Question about 2005 Pontiac Sunfire

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Getting way less milage after fuel was replaced : HELP

Was in Las Vegas Nevada for about a week. From May 11 – 16 2009. I live in New Mexico so I drove my 2005 Pontiac Sunfire about 750 miles on a 12 hour trip there for vacation. I got great gas milage. About an average of 30 per miles gallon. I have had the car since May 2008. I started using this additive called Marvel Mystery Oil in my gas tank about 16oz every fill up. My gas tank holds 14 gallons. Right before Las Vegas I had my oil changed and added the Marvel Mystery Oil to my oil change too.I have been through 2 oil Changes since I have gotten the car. The total Milage is at about a little over 64,000 miles now. Started out around 45,000 we I got the car. Well I heard about this other additive called BG K 44. I went through my 2nd fill up going to las Vegas at the half way mark to keep the gas tank full and I decided to put in the BG K 44 which is about 8 oz and is said to be put in every 3000 - 40000 miles. Well I noticed a little improvement but not much. My 2005 Pontiac Sunfire ran great to begin with but because I drive alot on the highway and use my car alot I wanted something to boost the fuel efficiency so I gave it a shot. I have been using the Marvel Mystery Oil a little after I got the car with no problems and it even boosted my some. I would say I was getting around 26 - 28 miles per gallon. Well BG K 44 is supposed to save you about $5 add every fill up and it costed me $25 versus Marvel Mystery Oil at 12 a gallon 8 - 16 oz used at every fill up so i thought I would give the BG K 44 a shot. Well when I got to Las Vegas Nevada i was able to drive around for 5 days on the half way mark until it got to Empty the day before we left I was at a gas station and need to fill completely up. I did that and added about 16 oz of Marvel Mystery Oil also I had been driving around all week with no problems. The car was actually running smooth and great which it always been since i had bought it. I used to have to drive 80 miles for 6 months when I got the car. Well on my fill up at the gas station my fuel pump went out. I know this because a mechanic that happened to be there at the time filling up checked out my car. He said that he could get the car fixed before we had to leave that very next day because it was about 2AM. It costed me $280 for the fuel pump and he charged me about $200 labor. Well low and be hold he had brought the car to me after I had given him the cash to buy the fuel pump he had it fixed within about 2 hours time. It started up great. Ran great and smooth still. No smoke from tail pipe. No power loss. Rmp's even ran great. I did notice a slight change in performance as in get up and go power, but I noticed a significant drop in my milage now that the NEW fuel pump had been installed like by a 100 hundred mile loss. Here's what I'm getting : my last fill up was 24 miles per gallon, a 6 mile per gallon loss another thing I noticed was befroe the New fuel pump was installed i had got 200 miles at the half way mark and almost close to 400 (380 - 390) NOW I get about 100 or maybe just a little more at the half way mark and almost about 300 at Empty. I have done my best to figure out possible solutions to this matter by googling this. Here's what I have come up with #1 changing the FUEL FILTER and #2 checking fuel pressure regulator and #3 looking into to this:
what happens if FPR vacuum hose is leaking? I have fuel injectors too. Got any other suggest to why so much gas is going out??? or why I am losing so much milage??? In serious need of help please. Thank You. Very Unhappy Car Owner.

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First off,If the mechanic didn't have the pump in his hand when you met,Have the car towed to his shop right then and go into work early,He didn't put a new one in and have your car back in 2 hours (since the pump is located inside the fuel tank and the tank must be removed to get to it and)

Not saying it can't be done in 2 hours,if all the tools,parts,and ducks are in a row waiting for you.

Secondly,Additives are great until you over use them,mix and match them,Etc.....

To the search questions
#1 The filter should have been changed with the pump or at least at the same time.
#2 The fuel pressure should have been tested by the mechanic after installing the new pump.
#3 If you have a vacuum leak,the car will run rough or at a higher or lower idle.

Try a good tune up.The additives have probably fowled the plugs and may even destroyed the injector seals inside.

Posted on Jun 01, 2009

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Posted on Jan 02, 2017

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