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Gas Mileage Dropping


jndnaps

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I have a 96 DeVille with the Northstar. I was getting around 18.1 to 18.4 around town. I always use premium gas. The last couple of weeks my gas mileage has dropped. It's down to 16.9 to 17.4.. I'm driving pretty much the same as always. Any ideas as to why the gas mileage dropped in just less than 2 weeks? Plugs going bad? Car runs fine and no check engine light on. No codes either.. Car just about to turn 90K... Thanks..

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Thats odd, however with the price of gas did you drop from 91 to 89 octane? a drop in octane could cause reduced gas mileage. If you use the same gas station, try another, maybe THEY are playing games with the octane, due to the prices...

Does it feel sluggish or like it lost power at all?

When did you change the air filter, pull it and hold it up to light and see if you can see light through it

How is the pressure in your tires?

Are you sure your trips on average are more or less the same...?

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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Perhaps the engine is need of a few WOTs. I know my mileage drops when I've pampered the caddy for about 2 weeks without WOTing.

"Burns" rubber

" I've never considered myself to be all that conservative, but it seems the more liberal some people get the more conservative I become. "

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Let's step back to the basics of what can cause fuel economy to lag.

How's your air filter? When was the last time you changed it?

Ditto for your fuel filter.

how's your tire pressure? Checked it lately? Lower pressure creates more drag between the tire and the road, thus reducing your gas mileage.

Let us know how these three things check out.

If you really want to make people safe drivers again then simply remove all the safety features from cars. No more seat belts, ABS brakes, traction control, air bags or stability control. No more anything. You'll see how quickly people will slow down and once again learn to drive like "normal" humans.

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I don't believe it can at all, it will just starve the engine and cause other problems.

Ranger, I keep forgetting to update my thinking on the air filter and fuel injection! Your suggestion about the FPR is a good one

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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I don't believe it can at all, it will just starve the engine and cause other problems. 

Ranger, I keep forgetting to update my thinking on the air filter and fuel injection!  Your suggestion about the FPR is a good one

So how do i check it do you guys no? I know nothing about them I dont even no where it is i asked before but i was still confused about where it was and how to check it!

user posted image

Defending Northstar perf a qtr mile at a time!!!!

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I am not sure where it is on your car. Just follow the fuel line from the tank and you'll find it usually mounted to the frame. It is a canister looking device with the fuel line running in one side and out the other.

You really can't check it. Just replace it when you suspect it is causing a problem. They rarely get so plugged as to cause fuel starvation but it does happen. I have expirienced it once or twice.

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If you don't have the history of your car, I would just change it. This way you have a starting point as currently you have no idea when it was changed last, not a good feeling to have.

I was lucky to know the former owner and he kept detailed maintenance records and I know when things were changed. I need to put those records on an EXCEL spreadsheet one of these days.

Are you getting any symptoms?

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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I drive the same way everyday and I pretty much drive like I always do. I'm using the same octane, 91.. And the car is running fine.. I changed gas stations and so far it's the same. The air filter is fairly new and the tire pressure is up where it should.

Ranger, If I had a leaky FPR, Wouldn't I smell some gas??

kger2, what are WOTs??

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WOT's are short for wide open throttles (kicking your gas pedeal to the floor :P )! I love doing them and i think everyone else on here does to they help keep your northstar engine free of carbon!

user posted image

Defending Northstar perf a qtr mile at a time!!!!

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Ranger, If I had a leaky FPR, Wouldn't I smell some gas??

Most likely not. The FPR is a small canister looking device on the fuel rail. It has a rubber diaphram in it with fuel pressure on the bottom half (fuel rail side) and engine vacuum on the top half (where the vacuum hose is). If the diaphram is ruptured, engine vacuum is sucking unmettered gas into the intake and burning (wasting) it. If it had an external leak (very unlikely) then, yes you'd smell gas. Check it by pulling the vacuum hose off while the engine is running and look for gas leaking out of the nipple. Replace it if you see any.

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OK, Thanks Ranger.. I'll check it out tomorrow and let you know.

cadillac_caddy_sts, That's what I was thinking WOT's were.. I did it today and all it did was bring my gas milage down even more.. :blink:

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OK, Thanks Ranger.. I'll check it out tomorrow and let you know.

cadillac_caddy_sts, That's what I was thinking WOT's were.. I did it today and all it did was bring my gas milage down even more.. :blink:

Yes doing some wide open throttles will bring down the gas mileage temporarily.... for obvious reasons. The trade off is that it blows the carbon and crud out. I did some 2nd gear stomps from 40-75mph (letting the engine slow the car down after hitting 75) the other day. Saw some crud fly out. After the 8th stomp all seemed clear. I reset the mileage indicator and what do you know.... better gas mileage driving the usual stretch i use to measure it. Don't mistake hard accelerations for WOTs.

"Burns" rubber

" I've never considered myself to be all that conservative, but it seems the more liberal some people get the more conservative I become. "

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Many things affect fuel mileage and one that many forget is the actual outdoor conditions. Dry air is better for combustion than damp or humid air. In the old days (of which I fondly remember) a high-rise manifold with a huge carb would actually ice up and constrict airflow thus increasing fuel consumption and give poor performance to boot! A carb mixes without the benefit of a computer and your computer measures air (for mixing with fuel) and then meters the fuel but I am not sure if it measures humidity as well. This could affect it to the degree you have realised.

How has the weather been?

MP

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On the subject of fuel causing your problem...pretty UN-likely. BUT ethanol has become very attractive in a lot of states lately. I think some recent tax beaks have kicked in around the country and new ethanol plants are being built. The addition of ethanol COULD cause a slight drop in fuel mileage just because the BTU content is not there. The OCTANE remains the same, but energy content may drop. A state such as Florida with it's agricultural economy might benefit greatly by selling corn to ethanol producers. Remember, the basic science behind internal combustion is the BTU content of the fuel creating useable horsepower by burning and expanding hot gases in a confined space.

Other than that I'd go with the FPR idea.

Never underestimate the amount of a persons greed.

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Thanks for the replies. The FPR wasn't leaking at all. In fact, It looks brand new.. May have been replaced just before it was traded in. As for the weather, It's really been about the same. This week it's been getting hotter though. But it's been getting lower weeks ago. I'm gonna do some WOT's and take it from there.. :blink:

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