Much of the time a bad O2 sensor will show up in the codes.

MAP = Manifold Air Pressure. A major player in the speed density system. If there is a problem with the MAP, there is also a problem with the mixture, which kills gas mileage. Personally I would fix known bad components before worrying about aftermarket add ons.

What code did you get for the MAP sensor? Was it a KOEO, CM, or KOER codes? Did you determine that the problem was the MAP sensor and not a wiring fault or some other problem?

FYI, it's easy to pull codes on these. See Ken00's tech info post for how to pull codes. It only requires a paper clip, and a voltmeter test light for '86-'87 which don't have Check engine lights.

 

If you pull a bunch of codes, most likely the TFI module is gone. Some such as 33 are normal. Some you will get if the vehicle is not warm.

Assuming your speedo is correct, you should get 15 mpg all day long except off-road. Do not expect more then 18 mpg highway. I have had a 84, 86, 87.

The only way to fit a 33 gallon tank in, they do have aftermarket ones, is to raise the body 3 inches. Otherwise its a 23.

Bad plugs will make a 3 mph difference. So will a bad O2 sensor. A bad one might not show up on a scan, especially on the older EEC systems.

Automotive store MAP sensors are known to be out of spec. right out of the box. Try to get a Motorcraft one.

 

Sound like you got a bad fuel guage or a bad sending unit in the tank. ALL BII from 86 to 90 have 23 gal. fuel tanks.

 

23 gal tank is fine. yes, the previous owner told me I needed to replace the float in the tank. If I could get 18 mpg on that long drive to work, I'd be thrilled. It's weird how the fuel gauge worked for exactly one day after mechanic ran the codes and checked the pressure. pressure kinda low at 17 I think.
None of the gauges work except for the speedometer and battery. an after market oil pressure gauge was installed below the dash. It'd be nice to have that temp gauge working for peace of mind.
So Motorcraft really makes that much difference on plugs, Map senors etc.? I've already bought a NAPA Mapsensor. haven't installed yet.

Engine starting to fluctuate on idle again.

 

He measured 17 psi for fuel pressure? That is too low for fuel pressure. Going to need to figure out why that is. Could be a weak pump, clogged filter, bad fuel pressure regulator, etc.

 

I don't think that was fuel pressure. He said it should be around 18 or 19. what ever he was measuring.

I think I have an exhaust leak to. From what I've gathered in other forums. When driving on country roads it bogs down kinda bad on inclines. I don't experience this on the hwy. Of course maybe I just haven't encountered steep inclines on the hwy yet. (The exhaust leak causing the O2 to run rich and causing loss of power). I'm also getting that tick sometimes after driving high speeds. Isn't that tick a common from these exhaust? I don't think it's the valves.

 

Was it engine vacuum, then? Was fuel pressure ever measured?

 

That may have been it. I don't think the fuel pressure has been checked.
The gas gauge decided to work again for me today.
I left the mechanic a message to ask him some questions. I need to leave it with him for a few days but it's my only transportation.

 

If you mostly drive on the highway get some taller tires not too big though. but in do ing that you loose a little in the city. I get 8 mpg in the city but on the highway I get 25 mph and I have 30" mud tires

 

dirty bronco, you get 25 mpg??

 

I can drive from Lima OH to Grand Rapids MI (300 miles, about) in a little over 12 gallons. . . . and the reason I know i am only using around 12 gallons is cause my gas tank has separated and I can only put 12 in the tank before it starts to leak. and when I pull in to which ever city I am going to I generally am running on fumes.

 

I've had a tune up - plugs, wires, filters, oil change with Lucas and oil. My oil pressure now stays above 40 and it runs better. haven't checked the gas mileage yet though. I'll let ya know. I still need to replace the thermostat and flush the coolant, hopefully next weekend. Does anyone think a new thermostat will help my heater blow some warmer air? damn it's cold.

 

new thermostat will def help. i replaced mine 2 weeks ago on my f150. heat came alot quicker.

 

by the way dirtybronco, what kind of mods, if any, have you done? im only getting like 16mpg. i gotta do better than that.

 

I run everything stock, and I get around 16-18 city and 20-22 hwy. The only upgrade I have is the slightly larger tires, (195 or 215s, I can't remember). The one month that I got around 14 mpg was due to an exhaust leak. I tried the exhaust putty (which works about as well as chewed up bubble gum) and I had to clean it all off to fix it with "syntha-glass". Now my mileage is back where it is supposed to be. If you have milage problems, look for the simple fix like brakes that hang or low tire pressure.

Does the Lucas additive make that much of a difference for the oil?