Gas mileage plummeted after fill up

atlantatjowner

atlantatjowner

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Jun 25, 2018
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43
Location
Atlanta
2000 TJ Sport with a new reman about 5000 miles ago. Been getting the normal 200 miles per tank. In fact the very last tank got exactly 200 miles out of it. I filled it up and have been driving the past 2 days and gas gauge is between half and three quarters after only 32 miles. I usually gauge around 50 miles per quarter of tank. O2 sensors were changed with NTK about 6 months ago. air filter is clean, new IAC and Map sensor. Could this just be a bad tank of gas?
 
Doesn't matter what the gas gauge is at.

You say you usually get around 200 miles a tank. How many miles did you get on this tank?
 
Chris said:
Doesn't matter what the gas gauge is at.

You say you usually get around 200 miles a tank. How many miles did you get on this tank?
Click to expand...

I have not gotten through the tank yet, I have just seen it going down super fast. 32 miles so far and its down in-between a half and three quarters already. I am Just going to keep driving till it gets down to E and see how many gallons it fills back up with. Definitely never had this issue before.
 
I'm only saying this because those gauges aren't necessarily the most accurate.

My TJ would rear completely empty (literally) on the needle and still have 7 gallons left in it.

I would wait until you actually get down to 1-2 gallons before assuming anything is wrong. My experience with TJs is that the gas gauge (just like the oil pressure gauge) is wonky at best.
 
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Are you using the same station as you normally do? Different gas stations have different pump rates, which can cause the nozzle to click off earlier or later.

On stations that normally fill slow, or if you manually slow the nozzle for the last few gallons, you can usually get a few more gallons in than just letting the pump run at full speed until it clicks off.

The TJ fill vent and rollover valve isn't of the best design, and can prematurely shut or flood with high fill rates, resulting in the pump shutting off earlier than normal. In some cases, this even results in gas splashing out of the filler onto the ground before the pump can shut off.

If you fill at a high fill rate station, try adding fuel at a much slower rate after it clicks off. You can usually get a few more gallons in before it completely fills.
 
Miles per tank is pretty useless information. You really need to calculate mileage fill to fill. Like @Steel City 06 say, it could have clicked off early. The TJ gauge is really good most people just don't take the time to learn how to read it. Take a close look at this picture, I hope it helps. Especially where 0% and 25% are. That's what most people miss.

view.jpg
 
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Just popped the hood and noticed my PCV elbow and grommet appear to be leaking which it wasn't before. That vacuum leak could be the cause of the gas mileage right?
 
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If your engine rpms are normal there's no vacuum leak. Wait until you refill your tank and then do the math on miles driven divided by the number of gallons it took to refill it. That's the only accurate way to know the true mpg since the gauge is notorious for being inaccurate. Especially as it ages.
 
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idle RPM is normal but I have noticed from time to time since the new engine that when I push in the clutch the engine idle will stick for a few seconds or sometime up until stop around 2000rpm but its intermittent. The throttle body and everything has been removed and cleaned very well and still does it sometimes
 
So I ran through that last tank and only got 155 miles out of it. I filled up and was able to add the normal almost 16 gallons in it so the gauge was correct. I changed both PCV Elbows and grommets as well as the PCV hose (it was crimped) that goes into the intake. I also went and changed out the air filter because it was about time. Just loaded some stuff up to take to someone up in the mountains. it's about 55 miles each way. Just got back after 110 miles and I am only at half a tank now.
 
Well finished the tank at 216 miles which is more then I was getting before the weird fluctuation. Could a leaky PCV and crimped PCV hose really cause that big of a discrepancy?
 
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