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'98 Grand suddenly minus 2 MPG?


 
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cybarracuda
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Joined: 24 Feb 2005

PostPosted: Thu Feb 24, 2005 10:40 pm    Post subject: '98 Grand suddenly minus 2 MPG? Reply with quote

Any chance that one of you Jeep experts can tell me what might lead to a sudden decrease in mileage in my GC? It's a '98 4.0L 4x4 with Selectrac and has 94,000 miles on 'er. I did recently notice some seepage of oil around the head gasket. Vacuum is a steady 15-16". Tuned up with new plugs, cap, rotor, and wires within past 10,000 miles. I changed the air filter last week. I haven't noticed a big decrease in power or anything (it's as powerless as always), just the sudden drop in mileage. Would the 02 sensors go bad that suddenly? I know that on my other cars, the 02 sensor is part of scheduled maintenance. For some reason, it's not on the Jeep?
I did attach an OBDII tool to the car and nothing came up, although my ABS light just came on, apparently to stay. Thanks for any help.
'cuda
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ThePhantum
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Joined: 23 Jan 2004
Location: I knew it...I'm surrounded by Assholes!

PostPosted: Fri Feb 25, 2005 12:12 am    Post subject: Reply with quote

Another thing you could try (if you have not already) is disconnecting the battery for 30 minutes or so. This will reset the computer and over the next 50 key cycles it will "learn" the engine again. It's helped my MPG in the past.

Having said that, I've been watching the MPG on the 4.0 in my XJ go into the toilet as well. I strongly suspect it's the O2 sensors as I'm rolling up on 87K and they are the originals. I have new ones sitting on a shelf, just gotta find the time to put them in.

HTH
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swamp boy
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Joined: 01 Jan 2004
Location: New Orleans LA.

PostPosted: Fri Feb 25, 2005 6:12 am    Post subject: Reply with quote

Ditto..
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cybarracuda
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Joined: 24 Feb 2005

PostPosted: Fri Feb 25, 2005 6:18 am    Post subject: Thanks for your input, phantom Reply with quote

As I said in my original post, my other cars ('87 BMW 535is and '99 528i) both require periodic change of the 02 sensors. If the sensor(s) were bad, and the mileage dropped, I suppose that this might be due to a richer mixture, triggered by the computer's leaving 02 input out of the loop. I'll try out the battery disconnect today and see how it goes. If that doesn't get me back around 17mph overall, I'll order the sensors. Thanks for your advice.
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1fox2go
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Joined: 01 Dec 2004
Location: Fishersville, Virginia

PostPosted: Fri Feb 25, 2005 7:21 pm    Post subject: Reply with quote

id checkem and your grand is powerless? mines got ooomph and shes stock Mr. Green MOPOWER
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cybarracuda
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Joined: 24 Feb 2005

PostPosted: Wed Mar 02, 2005 6:12 pm    Post subject: Reply with quote

I believe that the reason for my Grand being relatively powerless, is because of the highway gears that are in it. When you stomp in the gas there is power there, just not earth-shattering. I'm sure that it's from the gears. When I bought the vehicle, I specifically asked for 3.23's(?), or so. When I went to pick up the car it was pouring rain and I didn't crawl under the car to verify. They ended up being under 3.00 gears. I can't remember whether they were 2.90 or what. Needless to say, I took the car anyway. Not a mistake, but I'd have preferred the shorter gears.
'cuda
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laxwarriors21
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Joined: 02 Feb 2005

PostPosted: Sun Mar 06, 2005 12:10 pm    Post subject: Reply with quote

Couldnt it be a clogged catalytic converter maybe?
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