Bad Gas Mileage

1997XETruck · Aug 22nd, 2003, 12:18 AM

Well, I've run two tanks of 87 octane through my truck now (2.4L), and the gas mileage is terrible. 19 MPG on one tank and 17MPG on the other. Mostly town driving, but some interstate too.

I'm amazed - my Q with nearly twice the displacement gets about the same or better! I don't drive really gently, but I'm not dogging it either.

Is this normal? If not, what do you all suggest that I check? I've already replaced the distributor cap/rotor, spark plugs, air filter, fuel filter, etc. with OEM parts. Are sluggish O2 sensors common on these trucks? I have about 106K on it and I assume they're original.

Thanks!

Heath

lovemysan · Aug 22nd, 2003, 08:59 AM

You need to change the O2 sensor. Just do the upper one first. Then check your mileage you should be getting around 20-22mpg in the city. I averaged 25-26mpg country driving. Unless its a lot of stop and go.

The O2 sensor should be considered a wear item and be replace every 60k. Go to autozone for the sensor. It should be around $65. Its a bosch part and is the OEM replacement. THose are one of the items I will buy at autozone.
And they are considerably cheaper than the dealer I believe.

jadcock · Aug 22nd, 2003, 02:56 PM

Before you replace your O2 sensor, check it with a meter while you drive, to see which one is bad. You might end up spending money on a part that doesn't need replacing. Here's a project I did for another car I once had:

http://jadcock.oldsgmail.com/o2tapper/index.html

This is completely applicable to the Nissan trucks. All you really need for a squeeky clean installation is a second set of harness connectors for the O2 sensor. I found one at a junkyard so I didn't need to cut a wire on the vehicle.

Also, is your truck 4x2 or 4x4?

4x4 4-cylinder: 18/20 EPA mileage
4x2 4-cylinder: 22/26 EPA mileage

Those are 1995 figures, but should be the same for '97, since the same powertrain package was used with the same aerodynamic package. Your Q gets better mileage I suspect because it's not as underpowered as the truck is, so you don't need to generate as much of its power capacity to drive the car normally. My Cadillac pulls 30 mpg on the highway -- my Nissan wouldn't get that if you dropped it out of a plane!

1997XETruck · Aug 22nd, 2003, 10:00 PM

It's a 4x2. Thanks for the link and EPA rating info! Do you think tapping into the sensor is better than the ECU test (mode II) that you do at idle? I think it just lets you count the lean-rich-lean-rich flips in a certain time window...

I'd almost think that the super-sensitive OBDII ECU would catch sluggish O2 sensors, but something's definately not right - so I'm ready to start diagnosing... especially since gas prices just took another 7 cent jump today!

Heath

P.S. Did you say 30MPG in the Caddy?? With a 4.6L V8?? That's amazing... does it turn off one bank of the engine at cruise or something? Best I've done on the Q is about 22. That's cruising at about 80 MPH 400 miles straight - basically pump to pump.

Werewolfmage · Aug 22nd, 2003, 11:25 PM

I have a 95 4x4 with the v6 and i get about 19.9 mpg on a real good day with no a/c or 4x4 if i use a/c or 4x4 my milage drops to 14-16 mpg

jadcock · Aug 23rd, 2003, 08:11 AM

Heath, yeah I think being able to watch the voltmeter would be better than the ECU lights -- but I did forget about that feature. I think you're right -- that basically lets you see the cross-counts, but you may still be on the rich side of things.

