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Username Post: Fuel Pump Changed - now bad gas mileage        (Topic#178138)
Posts: 56

Reg: 06-19-03
12-28-07 12:42 PM - Post#1328848    


Had my fuel pump replaced on my '00 Burb, which included a replacement of the fuel filter. Thankfully, I now don't have to deal with the messed up gas needle, but I did run into a new problem.

The part was an AC Delco and it cost $700 total for the part/labor.

I used to get 430 miles per tank before I had the pump/filter changed. I now get 360. Nothing has changed in my driving conditions, car runs perfectly, just having a hard time understanding where my 20% loss is coming from.

So either there is a problem, or else my mileage was incorrect.. I checked around the tank, no leaks, perfect start up every time.

Any ideas?

LMC Trucks
Posts: 35

Reg: 12-05-07
01-02-08 11:15 AM - Post#1332845    
    In response to dx3

Are you going by the gas gage? I am willing to bet you are now filling up when the gas gage shows empty, when before you were using the trip meter.

You probably have the same problem that I have, since replacing my pump assembly. The gas gage works, but not accurately. As a matter of fact, mine is far more off than yours is. When it is time for me to fill up, the gas gage is indicating half a tank. I still use the trip meter.

Senior Member
Posts: 929

Loc: Lawrence, KS GO JAYHAWKS
Reg: 11-01-03
01-06-08 01:10 PM - Post#1336394    
    In response to BrokeDirtyBlazer

Another possable: New pump with good pressure acting on old fuelpressure regulator blows diaphram and causes excess fuel to go through the system. check the regulator.

If you don't like your job, don't go on strike. Just go in every day and do a really half a$$ed job. That's the American way----Homer Simpson

Junior Contributor
Posts: 206

Loc: minnesota
Reg: 06-23-07
01-06-08 01:14 PM - Post#1336399    
    In response to silveradolsz7153

Keep in mind cold weather will affect your fuel mileage. Not only that but winter, they mix a winter blend in gas and diesel. This will drop fuel mileage way down. On average my diesel get about 18.5 mpg during summer. In winter it's about 16 mpg.
2007 3500 duramax New body style
2005 2500 duramax sled puller
2000 malibu 3.1 vin"J"

Posts: 125

Loc: South Lyon, MI
Reg: 11-06-01
01-15-08 09:52 AM - Post#1343167    
    In response to justy

I have the same problem with my truck, finally read the service manual and checked the fuel pressure which was at 50 psi at idle. After applying 14 inch of vacuum on the pressure regulator the fuel pressure did not change. Indicating a bad pressure regulator.

If the regulator was good, the fuel pressure should drop to 3-10 psi at idle when the vacuum was applied.

I will be installing the new regulator tomorrow eve and will reply with the result mileage when ever I get it calculated.

1981 Silverado 2wd
2000 Silverado 4x4
1970 Chevelle

Posts: 56

Reg: 06-19-03
01-16-08 03:46 PM - Post#1344286    
    In response to schunt

As the first responder said - it was because of a bad callibration with the new pump. I was going by the gauge and it was saying low fuel after 300 miles, when I could usually go about 420 miles on a tank. So, when I went to fill up it was only taking 20 gallons instead of 30/31.

Do these fuel gauges callibrate themselves? Mine started saying low fuel at 300 miles, now the low fuel light doesn't come on until 350 miles. Getting better!

Thanks for all the responses.


Posts: 35

Reg: 12-05-07
01-16-08 04:24 PM - Post#1344328    
    In response to dx3

No, they don't seem to calibrate themselves. It has been about three weeks since I chaged mine, and it still reads off by the same amount. It almost sounds like yours is calibrated for my Blazer, and mine is calibrated for your Suburban.

Senior Member
Posts: 475

Loc: Virginia
Reg: 07-02-03
01-18-08 09:12 AM - Post#1345676    
    In response to justy

  • justy Said:
Keep in mind cold weather will affect your fuel mileage. Not only that but winter, they mix a winter blend in gas and diesel. This will drop fuel mileage way down. On average my diesel get about 18.5 mpg during summer. In winter it's about 16 mpg.

Interesting. I didn't know they had a winter diesel formula. Is that for emissions or


btw, here inside The DC Beltway, the tree huggers have stuck us with the winter blend(i.e., "oxygenated fuel") year round. So we lose 10% mpg all 12 months of the year!
2003 K1500 Suburban LT
1993 Caprice wagon
1998 Volvo S70 Turbo

Senior Member
Posts: 8242
Loc: Maryland
Reg: 02-25-02
01-19-08 07:03 AM - Post#1346340    
    In response to glsable

I'm with ya glsable, I feel your pain
'99 Silverado (NBS)

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