I have a 91 305TBI and I am getting terrible gas mileage. About 12-15mpg on premium gas. I also get smoke when I first crank it up in the morning. Only on the first start up though. Anyone know what may be wrong???


Any help would be greatly appreciated.



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<A HREF="http://formula305.cjb.net" TARGET=_blank>http://formula305.cjb.net
</A>
1991 Formula 305TBI
3" Flowmasters
Hypertech Chip
3.42 Posi on the way

 

GEt used to it. I've got an 89 305 TBI its milage seriously sucks. The smoke is called valve steam seals. I just switched to Mobile One Synthetic Oil. I hear all these guys on the board boasting how it gets rid of the smoke, I didn't think it would but it does. I switched from the Penziol 5W-30 to 10W-30 Mobile 1. I can feel the difference and there is no smoke.

My 305 gets pretty crappy milage to. Its only a 13 gallon tank, so that doesn't help. I get about 17 miles to the gallon. However since adding my Open Element its gone up maybe a point. Try using Regular, if you are using anythign higher than 89 otc. in a 305 you are wasting money, I tired switching thinking better milage, damn was I so wrong.

I had a whole forum post about it, read up (https://www.thirdgen.org/messgboard/Forum7/HTML/012272.html) it will explain why you are hurting yourself with higher octane. I didn't know till alot of people on here told me.

305's are soild runners but they are also pigs.

[This message has been edited by un4givin89 (edited September 25, 2001).]

 

I understand getting crappy mileage, but I only get about 12-15 mpg. That's way worse than 17. About 50 miles per tank. So that's pretty much much what I'm complaining about. Thanks for your help about the gas article.

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<A HREF="http://formula305.cjb.net" TARGET=_blank>http://formula305.cjb.net
</A>
1991 Formula 305TBI
3" Flowmasters
Hypertech Chip
3.42 Posi on the way

 

What could be wrong? In a word, ANYTHING. The most likely suspect would be a tired O2 sensor. Beyond that, any one or combination of tired/bad sensors could be hurting you. Or it could be as simple as your timing is retarded (i've seen more than one car gain 6+ mpg just by adjusting the timing, not necessarily even advancing it beyond stock.) A beat tranny/drivetrain could be eating power costing you mileage. Low air pressure in the tires fits in here too. Hell, for that matter, oversized tires can eat more gas, as can tires w/ inefficient tread designs. Cheap oil could be costing your engine efficiency. Maybe you drive w/ a heavy foot all the time. Your ignition could be weak. Maybe you live in an area w/ 'reformulated' gas. Chances are it's not just one, but a combination of these things ganging up on you.

In other words, there is way too much involved for us to guess here. These boards are about learning, not hand holding. Learn the basics of how your car works. Then you can start thinking of what might be wrong with it. Then learn how to check out the things you want to check...i just gave you a good start for things to think about at the top of this

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Ed Maher - Moderator @ The TPI & Carb Boards
92 Z28 Convertible - Quasar blue / Tan top
305 TPI A4 2.73 - 14.8 @ 93.1
Stock except ported plenum and dual cats
-=ICON Motorsports=-

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die

[This message has been edited by Ed Maher (edited September 25, 2001).]

 

DANG, he laid the smack down... I just assumed cuase we had v8s bad milage was a given.

 

Amazingly, by what un4givins post suggests, I get good milage with my car. Around 17 to 20 in town and 25 to 27 on the open road at 75 MPH. I just keep the car running good and I have to use 89 octane or I get some serious pinging.

Just my 2 cents.

Phil



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89 IROC 5.0 TBI
89 RS 5.0 TBI, T-Tops, Soon to be a IROC clone.

[This message has been edited by IROCZ89 (edited September 25, 2001).]

 

Wow I didn't know bad gas mileage was such a bad subject for that guy. At least I know he cares, because he took so much time to write a lengthy explaination. I'm sorry that I'm a beginner, but we all have to start somewhere. I'm sure there are tons of things that I know...and you have know clue how to do. Please keep that in mind. Thanks for your help everyone.

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<A HREF="http://formula305.cjb.net" TARGET=_blank>http://formula305.cjb.net
</A>
1991 Formula 305TBI
3" Flowmasters
Hypertech Chip
3.42 Posi on the way

 

Nah, i always sound like a **** , but really i don't mean to. I'm just a direct kind of guy. Like you said, at least i cared enough to list suggestions. I'm just so used to someone coming back with a 'yeah but how do i check that', or 'what is that' response that i tend to add a reminder to do a little of your own legwork to save me the trouble from responding again. These boards really are easily one of the best technical resources on the web, and to ignore the ability to search and browse to pick up tips is a waste of everybody's time, chiefly your own. Nothing wrong w/ asking a duplicate question (pretty much everything is), thats how fresh opinion/discussion happens. Like i said, it's the hand holding that gets annoying. Not that you were trouble, i just sound like adick when i'm not even trying.

 

Well if it is something to shot for I got 18-20 mile/gal in my RS and it was tuned (good not perfect - no sensors checked) So it is very possible to hit 23-27 no prob, people on the TBI board get that all day long.


Oh ya I get 14 in my 350TPI, but I know it needs major tune up.

Both cars run 94 octane.
but good luck with it.

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1989 Trans Am GTA, L98 5.7L TPI, TH700-R4, T-Tops, dual cats, 9-bolt rear, 3.27,
- K&N Air Filter
- Dynomax muffler

1992 Camaro RS, LO3 5.0L TBI, T-5, T-Tops, 3.08, L69 Dual Snorkel - Sold
- K&N Air Filter

Honda engines ROCK, I have one on my lawn mower but I still have to push it.

[This message has been edited by Drakar (edited September 25, 2001).]