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10.9 MPG ! ! ! !


Sniper602

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My 92 El Dorado is only getting 10.9 miles per gallon. What should I be looking for?

A hole in your tank!

Give us some more history here. How long have you owned the car? Did it just start getting poor mileage, or has it declined gradually over time? When was the last tune up on the car (plugs, wires, etc)? Where do you live and what are your driving habits? Obviously, your driving style alone will not produce mileage like that, but it could be a large contributing factor.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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My 92 El Dorado is only getting 10.9 miles per gallon. What should I be looking for?

A hole in your tank!

Give us some more history here. How long have you owned the car? Did it just start getting poor mileage, or has it declined gradually over time? When was the last tune up on the car (plugs, wires, etc)? Where do you live and what are your driving habits? Obviously, your driving style alone will not produce mileage like that, but it could be a large contributing factor.

I've had the car for about 5 years. I just tuned it up about 4 months ago, because of the decline in the gas mileage. I replaced the PCV Valve, Spark Plugs and Wires with AC Delco, and Platinum Plugs. I live in Phoenix. I have 20" inch wheels with 35 series tires. Now I know that may decrease the MPG. But i've had these wheels for about 4 years now. I used to get about 18 mpg.

I'm desperate. I might as well own a SUV.

Any help is appreciated.

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I get about 13 mpg in my 92 Eldorado... seems like i get better mileage in the summer though.... Sucks huh

I would happily take 13 mpg, right about now. But you are right about that...................it sucks in a major way.

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10.9...or 13 mpg...is way too low. Something is obviously wrong. Is your check engine light on? Have you looked at the computer codes? I believe there are instructions at the main www.caddyinfo.com site for pulling the codes on a 4.9L car (if they're different from a Northstar car). It's probably something like an oxygen sensor or possibly an air temperature or coolant temperature sensor, but I would think the computer would be able to find that and display the check engine light.

If all else fails, take it to the Cadillac dealer -- they may be able to plug into the car and access what the computer is showing for the coolant and air temperature. You may discover that they're incorrect but the computer doesn't show the check engine light? It could also be that the check engine light IS illuminated -- but the bulb is burned out? Many possibilities.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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But its cheaper to just settle for the crap mileage than to pull the thing apart and find nothing wrong as I have always done.

I beg to differ, 10 MPG is excessively low. Read bbobynski's post to diagnose the problem. If you have had a drop in MPG, from 18 to 10 with the same wheels OBVIOUSLY something is WRONG. You are not driving a 5,000 pound 1974 Eldorado with a 500 ci engine (was it 8.2 liter?) now that was a gas sucker, I know, see below, notice NY plate 1974ELDO. The 4.9 gets good mileage as you have experienced.

Start with bbobynski's suggestions... To accept this drop is silly, there is a cause.

post-3-1109872122_thumb.jpg

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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But its cheaper to just settle for the crap mileage than to pull the thing apart and find nothing wrong as I have always done.

There IS something wrong if you're getting 10 mpg. If you haven't found something wrong, you just haven't come across it yet. Bbobynski gave good advice on checking the computer vs. your calculated readings. If the computer itself is reporting 10 mpg or so, something's wrong in a big way. Remember, spewing unburned or excessive fuel into the air has a much greater cost other than what comes out of your wallet.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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I cant remember the last time I went more than 225 miles between fill ups. This is highway and city driving combined. And I dont drive crazy. Lets see, the owner manual claims the tank holds 18+ gallons... which may or may not be true, but I know for a fact that the blinking E comes on before I have used 16 gallons. And if i turn corners at high speeds, the engine sputters. Thus the most fuel i usually get ito pump into the tank is 15.5 gallons. So 225 / 15.5 = 14.5 mpg. These are high estimates too... and the gages say about 13.5. But I am absolutely positive I get better numbers in the summer time. Near 18 mpg if not higher.

