gas mileage

mjskipper · Post by **mjskipper** » Mon Jul 05, 2004 8:13 pm

Im having problem with my mpg. i have a relativly low milage engine at 150,000 original miles. i used to consistantly get about 25 city 32 hwy. plugs,cap,wires,are all new, coil is new, carb is new, and the exhaust oxygen sensor apears to be new also. i now get about 20 miles to the gallon. ive made no changes to the car before i developed the problem. it seems to run great and the plugs are clean(no carbon). all fluids are syn. and i dont seem to have anything draging. Any one else have any ideas.

sacwac · Post by **sacwac** » Mon Jul 05, 2004 11:00 pm

Sounds like my car... when the transmission is in it.

I have two ideas, EGR and distributor vacuum advance. EGR can be tested my attaching a vacuum pump to the egr control valve (you force the egr to turn on). When the engine rough idles, or dies, egr is probably ok.

The vacuum advance might not be advancing, also attach vacuum pump, and check for proper function.

I would also suggest examining all your vacuum hoses, one tiny cut, and it could cripple many systems.

If you don't have the factory manual, no big deal, I'm almost done scanning one to pdf, which I will post in a few days.

Guest · Post by **Guest** » Wed Jul 07, 2004 3:48 am

I have previously checked the function of the vacuum advance and the unit itself seems to work properly with a mity vac, the manual doesnt state how much pressure should be used. i did this with the distributor out of the car. when i go to time it i capped off the middle vacuum line like the manual says and then reconnect and it is supposed to advance to 13 degrees but it doesnt. One question i had was on the vacuum advance unit there are three line are all three conections supposed to advance the timming because only the upper and lower connections will move the armature in the distributor. ive checked and replaced many of the vacuum lines(one at a time so the dont get mixed up) and cant find a leak. ive tried to buy a replacement vacuum advance and cant seem to find one. (when in doubt just change it.) i have a factory repair manual but most of the pages for the distributor are missing. if somebody has those pages it might help.

takza · Post by **takza** » Wed Jul 07, 2004 6:33 am

I couldn't find a new vac advance without buying a dist either. Considering the cost involved...I'd do some testing first. Glad I did. Found that my dist was OK.

The dist has centrifigal advance as well as 2 vac advance diaphrams.

You need to be sure that the source for the vacuum is good...whatever "gizmos" give the vac "signal". Since you have the vac tester...it's a matter of going thru all of them and testing them...might find somethng wrong.

I'd also go thru ALL electrical connxs under the hood.

Might check your cat converter to see if it's plugged?

With my new cat converter, I have a steady stream of converted cats coming out of the tailpipe.

I'd do a decarboning and then set the timing on the road and run thru a tank to see if you mgiht get an MPG gain. Just because your plugs are clean doesn't mean that you don't have a good carbon collection.

** This list is a bit on the lame side....I had a POLL set up on MPG, but got only maybe 2 responses. People don't want to participate so we can establish a baseline for MPG and then find methods to improve it...so.........? <_<

arbskynxnex · Post by **arbskynxnex** » Wed Jul 07, 2004 11:14 am

Did the new carb have larger jets than the original? If so you would be using more fuel for supposedly more power. I saved the pics sacwac posted of the distributor for me, I'll re-post them later today.

I get about 23-25mpg in my tercel 240,000 miles on it. My old tercel (300,000 miles) with a plugged jet in the carb got about 21 city and 30 freeway at 60mph.

takza · Post by **takza** » Wed Jul 07, 2004 5:43 pm

I've gotten anywhere from 28 to 37 MPG overall (city/highway) with my Tercel over the 30 K miles I've driven it.. Currently doing 30 MPG or above. This is with a city/highway mix.

Right now I'm testing a tank without EGR, since my last 2 tanks with the EGR fixed have been around 2-3 MPG lower. Should get back to 32-33 MPG.

As to why my Tercel does so well?

* engine is in good condition (I think) though it has at least 100K miles on it with the seals I've replaced being real brittle....car has over 200K miles & engine might too.

* have the '83 California model which was geared higher in 5th?

* heated fuel has resulted in maybe a 10% gain from 30 or so, but not back to 35-37 as with old tires.

* best MPG at 37 was when I had 175/80/13 tires on OEM wheels...probably due to driving fairly easy.

Will retest the old wheels/tires sometime and might manage 40 or so?

If I get my fuel atomizer going....I'll be SELLING GAS along the highway just to keep the tank from overflowing.....

<span style='color:blue'>Why other Tercels aren't doing so well? I DON'T KNOW.</span>

arbskynxnex · Post by **arbskynxnex** » Wed Jul 07, 2004 6:58 pm

Why other Tercels aren't doing so well? I DON'T KNOW.

