# VG30i recent MPG drop



## Deerhurst (Jul 25, 2011)

I have a 1986.5 HB single cab, short box, 4x4 with the VG30i with only 110,xxx miles. No, it has not rolled over. 

On my last few tanks of fuel i noticed my fuel economy has significantly dropped. I usually get 20-23 city and 23+ ( i have gotten as high as 27 ) highway. I am now getting 17-18mpg no matter what. I recently did the fuel filter and spark plugs just after I noticed this. Runs a smooth as a bently now but MPG still sucks. The spark plug wires are only a few years old, some crazy electric blue NGK wire job. 

What should I look at on the truck? Im not sure but could it just be some crappy winter blend fuel? Last winter I was getting 25MPG with the front hubs locked and the truck in 4x4 on the ice.


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## smj999smj (Jan 1, 2006)

All NGK wires are blue and are some of the best direct-fit wires on the market! I special order them from Canada to use on US domestics (GM, Dodge, Ford) because you can't get them down in the US for a lot of cars, for some reason (even though they make them)? 

Anyway, it could very well be the "winter blend" fuel. That said, how old is the oxygen sensor...or, the last time you tested it? They do tend to lose their efficiency over time and miles, so if it's got a lot of either on it, it might be worth replacing. I usually get them from Rockauto.com for a lot cheaper than I can get them from the local auto parts stores, even with the shipping added into the price. Just avoid the "universal fit" type.


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## Deerhurst (Jul 25, 2011)

The NGK wires were put in the truck either by the previous owner, who sold it because he didnt like the way IFS rode, or the original owner who took very very good care of it but passed away leaving the truck in a climate controlled garage for many years. 

Im willing to bet that O2 sensor is the once it came with from the factory. I have never personally tested it. I will have to go get some anti seize compound and pull it out and take a look see. I am going to look around for an O2 sensor too. Might as well replace it since I plan on keeping the truck till it fall apart being it my first and only vehicle. I has many many years and a relatively low amount of miles on it if it is the factory one.


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## SPEEDO (Jun 9, 2003)

on a side note, when was the last time the t-belt was changed?
by the way, it probably is your 02 sensor


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## Deerhurst (Jul 25, 2011)

I am assuming timing belt was 60,000 when the original owner had the truck. i will need to do that again some time in the next 10,000 miles. My aunt did her first t belt change, in a 90s era pathy, last year at 150,000 and boy does it help. ha! 150,000 is too late for even the 2nd t belt in my opinion.


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## SPEEDO (Jun 9, 2003)

cheaper to replace the t-belt before it breaks, than after....


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## Deerhurst (Jul 25, 2011)

so very true. i do need to get on it and change that t belt.


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## Deerhurst (Jul 25, 2011)

i have one more question. how can I test the current O2 sensor. what voltages/resistance in the unit should i be looking for?


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## bascom01 (Feb 22, 2012)

So I'm having the same problem but my truck is a 2wd 93 w/ ka24e... I was getting (not even joking) 35 mpg and now I'm at 18 highway, I have done everything from wires and plugs and fuel filter and air filter and o2 sensor. I even put in a new tranny and clutch and most recently I just rebuild my entire motor.... But nothin fixes my mpg  Wtf gives? Any more ideas? 

Sent from my ADR6400L using AutoGuide.com App


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## TheRepairMan (Jun 30, 2009)

bascom01 said:


> So I'm having the same problem but my truck is a 2wd 93 w/ ka24e... I was getting (not even joking) 35 mpg and now I'm at 18 highway, I have done everything from wires and plugs and fuel filter and air filter and o2 sensor. I even put in a new tranny and clutch and most recently I just rebuild my entire motor.... But nothin fixes my mpg  Wtf gives? Any more ideas?
> 
> Sent from my ADR6400L using AutoGuide.com App


You've done a lot of work, but there's still a lot of things that can affect fuel mileage.

Most recently, like the last year or two, the introduction of higher and higher oxygenated fuels, or alcohol blends, can reduce mileage 10 to 15%. Not much you can do about that other than hunt down some straight gas, fill up, and recheck your mileage again.

Make sure your Odometer is reading accurately. Compare it to a GPS to be exact. Run your gas mileage tests over several full tanks of fuel for a more accurate average. Your test results are only as good as your testing methods.

Stay with me... I'll try to cover all the possibilities affecting fuel mileage here. 

Some of the more common things that can affect mileage are... Winter fuel blends, the weather, a change in driving habits, tires, tire pressures, alignment, brakes dragging, wheel bearings, and/or drive line bearing problems including Differentials, Transmission and Transfer Cases, tight Universal Joints, a bad MAF (Mass Air Flow Sensor), dirty Fuel Injectors, a faulty Fuel Pressure Regulator, CTS (Coolant Temperature Sensor), worn out TPS (Throttle Position Sensor), a bad IAT (Intake Air Temperature Sensor), 02 (Oxygen Sensor), vacuum leaks, a dirty air filter element, or something blocking the intake duct work. 

Others include a weak Ignition Coil, fouled or incorrect Spark Plugs, defective Distributor Cap, Rotor, or Wires, incorrect ignition timing, or advance. Even an EGR Valve (Exhaust Gas Recirculation) staying open all the time, or a stuck open Purge Control Valve in the EVAP (Evaporative Emissions System) can all have an affect on performance making the engine less efficient. 

Some less common things like all the engine electronics circuits, faulty grounds, and wiring that affect the control of the fuel and ignition systems, and the above list doesn't even begin to cover all the mechanical things that can be off just a little inside the engine, even if it's recently rebuilt. Be sure to take into account the mileage on your engine... is it still in the "break-in" period, within its correct oil change period, and which motor oil formulation and weights are you running? All are factors.

Then there's my favorite... ALL OF THE ABOVE!

Yes, you can easily have multiple problems creating the perfect storm in the form of a gas eating monster. On fuel mileage complaints in which there are no other symptoms, most often there's no one single cause that can be nailed down due to so many variables, but you CAN make sure through persistent diagnosis, testing and repair that your vehicle's systems are in tip top condition.

Always start by pulling up any Diagnostic Codes from the ECU first, and proceed based on the results. Then back to the basics.

-R


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## veesix (Jul 18, 2004)

I would consider 17-18-19 mpg for a 4wd v6 Nissan to be just about right. To get 23 to 25 mpg would require divine intervention.

A 2wd vg30i can get 21 or 22.5 mpg, on a perfectly flat highway. But because of tires and stuff, 4wd use more gas.

I think that even the 2.4l gets about 20mpg


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