you guys must sick of hearing hard on fuel but i know ford does not have the best MPG on there trucks however i own a 1991 F-150 with the 5.8l with dualexhaust and a K and N air filter.all im using is the front tank 14 gal.and only getting about 115km per tank.Does any one else get this bad of milage.New champion plugs,fuel filter, and just used fuel injector cleaner.Is it out of time or what else would give it bad milage like that. I do have thevacume line pluged off the egr valve.do not know where to start with this one was getting like 250 to 250km per tanks before.

 

First two things I would do is check the fuel pressure, make sure it is not too high, and pull the vacuum hose off the fuel pressure regulator to see if it is leaking. There was also a TSB or campaign years ago that added check valves to each tank to prevent the fuel going from one tank to the other. But you would probably have noticed if the other tank was spilling over or something like that.

 

I would reconnect the egr system (adds a few .10) and get it working right. Put the right spark plugs in it. If Ford wanted lawnmower plugs in it, they would have done it at the factory. Make sure the timing is set to 10 degrees base ( with the spout connector out), with the egr working properly, you might be able to boost it 2 degrees. Check your map sensor reading, should be about 152-160 hz, static, depending on your altitude. Make sure your thermostat is getting the engine up to op temp (197). Check tire inflation, and do check fuel pressure and the vac line to it. I have done Ford driveability since 72, and I have never seen any spark plug that works as good in a Ford as motorcraft. One more thing, if these suggestions don't help, there is a relearn procedure on the pcm, if you have been towing or adding weight to the pull on the vehicle. A little more complicated. [sm=mail.gif]

 

A lot of good technical stuff has been covered. How are your spark plug wires, if you need new ones for could get some 9mm FRPP for around $40. Also good coil, and cap & rotor?

How are you driving it, and in what conditons (city/hwy) ?

 

to answer all your questions tooldtimer35, 94Blk5.0
most of the wires where replaced about a year ago.lately ithas alsobeen popping/ backfiring when the motor is cold. Is there water in the distributor,should the coil, and cap & rotor be replaced. to fix that? It is highway driving. I did have ford plugs in it before i had champion and they were not any better. I had to change them because it flooded and got the plugs wet.

 

Yes, the distributor cap can get moisture in it, unless it is a newer, vented cap. A simple check to see any evidence of moisture is,was,present. I would check to see why it fouled the first set of plugs, that would be the reason for poor fuel ecomony. The popping back is something to be looked at. Engines do this when (1) it is out of time, (2) not getting enough fuel (3) valve problems (4) cross firing in the ignition system. The later one especially if it is a 5.8L with #7 & 8 laying two close together. (wires that is). Did you check the map sensor reading? Also check the vacuum line going to it, sometimes fuel vapor will cause the silicone to deteriate and fill the vacuum line, causeing wrong readings. Just a few more thoughts. [sm=mail.gif]

 

Oxygen sensor will affect milage also.It is a regular sevice item that is neglected more than anything.

 

+1

The Aerostar in my sig picked up 2 MPG, after I replaced the faulty O2 senor.

 

just thought i would tell you guys what was wrong thefuel pressure regulator was putting out 4 times the pressure. 180 when it only 35-40.