Horrible MPG, No Apparent Problems

[86.5]

Hi,

I have recently acquired a 1986.5 Supra N/A with 103k on it. It's a beauty, and in fabulous shape. I'm loving it. However, the mpg has been horrible. On my last tank, I got an average of 12mpg, and my monthly average has been about 10. I haven't really stomped on it THAT much... This month alone I've burned $230 of gas on about 650 miles travel. There is no check engine light, the tires seem to be properly inflated, and the car runs great. (No rough idle hot or cold) I'm at a loss here. O2 sensor? I had the check engine light come on one time, but it hasn't shown its face since. I've heard that the accordian hose can be suspect, but with the engine bay looking as clean as it does, I doubt that it is the culprit.

What to do?

Thanks

 

[spooln30]

If the rubber intake hose was busted it would run like crap. Pull a spark plug and check if they are worn or if the gaps to big. Also check the air filter and replace if nessesary. Just cuz the CEL went off doesn't mean its fixed, the code will or should be stored in the ECUs history memory. A few more things might be a clogged cat or even a brake caliper that is hanging up. Hope this helps you and GL.

 

[86.5]

If the rubber intake hose was busted it would run like crap. Pull a spark plug and check if they are worn or if the gaps to big. Also check the air filter and replace if nessesary. Just cuz the CEL went off doesn't mean its fixed, the code will or should be stored in the ECUs history memory. A few more things might be a clogged cat or even a brake caliper that is hanging up. Hope this helps you and GL.

Thanks for the reply. I'll check the CEL code(s) (hopefully just 1 or none) tomorrow. I'll have to find the tut for that again... Lol. But it sounded similar to what I had to do with my 5th gen civic. I doubt that it is a hung up brake caliper, as the owner had the brakes done right before I got the car. (I have documentation). However, I'm not sure of the last time the spark plugs or air filter were changed. What is an acceptable spark gap?

 

[tfhorst]

http://www.cygnusx1.net/Supra/TechTips/engine_error_codes.aspx

That is the link you want.

There are so many things that could be, what spooln said is right, a big thing that will help to boost your mpg is getting things clean again, new rotor to plugs, on the hot side and screen to injectors on the gas side. Another big one is vacum leaks. Change out your 24yr old lines if they are still there.

The milage is not great
http://www.fueleconomy.gov/feg/findacar.htm
But should be better than that. Lot of people are getting up to 28mpg on the highway.

Open her up front and back, lower her a bit and get 18's and you will see your milage go up too...or just don't hit the gas as much. Either way works, both together do a lot.

 

[xzeror]

i get about 16-18 in my 86.5

 

[radiod]

The milage is not great
But should be better than that. Lot of people are getting up to 28mpg on the highway.

Pretty sure that's not without some electronics/tuning that you'll get 28mpg on the highway. Most cars will get about 16 in city driving and maybe just over 20 highway.

With it getting colder, it does take the car significantly longer to warm up. If you are taking it on very short trips all the time it may not be getting out of enrichment which would also hurt your gas mileage a lot. I was getting as low as 12mpg with my car when it was dead cold out for that reason. Come summer time I was back up to my typical 16 - 18.

 

[te72]

With my 88 NA, I regularly saw 26-30mpg on the highway. Granted, I'm at a fairly high altitude here. That same car would get around 25mpg highway in Phoenix.

Among things to look into inspecting/servicing is your alignment. How do the tires look? If it's sitting funny on the alignment specs, you could be dragging a tire around that shouldn't be. All that said, I get around 18-20mpg in my car, and I'm sitting at around 320rwhp here, so it's not for lack of trying, and your suspicions are correct that your mpg isn't great by any means. What transmission are you using?

 

[Silver MK3]

In my stock 87 N/A(74k miles) I get around 17-21 driving mostly city. My air filter has only a few thousand miles on it, and since I changed my plugs a couple of weeks ago, I seem to be getting slightly better MPGs. When I changed my plugs I also saw that my throttle body and y-pipe were very dirty, and they looked like they had never been cleaned before. I cleaned them and the car has a better throttle response and like I said earlier it seems to be getting better MPGs. Maybe your plugs haven't been changed in a while, and the throttle body and y-pipe hasn't been cleaned before either and that is what is hurting your fuel economy.

I believe that when I did mine the gap on the new toyota plugs was .043 - .044.

 

[86.5]

Pretty sure that's not without some electronics/tuning that you'll get 28mpg on the highway. Most cars will get about 16 in city driving and maybe just over 20 highway.

With it getting colder, it does take the car significantly longer to warm up. If you are taking it on very short trips all the time it may not be getting out of enrichment which would also hurt your gas mileage a lot. I was getting as low as 12mpg with my car when it was dead cold out for that reason. Come summer time I was back up to my typical 16 - 18.

