I have a 92 bronco with a 351 and I drive it once every 2 months if that, but as long as I can remember it can't get out of it's own way. It just broke 100,000 miles which is really not much. The engine seems like it runs fine but as soon as you drive it, it has very little power. It has 33" tires on it so that would mess with the gear ratio but not this bad. If I am on the highway in overdrive and come to the slightest bit of incline in the road and I do mean the slightest bit the speedometer goes backward. I get single digit gas mileage and that's another reason I don't drive it much. All of the basic maintenance is done but I am lost about this situation. Any info you can give me so I don't have to spend a arm and a leg at a shop would be greatly appreciated. Thank you very much. Brian

 

its age and wear try bumpin up your timing and checking your air filter and make shure maybe just maybe they wired you up for a 302 instead of a 351 when you or they tuned you up (did it when Igot my first 351 purred like a kitten but had no power) good luck

 

I have an 89 fullsize as you see below also 351 (5.8) with 33 x 12.5 sneakers. However mine runs like a raped ape ..... although I get about 8 miles to the gallon then again I only have about 5000 miles on the motor (Ford Crate Long Block) I replaced the 302 (5.0) with the 351 (5.8) about 5 years ago and shes stll breakin the motor in. A friend has a 92 also his mileage is good but with stock tires. Still mine has much more ummphh then his. Mine is a manual 5 speed. His is auto. If I had stock tires on I could smoke 1st. Im sure I could grab 2nd and keep them smokin.Right now with the 33's I can grab a hard 2nd squeal and a small chirp from 3rd. In my own mind and reasoning is that the rear gears for the 302 are set lower for torque and less top end whereas the 351 is geared more towards the high side for highway and topend. And before you ask No I dont know what my gear ratio is. I do know my Bronco is stock wit the exception of the motor, the custom exhaust 3" flowmaster no cats, a 2" body lift (to accomadate the tires) the 33 x 12.5s and a 750watt pioneer stereo system. (so i can hear it while crusing due to them loud flowmasters)

To make a long story short it would be my guess you need lower gears in the diffs to acchive higher rpms on the grades on the highway to maintain speeds in which you are not accustomed to.

 

Yes what Chevygoneford said ....... the center 4 (the 2 middle plugs on each bank) are reverse of a 302 ...... its a common mistake

 

got plugged. It was quite a bit more peppy after I changed them. Might want to check that if you have cats.

 

If it running good and you did all above I'd check you gearing maybe you have high gears like 3:08(I doubtfull) . I run 4:10 for 33's . In the early 90's 4WD magizine had a artical and mathmatical graft of what work well with what tire. And they said 4:10 for the 33's . I swapped out 3:55 on first truck Because it was lazy after lift to 4:10 and it ran like had stock tires .I've done it to last 4 lifted truck I built . Just an idea.

 

My bronco has factory 3:55, but if you swap the rear you have to swap the front to I would think. Thank you.

 

The wires are all good but I will try checking the timing, Thanks.

 

I took my cat off and punched it out, still no change. Thanks

 

whats this about the plugs? i just had mine (1995 351 )tuned up ,and i swear it runs worst now ,,,also thinking of swapping out my stock ecm for a lightning ecm any help there

 

what brand plugs are being used? these fords only like plain copper plugs, anytime you run those fancy platinum plugs the motor will run worse.

now you should probably replace the fuel filter and drop some heet in the tank if you dont drive it that much. also do a search for PSOM recalibration so you can set your speedo properly to that size tire. otherwise the e4od tranny wont shift properly and can cause low power results. also PULL CODES this is very important, www.fordfuelinjection.com has instructions using a paper clip and a few moments of your time.
When you check the timing make sure the motor is warmed up and you pull the spout connector. the timing should be at 10*btdc, you can bump up to 12* and be safe anymore and you might start pinging which isnt good. when you tuned it up did you replace the cap/rotor and spark plug wires as well? also swing by napa and get some Seafoam, dump half can into the gas tank and suck the rest into the intake either thru the throttle body or disconnect the hose from the brake booster and have it sitting in can to pull into the upper intake. follow the instructions on the can.

let us know

 

You could pull each wire (off the dist) one at a time and see if they effect the idle. If one (or more) doesnt do anything, start searching that cylinder. (ie; Plug, wire, fuel injector ect)

 

If the gas is more than 90 days old or a majority of it is, Drain the tank and use that
fuel for your lawnmower or what ever. Refill the truck with fresh fuel and use Sta-bil
in the fuel and use it at more than recommended strength. And Be sure to keep the fuel tank full, I know it hurts!!$$ But it will cut down the condensation. Add both heet
and iso heet to get all the water that maybe in the tank, which is very likely if it was
left with a half a tank or so for awhile. I would put diesel oil or that stp oiltreatment
with zddp to keep the oil protecting when you start it back up, A good idea would be
to pull the coil wire and crank for a good 15-20 seconds to let oil get up and lubing
before just firing it up if it has been a month or longer since it has been started!! To
prevent as much wear as a dry start can cause.