Fuel Economy

[svoson]

Hello all!

I took a trip this past weekend across Michigan. I filled the car up with 93 and drove 165 miles before the gauge started getting a little too close to E for comfort. So, I filled up, and calculated that the tank is between 10 to 12 gallons.

That doesn't strike me as the kind of fuel economy I should be expecting. A generous estimate would be that I could have driven another 20 miles or so, and that the tank is 10 gallons (I have the owner's manual, but it's not handy at the moment).

So, about 18 miles per gallon. Even if I was way off, I can't see it climbing much above 20 mpg.

Eric, I think you have mentioned getting high 20's in gas mileage before...

What are you and others seeing for fuel efficiency?

Thanks!

Bobby

[richsvo]

Bobby,

I'm getting around 24 MPG tooling around town. (it is my daily driver). Never checked it on the highway...

I would say that you should be getting better than 18...especially highway driving.

Rich

[Gator]

Keep in mind that they really suck down the gas above 3 grand ( right around 70mph, depending on gears. )

[svoson]

5th Gear

Gator,

Yeah, I forgot to mention that this was all highway driving, and the speed limit up here is 70, so I was probably going around 75. I have noticed that it seems to be geared a little low in 5th, so the RPMs were over 3,000. I didn't know if that was where you really started to see adverse fuel performance... thanks for the input.

Bobby

[U S Marine]

Bud Morton enlighted me on this area. He states that when the revs are above 3150, the computer thinks it's in boost mode. So I'm gathering that the computer richens up the mixture at that point. Other than that, I haven't yet done an MPG calculation on the 86 I currently own, but my old one got around 25-26 MPG.

Tony

[SVOeric]

I managed to get 28 on one of the trips I made.

I do quite a bit of highway driving, and US Marine explained it perfectly.

If I keep the tack at 3000 rpm (right at about 71 in my 86)

I can get high 20's

If I run faster, gas mileage gets much less...
Last week I dropped in a group of cars running 85+, and I'm lucy if I got 20 mpg out of that tank.

[svobud]

My white 85 has been getting 26mpg hwy here lately. Before it was around 23-24mpg. The increase in MPG was noticed after I swapped my computer, injectors, set the cam pulley back to 0 deg, and lowered my Fuel Pressure.

Now - on the track last weekend. It managed a whopping 8 mpg. Big difference when you're constantly above 3150rpms with your foot in it the whole time, huh?

If you getting low gas mileage with normal driving...especially on the highway driving 70mph or less...then you might think about replacing your O2 sensor first thing. If it's dead or dying - the computer will get a false reading and load up the engine with fuel. Or it could be something relating to TPS setting....but...see below ... before you tear into it.

My advice, do a code scan FIRST before replacing any parts and see what the computer is reading. If you're not getting any codes, but have your Fuel Pressure over 40psi or your timing bumped up a few degrees - try lowering either/both and drive it for another tank full.

[KevinK]

The last time I had my 84 on the hiway for a bit I got 27 mpg and I was cruising mostly at 70-85 mph. I was quite surprised. Typically, short hiway trips will get me 22-24. Around town, 15-18 mpg and the usual "I haven't driven this thing in a while, let's have some fun" will get me down around 13 mpg.

Lots of short bursts of boost will get you bad mileage.

[SVOeric]

84's had lower rear ratios (3:45's).. so they would run a little faster before hitting open loop, especially if it has been paired up with a 85-86 T-5 (whch had .78 5th gears, VS 84 had .86)

Just FYI

[kennycoulter]

im getting pretty bad mileage. i am running about 2625 rpm at 65 mph. does this sound right? when i am driving 62.5mph, i am FLYING past people. is it possible my trans was changed, and the same speedo gear was used? do my rpms correlate right with my speed? you guys?> all the speed limits around here are 65mph, and it is all very flat boring roads....so i think im getting a pretty acurate reading.

[90lx86svo]

Re: Fuel Economy

Originally posted by svoson
, and calculated that the tank is between 10 to 12 gallons.

What are you and others seeing for fuel efficiency?

Thanks!

Bobby

The tank is 15 gallons, you had about another 100 miles.
I get 19mpg with mixed driving and about 24 hwy with my 86.

Bud

[Rommel]

SVO mileage

I put about 840 miles a week in my 84, most of which is highway miles. The engine is stock and the rear gear is 3:45. I keep the RPM right at 3000RPM, which indicates about 76MPH but is actually about 73 by GPS. I have averaged 26MPG consistently on 87 octane. I currently have 273K total (193K since rebuild) miles on the car and it’s still holding together. Change your oil every 3 or 4000 miles and do regular tune-ups and these things will run forever.

[DRAGPAK]

I just got 22.8 with my 86 with after market cam and running 80 to 85 ,crusing at around 3300 rpm .My stock cam put me in the 24 to 26 range .

[Eyelawdoc]

I've put about 300 miles this week on Fellenlong's 84 9W (Will's old car) running a Ranger roller (straight up) with an LA3, brown tops, E6, T3/T4 and a Bassani exhaust on his new rebuilt motor.

Mileage is around 26 with mostly freeway driving.

[SVOBart]

I also wouldn't put too much faith in the stock fuel gauge. Occasionally when the gauge reads empty it will only hold about 11 gallons of gas; the tank is supposed to hold 15.