I'll personally vouch for poor maintenance, and driving the car through terrain that you're not supposed to.

mjskipper · Post by **mjskipper** » Thu Jul 08, 2004 3:48 am

I suppose my cat is fine, i had the exhaust changed about 3 months ago and they said there is no problem with it. How do you check to see if it is clogged? i have good stedy flow out of the pipe. my gas milage problem started before the carb change, before the tire change, before the new exhaust. the carb is a stock rebuilt unit so i can only assume the jets are the same size. I dont want to take it apart to see because it will void the lifetime warrenty. When i checked the vacuum advance off the car two of the 3 ports moved the armature so i can assume since there are 2 vacuum advances the actual vacuum unit is good. i will hook the mity vac to the distributor and see if i can advance the timing that should determine if i have a vacuum soure problem. One item to mention i drove the car for 4 or 5 months when i first got it before i found out the middle vacuum hose for the distributor was disconnected and had a small pencil sealing it up. reconnecting it didnt see to affect anything, i still got the 25/32 mlgs i had always gotten. the tires i have are exactly the same outside diameter as the previous one only a lower profile bigger wheel, they are real lightweight and didnt make a difference in the gas when i put them on.

tercel4wdrules · Post by **tercel4wdrules** » Fri Jul 09, 2004 10:20 am

takza wrote: <span style='color:blue'>Why other Tercels aren't doing so well? I DON'T KNOW.</span>

When my dad used to drive the Tercel he would drive it around 160 miles a week and he said he was able to go with about $5-7 a week when gas prices were in the $1- 1.30's range. That means he was getting around 32 miles per gallon and he drove it in the city, so I was kind of impressed. Oh yeah most of the time he drove it slow but when he needed speed and power...

takza · Post by **takza** » Sat Jul 10, 2004 4:34 am

mjskipper wrote: I suppose my cat is fine, i had the exhaust changed about 3 months ago and they said there is no problem with it. How do you check to see if it is clogged? i have good stedy flow out of the pipe.

Maybe 2 ways to check the cat:

* take the pipe off of it and look inside and count the number of "cells" that are visibly clogged. There is a certain % that is allowed. My old one had maybe 10 out of ??? cells you could see clogged.

* have a backpressure test done...where they drill a hole in the pipe before the cat and test the pressure as it runs...then weld the hole closed.

Could have the timing belt off a tooth or the ignition timing/advance off. Carb could be defaulting to a rich condition due to the ECU or O2 sensor failing.

sacwac · Post by **sacwac** » Sat Jul 10, 2004 3:21 pm

The ECU... Are you reffering to that computer that sits under the passenger side dash inside a white plastic container?

I've taken that thing apart before, it has amazing mid 80's technolgy. Nothing that probably couldn't be handled by a modern microcontroller. I'd love to reverse engineer that thing, I've always wanted to know exactly what it did.

Maybe there is a good use for my 2nd tercel after all!

mjskipper · Post by **mjskipper** » Sun Jul 11, 2004 1:54 am

i checked the timing belt and it is tight and aligned properly, its only has about 15 on it. im leaning towards the timing problem. i couldnt seem to get it to advance to 13 degrees after setting the base timing and connecting everything back up. i tested the vacuum unit itself and it works so it must not be getting a vacuum signal. i guess now i have to figure out what signals it and when. i currently get 170 miles to 8.5 gallons of gas. used to get 240-250. car always ran fine just had the decrease in gas milage. it now is hard to start and desiels sometime when shutting down. sounds like timing to me but dont know what could be causing it. ill also try to check the catand see if the honeycomb is clogged if so ill just remove it or install a test pipe. Does the "computer" have codes to scan.

sacwac · Post by **sacwac** » Sun Jul 11, 2004 10:28 am

No, the computer probably doesn't have codes to scan.. It doesnt seem like that advanced of a computer.

takza · Post by **takza** » Sun Jul 11, 2004 4:42 pm

mjskipper wrote: it now is hard to start and desiels sometime when shutting down. sounds like timing to me but dont know what could be causing it.

Sounds like carbon buildup and/or it is running hot? A blocked exhaust could cause this?

* Since I replaced my exhaust and cleaned the EGR within 100 miles of each other...what I think was a drop in MPG due to getting the EGR going might be due to the freer flowing exhaust. Will need to test this out.

* Also, my adventures into fuel atomizer land aren't bearing fruit....no MPG gains so far...

Fingers · Post by **Fingers** » Wed Aug 04, 2004 10:56 pm

Alright, I'll give you my gas mileage stats, as I have finally been able to record and figure them all out.

On the highway I averaged 31 mpg without a/c, and just under 30 with a/c.
City driving, I tend to get around 27.
With a manual I could hope for possibly a 3mpg gain, or so I figure.