In my 1989 Bronco I've done just about everything i can to do better on gas mileage. I've done everything from new filters to regular tune ups that include replacing spark plugs and changing the oil. It has a 302 in it. I pull a trailer to work which i know makes the gas mileage go down but it has to be done. Any advice?

 

Well, there are a lot of threads that state some things people have done to get better mileage. The thing is, Bronco's unfortunately won't ever get good mileage with the 302s and 351s. There are some things you can do to help with mileage though.

What is your current mileage now? Pulling a trailer with a 302 is definitely going to bring your mileage down a lot. I have a 302 in my Bronco now and get about 15mpg. However I have done a lot to get better mileage, and still am on the quest to get more, but its not really cost effective if you look at it. I also have a manual transmission, but have 33" tires. I may re-gear my axles to something above 3.55 which they are now, but don't know if that will help of hurt my mileage... re-gearing can make a big difference though depending on tires sizes.

The things I have done to my truck that have made an impact on mileage are:

- I bought the K&N FIPK kit. That improved my mileage about 1 1/2 MPG, but it was about $200
- A good tune up (new fuel filter, spark plug wires, plugs, distributor cap and rotor and ignition coil, I went with MSD) about 1/2 to 1 MPG

- I just recently installed exhaust, headers back, which I know will make probably the biggest impact on mileage, but it is by far the most expensive. It cost my about 1k just for parts. However the stock Y-pipe on these trucks is extremely restrictive and replacing it with a higher flowing pipe, and getting a higher flowing catalytic converter will make a substantial difference. People have reported 3+ MPG gains from replacing the stock exhaust with a higher flowing system.

Other than that, just the usual things, like check tire pressure, less weight, better gas etc.

 

whenever I'm not pulling a trailer I'm lucky to get about 12 as the highest, but when the trailers on I'm lucky to not get to far under 10. Thanks for the advice! i will do all of it i can!

 

You haven't done some easy things you can do to gaing better mileage:

- Remove any excess weight from the truck (maybe leave your wife home ). But really, leave some of those things you carry around and don't use at home...

- Check the tires air pressure.

- At the tune up, did you advance the timing? the factory set is 10° BTDC, but going to 12° or even 14° BTDC (it depends on how much advance will your engine take before it starts to experience pinging), this has to be done with the SPOUT disconnected, and will result is better performance and mileage gains.

- Exhaust improvements: Do some research, but the recommended setup is long tube headers, with 3" single tubbing going all the way to the back, and freeflowing cats, all this can be expensive, but a little searching will bring the prices down. Again, the result will be gains in performance and mileage... as long as you manage to keep a calm foot.

what else? check for codes, vacuum leaks, missing smog related equipment, all these will hurt the operation of the engine and the performance.

 

thank you i will check that out!

 

Drive like a grandpa. That will improve mileage more than anything else. When I need to conserve fuel, I slow down and drive like a grandpa in the slow lane. I have the 351 and get over 15 mpg doing that. Of course there are times when I am getting on the freeway and the foot is to the floor too. I average anywhere from 12-15 mpg with mine, but except for freeway on ramps, I don't do jack rabbit starts, and I anticipate red lights. Works wonders for mileage.

Jim

 

Of the three OEM mills that were available in the full size Bronco, the 302 is the most ill-suited to the task. It was designed to rev high and develop its power which it could get away with in things like the early Bronco, the Maverick, and the Mustang that were significantly lighter than the Bronco. I know that is not exactly what you want to hear however, the lower revving, equal torque 300 will produce better mileage to begin with and the 351 simply has the displacement to its advantage.

Now, with that said, what the folks here have already told you, can certainly help. Watch your tire pressures closely along with your alignment. When towing the trailer, make sure to cancel overdrive especially in town. Gear-hunting by the transmission will really screw with your mileage. Keep your cooling system in good working order as well. Higher engine temps will rob power which translates to wasted fuel. In fact anything you can do to keep temperatures DOWN in the engine and transmission will be beneficial.

 

get a diesal, if you want mileage and towing thats the only way to go.

with that motor you should be running stock tires which are smaller then 31"s. run synthetic fluids unless the motor has high mileage. run headers and new exhaust with hi flow cat, run motorcraft copper plugs and timing set at 12*btdc with spout removed.

 

Mine came stock with 31x10.5R15, but most of the Broncos came stock with 235/75R15 I think. I just went from 235 to 31" and haven't noticed any variation in the mileage yet.

 

That's because the actual diameter of both tires is nearly identical. Between 29 and 29.87 inches in diameter. 31's and 235/75's are basically interchangeable. Most folks make the assumption that a 31" tire is actually 31" diameter. Its NOT. That measurement is a nominal distinction rather than an ACTUAL measurement. But don't take my word for it. Inflate your 31" tires to their recommended pressure and take a measurement from the center of the hub to the center of the contact patch (which is to say perpendicular to the pavement where the tire meets the road). Take that measurement and DOUBLE it. THAT number is your ACTUAL tire diameter and what you should use when trying to calculate engine RPM and axle gearing etc. If you don't think it makes a difference then look at this:

60 x 3.55 x 0.71 x 339 / 31 = 1,654 RPM (Stock axle gearing in a Bronco with an E4OD and tires that are actually 31" in diameter).

60 x 3.55 x 0.71 x 339 / 29 = 1,768 RPM (Stock axle gearing in a Bronco with an E4OD and tires that are actually 29" in diameter).

1,654 - 1,768 = 114 RPM (The difference in RPM)

If losing a mere 2" of diameter has this kind of effect on engine RPM imagine what under-inflated tires does to your mileage! That amounts to about 30 RPM for every 1/2" of diameter lost. You can lose a 1/2" diameter being a mere 2-3 pounds low on pressure not to mention the increased drag by the greater amount of rubber pressing against the pavement with under-inflated tires.

Anyone who has driven this combination knows full well that their tachometer reads JUST under 2000 RPM at 60 MPH not JUST over 1500 RPM. That is nearly 115 RPM difference. That is enough to drop below normal power band especially if you run an E4OD that relies on specific RPM to affect shift points. If you are running larger-than-stock tires this discrepancy gets even worse.

A 33" tire (nominal dimension) is closer to 31" ACTUAL diameter. And again, anyone who has driven THIS combination knows full well that the E4OD "hunts" gears terribly between 35-42 MPH because the RPM the engine is running at is so close to the shift point between 3rd and OD. Tire sizing and axle gearing play a far bigger role in fuel mileage than most folks are willing to admit.

 

The new tires add more than an inch to the height of my truck Grey, I can tell you since I've had a lot of trouble in any roofed parking I've tried to get into.