post #1 of Old 12-18-2007, 04:41 PM Thread Starter
Cobra Jeep
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1993 YJ Wrangler 
 
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New fuel pump = bad gas mileage?

93 YJ 4.0L. My fuel pump went out the week after thanksgiving. I replaced it with a new pump and all seems good. Except for the fact that my gas mileage has droped big time. Before, I was getting 18-20MPG, now I cant get any better than 15-16. I dont get it? The fuel pump is the only thing that I changed (except filter) How can a new pump give me worse mileage? I havent noticed any change in power, no more or no less. Its not really cold down here yet, so I haveing been letting it idle in the AM to warm up. So its not that.

Any ideas??

The old pump was the factory one, made by bosh. The new pump looked just a little diffrent and was made by carter. But no one had a bosh pump, only the carter.




'93 YJ 4.0L, AX-15, NP-231HD/SYE, 8.8in rear, OME 2.5 lift, home made front hub conversion, hydroboost. Warn M10000 winch. Currently building a stroker.

'79 Cherokee Chief, 401 MPFI fuel injection, T-18/D-20 and hydroboost. Otherwise stock.
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post #2 of Old 12-18-2007, 05:29 PM
pat8942
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The only reason the pump would cause poor MPG is if it is not keeping up pressure/Volume wise.
Before you condem the pump check the other obvious things.
It might be something else that crapped out right after you changed the pump.
Just my thoughts.
Quote:
Originally Posted by Cobra Jeep
93 YJ 4.0L. My fuel pump went out the week after thanksgiving. I replaced it with a new pump and all seems good. Except for the fact that my gas mileage has droped big time. Before, I was getting 18-20MPG, now I cant get any better than 15-16. I dont get it? The fuel pump is the only thing that I changed (except filter) How can a new pump give me worse mileage? I havent noticed any change in power, no more or no less. Its not really cold down here yet, so I haveing been letting it idle in the AM to warm up. So its not that.

Any ideas??

The old pump was the factory one, made by bosh. The new pump looked just a little diffrent and was made by carter. But no one had a bosh pump, only the carter.

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post #3 of Old 12-18-2007, 05:32 PM
pat8942
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If yuo were getting 18-20 you are probably the only person who has ever gotten that kind of MPG in a YJ actually 15-18 is closer to real good.

Quote:
Originally Posted by pat8942
The only reason the pump would cause poor MPG is if it is not keeping up pressure/Volume wise.
Before you condem the pump check the other obvious things.
It might be something else that crapped out right after you changed the pump.
Just my thoughts.
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post #4 of Old 12-19-2007, 03:49 PM Thread Starter
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I replaced the hoses that run from the tank to the frame with new ones. About $60 worth. High pressure hose is not cheap! But that about all I did. I picked up a large bottle of fuel injector cleaner, figured it couldnt hurt. Tomorrow I will check the fuel pressure, make sure its still up to par.

'93 YJ 4.0L, AX-15, NP-231HD/SYE, 8.8in rear, OME 2.5 lift, home made front hub conversion, hydroboost. Warn M10000 winch. Currently building a stroker.

'79 Cherokee Chief, 401 MPFI fuel injection, T-18/D-20 and hydroboost. Otherwise stock.
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post #5 of Old 02-14-2015, 04:54 PM
dign
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lost gas mileage with new fuel pump..

The same thing happened to me. I've had a 91 Cherokee 4.0 for 6 years and always got 20 mpg. I changed my fuel pump and gas filter and now get 13 1/2 mpg. Everything works great, runs great, no leaks just big time loss of mpg. I also have a 98 Cherokee 4.0 that gets 20 mpg, I sure hope the fuel pump never needs replacing on that one.. ???
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