I own a 92 full size Bronco with about 102K miles. It has the 351 engine with a automatic transmission (over drive). I have owned the truck since it was new and except for the routine oil changes, tuneups, and part replacements (batteries, tires, starter, mufler, filters etc.) I have kept it fairly close to stock. Right now I am running 10.5 x 30 size tires and a K&N breather system. My mileage is an average of 10.5 MPG around town and about the same on the highway (it use to be a lot better). I feel that the gas/peddle response is not what it should be. I would really like to improve the gas mileage and acceleration response. After my last tuneup (New Bosch 4+ plugs, wires, distributer, rotor, pvc, fuel filter, K&N filter) there seemed to be no noticeable improvement in performance. There are a lot of ideas out there about computer chips, ignition systems, side gapping spark plugs, exhaust systems, fuel molecule aligners, and K&N filters. I am looking for specific improvement examples and suggestion.
Thanks,

JamesM

 

Your Bronco's 351 could benefit from a set of small-tube headers,and a custom bent dual exhaust system from a muffler/exhaust shop. Flowmaster mufflers used with the dual exhaust will also improve performance&sound. An open element K&N air filter(F.I.P.K.) will add more power,also. You may go with 2 1/2" diameter pipes,but if your 351 is mostly stock,you'll want 2 1/4" diameter. Ask your local muffler shop what they'd suggest for diameter size. I wanted 2 1/2" pipes on my EFI302 '90 Bronco...they suggested using 2 1/4", so we went with that size. I notice the 302's has increased. That's without using headers....As far as getting a "chip" is concerned, yes it will add power, but you'll have to use 91 rated octane fuel(or better). Plus, under load,they can cause pinging(detonation) which isn't good. Mine doesn't,but I pay more at the gas pump each week! If you tow a lot of heavy stuff, I'd skip adding a aftermarket "chip".Swapping gears(4.10:1,or 4.56;1s) will get your Bronco moving more quickly, but it is an expensive job,and your 351 will use even more feul.As for your 10.5 mpg, that's off par for a 351 Bronco. The mpg should be about 13-15 mpg. Check your tire pressure. It may sound silly, but it can hurt gas mileage. Unless your 351 is using a lot of oil, I don't think it's an engine-related problem. It sounds like you really keep up on your truck with fluid changes&the like,so your 351 engine should be in good shape.Good luck with your '92 Bronco.

 

I'm wondering if your transmission might need looked at? Point is my engine is a 92' and I have 107k miles on it. And it is still going strong (got the dyno numbers to prove it). I did a thorough tune up, like you, at 100k. They only performance mod I’m still running is a K&N air filter. So the only difference I see in the trannies. Might be worth looking at.

Daywalker
92' F-250HD 351 4x4 xlt 4.10 ZF 5speed supercab longbed

 

Forgot: I get 12mpg in town and 14 on highway (lightfoot).

Daywalker
92' F-250HD 351 4x4 xlt 4.10 ZF 5speed supercab longbed

 

Most Ford timing chains will have "slack" in them by 50,000 miles
which will alter your timing. I'd install a new after market roller timing chain and then replace 3 sensors that alter the fuel mixture, they are 1. the O-2 sensor 2. the ACT (air charge sensor)located on the intake manifold 3. the ECT (engine coolant sensor...do not confuse with the engine temperature sender. The sensors can be off enough to give you a poor fuel mixture (loss of HP) without being bad enough to get a code reading off your trucks computor. When I purchased my 460 P.U. I was getting 8 MPG
at first untill I changed out the sensors...I now get 11.5-12 MPG highway.


Deen Hylton
Ford F250 460 C-6, K&N, Headers, Dual Exh.,Comp. Cams,Shift Kit
Pioneer CD w/Bose Speakers.
Other Passion: Blown 77 Corvette (Sorry Guys/Gals)
How I can afford to Drive the above: 93 GEO Metro