I often reset my guage that calculates the average fuel mileage.... because I cant believe I get so little. But seriously. I already wasted $500+ on a tuneup to fix this problem and the rotten egg smell from my exhaust. The dealership, and I will name names if you want, does the tuneup, which is a joke if you ask me cause the car had like 30k miles on it. And the solution to my exhaust smell is to use lower octane gasoline.... LOL So I still get crap mileage and the nauseaiting smell embarasses me w/ hot chicks who think i am weird as it is to drive a white diamond eldorado with gold trim. So anyway, if i still had that extra $500, I could fill my car up with the extra $4 worth of gas 125 more times and still be ahead. Instead all i got was 8 spark plugs and a pcv valve, all in mint condition (and I assume they would show some sign of carbon buildup if an injector was leaking).

Sorry I am so bitter.... I guess I can read my $30 helms service manual i bought this past february and realize i need a new car

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I cant remember the last time I went more than 225 miles between fill ups.  This is highway and city driving combined. And I dont drive crazy.  Lets see, the owner manual claims the tank holds 18+ gallons... which may or may not be true, but I know for a fact that the blinking E comes on before I have used 16 gallons.  And if i turn corners at high speeds, the engine sputters.  Thus the most fuel i usually get ito pump into the tank is 15.5 gallons.  So 225 / 15.5 = 14.5 mpg.  These are high estimates too... and the gages say about 13.5. But I am absolutely positive I get better numbers in the summer time.  Near 18 mpg if not higher.

I often reset my guage that calculates the average fuel mileage....  because I cant believe I get so little.  But seriously. I already wasted $500+ on a tuneup to fix this problem and the rotten egg smell from my exhaust.  The dealership, and I will name names if you want, does the tuneup, which is a joke if you ask me cause the car had like 30k miles on it.  And the solution to my exhaust smell is to use lower octane gasoline.... LOL  So I still get crap mileage and the nauseaiting smell embarasses me w/ hot chicks who think i am weird as it is to drive a white diamond eldorado with gold trim.  So anyway, if i still had that extra $500, I could fill my car up with the extra $4 worth of gas 125 more times and still be ahead.  Instead all i got was 8 spark plugs and a pcv valve, all in mint condition (and I assume they would show some sign of carbon buildup if an injector was leaking).

Sorry I am so bitter....  I guess I can read my $30 helms service manual i bought this past february and realize i need a new car

This is histerical! The reason you are getting the rotten EGG smell is because you are running RICH which is contributing to your mediocre gas mileage. Something is wrong, either a leaky injector or an O2 sensor problem. Have you run diagnostics on it? You should also try a different brand of gasoline, not grade, use what the car calls for (octane).

If you correct this you WILL get better mileage, how much I don't know based on your driving habits, but it will be better. I will be back later to ponder on this... Try not to accept and give up on problems, we can help you, be patient.. Mike

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 cant remember the last time I went more than 225 miles between fill ups.  This is highway and city driving combined. And I dont drive crazy.  Lets see, the owner manual claims the tank holds 18+ gallons... which may or may not be true, but I know for a fact that the blinking E comes on before I have used 16 gallons.  And if i turn corners at high speeds, the engine sputters.  Thus the most fuel i usually get ito pump into the tank is 15.5 gallons.  So 225 / 15.5 = 14.5 mpg.  These are high estimates too... and the gages say about 13.5. But I am absolutely positive I get better numbers in the summer time.  Near 18 mpg if not higher.

I often reset my guage that calculates the average fuel mileage....  because I cant believe I get so little.  But seriously. I already wasted $500+ on a tuneup to fix this problem and the rotten egg smell from my exhaust.  The dealership, and I will name names if you want, does the tuneup, which is a joke if you ask me cause the car had like 30k miles on it.  And the solution to my exhaust smell is to use lower octane gasoline.... LOL  So I still get crap mileage and the nauseaiting smell embarasses me w/ hot chicks who think i am weird as it is to drive a white diamond eldorado with gold trim.  So anyway, if i still had that extra $500, I could fill my car up with the extra $4 worth of gas 125 more times and still be ahead.  Instead all i got was 8 spark plugs and a pcv valve, all in mint condition (and I assume they would show some sign of carbon buildup if an injector was leaking).

Sorry I am so bitter....  I guess I can read my $30 helms service manual i bought this past february and realize i need a new car

This is histerical! The reason you are getting the rotten EGG smell is because you are running RICH which is contributing to your mediocre gas mileage. Something is wrong, either a leaky injector or an O2 sensor problem.

