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Chieftitan
Dodge Dakota
JOIN HERE
6/01/2004
18:16:03
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 Subject: Gas Mileage on my 3.9
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Message:
Hey out there, I was getting 20 MPG with my 2000 3.9 Sport, and all of a sudden I am getting 10 MPG? What the heck is going on? I put an analizer on it, and I get NO codes... I get nothing other than normal ops. I have noticed a strong scent of gas in the exhaust when I start it, but that's it! Performance is good, and no other symptoms except MPG, and smell of gas in the morning/cold start-up.
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GB2000
GenIII
6/01/2004
20:28:41
|  RE: Gas Mileage on my 3.9
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Message:
Most definitely your O2 sensor(s)... they are known to go out around 60k miles (though some will go MUCH longer).
Josh
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Bob Lincoln
Dodge Dakota
JOIN HERE
6/02/2004
08:24:00
| RE: Gas Mileage on my 3.9
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Message:
Really????? Well, no, they don't often fail that early; they are still under federal warranty if they do; and there are MANY other possible causes of his problem - MAP sensor, EGR, a fuel leak...approach it methodically instead of jumping to conclusions.
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93Dak
Dodge Dakota
JOIN HERE
6/02/2004
11:36:01
| RE: Gas Mileage on my 3.9
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Message:
If you are smelling gas, I would think that you might have a fuel leak. In my 93, the fuel lines were rubbing on the frame, and rubber through the galvanized coating and then rusted and began to leak. I smelled gas quite a bit, and my gas mileage went down. Performance was still good.
If I were you, I'd carefully inspect your rubber fuel lines. (Remember that the lines may only leak when the fuel pressure is high.)
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J and J Auto
GenII
6/02/2004
11:51:17
| RE: Gas Mileage on my 3.9
IP: Logged
Message:
On the 99 or any 96 or newer obd 2 system the pre
cat or upstream o2 sensors do fail sooner and more
often than the obd 1 systems
Scan live data and watch it warm in closed loop
should change from aprox .1 to .9 volts and keep
changing constantly
IAT or engine temp reading cold will also richen
the mixture, a lazy map will usualy cause ping
if it reacts slow, if it only reads a small change
like between 17 and 14 never droping lower or
going higher it will display symptoms like only
running good at a certian rpm all other will run
bad
On the 99 it would most likly be the o2 or a bad
vac leak
Larry
J&J Auto
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Chieftitan
Dodge Dakota
JOIN HERE
6/02/2004
14:34:23
| RE: Gas Mileage on my 3.9
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Message:
I am looking at all the above suggestions... I analized again this AM, and the 02 was acting normaly while in open and closed loop, and we could smell the gas at the exhaust until the engine was warmed up real nice. I replaced the plug wires today, and I did find one that read open to 88.1 K ohms. I haven't driven it yet, but will be going to a friends to check the fuel pressure. Thanks for all your ideas, and keep them coming if you have any others as people like me come to this site for ideas/support all the time!
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Bob Lincoln
Dodge Dakota
JOIN HERE
6/02/2004
16:04:36
| RE: Gas Mileage on my 3.9
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Message:
I hope that's a typo. Ignition wires should be 3K to 7K ohms, maximum of 15K (although that's so bad, you'd have to replace them before that). If you're getting 88K ohms, it would be amazing if the truck ran at all.
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Chieftitan
Dodge Dakota
JOIN HERE
6/02/2004
20:54:03
| RE: Gas Mileage on my 3.9
IP: Logged
Message:
Not a typo. You can't imagine how many times I checked that one wire!
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