New sparkplugs/air filter = bad mileage

J

jasons

New member
My wife daily drives a 99 4Runner. I replaced the spark plugs with the correct Toyota dual electrode plugs. I also replaced the air-filter with a new Toyota filter. Now her gas mileage seems bad. I have an OBDII scanner so I connected it, and it shows no codes. If the truck was misfiring, wouldn't the OBDII tell me?

The truck drives as I would expect, with no power loss.
 
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I don't know about before, but I just filled up the tank and she used almost 1/4 of a tank in 30 miles. She says it used to stay at the Full mark longer than it is now(as most cars will). When I filled the tank, I zero-d the trip OD so I can see how many miles to the tank.
 
Lexusbstrdchild said:
did you gap the plugs and make sure they were the correct spacing?
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I didn't think you were supposed to gap those dual electrode plugs?!?!

I got some advice at yotatech to reset the ECU. I didn't do that when I changed the plugs. I'm gonna try that tonight.
 
Lexusbstrdchild said:
did you gap the plugs and make sure they were the correct spacing?
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Plugs should be pre-gapped. Stupid question but did you put the wires back on correctly (in the correct order)?
 
tomhaney1 said:
Plugs should be pre-gapped. Stupid question but did you put the wires back on correctly (in the correct order)?
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Yeah, Its pretty hard to screw that up the way they are wired. On the left bank(looking at the engine) I did those one at a time. On the right bank, they can really only go one way since they are correct length. If I did screw that up somehow, I would think the OBDII would catch it.

Also, the truck runs smooth, not missing.
 
jasons said:
Yeah, Its pretty hard to screw that up the way they are wired. On the left bank(looking at the engine) I did those one at a time. On the right bank, they can really only go one way since they are correct length. If I did screw that up somehow, I would think the OBDII would catch it.

Also, the truck runs smooth, not missing.
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It should and you're right it is pretty difficult to mess that up! Maybe you should drive the vehicle for a week and see how things go. Did you also replace the wires? Did you use a different gas type/brand?
 
gapboi210 said:
mine is at 3 quarters usually after 34 miles.
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So lets make this easy...at 17 mpg that is 2 gallons. Multiply that by 4 (2 gal./quarter tank), assuming the gauge is completely accurate, which they are not. That would be something like an 8 gal. tank for a range of 136 miles. Something is seriously wrong if either of these values are accurate. It has a 70 litre (18.49 gallon) fuel tank so you should be getting 314.5 miles per tank, if averaging 17 mpg.
 
i get 210-240 miles per tank, and i have lift and MT's....

stock id get closer to 280-300.
 
Yeah my wife was averaging 15-17, just by a seat of the pants estimate. When I saw the tank go down a quarter in 30 miles, thats like 8 mpg. AND, fuel gauges tend to stay on the fuel mark longer, just because the fuel is above the float in the tank. Her truck is bone stock, with the 16 inch wheels. We just put new Michelins on it as well.


BTW, I reset the ECU last night. Hopefully that fixes it.
 
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My mom has a bone stock '99 limited with an automatic and she sees 270ish and she drives fairly conservative and with mine (auto tranny also) I have a bit of a leadfoot and with my slightly larger and heavier than stock tires I get roughly 240ish a tank.
 
Just filled up today. 295 miles. Dont remember the exact amount of gallons but it worked out to 17.55 MPG. Someone good at algebra can tackle that one.
 
97

I track the mileage on my 97 pretty close and it ranges between 17 and 20.

When I changed plugs and wires this past summer I noticed about a 2 mpg decrease, don
 
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