Sniper,add a faulty "FPR" (fuel pressure regulator) to Scotty's list! As bbobynski posted earlier, that could be creating the way over rich conditions the motor is seeing by the symptoms you've described.

Not a terribly unusual problem with older motors, and easily fixed. Just follow bboynski's easy diagnostic steps. ;)

'93 STS.. opened, dropped, wide...fast.

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Yes Bob D, I forgot that, good point, its on both Snipers and JoeM's list

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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If you got 18 MPG from 18 gallons of gas, you could drive 324 miles. Your current figures of 10.9 MPG on 18 gallons will only give you 196 miles per tank. If you drive 15,000 miles this year your currently going to spend $2752 on gas (at $2 per gallon). With repairs, it would be more like $1666. Thats a difference of $1086.

Here are some repair estimates. (If you do the work)

May not be accurate, but should be reasonably close.

Replace injector = $150-300

Replace O2 sensor = $70-150

Fuel pressure regulator = $70-140

Fuel costs for not making repairs = $1086-plus any repairs caused by the current problem.

As you can see, you could replace every part that has been mentioned so far and get your money back on gas mileage over 3-6 months.

Just some food for thought

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I checked for the leaky FPR... twice. nothing. Could be one of the O2 sensors... but all I can do is spend a bunch of money and replace them. What are the chances both are bad? If one was bad wouldnt I get an error code about one bank being rich? As for testing the injectors... it doesnt seem feasible in sub freezing weather. So basically, I know something is wrong, but to fix it costs more then the thing is worth at this point. Still... if it was running rich, I still think there would have been some evidence on one of the spark plugs when they were replaced. Seems like I should have seen something on them other than the light white color of gas additives...

I have tried many different brands of gasoline, BP/Amoco is the best for the sulfur content/smell, and thats all I use of late. I do normally switch between premium and midgrade too. Anyways, I have put alot of thought to all of this. I have basically reached a point though where the work is over my head/skill.

And still I will get better mileage in the summer for whatever reason..

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It sounds like you have a leaky injector. Are you setting any codes at all, it doesnt sound like you are from your writing. I am not sure how handy you are, but to check for a leaky injector, you can pull your fuel rail and have someone go into the car and turn on the key, the leaky injector will leak... Then you can replace the leaky injector, and be done with the rich mixture that is causing you to have WOMEN and Rotten Egg problems... :lol:

I have a manual on the 4.9 if you want I can scan the pages on removing the fuel rail..

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 get 12mpg. or so regularly, with 70k miles on a 98 ETC.

A friend uses my car once a month or so and he gets 18mpg.

I have ALOT more fun when I drive than he does!

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I just saw all of your suggestions.

As far as the mileage, I got it from the "fuel economy readout". There are no error codes, and the old plugs were not fouled.

I also failed emissions this weekend. These were the numbers:

Vehicles Emission: Applicable Standard:

HydroCarbon Grams/Mile 4.49 1.00 Fail

Carbon Monoxide Grams/Mile 32.37 12.00 Fail

Oxides or Nitrogen 2.27 2.50 Pass

I will follow "bbobynski's" suggestions this afternoon, and let all of you know the outcome.

Thank you all for all of your help.

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Sorry about the emission numbers: I did not post them that way. They got all messed up for some reason.

These are the numbers:

HydroCarbons: Vehicles Emission 4.49 Applicable Standard 1.00

Carbon Monoxide: Vehicles Emission 32.37 Applicable Standard 12.00

Oxides 0f Nitrogen: Vehicles Emission 2.27 Applicable Standard 2.50

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I checked the Fuel Pressure Regulator, and it was not leaking. I will check the fuel injectors over the weekend, to see if they are leaking at all. It looks like it is going to take me a little time to get the fuel rail up.

Does anyone, know where I should begin, with the emission numbers I posted up?

Any help is greatly appreciated. Thanks again for all of your help.

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Worse comes to worse a new cat might get you through the emissions tests. I think I have even read where someone put two cats on to get through emissions.

Oh and I have a 92 service manual. As for handy, I am not nearly enough in sub freezing weather. But I agree, the injector test is about all I have left to check for. Still, if you check the archives here and the old msg board, alot of people complain about the smell and the only fix seems to have been a new cat.

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