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Nicegy525
Dodge Dakota
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6/25/2007
17:17:55
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 Subject: Poor Gas Mileage
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Message:
1990 Dakota 3.9L V6 When I bought this I did a full tune up (plugs, wires, cap & rotor, air and fuel filters) And I was getting 22 hwy 18 city. Since then it has gone down to 17 hwy and 16 city. It has only been 10,000 miles since the tune up and I have changed the air filter and oil regularly. I have adjusted the timing, replaced the smog pump, replaced the catylitic converter, cleaned the throttle body and run nothing but Chevron 89 octane gas and am running out of ideas as to why the MPG has decreased. Any tips would be appreciated!
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why would you
Dodge Dakota
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6/25/2007
20:07:28
|  RE: Poor Gas Mileage
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Message:
why would you touch the timing and # 2 run 87 oct...it wont ping.....if its not broke dont fix it.........
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Nicegy525
Dodge Dakota
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6/25/2007
20:14:05
| RE: Poor Gas Mileage
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Message:
The distributor was loose and the timing was slightly retarded. That fixed the slight roughness in the idle as well. I am a firm believer in running good gas in all of my vehicles. I have tried 87 octane and the truck just doesnt like it.
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dakota49
Dodge Dakota
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6/25/2007
23:36:31
| RE: Poor Gas Mileage
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Message:
I have an 88 3.9 4X4 5 speed
I was getting good fuel mileage then mine went south as well, it turned out to be the fuel pressure regulator. Mine has the reg. on the back side of the throttle body. Mine is the 2 barrel type of fuel injection. I don't know if the 90 would be the same or not, if so could be it. Check your plugs and see if they are black.
I did a lot of changing parts before I found out what was wrong, didn't get any trouble codes either.
Good luck
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nicegy525
Dodge Dakota
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6/26/2007
00:05:06
| RE: Poor Gas Mileage
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Message:
Thanks! I will check it out. My 3.9L has the Throttle body injection. not sure if its the same as the '88.
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J and J Auto
GenII
6/26/2007
00:15:03
| RE: Poor Gas Mileage
IP: Logged
Message:
The throttle body injection is controled basicly
the same as the multiport
throttle position sensor
IAT air temp located on throttle body
AND The o2 sensor is also the most important
sensor on this system replace it
Also engine temp sensor
Any of these sensors can be off a little as long
as the o2 is working properly the air fuel ratio
will be ok
ngk.com for the same as org NGK NTK sensor for
half the price the dealer wants
Larry
J&J Auto
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