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Alan
Dodge Dakota
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7/07/2009
17:16:10
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 Subject: Bad Gas milage after removing cat
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Hey guys I have an '02 4.7L Dakota and I just had the cat removed and ran true duals out of the motor with 24'' glass packs. It runs great but I'm only getting like 8mpg and it runs really rich and blows a little black smoke when it idles. I only had one cat with two o2 sensors. Is there anything I can do to help the mileage.
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daddio
Dodge Dakota
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7/07/2009
17:57:26
|  RE: Bad Gas milage after removing cat
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"Is there anything I can do to help the mileage."
yes, reinstall the O2 sensors back into the exhaust piping. It will help.
I bet your oil smells like gasoline now too. You might want to change it also.
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No kidding
Dodge Dakota
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7/07/2009
20:39:53
| RE: Bad Gas milage after removing cat
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"Bad Gas milage after removing cat"
Mileage!
and this has been talked about
Removing the cat you lost back pressure!
You dumb azz back woods Hill Billies never learn
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Kowalski
GenIII
7/08/2009
07:56:53
| RE: Bad Gas milage after removing cat
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Ah, another common misconception. Engines don't require back pressure to run right, what is needed is enough exhaust velocity for decent scavaging at the exhaust valves. That is why low rpm power can go away when people get carried away with exhaust mods. I guess the dumb azz hillbillies never will learn, because this has been discussed before ;)
Alan, what size pipes did you run ? Daddio's suggestion could help, and might be better if you put the cat back on. But if you ran dual pipes bigger than 2 1/4" on your 4.7, you killed the exhaust scavaging. Flogging it to try to get low rpm power could be what is killing your gas milage.
Lead, follow, or get out of the way
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Alan
Dodge Dakota
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7/08/2009
15:41:33
| RE: Bad Gas milage after removing cat
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Im running 2 1/4" but it was already running rich when I got it I just want to know if there are any tune ups I can do to make run less rich.
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daddio
Dodge Dakota
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7/08/2009
15:51:26
| RE: Bad Gas milage after removing cat
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The PCM relies on the O2 sensors, as one measure, to adjust the fuel mixture. If they are not there in the exhaust, or malfunctioning there is nothing else you can do but replace them. Especially the one that is before the catcon.
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Alan
Dodge Dakota
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7/08/2009
16:15:38
| RE: Bad Gas milage after removing cat
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Ok so your saying if I put the o2 censors in the pipe itself without putting the cat back on the computer will adjust the fuel mixture correctly or some what right. Is it still going to run ok or is it gonna throw codes.
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daddio
Dodge Dakota
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7/08/2009
16:22:15
| RE: Bad Gas milage after removing cat
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"Is it still going to run ok"
If you call spewing black soot out of the exhaust running ok then NO. Yes, it will run much better.
"or is it gonna throw codes"?
Your CEL must be lit up like a christmas tree now. And it will still throw a code even if you put the sensors in the exhaust. The PCM needs to see a difference in readings between the front and rear O2's or it will throw a code.
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daddio
Dodge Dakota
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7/08/2009
16:27:24
| RE: Bad Gas milage after removing cat
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Something I just noticed on your original post that doesn't seem right.
"I have an '02 4.7L Dakota"
"I only had one cat with two o2 sensors"
I could be wrong but, I thought that the '02 4.7's had (2)cats, one right after each exhaust manifold and then the third cat? Maybe someone with the same year and engine can verify this.
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Alan
Dodge Dakota
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7/08/2009
16:39:27
| RE: Bad Gas milage after removing cat
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Yes I did only have one converter I looked before I cut it off and only my check engine light is on but thats normal. How come the Chevrolet doesn't run really rich my buddy has an 08 chevy with straits and it doesnt run rich at all. But anyway thanks for the help bro. I gotta put a Performance Accessories lift on it this weekend gonna be a back breaker:)
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daddio
Dodge Dakota
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7/08/2009
16:52:14
| RE: Bad Gas milage after removing cat
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"and only my check engine light is on but thats normal.How come the Chevrolet doesn't run really rich my buddy has an 08 chevy with straits and it doesnt run rich at all."
I give up. Anyone else?
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LOL
Dodge Dakota
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7/08/2009
17:32:49
| RE: Bad Gas milage after removing cat
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"my check engine light is on but thats normal"
yeah
hell they put them there to help light the dash
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Alan
Dodge Dakota
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7/08/2009
18:06:11
| RE: Bad Gas milage after removing cat
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I meant its normal if you remove your o2 sensors
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my turn
Dodge Dakota
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7/08/2009
18:42:46
| RE: Bad Gas milage after removing cat
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Daddio...let me try..
I suspect you bought the truck used. I have the same year and engine. I have 4 o2 sensors on my stock setup which has 3 cats. Your truck was probably modified before you got it. The two cats connected to the exhaust manifold have sensors on the input and output of each one. The third cat does not have sensors. You gotta have good signals from 2 sensors at the cat inputs(sensor 1 bank 1 and sensor 1 bank 2) in order to get a good fuel mixture. The two sensors before the cat are used to control fuel ratio. The two sensors after the cat are used to determine cat converter efficiency but should not affect engine performance. Install the sensors and be done!!! I can't tell you about your buddies chevy, you came to this site about your Dodge!!!
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Kowalski
GenIII
7/09/2009
07:14:01
| RE: Bad Gas milage after removing cat
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Some years came with differing cat set ups depending on the emissions package. For example, I can say for sure that '00 was like that for the 4.7. A single cat with 2 sensors for the federal emissions. And 3 cats for the cali emissions, now adopted by many other states. That came with 4 sensors; 2 on each forward cat.
If the truck was modified, from a 3 cat set up, you should be able to find where the sensor wiring was lengthened on one side, and a sim added on the other - otherwise it would have been throwing a mil code. I'll be surprised if that is the case.
Alan, how do you know you were running rich before, did you read the plugs ? Usually it is better to correct any problems before modding.
Lead, follow, or get out of the way
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Alan
Dodge Dakota
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7/11/2009
21:34:57
| RE: Bad Gas milage after removing cat
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Tap and died the sensor back into the pipe runs fine now thanks for the info.
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mario
Dodge Dakota
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7/12/2009
03:06:27
| RE: Bad Gas milage after removing cat
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i removed my cat and welded a bung for the o2 in the replacement pipe and my truck doesnt throw any codes...
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