90 deville - premium gas required?
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1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 90 deville - premium gas required? in Past Cadillac Vehicle Discussion; just wondering... didnt think anything of it until i started reading some blurbs about the 90 deville's requiring premium gas. ...
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    90 deville - premium gas required?

    just wondering... didnt think anything of it until i started reading some blurbs about the 90 deville's requiring premium gas.

    i've been running it on regular (at least a tank of it since i bought the car)

    i dont have a owner's manual or shop manual yet.

    is this a problem? should i use premium?

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    Re: 90 deville - premium gas required?

    ok answered my own question... it says use premium only on the fuel center display. helps to read things. lol.

    just curiuos, is it normal to get 30MPG avg. on a 90 deville?

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    Re: 90 deville - premium gas required?

    Yah Premium is suggested but I have no probs in my '90 if I put in a half tank of mid grade now and then.

    30mpg! Wow, Mine averages 21mpg city/highway and I thought I was doing well. Best sustained average highway mileage I've ever seen was around 26-27 mpg.

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    Re: 90 deville - premium gas required?

    I've gotten 30 MPG with sustained highway driving but that is on a Northstar.
    The 4.9 does not have a knock sensor like the Northstar does so it will knock or ping when you accelerate if the octane is too low. I think I used to get away with mid-grade when I had my '92 but it's been a while and I am not positive. Try it, if it knocks go back to premium.

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    Re: 90 deville - premium gas required?

    ok, after a day of driving it (approx 60miles), with half and half regular and premium, i'm getting about 27.5MPG avg. not bad for a 1990 v8, eh?

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    Re: 90 deville - premium gas required?

    oftentimes computer reading is off by a few.

    case in point for 250 miles my computer will tell me anywhere from 20-22AVG, when in reality it has never exceeded 20, not even once. usually around 18-19

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    Re: 90 deville - premium gas required?

    Quote Originally Posted by cad_90
    just wondering... didnt think anything of it until i started reading some blurbs about the 90 deville's requiring premium gas.

    i've been running it on regular (at least a tank of it since i bought the car)

    i dont have a owner's manual or shop manual yet.

    is this a problem? should i use premium?

    I did the same thing when I got mine. see the link below

    http://www.cadillacforums.com/forums...ad.php?t=12465

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    Re: 90 deville - premium gas required?

    Damn.. this sucks i only get 15.5 at most on highway and 14 on side roads and stuff.. I put a new o2 sensor in.. I cleaned the egr tubes and intake. What else should I do? I was thinking tune up when I get the money for the stuff. I just got a service manual from ebay for 38 bucks 2 days ago. The guy had like 6 manuals go for other caddyz around 29-35 bucks. I would have told you all but I wanted mine cheap. The guy on ebays user name is strassfarms

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    Re: 90 deville - premium gas required?

    Quote Originally Posted by chuckdobbins
    oftentimes computer reading is off by a few.

    case in point for 250 miles my computer will tell me anywhere from 20-22AVG, when in reality it has never exceeded 20, not even once. usually around 18-19
    i know what you mean, but ive driven about 108 miles since reset the fuel center data... and it says i've used 4 gallons since. so the thing should be telling my around 27MPG avg, and it is. so far its pretty accurate. and this is mostly highway driving by the way.

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    Re: 90 deville - premium gas required?

    The fuel center data, especially for gas used in gallons, is HIGHLY inaccurate. My '93 deville will let me go 130 miles from the tank reading full till 15 gallons (its first reading from full, my guess a max of 16-18 total gallons I have been getting mixed numbers from the pump and fuel center to really nail it down since Feb.), then 25-30 for the next three to four gallons. It also tells me my avg of 23 (city/highway) is good for the 15 or so gallons of Ultra/Premium I put in, but I end up filling up well before the 345 miles (usuall around 300 mi) I should get holding the 23 avg constant.

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    Re: 90 deville - premium gas required?

    If yall want to know how much gas you are using, fill up your tank, measure how far you drive, then go into diagnostic mode and check the actual fuel level, depending on what grade fuel you use, then calculate how far you have gone and you will find out your mpg. good luck.

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