how to increase acceleration or mileage (or both)?

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j0fish
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Joined: Tue Jan 31, 2017 6:22 pm
My tercel:: 1984 toyota tercel 4wd

how to increase acceleration or mileage (or both)?

Post by j0fish »

Please inform me if this is the wrong place to put this, but I recently got a 1984 toyota tercel 4wd wagon with 350,000 miles on it. I love the car, but it seemingly has horrible mileage. Its acceleration is bad, but I expected that (with a full tank I get about 1.5 - 2 round trips to atlanta or ~120 miles averaging around 12 - 16 miles a gallon). It idles around 1000 and I've had the timming replaced by a mechanic and the carburetor is newly rebuilt (closest to new I could find). I don't care so much about acceleration because it does fine on the highway, but it can be annoying having to sometimes redline to avoid being t-boned by a speeder when I'm just driving around locally.

Also, I (believe) the gas tank reader is broken to some capacity. At a full tank it only shows about 75% and it will sometimes drop a great deal and sometimes rise depending on downhill versus uphill and how low it is (it drops slowly above roughly 50% tank but once below it drops quickly)

I will end on a good note saying that this is my first car and I love it, its so amazingly fun to drive
teranfirbt
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Posts: 519
Joined: Mon Mar 30, 2009 12:58 am
My tercel:: '86 SR5 4WD, 5AFE, lifted rear, 195/70/14 tires
Location: Seattle, WA

Re: how to increase acceleration or mileage (or both)?

Post by teranfirbt »

Should definitely be getting better mileage, 25-30 is pretty common depending on where and how you drive. Generally mileage issues come from improperly routed vacuum lines or a malfunctioning/leaking accelerator circuit. Other folks can comment on the carb itself, I never had a stock one, but find the link to download the factory service manual (FSM) and trace down all of the vacuum lines running around the engine bay. Other common problems that can cause poor mileage are the weights in the distributor sticking, causing lack of timing advance, which will cause your acceleration issue as well. The FSM should have a way to diagnose an issue there...
A ~common swap on these is a Weber 32/36 carb. They're dead simple and easy to tune, but aren't as good at dealing with all conditions (changing elevation or large temperature swings makes things get pretty wonky). Some people say to just fix the stock carb, and as long as all of the bits work it's a fine carb.
Another possibility is a plugged catalytic converter, although that's much less common than carb/vacuum/distributor issues.
The fuel level sender in these cars tends to wear out, especially with how many miles you have. It's not uncommon for them to move a bit when you go around corners and point the car up or down a hill. 1/4 tank swings are definitely possible.
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ARCHINSTL
Goldie Forever
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Joined: Sat Apr 30, 2005 1:52 pm
My tercel:: Goldie is a 1986 SR5 attualmente con Weber/also owned the first T4WD in STL in late '82
Location: Kirkwood, a 'burb of St. Louis

Re: how to increase acceleration or mileage (or both)?

Post by ARCHINSTL »

teranfirbt wrote:The fuel level sender in these cars tends to wear out, especially with how many miles you have. It's not uncommon for them to move a bit when you go around corners and point the car up or down a hill. 1/4 tank swings are definitely possible.
I have noticed this with Goldie. Now, the sender is dead accurate, per various "tests" I have performed, but - I have a Mobil card, so I exclusively use its fuel. However, there is one Mobil station in my 'burb that has a just slightly less-than-level area - and I mean "off" by just a few degrees "downhill." I avoid it, because it makes the difference between a "full tank" and one that can still hold up to almost 2+ gallons!
I noticed this, because that particular tank filling gave me almost 40 MPG, far above my usual in-town rate of 27-8 MPG!

I installed a Weber 32/36 8 1/2 years ago, primarily to get rid of the non-functioning emissions systems and the drama that came with dealing with them. I've not had any probs with it (save a leaky throttle shaft) - but then, I've not strayed from the 6-700' altitude of St. Louis in the whole nearly 12 years I've owned her.
Tom M.
T4WD augury?
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Petros
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Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: how to increase acceleration or mileage (or both)?

Post by Petros »

welcome to the forum,

go find the correctr vac routing diagram for your car elswhere on this site, and follow each vac line, check routing, and for any leaks. do not assume that just because a mechnic work on it last they got all the vac lines correct. It should not take too long to check them all.

once that is corrected, typical poor economy can be coming from a leaky AAP diaframe (see where it is located in the FSM) easy check, pull the vac line, if it has fuel in it you can cap both ends and it will drive fine once warm. Also, use a timing light and set spark timing at 10 or 12 deg BTDC (not the factory 5 deg). Verify your brakes are not dragging (jack up and spin each wheel), and your air filter is good.

if still no good, pull off the front plastic timing belt cover and verify the timing belt is installed correctly by lining up the marks on the front pulley and the cam sproket (see FSM for location and alignment of marks).

You also might do a compression check to verify something is not really bad inside the engine. You can rent both the timing light and the compression tester from an Autozone for free.

good luck.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
teranfirbt
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Posts: 519
Joined: Mon Mar 30, 2009 12:58 am
My tercel:: '86 SR5 4WD, 5AFE, lifted rear, 195/70/14 tires
Location: Seattle, WA

Re: how to increase acceleration or mileage (or both)?

Post by teranfirbt »

ARCHINSTL wrote:
teranfirbt wrote: I noticed this, because that particular tank filling gave me almost 40 MPG, far above my usual in-town rate of 27-8 MPG!

Tom M.
I have similar issues with stations around Waco, sometimes I'll get a good fill and my mileage will look "low" (25ish) and other times I'll get a bad fill and my mileage will look "high" (33ish). I usually keep track and average out a few tanks, 29ish MPG is what I average, but my speeds tend to be pretty high. I would probably do better with lower speed limits (75 in some areas).
xirdneh
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My tercel:: 87 tercel 4x4 wagon w/reringed engine, 83 tercel 4x4 wagon w/salvaged engine and 4.1 Diff's
Location: seabeck, washington, USA

Re: how to increase acceleration or mileage (or both)?

Post by xirdneh »

Check tire pressure and for dragging brake.
After tires its usually the carb
I have rebuilt some that did not get good mpg
Not sure what was wrong
Love those Tercell 4x4 wagons but they sure suffer from road noise.
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