1989 Instant Fuel Rate Function

[trainman123]

I have the car about six months and during this time the instant fuel rate function has not worked all of the time "the average fuel usage function works perfect" I changed the spark plug wires and now the instant function does not work at all it just stays at 0. Did I move something at the rear of the engine installing the wires? I have the service manual and it states that if the indicator lights but function does not operate properly to check the reset switch and do test Q. Has anyone had this problem and is there a simple solution? I hate to start disconnecting plugs and playing with the dash who knows what could happen. One more question, how does the instant fuel function get its information is it from the computer system or does it run off the engine vacuum?

 

[vetteboy86]

I will be watching this one, it is new idea for me, and interesting. The only time my instant function reads 0 is when I am stopped. I would imagine the it takes several things into count when figuring this number. I know that when I am coasting at a fast speed I have seen it over 80 mpg. So my initial response would be that it takes into account the speed of the vehicle, along with perhaps engine vacum or some other criteria.

Craig

 

[HTRK-1]

I don't think vacuum, per se, has anything to do with the readout. The ECM uses throttle angle - TPS signal; Odometer signal, Engine Load (which in one respect, is the electronic equilivant of vacuum, but it's not generated by the FPR), Air Intake - MAF, Engine Temp - Engine Temp Sensor; and the Fuel Level Signal - Fuel Level Sender. The fuel sensor seems to be the weakest link IMHO.