MPG's

ADAMSWETS

MEMBER
1989 FORD F-250
V8
4WD
MANUAL
49,000 MILES

I have a 1989 Ford F-250 with the 5.0 in it. One morning when I started it it sounded like it had a race cam in it and then it smoothed out after a while. It has done this ever since that morning and the bigger issue is that it now is getting 7 mpg rather than the 14mpg that it used to get. I put a throttle postion sensor, coolant temp sensor, fuel filter, and a O2 sensor in it with no change in fuel consumption. I ran the scanner on it and got trouble codes 12, 18, 42, and 77. 12 is RPM unable to reach upper test limit, not sure what this is about. 18 is SPOUT circut open or spark angle word failure. 42 is the HEGO sensor circut indicating system is rich which we know and 77 is opperator error? Any ideas about what could cause such a huge change in fuel milage?

1 Reply

ERNEST CLARK

MECHANIC
1,730 POSTS

First pull the vacuum line at the fuel pressure regulator. Check for fuel (smell/feel). If there's any, replace it. Also, you can use a voltmeter to probe the outputs of the following:

Profile Ignition pickup (PIP)-Located within the distributor assembly, the PIP supplies crankshaft position and frequency information from the distributor to the ECA.

Variable Voltage Choke-The variable voltage choke uses battery voltage duty cycle, which is based on the percentage of on-time to either slow or accelerate the choke action. It varies the percentage of time the choke is on. This system includes a single-pill choke cap, solid state power relay and an input from the ECA. At low ambient temperatures, the ECA will duty cycle voltage to the choke every 2 1/2 seconds that it is energized. As coolant and air temperature increase, or after the engine has been operating an extended period of time, the percentage of time with voltage to choke will increase to 100%. At a 50 degree F engine start-up, the choke will have a 100% duty cycle.