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Within the past 2 or 3 weeks I have noticed a steady decline in my gas mileage on my 90 Deville 4.5L....the computer doesnt show it but when I fill up I calculate myself and it is down to about 10.5 mpg from about 16...dont know why either. It smells like its running rich because when I turn the car off and get out I can smell gas...any ideas as to whats causing this.
 

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ACDC686 said:
Within the past 2 or 3 weeks I have noticed a steady decline in my gas mileage on my 90 Deville 4.5L....the computer doesnt show it but when I fill up I calculate myself and it is down to about 10.5 mpg from about 16...dont know why either. It smells like its running rich because when I turn the car off and get out I can smell gas...any ideas as to whats causing this.
Check for diagnostic codes and let us know. It could be an oxygen sensor or a number of other things. The codes will tell us if it's a problem with a monitored electronic system. Look at this link:

http://www.cadillacforums.com/forums/showthread.php?t=53635
 

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1993 Fleetwood Brougham
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[/the computer doesnt show it but when I fill up I calculate myself and it is down to about 10.5 mpg from about 16...dont know why either. It smells like its running rich because when I turn the car off and get out I can smell gas...any ideas as to whats causing this.QUOTE]

Are you sure you are not leaking gas somewhere from the tank or line?
 

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fullserviceman said:
[/the computer doesnt show it but when I fill up I calculate myself and it is down to about 10.5 mpg from about 16...dont know why either. It smells like its running rich because when I turn the car off and get out I can smell gas...any ideas as to whats causing this.QUOTE]

Are you sure you are not leaking gas somewhere from the tank or line?
Positive its not a gas leak since the gas amount stays the same when it sits, it just drops like a rock while driving

As for the codes, I got E32---Open MAP sensor signal...think that might be my problem..never noticed it before. Also got a no cam reference signal from ICM (ignition control module), would that happen to do with it also?
 

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You smell gas when you stop the car? Could it also be a leaking fuel line or valve? They would only leak when running.. I dont know but the gas smell you talk about is what bothers me.
 

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2003 STS w/BoseNav, 1993 Deville, 1985 Deville
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ACDC686 said:
fullserviceman said:
As for the codes, I got E32---Open MAP sensor signal...think that might be my problem..never noticed it before. Also got a no cam reference signal from ICM (ignition control module), would that happen to do with it also?
PCM wants data from the MAP sensor (among other data) to calculate how much fuel to inject. It also needs the cam reference signal to know when to inject fuel.

Your PCM may be perpetually operating in 'open loop' mode. That would definitely explain the poor gas mileage. I'd start checking wiring harnesses associated with these components.
 

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thu said:
PCM wants data from the MAP sensor (among other data) to calculate how much fuel to inject. It also needs the cam reference signal to know when to inject fuel.

Your PCM may be perpetually operating in 'open loop' mode. That would definitely explain the poor gas mileage. I'd start checking wiring harnesses associated with these components.
Thanks a lot, Ill check the harnesses. My dad said he had an older Ford truck that was throwing a bunch of sensor codes and messing the gas mileage up and it ended his ground wires werent grounded too well, so Ill take a look at the grounds too.
 

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What fixed this problem? I find all sorts of things searching here but nobody bothers to put what actually fixed their cars.


I am getting 12.8 MPG and have one engine code E41 (cam sensor signal reference)

Also experiencing stumbling on light acceleration and a horrible fuel smell.
 

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Anyone? Could someone point me in a good direction to read about the cam reference signal. I don't understand how or if that could cause my poor gas mileage.

Thanks
 

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The very best place to read about it is a factory service manual. They describe everything about them in that book.

I looked through mine here, and poor fuel economy doesn't seem to be caused by an E41 code. They mention checking lots of other things like tire pressures, how long you drive the car (whether it gets to full operating temp or not), how hard you accelerate, whether your A/C or defrost is on all the time, how the plugs look, whether the brakes are dragging, etc.
 

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2008 SRX-V8, 1991 Eldorado
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Stock90DeVille said:
Anyone? Could someone point me in a good direction to read about the cam reference signal. I don't understand how or if that could cause my poor gas mileage.

Thanks
The cam reference signal is an anti-knock sensor in reality. The 4.X engines have them while the N* does not. You need this signal for optimum engine efficiency. Open loop means that the computer is compensating for low octane gasoline to prevent valve ping so in effect you are running rich and smelling unburned fuel. If allowed to continue over an extended period of time you will eventually destroy the catalytic converter and foul the oxygen sensors. If you do not have a factory service manual (FSM) you can get the proper maintenance procedure from alldata but you will pay for it in either case. You will be far better off with the FSM in the long run. You are likely to find the FSM on ebay, otherwise try www.helminc.com.
 

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91TexasSeville said:
The cam reference signal is an anti-knock sensor in reality. The 4.X engines have them while the N* does not. You need this signal for optimum engine efficiency. Open loop means that the computer is compensating for low octane gasoline to prevent valve ping so in effect you are running rich and smelling unburned fuel. If allowed to continue over an extended period of time you will eventually destroy the catalytic converter and foul the oxygen sensors. If you do not have a factory service manual (FSM) you can get the proper maintenance procedure from alldata but you will pay for it in either case. You will be far better off with the FSM in the long run. You are likely to find the FSM on ebay, otherwise try www.helminc.com.
Thank You!! That is a very detailed and informative response. I also noticed that my gas tank looks a little moist, I will update after this weekend when I put her on a lift. IYHO should I or should I not run 93 gasoline? I just bought the car and when I put gas in I used premium fuel.

Thanks again
 

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Stock90DeVille said:
Thank You!! That is a very detailed and informative response. I also noticed that my gas tank looks a little moist, I will update after this weekend when I put her on a lift. IYHO should I or should I not run 93 gasoline? I just bought the car and when I put gas in I used premium fuel.

Thanks again
IMHO...I would stay with premium fuel for several reasons. The most important reason now is that you are trying to get back the performance and economy of your engine. Along with the essential tools to make the corrections and or adjustments, you also need to use the recommended fuel.
 
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