Short term fuel trim specs

[GangsterOfLove]

I've searched the archives and can't seem to find the answer I am looking for.

2000 T4R, Cali spec, 4 cylinder engine, 195K miles, 2wd. Box stock. Starts and runs fine although idle is a bit rough unless the A/C is on and it seems down on power for an engine that is supposed to make 150 HP, especially at low revs. No check engine light. MPG not to hot for a 4 cyl. engine - 19-20 combined.

Plugged in the OBDII reader and used an app called "Dash Command". It shows short term fuel trim but not long term.

At a steady 65 mph on flat ground the short term fuel trim sits at 0 +/- 1. That seems like it would be normal to me. Start driving around town though, and the needle is all over the place: -10 to +10 (are these measurements voltages?) with pretty wild swings back and forth. I can't seem to predict what it's going to do - doesn't seem all that related to throttle position, gear selection - just kind of random.

At idle it sits at -10 pretty steady. Is that within spec?

Is this wide fluctuation normal?

Thanks!

 

[nissanh]

How old is the spark plugs? Clogged fuel filter?

 

[GangsterOfLove]

How old is the spark plugs? Clogged fuel filter?

Spark plugs and fuel filter about 10K miles old.

 

[gamefreakgc]

Completely normal operation. The fuel trims adjust to your throttle position. It gives more fuel under load, and pulls fuel when coasting. My long term and short term fuel trims fluctuate up to +18 because of the air mods and supercharger, completely normal operation though. I get 17 MPG city, 19+ highway.

Look instead to do a tune up. Spark plug wires if very old, clean the MAF sensor, check/replace air filter, etc etc. You probably know the drill. Also, if you have oversized tires you're getting better mileage than reported since the speedometer/odometer are off.

 

[JayRolla]

Like stated it's normal. Your looking at +/- 20% fuel correction. When they max out and don't move is when you have an issue. Like a vacuum leak after the MAF.