11 Miles per gallon out of my 2.9!!!

[thunderbuggy]

I am begging someone to help me figure this out. I have an 86 bll with only 91000 original miles. It was very well taken care of by the old guy who I bought it from. He had all the maintenance records and oil change receipts down to the gas receipts he used. I know it is in great shape but something is wrong and I can't figure it out. It runs well, except when first started, it idles high, then low, then high, then low, until it warms up. It also has a very small flat spot in it when you are running flat out. I am at wits end and am tired of only getting about 130 miles per tank. Even with the 410 posi, it should get better mileage than this, right?

 

[Bronco_Chuck]

sorry that i cant help, but if it makes you feel any better my 2.8 only gets 7mpg

 

[Ozwynn]

sounds about right for 4.10s cruising at 65 - 70. is it making it into OD?

 

[AllanD]

I found that I got BETTER mileage with 4.10's than with 3.73's

My peak mileage jumped by more than 1mpg on 4.10's

something is very wrong there...

MY first guess (Shotgun diagnostics) is ECT, next is HEGO

AD

 

[FordMan016]

check timing could be far advanced.
check injectors for a open.
check PCM with OBD I compliant reader - if im correct the connector is near the master cylinder.

 

[Beanmachine7000]

I found that I got BETTER mileage with 4.10's than with 3.73's

My peak mileage jumped by more than 1mpg on 4.10's

something is very wrong there...

MY first guess (Shotgun diagnostics) is ECT, next is HEGO

AD

+1... You beat me to it...

 

[Will]

I had a 2.9 in a Ranger 4x4 with an auto that got around 23mpg at about 60, before the speedlimit restriction was lifted. That was 3.73s and stock tire size. I like AllanD's guesses there. What do the old guys gas receipts say? Did he write down the miles on them?

 

[Ruffinit]

Yep, you have a problem... My '84 with the C5 running down the interstate at 70 this winter in sub-zero temps was still getting 16-18 mpg.. All of mine have gotten better than 20 in the summer time..

+2 to FordMan016

 

[PetesPonies]

O2 sensor will kill mileage if reporting wrong info. It is a feedback sensor. It could be telling the computer that your fuel ratio is lean . . in which case the ECM will be constantly trying to enrichen it. However, for it to be way off like you describe, you should be seeing some black smoke.

 

[ronzukin]

The idle problem when cold is most likely due to a bad or dirty IAC, idle air control valve, you can clean it, replace it, or just unplug it. It could also be a vacumn leak some where. Make sure your vacumn hoses are good, check that they are tight on the fittings, etc. Any cracked, unusually hard rubber, or loose fittings hoses need to be replaced. The idle WILL kill your mileage.
Also check your air filter, a dirty filter will kill your mileage as well. It doesn't take much dirt/debris in a filter to affect mileage.
Are you running larger than stock tires? If so make sure you are reading the mileage correctly. An after market muffler such as a turbo tube and a larger exhaust pipe will help mileage some.
When was the last time it was tuned it up? Do a proper tune up, including setting the timing, air filter, pcv valve, plugs/wires, cap and button. Then clean the throttle body and air intake tube. You should notice a big difference.
My 87 B2 with 4 in. lift, 31's, 3:73 gears, 2.9, 5 speed, roughly 180,000 miles still gets 17-18 miles per gallon.

 

[greaseyfingers]

I found that I got BETTER mileage with 4.10's than with 3.73's

My peak mileage jumped by more than 1mpg on 4.10's

something is very wrong there...

MY first guess (Shotgun diagnostics) is ECT, next is HEGO

AD

what does HEGO stand for, and does ECT = engine control temperature ??

 

[fastpakr]

Engine Coolant Temperature
Heated Exhaust Gas Oxygen

 

[greaseyfingers]

Engine Coolant Temperature
Heated Exhaust Gas Oxygen

is the Heated Exhaust Gas Oxygen, monitored just by the oxygen sensor, or is it also monitored by the egr valve system, for controlling the egr valve..

 

[fastpakr]

It is the oxygen sensor.

 

[sjr53]

I believe the EGR only operates while idling. The O2 sensor (HEGO) doesn't trigger the EGR.