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Old 07-20-2011, 02:30 PM   #15
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Hello Arnold, 3 speed trans, 4.88 or 5.13 rear axle gear= poor fuel mileage, not much you can do about it without guite a bit of $$$, and then you would do good to get 1-2mpg better. I had an 89 34' with a 454 custom ignition system, headers, free flowing exaust. pulling a 20' trailer, never saw the north side of 5 mpg. Sold it quickly.
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Old 07-20-2011, 02:35 PM   #16
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At ths period of time GM was using a plastic float. As the floats aged, they became saturated in fuel. This caused them to sink in the bowl and run very rich, We rebuilt the carb. and used new floats. Most of the time that cured the problem.
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Old 07-20-2011, 02:38 PM   #17
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Something has got to be wrong. I have a carbed 454 in my 95 Winnebago Brave and we just got back from a 2700 mile trip. I ran the Onan most of the time driving and drove between 60 and 65. For the whole trip, idling time, city traffic, the whole kit and kaboodle, we got just over 8 mpg. I wanted to find out what a real average was and not just a tank full. See if the exhaust smells like gas. If you are driving mostly in big hills and mountians, that may explain it.
If you have a 95, you have a trottle body, not a carb.
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Old 07-20-2011, 05:17 PM   #18
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Yup, you're right. My bad.
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Old 07-20-2011, 05:49 PM   #19
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Originally Posted by ga traveler
If you have a 95, you have a trottle body, not a carb.
Another thing to think about besides your throttle body is temperature. High temps cause fuel to turn to vapor before it get through the throttle body into the engine to burn.
On our trip around Colorado last July my 94 454 was acting funny, poor mileage, etc.. I spoke with 3 mobile mechanics and 2 shops in Colorado Springs while visiting family and replacing sway bar bushings(easy job). I thought it was a tranny issue. All of the the shops told me don't waste your money on a known issue ( nice to get honest folks not out to take the cash)

I said what issue? Response was replace fuel filter and find away to cool the motor- another fan, increase airflow through radiator and around headers. GM routed the fuel lines too close to heat sources under the rig and especially as the line comes to the TBI unit, that causes fuel to boil or vaporize prior to ignition resulting in power and fuel economy loss.

Did change electric fan to run on command and added vent lines to bring air near the headers and fuel intake, seemed to help.
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Old 07-21-2011, 11:51 AM   #20
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Have you checked you MPG without running the generator. I know my generator uses around .5 gallon a hour under a light load. The generator could greatly affect your mileage. My 454 gets 8-9 MPG.
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Old 07-21-2011, 06:19 PM   #21
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Have you checked you MPG without running the generator. I know my generator uses around .5 gallon a hour under a light load. The generator could greatly affect your mileage. My 454 gets 8-9 MPG.
Have you tried running through 98 degree heat without your roof air on? I don't care if it uses 2 gal an hour.... We couldn't get the MoHo under 84 today with the roof air and dash air on. We averaged 7.1 mpg....
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Old 07-22-2011, 12:29 AM   #22
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OK HERE IS THE UPDATE.
After much reading on this site and others and speaking with my mechanic this week we went ahead and had a tune-up today. When speaking with the mechanic (who has a large toyhauler) he was shocked at my mileage. He did it today and boy what a difference driving home. More power, less peddle and climbed the 2 hills coming home with ease. He said I should get between 8 to 10 and have no problem on my trip over the Cascade Mtns.

The nice thing about him doing this was we found that the oil sending unit had blown off and was spitting oil on the engine. That would explain the smell and minor smoke. 2 birds with 1 stone.

Can't wait to leave on Saturday. Again thanks to all who gave me insite to the issue.

Arnold
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Old 07-22-2011, 08:54 AM   #23
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Glad to hear it was a simple solution.
Let us all know if your mileage has improved.
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Old 07-22-2011, 09:39 AM   #24
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8 to 10 would be nice.

My last trip over Snoqualmie pass was Gig Harbor to Sunnyside. I averaged 6.7 MPG. Mine is a 37' with carbed 454. It is freshly tuned but still have the OEM equipment.

45mph on the pass, 60 everywhere else.
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Old 07-22-2011, 02:06 PM   #25
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This is what i did to my old 454 carbed engine; advanced the timming 10 degrees added a water injector that I could turn on when the old girl would start pinging; got 8 to 9 MPG out of her (32 foot southwind motorhome) pulling a pickup truck, drove it 152,000 miles; was running like a top when I sold her. Never drove over 55 MPH
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Old 07-26-2011, 10:56 AM   #26
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Go to autozone or Advance and get an Edelbrook carb. Rejet it adequately and you will get better mileage and you will be able to go uphill faster.I tried it and it works..Yvon
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Old 07-26-2011, 04:32 PM   #27
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I had an 84 pathfinder 36 ft 454w/headers.
i consistiently got 10 mpg. i did drive less than 50-55 and kept rpms at about 2000 rpm, I accelerated very slow from stops,no passing etc.
Around town it was 5-6 mpg as i recall

BTW my 01 rex (pic on the left)w/ v10 gets 10-11 driven same way
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Old 08-03-2011, 11:24 PM   #28
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I have a 89 Executive 34' with Cummins diesel and Allison Transmission and Gear Vendor. There have been at least 7 Gear Vendor replacements on it that I know of. One replaced when I bought it used six years ago and that one lasted 10K miles until it failed this year. So to avoid wasting money I removed the GV and had the differential changed from 4.88 to 3.73 which gives me the same cruising speed and RPM as the GV did without no concern of a failure again. Hope this helps you.
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