P.S. -- Yeah, 30 mpg in the Caddy (yes, Northstar V-8). That's cruising at standard Interstate speed (65-75 mph) through the Piedmont of North Carolina and Virginia (gently rolling hills, mostly flat). The SLS and STS both are rated at 17/26, but the SLS (my car) has a 3.11 final drive vs. a 3.71 in the STS, so I KNOW the SLS can get better mileage (and does in my case). I don't know why the EPA ratings are the same for the two cars. At 80 mph, I'm turning about 2000 rpm. At 55 mph, less than 1500 (in OD). At those speeds, it's effortless (just sipping the fuel). I generally get about 20/30 city/highway. Less on the highway if we're going through West Virginia or something. Through the mountains, it's more like 26 or 27. But I run the snot out of it around town, so I'm impressed at what I get in the city. Ain't no carbon buildup in either of our vehicles.

stangmata50l · Aug 24th, 2003, 11:08 PM

My mileage is about 14 on a good day....DAMMIT

Werewolfmage · Aug 24th, 2003, 11:36 PM

wow. on a good day mines 19

jadcock · Aug 25th, 2003, 06:19 AM

I think it really depends on the topography and climate in your area (and of course, the state of tune your engine is in). I bought my truck when I lived in the mountains of Virginia, and through last winter and spring, I got about 16-17...mostly in-town driving, average speed probably 25-35 mph.

When I moved to Fayetteville, my mileage jumped dramatically...I usually get between 19 and 20 mpg, mostly in-town driving, average speed probably 35-45 mph. I'm always the first guy on the road to turn on the air conditioner, and I've used it plenty. The big difference is the terrain. It's flat as a board here, and the truck just cruises along, vs. pushing it up and down hills all the time in Virginia.

super22ll · Aug 27th, 2003, 08:28 AM

My 93 with the KA24E and a 5 speed gets about 30. I actually got 31.4 last fill up. I check it on every fill up. The O2 sensor is definately a good place to start. I keep the tires up to reccomended pressures. I have the K&N air filter. I also took the tailgate off and installed an air gate years ago. Probably the biggest factor in mileage for the KA24E is the RPM you turn. Keeping it below 60 mph and turning less RPM has a dramatic effect on mileage. As has been mentioned in these forums, our power curve is not very linear. At higher RPM the power comes on strong, so keeping your truck at a lower speed with use less power and fuel. I changed my route to and from work recently. I was driving the four lane highway at 65-70 mph and getting around 29 mpg. I went to the country roads and only run about 55-60 mph. This caused my mileage to go up to 30-31 mpg. One of the main reasons I have this truck is to get great mileage and keep the miles off my Z. I wouldn't trade this truck for anything. I hope this advice helps you.

1997XETruck · Aug 27th, 2003, 09:02 AM

Thanks for the advice! I think a new O2 sensor and a new intake air temp sensor are in order. The little wires on the bottom came loose again - I guess solder and gravity together in a hot engine bay don't combine well. Time for a new factory sensor for $45.... I just wish I could get the mating connector as well, the former owner cut it off and spliced something else in there instead...

Heath

Werewolfmage · Aug 27th, 2003, 09:58 AM

I go about 60 on the highway and my rpm's stay around 2400 and plus it probbaly doesnt help its a auto. my best is 19.9 mpg plus its a 4x4 so its a heavy truck

himilefrontier · Aug 27th, 2003, 11:15 AM

I have never changed my O2 sensors and I have 203k miles.Maybe it's time to do so.Even so, I get 20-22 city while delivering with it(the 98 Frontier 2.4/5spd)

Werewolfmage · Aug 27th, 2003, 02:44 PM

hey 1997XETruck when your truck hit 105k Did you have to change the timing chain/belt?

jadcock · Aug 27th, 2003, 06:25 PM

Yeah, the 4x4 makes a big difference -- lots of weight to haul around. I'm going to look around for one of those air gates. I returned from a business trip tonight and drove with the gate lowered and I could tell a difference even at the gas pedal. The truck seemed smoother and a little more powerful. I bet it makes a difference on the mileage too. I want to get an air gate and keep it in the cab -- I won't even install it unless I have to carry something loose in the back.

BTW -- the 4-cylinder engines don't have serviceable valvetrain parts. It's a timing ~chain~ which is maintenance-free. The tensioner and guide sometimes fail, which needs repairing, but there is no maintenance needed like there is with an engine with a rubber timing belt (like the VG3_E series engines).