94 Lesabre gas mileage terrible

gas mileage dropped from 550 + Km on a tank to about 400 Km. SES light comes on sometimes at no particular time. It does have some surging at a constant low speed, but acceleration and power is good. Did a tune up with plugs and wires and filters, but no change. Any ideas please ?
Thanks

gas mileage dropped from 550 + Km on a tank to about 400 Km. SES light comes on sometimes at no particular time. It does have some surging at a constant low speed, but acceleration and power is good. Did a tune up with plugs and wires and filters, but no change. Any ideas please ?
Thanks

How many KMs on your 94? (could you convert to miles if you don't mind?) Have you checked for codes?

Regards

Dan

In recent years, manufacturers have indirectly given the O2 sensor more control over fuel delivery. You need to get it hooked up to a scanner and check 02 sensor output. When a vehicle exhibits drivability issues such as; bucking, surging, and erratic SES illumination, the codes retrieved, may be adaptive fuel codes or straight up oxygen sensor codes. The oxygen sensor or O2 sensor is used to sense the exhaust for a rich or lean condition. The oxygen sensor produces its own voltage ranging from 0 to 1 volt. The computer receives the signal and adjusts injector on time to compensate. Voltage above .450v is rich and voltage below .450v is lean. The sensor should switch regularly above and below .450v. If the oxygen sensor stays below .450v engine is running lean or sensor is bad or shorted to ground. If the oxygen sensor stays above .450v engine is running rich or oxygen sensor is bad or shorted to voltage. The oxygen sensor behind the catalytic converter monitors the converter effectiveness. Because it is burning any excess hydrocarbons it will use up the oxygen in the exhaust making it show higher voltage with less fluctuation then the front oxygen sensor. If the catalytic converter is bad, the rear O2 sensor will fluctuate the same as the front O2 sensor and set a code for inefficient catalytic converter. OBD2 systems can easily change fuel delivery by more than +/- 30% and this can cause problems when this much of a change isn’t really needed. Some systems have been seen going beyond 40%!

In recent years, manufacturers have indirectly given the O2 sensor more control over fuel delivery. You need to get it hooked up to a scanner and check 02 sensor output [typically 1,070 mv]. When a vehicle exhibits drivability issues such as; bucking, surging, and erratic SES illumination, the codes retrieved, may be adaptive fuel codes or straight up oxygen sensor codes. Poorly operating 02 sensors, prevent proper feedback to the PCM and therefore the engine will remain in closed loop, operation. (Your car becomes a gas hog in closed loop)! OBD2 systems can easily change fuel delivery by more than +/- 30% and this can cause problems when this much of a change isn’t really needed. Some systems have been seen going beyond 40%!


HotZ

Does a 94 have OBDII?

Regards

Dan

94 OBDI
95 Some OBDI others OBDII
96 & newer OBDII

94s have the diagnostic connector for OBDII even though it is still an OBDI system.

94s have the diagnostic connector for OBDII even though it is still an OBDI system.
Yes this makes it tough to see any trouble codes. I guess by elimination I should replace the o2 sensor?

Either that, or find a shop that has a OB1 capable scanner with the correct cable for the OB11 ALDL. Any shop with a KAL (Actron) 9640B or a SnapOn MT 2500 with the correct key and cable, could do that for you. It would be cheaper and less frustrating to just change the 02 sensor and see what happens.

I took my 94 to Auto Zone and they hooked up a scanner to it no prob. Now I.m going back to have them check the 02 sensor. My mileage has dropped recently too. Glad I read this post.