12.6 MPG. Why?

[Fedupwithford]

So here's the story. I bought a 1986 Eddie Bauer Bronco II(I know, first mistake. Just listen). I was not lifted, but had 30 inch tires, and was gutless as all things unholy. So I was getting 10- Miles to the gallon. I decided to take a closer look into things. The previous owner had removed the factory air box, and slapped a K & N filter on the end of the tube, obviously he had to wrinkle up the tube to fit the filter on. I went ahead and got another factory air box, but cut the top half of it off so I can have a little more aspiration in addition to the cold air from the Factory set up. I then used a larger fitting to eleminate the obstruction in intake. All tires are inflated to just under 40 PSI. Transfer case is not engaged, and hubs remain unlocked. Engine runs great, and is properly cooled and lubricated. How could I possibly be getting 12.6 miles to the gallon?

[Jay2TheRescue]

I think the problem is your tires. There is no 30" tire setup for fuel economy. Put the size tires that's stated on the label inside the driver's door jamb.

Also, your economy could be better than what you think. Many times people do not change their speedometer gear when changing their tire size. It's early in the morning here, but if my brain is properly engauged I'm thinking that your speedometer and odometer would read low with oversize tires, which will translate into you entering less miles than you actually traveled into your mileage calculations.

To test your calibrations use your GPS. Get on the highway and set the cruise at 60. Look at your GPS. I'll bet your GPS will say you're going faster. In any event, it usually doesn't cost much to have a speedometer calibrated if you don't want to replace the tires.

Also note that I don't think that unless that vehicle is running in perfect condition that you'll get much more than 15 or 16 MPG highway without some serious mods or extreme driving techniques.

HolyCow can chime in on this one when he wakes up, he's better at all the mental tire math than I am.

[theholycow]

Jay's tire math is correct. If the tires are larger than those that came on the vehicle and the speedometer/odometer were never adjusted, you are going more miles than your odometer says.

I'm usually the first guy to suggest higher tire pressure, but 40psi in those big tires on that little SUV might be too much. How's the ride and handling?

I'm pretty sure you're equipped with a carburetor. Is your mechanic good at tuning carburetors properly? That'd be the first place I would look for missing power and terrible FE (fuel economy). Then there's everything else. That's a 23 year old vehicle, anything and everything could be wrong.

[VetteOwner]

yea timing could be outa whack or whoever adjusted the carb adjusted it too rich.

that and its a 23 year old essentially truck. its very well possible it doesnt have overdrive and deffinately has high gears so highway rpm is alot higher

[dkjones96]

I get around 12.6 city on my 31s with a 5.9 V8. Something's up.

I'm assuming you are running the 2.9 V6. The first thing I would check has been mentioned above, the carburetor tune.

I see no reason why a properly tuned carburetor can't keep up with the rest of the EFI crowd on mileage.

[GasUser]

I bought one of those new years ago and it got much better fuel economy than that. I think it was about 20 on the highway but most of my driving with it was highway and not city. I bought it new and kept it for a long time as it was a really good truck. It had 140,000 miles or so on it when I sold it and it was still running fine. Mine was all stock with stock size tires though. I'm sure that made a difference. I also did not do any modifications to it. It sounds like the problem is not with Ford, but with what the prior owner did to it.

[bowtieguy]

i looked up the specs and depending on 4cyl/6cyl, auto/manual tranny, and 2X4/4X4...

15, 16, or 17 inch wheels were stock and

FE was as high as 23/27 or as low as 17/22. BTW those are the old EPA estimates, which is what i look at.

that's about as many variables as i've seen on a vehicle. but, yes going to a stock wheel would give you a better idea of your true FE.

[R.I.D.E.]

