25MPG. What's the problem?!

 

Sounds like its time for a tune-up.

 

I bought the car with a new alternator, water pump, plugs, wires, radiator, air filter, cap and rotor, EGR, and about everything else you could thik of, the transmission had just been serviced and I had the oil changed. I just dont see why it only gets 11MPG!

 

so they say... are you sure everything is new? was it by any chance driven only by his grandmother, god rest her soul, on sundays to church and back?

 

The guy that owned it last saved every reciept for everything he bought for the car in the 4 years he had it. He said he never really drove it hard or anything and I haven't been too hard on it. Well....

 

just because all the stuff is one there, doesn't mean its in tune.

 

Sounds kinda shady....I'd double check the plugs and wires or get another tune up. Also check the 02 sensor. Is there any black soot on your tailpipes? If there is then you may be getting either too much fuel or not enough spark. Checking these items would help you find the prob. BTW the lowest MPG I've ever got was about 17 driving in the city

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92 Camaro RS LO3, 5-spd, T-tops
Mechanics:
Open Air Element w/K&N Filter, Flowmaster 3" Cat-back Exhaust, Z28 Grille w/aftmkt fog lamps
Electronics:
Alpine 8030 Alarm System, Valentine One Radar Detector (How did I ever drive without one?), Pioneer DEH 7450 Head Unit w/6-pack CD changer, Pioneer DEQ 7600 Sound Processor, 2 Kenwood KAC-90 Amps powering 2 12" Pro Red subs and 4 Infiniti speakers.
NEXT UP: SLP 1 3/4" Headers/Y-pipe, Centerforce Dual Friction Clutch kit

 

U have to ask yourself this too, why did he have to replace the water pump, the EGR and other odd replacments.

 

well, whether he lied or not, you have a problem. try buying your gas at a differnt station, check your plugs, and maybe have your coil / ignition checked at napa. a better solution that finding out if who sold it lied i guess.

 

give it a tuneup, and put a new 02 sensor in it

also, check your timing

 

I would definately, as posted earlier, try a new O2 sensorand check the timing. I would also look for a bad fuel injector or a bad map sensor. While your at it I would also change the fuel filter, just to complete the tune-up.

[This message has been edited by TunedPort350 (edited November 30, 2000).]

 

I think I found my problem. I was watching Crank & Chrome on TNN this past weekend and they said that their jeep was getting bad gas mileage and they sould smell gas sometimes while driving. It ended up the return fuel line was disconnected from the pump. I guess I need to check my fuel lines, huh? I read in GMHTP that it's really a pain in the butt to get to the fuel pump in 3rd gens. Any suggestions?

 

yeah, do the tune up first.

Don't pull the tank unless you know you need to replace the fel pump. I very seriously doubt it's the return line came loose. Check your fuel pressure and see if the pump is putting out enough pressure and check your injectors to see if they are dirty, clogged or plain out stuck open.

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1988 TA 300+hp 350 w/ TBI and Holley TB unit, Holley projection intake,
WC T-5, 3.42 gears w/ Auburn posi. MSD 6A, edelbrock TES headers, dynomax 3" cat and cat-back system, ACCEL coil, polyurethane bushings all around, aluminum driveshaft, Mr. Gasket open air cleaner.

1993 S-10 w/ 4.3L V6 TBI, slightly bigger cam, Mild polish job and 3 angle valve job on heads, Edlebrock TES headers, Dynomax cat back, MSD 6A, ADS chip

2000 Kawasaki KX 125

 

Along with checking your map sensor, check the vacuum lines. I was getting really sh!tty mileage, and thats what my problem was. My car ran really rough though, till I fixed the hose that went to the map sensor.

Does you car idle rough??

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Godti
'89 Trans Am (Red)
305 TBI 5spd

 

I have the same problem. I can't get more than 10mpg. I had the fuel filter, and pump replaced. TBI checked and cleaned. I had rough idle too. Now it just "loops" between 600-700rpm. I have no idea what it could be. New rotor, cap, wires. The car only has 50,000 miles on it. I don't drive like my grandma, but I'm no maniac either.

Ethan

 

What's wrong with our cars? I friend of mine told me just about an hour ago that he thought I had a vaccum leak because when I put my car into gear the revs went way down. I do have a little bit of a rough idle. It sounds like I have a mild cam. I'll look at it.

 

Do you have black exhaust gases?? Is there a build up of black carbon on your back bumper??

 

No, no black stuff.

 

No black stuff for me either!!



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'88 T/A
305 TBI with WC-T5
50,000 miles
Flowmaster 3" exhaust
14" K&N Open Element

 

Do you smell gasoline when driving? If so, also check to make sure your TBI isn't leaking from the bottom where it mounts to the intake manifold. I would smell gas once in a while while driving and couldnt tell where it was coming from till I found the leak which leaked onto the intake manifold when i poured some gas through the throat of TBI to attempt to start it(since the in-tank fuel pump wasnt working).

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Shouldn't bother putting this but hey what the heck:
1988 Maui Blue Firebird 305 TBI stock (WITH NEW PAINT!! YAY! )

 

Yeah, sometimes I do smell gas when I drive. I guess I'll look at it in the morning.

 

start with the basics guys

check to be sure you have all the wires on the right plugs

If you have headers, try the crayon trick, touch a crayon to each primary tube while the car is running
if the crayon instantly melts (just a little is needed) then the cyl is fine

do this on every cyl... youll find a dead cyl easily when you see it not melting

and stop watching crank and chrome

 

Goti, I know what ur talking about. I have the black stuff on the bottom of my bumper too. I thought it might be like that because I am running rich. We'll have to see when I hook a scanner up to it. But I know what ur talking about.
BTW: All my smog devices are gone, maybe that has something to do with it???

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Eric Natzke
91 Firebird 305 TBI

ASCD Ram Air Hood-3" custom exaust-Flowmaster 80 Series-No Cat-Edelbrock TES Headers (coated)-March Pulleys-TBI Spacer-K&N Open ELement-TransGo Shift Kit-B&M Supercooler 28,000 GVW-Hypertech Thermomaster-160 Stat-3:42 GM Gears-Auburn Posi Unit-Edlebrock Strut Tower Brace-MSD Superconducters-MSD Cap & Rotor-MSD Blaster Coil-Rapidfire Plugs-265/50/R15 Tires-Emmison's all Gone
http://members.aol.com/j007golden/91firebird.html
For info on certain parts or mods go to the site below
http://members.aol.com/j007golden/modeval.html

 

One of the vacuum lines that went to my map sensor had broken off, my car was idling like crap, and I had a bad smell coming from my exhaust. Plus I had that black carbon build up forming on my back bumper. As soon as I fixed then vacuum line, it corrected my problems.

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Godti
'89 Trans Am (Red)
305 TBI 5spd

 

Where is the Map Senser? Is that the thing on the top right of the engine bay with the green connectors plugged into it? I never had to work on it before so I have no clue where its at.

 

Yes, its on the passenger side.

 

Ok, I did a quick check and my throttle body didn't seem to be loose. I haven't checked my vacuum yet, that's next. But I did put in some fuel injector cleaner and got 20 MPG this time, but that includes 200 highway miles I dont usually get.