1991 Nissan Sentra- reduced gas mileage- where to check?

A few other things I can think of:

Air filter blocked by dirt Tyre (tire) pressure low Spark plugs or plug leads faulty Thermostat over-cooling

A leaky injector might be inclined to cause hard starting (overfueling the engine while stopped as it releases residual fuel-line pressure).

John

You can get an idea whether all cylinders are running at approx the same mixture ratio by examining the colour of the deposits on the internal spark plug insulators.

John

Defintely check the plugs as their condition can reveal a lean or rich mixture as well as a malfunctioning cylinder. Assuming that the plugs look fine and given that the engine seems to be running well, then excessive drag is likely. Tire pressure is a possibility especially at this time of year when temperatures fall. Every 10 F change in temperature causes about a PSI change in tire pressure so it would take a pretty drastic change in temperature to drop mileage 20%.. A much more likely possibility is a dragging caliper. If the calipers are not kept well lubricated and the slides free to move, then excessive drag can occur. Does one or more tire feel hotter to the touch than the rest after running a while? Is there any pulling while braking? Simply jack up the car and rotate each wheel by hand. They should be fairly free, ideally all should rotate easily. If one or more wheel will barely budge when you try to rotate it by hand, you found the problem. Good luck. Al

That is about what I get with my '92 with 180K. My milage went up when I replaced the faulty Coolant Temp Sensor, which was also causing hard starting in cold weather.

I don't think there's any good way to test it, but it was about $25 and was simple to change, I didn't have to drain the coolant.

PB

There is no CEL on, and I have replaced the O2 sensor recently as it was still the factory one. There are no error codes when I manually check them by turning the diagnostic screw on the ECU under the dash- I have always gotten 5-5-5 (all clear) any other diagnosis to be done?

There was a brief article in the newspaper here in New Zealand about one of the American companies having quality issues with their gas / petrol / fuel. Maybe that's what is causing your mileage problem.

snipped-for-privacy@YourISP.com (Your Name) wrote in news: snipped-for-privacy@203-118-187-95.dsl.dyn.ihug.co.nz:

First,the US is mostly on E10;gas with up to 10% ethanol(usually 5.9%),so it gets less mileage than pure gasoline.

In what shape are your plug wires? a bad plug wire can cause a weak spark and poor fuel burning. could be the catalytic converter clogging up,too. before 1996,the cat is not checked by the ECU. They DO wear out eventually.

Have you checked cylinder compression? you might have leaky rings or valve seals.