The car seems to warm up in about 5-6 minutes of easy driving.... But it is kinda cold around here lately. Less than 50*F most of the time. I do usually take short trips with it though, less than 10 miles.

With my 88 NA, I regularly saw 26-30mpg on the highway. Granted, I'm at a fairly high altitude here. That same car would get around 25mpg highway in Phoenix.

Among things to look into inspecting/servicing is your alignment. How do the tires look? If it's sitting funny on the alignment specs, you could be dragging a tire around that shouldn't be. All that said, I get around 18-20mpg in my car, and I'm sitting at around 320rwhp here, so it's not for lack of trying, and your suspicions are correct that your mpg isn't great by any means. What transmission are you using?

My car is sitting on brand new tires. It has the stock W58 tranny. To be honest, I don't know a lot about checking vacuum lines or any of this hot/cold side stuff you tfhorst is talking about. Thanks for the link btw. The car has been kept in a garage for most of it's life, so I'm kinda irritated with this stuff lol.


About the spark gap. Haha, I have no tool that can measure with that much precision. My only option would be to get new plugs at that point.

 

[Poodles]

The car seems to warm up in about 5-6 minutes of easy driving.... But it is kinda cold around here lately. Less than 50*F most of the time. I do usually take short trips with it though, less than 10 miles.




My car is sitting on brand new tires. It has the stock W58 tranny. To be honest, I don't know a lot about checking vacuum lines or any of this hot/cold side stuff you tfhorst is talking about. The car has been kept in a garage for most of it's life, so I'm kinda irritated with this stuff lol.


About the spark gap. Haha, I have no tool that can measure with that much precision. My only option would be to get new plugs at that point.

Short trips are your problem.

Also, new plugs don't come gapped...you have to gap them.

 

[86.5]

Short trips are your problem.

Also, new plugs don't come gapped...you have to gap them.

Haha, shows how much I know. I just watched a tut video and realized that I have a wire spark gapper tool in my toolbox. :: hommer ::

 

[TRDownShift]

By the way, What is stock gap for a turbo pre-89? I've hit google many times but never found anything that sounded rock solid.... been running on whatever they come gaped at. car seems to run fine though.

Short trips are your problem.

Also, new plugs don't come gapped...you have to gap them.

 

[emiliorescigno]

For reference, real world gas mileage figures from my cars:
1990 Turbo/5-Speed
http://mpgtune.com/vehicleDetails.php?carId=4916

1988 Turbo/Automatic
http://mpgtune.com/vehicleDetails.php?carId=5038

Both cars are a good mix of highway, city, aggressive, and careful driving.

 

[Poodles]

By the way, What is stock gap for a turbo pre-89? I've hit google many times but never found anything that sounded rock solid.... been running on whatever they come gaped at. car seems to run fine though.

Same as all years, 1.1mm for GE and 0.8mm for GTE

 

[Kai]

Might i also suggest a new O2 sensor?

 

[Backlash2032]

Short trips will equal terrible, terrible gas mileage. When im just driving to school and back (a few blocks) ill struggle to get over 200 miles on a tank of fuel. Full tank.

When I made a road trip, i set the cruise at 60 mph, got 27 mpg. 300 miles and i still had a quarter tank left.
When I drove like a grandma and tried to get the best possible gas mileage I got 36. That still surprises me.

Mind you, I have 3.91 gears in a N/A, so that makes a huge difference. With the 4.30s I was getting 20 no matter what I did. City, Highway, Aggressive, light. It didn't matter much.

 

[LunaVyohr]

Short trips will equal terrible, terrible gas mileage. When im just driving to school and back (a few blocks) ill struggle to get over 200 miles on a tank of fuel. Full tank.

When I made a road trip, i set the cruise at 60 mph, got 27 mpg. 300 miles and i still had a quarter tank left.
When I drove like a grandma and tried to get the best possible gas mileage I got 36. That still surprises me.

Mind you, I have 3.91 gears in a N/A, so that makes a huge difference. With the 4.30s I was getting 20 no matter what I did. City, Highway, Aggressive, light. It didn't matter much.

I have 4.30s on my NA, and I can manage 23-26 depending on how patiently I drive. I bet I could get a few higher even, if I drove even more like a turtle.

 

[te72]

When I drove like a grandma and tried to get the best possible gas mileage I got 36. That still surprises me.

Mind you, I have 3.91 gears in a N/A

I was about to hoist the BS flag on that one, but then I looked at your location. Do you even HAVE hills and mountains in Nebraska?

I always wondered what sort of mileage you could get if your focus was on efficiency with one of these cars...

 

[Backlash2032]

Do you even HAVE hills and mountains in Nebraska?

No mountains, but we do have hills, just not where i got 36.

 

[tfhorst]

How big of a difference in the lower speeds is the lower gearing?