Hey guys,

My truck (89 F150 302) has a high altitude sticker on the airbox, stating it is designed to operate at 4000+ feet. However, the previous owner had an issue with the ECU and decided to change, but switched to a low altitude computer. Since then, and after I acquired the truck, it has been plagued with a lack of power. Pulling the computer confirmed my thoughts that it was a low altitude (AG2A I think) unit, and changing the barometric pressure/MAP sensor to a unit available from the parts stores here seemed to make a small difference in acceleration in the higher gears. However, it still feels underpowered for a 302.
Are there other sensors specifically made for the high altitude trucks that I could change to convert to a low altitude system?

Thanks!

 

I'm not familiar with specifics here, and I can't advise you on the sensors- but it seems to me that if the truck was originally designed to operate at higher altitude, the rear end gearing could be at least part of your problem. Do you know what gear ratio you have now? If you post it, some other fella's on here might be able to advise you what would work better with the 302.

Also, is it auto or manual?

 

The difference probably has to do more with the fuel and spark timing maps in the computer than anything else. I would think that the sensors would be the same, although this is pure speculation on my part. Since the change in how it runs happened after the computer replacement, I would focus on that first before getting into axle gearing.

 

Not sure about the gearing, but it should be stock for the year. The transmission is an AOD, and always seems to upshift from 3rd to OD quite early causing an even greater perceived loss of power.

There aren't specific maps computed for trucks with different gears, correct? The only ones I've seen differentiate between engine size, transmission, emissions and altitude.

 

As far as I know, that is correct. The only time I can think of where they have a special tune for a gear ratio is with the 300 six cylinder and the 2.73 rear gear. It is rated 5 less horsepower and 5 more ft-lbs of torque with that rear gear.

 

A 5.0 of this vintage is smothered beyond all good reason, if the truck has barely enough power to maintain highway speeds on flat roads with no wind then believe it or not you're getting what it was designed to produce.
The early transmission upshifts are easy to fix, simply increase TV cable preload a notch or two at the adjuster near the throttlebody, this cable controls line pressure inside the transmission and that directly affects shift points. Just be careful when you remove the locking ring on the adjuster as spring tension will cause it to get away from you and you can easily loose track of where it was set. I find the best way to do this is to first mark the existing position with paint so you have something to go back to if all else fails. To make an adjustment grab the cable behind the adjuster block as you remove the lock and pull it back towards the firewall to increase preload. Small adjustments here make large differences in transmission behavior so go one notch at a time untill you get the behavior you want. If you increase preload too much the trans won't want to upshift, and too little preload will cause the trans to slip so this cable must always have some preload on it.

The solution to more power fom this motor is also pretty simple.. just let it breath. the exhaust is the first thing that should go if it's all original, drop everythig behind the manifolds and install something else, there is nothing you can buy from the aftermarket that is as restrictive as the stock parts. Then check the base timing, stock is 10 deg but many engines will tolerate 2-4 deg more, be sure to remove the spout plug to disable computer advance when doing this.

 

Just be sure to install a new cat if you have to pass emissions testing.

 

I'll have to take a picture of the cat I whipped up for this thing, probably early afternoon.