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Old 08-11-2012
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Strange Fuel Reading: Help? (2000 3.0 Ranger)

Aloha everyone,

I recently purchased a 2000 3.0 Ranger with an automatic transmission. The truck and everything works well and runs out nicely for a car with 140,000 miles. The only strange thing is the gas gauge seems to move back and forth a lot. I filled it up to 3/4 of a tank today, and a mile down the road I hit a light and sat there for a few seconds, and suddenly the gauge dropped to half tank (I freaked out) but then when I put my foot in it and got up to highway speed, it shot back up to 3/4 again. Seems really strange. It would be really nice to know exactly how much gas I have since this thing likes to move back and forth so much. Any suggestions? My natural assumption is that the gas tank sensor is a little off but I'm not sure.

Also, the truck is leaving behind a very tiny leak of oil whenever I park it. I looked underneath it and it looked like it was coming from the drain plug, but i tried tightening it and nothing. How do I go about diagnosing where the trouble spot is?

Any help would be very useful,
-Steven
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Old 08-11-2012
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I'm no help but I will be watching closely. My Ranger's fuel gauge is a little messed up too, it doesn't leave Full until 100 miles, then it is at half a tank by 200 miles. At a quarter of a tank by 250 miles and at 350 by Empty.

Good luck with the leak.
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Old 08-12-2012
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Let me give you a little lesson on how the gas gauge works:

The PCM gives off a regulated 5V signal (with a pull up resistor most likely around 1k ohms) to your fuel sending unit which is essentially a potentiometer that ranges in resistance of around 145 ohms to 22 from full to empty respectively. Your cluster is connected between these two components (pcm and fuel sending unit) and reads the voltage in between these two resistances (pull up resistor and fuel sending unit resistance).

R1=1k pull up resistor
R2=145-22 ohm fuel sending unit
V1=5V regulated voltage
V2=voltage seen by cluster

Using voltage division law/rule:

V2=(R2/(R1+R2))*V1
V2=(R2/(1k+R2))*5
V2 should range between 0.63-0.11 Volts

Now this is assuming a 1k pull up resistor which gives a pretty linear curve. Now I'm thinking that the pull up resistor isn't that high, because that is such a small voltage range to read accurately. Look at the graph below with different values for the pull up resistor (1000, 500, 100, 50). With high value of PUR you get small range but more linearity, with low value you get more range but more exponential output. If our trucks have a low value that would explain the fuel gauge not moving quickly on a full tank and then accelerating the movement as the fuel level gets lower.


Now for the question about smooth movement of the gauge needle. The cluster has whats called a Anti-Slosh module and what this does is acts like a low pass filter or running average filter of the voltage its receiving. It takes voltage measurements over a certain interval and averages them before sending the new voltage to the needle. This gives a more smooth needle movement.

I think there is something wrong with this module in your cluster and its not averaging the voltage signals properly or allowing the voltage signals to be sent straight to the gauge.
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Old 08-13-2012
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That's quite a bit of impressive knowledge there shelton, but I do believe you're on the right track. I watched the gauge more closely today while I drove up and down the mountain and it climbed when i went uphill and dropped when I went down. So it's obviously an issue with the sloshing. At least now I've gotten used to the movement and I know that it reads most accurately when I'm sitting in my driveway with it turned off. The good news is I recorded my mileage today and I'm getting around 25 mpg combined with that 3.0 V6. I'm stoked!
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Old 08-13-2012
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I would try another cluster. A good swap is the White Face Ford Explorer Sport gauges or the 2003 ranger with the silver face gauges. Direct plug and play and those gauges give you tachometers (which is plug and play).

Also any Explorer gauge will work (I know at least 98-01).
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Old 08-13-2012
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Quote:
Originally Posted by sheltonfilms View Post
I would try another cluster. A good swap is the White Face Ford Explorer Sport gauges or the 2003 ranger with the silver face gauges. Direct plug and play and those gauges give you tachometers (which is plug and play).

Also any Explorer gauge will work (I know at least 98-01).
He stated that the issue was noticeable when he was going uphill or downhill. Nothing in the actual cluster would be affected by the vehicles axis. The problem seems to emanate from the gas tank.
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Old 08-14-2012
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If I get the chance to do the gauge cluster I certainly will, I wouldn't mind some nice white gauges to offset my gray interior and black paint. Even if that doesn't solve the fuel gauge issue, I'll need to do something about the other gauges anyway. My engine temp gauge doesn't work at all.
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Old 08-14-2012
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Quote:
Originally Posted by Red_Ak_Ranger View Post
He stated that the issue was noticeable when he was going uphill or downhill. Nothing in the actual cluster would be affected by the vehicles axis. The problem seems to emanate from the gas tank.
This is normal but the change from 3/4 to 1/2 is a big difference and doesn't seem right to me. My gauge will go up 1/8 at the most when facing up a hill.
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