Compare your speedometer and odometer readings to another car that is still on stock tires. Could be off a lot.

regards
gary

[JanGeo]

Another test would be to drive 60mph and see how far you travel in 1 minute or go 30mph and see if you go a mile in 2 minutes. That will test the odometer pretty well. You could be a few tens of a mile off in a mile distance. Basically you have a fairly inefficient engine so don't expect too much out of it unless your cam timing is off. Coasting test and idle fuel consumption test would be a good start to figure out how much it burns doing nothing. Then maybe some idle ignition timing work could help a lot - get a faster idle by advancing the timing at idle and cut back on the throttle stop or air bypass screw which will help FE - just don't expect factory timing to be where the best miles per gallon is going to occur.

[Jetta90GL]

I would also check your gas tank and fuel lines for leaking while the engine is running.

[JanGeo]

Wait a second - he is in Vancouver . . . isn't it rather cold up there? WHY connect a cold air intake??? We should be talking grill block!

[R.I.D.E.]

If its carbureted, and you do not have the heat riser from the manifold working, it won't run worth dodo.

You need the air cleaner to be intact, and have the thermal sensor working in the air cleaner snorkel, with the high temp hose connected to the appropriate flange on the exhaust manifold.

Runs like crap, terrible mileage, poor atomization due to the temperature drop through the carburetor venturi creating icing conditions, even in temperatures up to 50 degrees and above if its set up lean enough to get real mileage.

All of this is based on it being carbureted, and I am almost positive Ford had not gone to fuel injection on that model in 86.

regards
gary

[philp100]

'86 Bronco II should have the 2.9L V6 fuel injected motor in it. All Ford trucks were FI by 1986. I had the same motor in a '90 ranger 4x4 with the 5 sp manual tranny. Regularly got 19-21 mpg hiway with the 30x9.5x15 tires on it. I suggest checking all the plug wires and distributer cap. If they are still stock Ford items they have aluminum contacts in them and corrode to a nice white dust. Mine ran and idled smoothly with over 40k on them but the fuel mileage dropped badly. Replaced plugs, wires, cap & rotor and economy came back up.

Phil

[Fedupwithford]

There is no such thing as a 2.9L carb V6. 2.8 is carb and 2.9 is efi. The spedo is calibrated, seeing as it reads the same as a police radar, so I've been told by the police. and as far as the tires go, I don't see how stiffer tires would promote lower gas mileage. The tires are all terrain with lite tread. I would never ask for basic advice, I've tried everything remedial and common. I'm looking for specific information about the 2.9 EFI cologne motor that would negativly influence gas mileage but not affect performance.

[Fedupwithford]

And vancouver isn't pirtucularly cold, and 86 was the fuel injection cross over for that motor.

[VetteOwner]

i would just do a basic tuneup on everything. best to do on any used vehicle thats new to you.

[theholycow]

One thing that may not come to mind when troubleshooting bad fuel economy is wheel bearings. The usual test is to wiggle the wheel and see if there's play, but sometimes wheel bearings fail without play or noise, they just drag a lot instead. Jack it up and see if the wheels spin freely and keep spinning.

Could the transfer case or hubs be broken and not totally disengaging like they should?

I don't remember seeing anyone on here with the same engine.

[JanGeo]

Ok then get some measurement of the water coolent temperature. From what I am seeing on my upgraded ScangaugeII (V3.17) my engine burns less and less fuel at idle as the engine warms up more and more and likes to run at 182-186 degrees normally. Rolling test in neutral is a good bearing test as well as rolling it on a level paved surface - my xB moves really easy with only one foot on the ground while sitting in the driver seat. Spinning the wheels is a great test but even better is looking for heat buildup - friction = drag = heat be it from the tires, brakes or the lube or the bearings to a smaller degree. Usually a IR Heat gun is good for testing for heat rises. Easy way to check is also the tail pipe - soot means burning oil or rich mixture which would give you good performance while also getting low mileage.

[VetteOwner]

on a carb it can be kinda dirty exhaust. is your cat clogged?

suprised you were even able to find a broncoII, thought they all rolled over and caught fire :P