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LESchwartz
Dodge Dakota
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10/14/2005
12:04:06
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 Subject: Are Gen 3's Really This Hard On Gas?
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I recently traded my '94 Gen 2 (4x4, reg cab, 5.2, AT) for a '99 Gen 3 (4x4, reg cab, 5.2, AT). Both trucks are equipped virtually the same: tires are equivalent, rear end gears seem similar, etc. Both had Gibson exhausts with low restriction cats (installed by me). Both trucks seem to perform identically, with one big exception: The Gen 3 is really hard on fuel! We're talking like 13-14 mpg with the Gen 3, verses 16-17 mpg with the old Gen 2.
The Gen 3 has new plugs and air filter, the plug wires seem almost new (though I haven't replaced them myself), no diagnostic codes, and the Gen 3 seems in otherwise excellent shape.
So are Gen 3's really this hard on gas, or do you folks think something else might be wrong?
thanks in advance,
Larry
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daddio
Dodge Dakota
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10/14/2005
12:06:31
|  RE: Are Gen 3's Really This Hard On Gas?
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one reason, Gen III's are heavier than Gen II's.
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Mark
Forum Moderator
10/14/2005
13:32:52
| RE: Are Gen 3's Really This Hard On Gas?
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I get 15-17mpg with my gen 2 as well. I dont have 4wd.
-Mark Hryckiewicz
1993 Sport RC SB 5.2L Auto
Mark.DodgeDakotas.com-Mark Hryckiewicz
1993 Sport RC SB 5.2L Auto
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cuzindoug
GenIII
10/14/2005
13:45:41
| RE: Are Gen 3's Really This Hard On Gas?
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19-21 City and 24-26 Hwy. (3.9 RC 2wd manual)
If it ain't broke, fix it til it is.
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Craig
Dodge Dakota
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10/14/2005
14:18:14
| RE: Are Gen 3's Really This Hard On Gas?
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18/24 with a 3.7 manual 4x4. The Gen III is a good deal heavier then the Gen II, but of course I have the new 3.7 which is pretty easy on gas.
If you think those fuel econemy numbers are excessively low, you might look into the O2 sensors- one ore more could be getting a little lazy and might bring your fuel econemy up a few points. A proper scan tool (like the Snap-On scanner) would tell if one O2 sensor is switching slower than the others. A lazy O2 sensor doesn't necesarily set a code.
Otherwise, you started in the right place with plugs, air filter, etc. Try all the simple and cheap stuff first.
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Mark
Forum Moderator
10/14/2005
14:23:12
| RE: Are Gen 3's Really This Hard On Gas?
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Hmmm o2 sensor.. I still have my original from 1993 with 140k miles on it.
-Mark Hryckiewicz
1993 Sport RC SB 5.2L Auto
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LESchwartz
Dodge Dakota
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10/14/2005
16:19:51
| RE: Are Gen 3's Really This Hard On Gas?
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I know that the Gen 3's are somewhat heavier. But my Gen 2 4x4 came in at 4200 lbs. I have another Gen 3 as well (v6, 4x2, reg cab) that weights in at about 3800 lbs. So I wouldn't imaging that my Gen 3 4x4 would weigh in significantly more . . . at least I wouldn't expect the added weight to be entirely responsible for a 20% mileage reduction.
Mark mentions an O2 sensor. If I had a bad 02 sensor, wouldn't I typically see a diagnostic code?
Larry
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LESchwartz
Dodge Dakota
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10/14/2005
16:25:51
| RE: Are Gen 3's Really This Hard On Gas?
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Err, sorry. That was Craig (and not Mark) that mentioned the O2 senser.
Larry
PS: My '94 looked almost identical to Marks '93 ;^)
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daddio
Dodge Dakota
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10/14/2005
16:39:02
| RE: Are Gen 3's Really This Hard On Gas?
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not necessarily. if it's "lazy"/ reacts very slow, it would not throw a code. i've had this problem before, just not on my dak.
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LESchwartz
Dodge Dakota
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10/14/2005
16:59:46
| RE: Are Gen 3's Really This Hard On Gas?
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Hmmm . . . I wonder if I didn't mess up the O2 sensor when I replaced the cat?
I have SuperChips tuner I've been using to read the codes (but, I don't want to try tuning until I'm sure everything is OK with the vehicle) . . . is there any easy way to test the sensor?
Larry
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daddio
Dodge Dakota
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10/14/2005
17:10:54
| RE: Are Gen 3's Really This Hard On Gas?
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it could be the other way around. if you changed the cat because it was bad it could ahve been the O2 sensor that destroyed the cat by telling the pcm to run richer than it should.
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N56629
Dodge Dakota
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10/14/2005
17:24:26
| RE: Are Gen 3's Really This Hard On Gas?
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Larry, I get about 18 with mine.
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LESchwartz
Dodge Dakota
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10/14/2005
17:42:52
| RE: Are Gen 3's Really This Hard On Gas?
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daddio,
I changed out the cat because the muffler on the Gibson exhaust I bought is longer than stock. To make up for it I went with a shorter aftermarket hi-flow cat.
Larry
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95V6
GenI
10/15/2005
00:57:06
| RE: Are Gen 3's Really This Hard On Gas?
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I'm doing 14mpg in the city on a good day with 4wd ext cab. But I had to change cat cause it was bad. I'm gonna check daddio tip about O2.
95 SLT 3.9L V6, K&N, Gibson exh, JBA hdrs, JET stage II, MSD 6A and more..
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Craig
Dodge Dakota
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10/15/2005
02:48:09
| RE: Are Gen 3's Really This Hard On Gas?
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I didn't mean to cause any controversy. I have never seen this happen in a Dakota, but being that our shop worked on every make and model, that's not all that surprising.
I mentioned it as a guess as a possible cause. It doesn't mean that what I say is the case. But a dip in fuel mileage can sometimes indicate on 02 sensor begining to switch a little slow. This does not set a diagnostic code, or make your car fail its emissions test. It can make a little dip in your fuel mileage though.
EVENTUALLY, it will set a diagnostic code, once the sensor goes "bad enough" if that makes sense.
There are, as in most situations, many variables though. I'm not saying it IS an O2 sensor though.
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Adam
Dodge Dakota
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10/15/2005
13:33:15
| RE: Are Gen 3's Really This Hard On Gas?
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My '00 4x4 CC weighs in at 4500 with absolutely nothing in it. I was getting 18-20 mpg when I first got it and now things decide to crap out on me I'm getting 15. All new plugs, wires, cap & rotor, just replaced o2 sensor and decided to have a look at the plenum gasket.
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LESchwartz
Dodge Dakota
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10/15/2005
23:54:29
| RE: Are Gen 3's Really This Hard On Gas?
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OK, last night I went ahead and changed out the air filter, plugs, plug wires, cap and roter. (Second time in a couple thousand miles for the plugs and air filter.) I had some driving around town to do today, and got a wopping 13.6 mpg on half tank of fuel . . . 8.8 gal for 110 miles.
So somebody is gonna have to explain to me how to test the O2 sensors . . . ;^)
Larry
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johnny5
GenIII
10/16/2005
07:24:13
|  RE: Are Gen 3's Really This Hard On Gas?
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I had a 2000 R/T CC. Mileage sucked, I tried everything including the O2 sensor. I could never get it above 12.5mpg. I eventually sold it and bought an S10 Extreme for the better mileage. Worst mistake I ever made. The mileage was the ONLY thing better! Those trucks are crap. I dumped it after 3 dreadful months. My 2001 2wd 4.7 quad cab gets a little better mileage at 14.5 but the motor is smaller, tires are narrower and gears are higher. I hear the 5.9 mopar pcm is supposed to give you better mileage. Is this true?
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N56629
Dodge Dakota
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10/16/2005
08:29:07
| RE: Are Gen 3's Really This Hard On Gas?
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A 5.9 PCM in a 4.7? I don't think so. Could it be that you mean putting the 5.9 PCM in a 5.2? Some people have successfully gone either direction but I've never hear anyone bragging about increased or decreased gas milage.
Larry, why don't you try your Superchips on that truck? What is your v6 getting with the SC and modified tb?
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johnny5
GenIII
10/16/2005
08:47:33
| RE: Are Gen 3's Really This Hard On Gas?
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No, that's not what I meant. Does a 5.9 MP pcm get better mileage in an R/T (with a 5.9 motor), not a 4.7...
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LESchwartz
Dodge Dakota
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10/16/2005
12:39:01
| RE: Are Gen 3's Really This Hard On Gas?
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N56629,
My other truck (3.9L, 5spd, 2wd, CAI, and one of your TB's) always gets 17-18 -- and I've never "baby it" trying to get better mileage.
Based on past experiance with my old '94, I would expect something more like 15-16 mpg. I'm hesitant to try the SC tuning on this truck until I'm sure that it's running correctly.
Larry
PS: When I bought the '99, I considered going with a 5.9. But reports were that 5.9's were "super hard on fuel".
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