'92 DeVille with Poor MPG's
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  • 1 Post By dennis93coupe
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, '92 DeVille with Poor MPG's in Past Cadillac Vehicle Discussion; Hey guys been a while since I posted. My '92 DeVille has been worked on since last October. I did ...
  1. #1
    CaddyDeville92's Avatar
    CaddyDeville92 is offline Cadillac Owners Member
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    '92 DeVille with Poor MPG's

    Hey guys been a while since I posted. My '92 DeVille has been worked on since last October. I did a tune-up, installed a new Map Sensor, ISC Motor,Hall Effect Sensor, Fuel Pump & Fuel Tank and most recently a Fuel Filter & EGR Valve. I still have a ways to go in restoring her but now at least I can drive her to and from work. I noticed something strange though as of recent. I only use 93 when I fill her up and it seems while after all the work I done on her so far Im getting shitty Gas Mileage. What is the typical MPG for this vehicle? Im mostly on the highway and I'm getting 12.6 on the FDC, but to be honest I think its less than that. What else can I do to get better gas mileage? I notice too that I have a dent on the new fuel
    tank that was just installed. ( Due to my mechanic disconnecting the ELC and telling me I need rear struts the car is kinda low). Is this safe can thisadd to the MPG problem? I noticed for while now that when I go to remove the fuel filler cap I hear a "whoosh" noise and feel air expelling. I wasonto changing the vapor canister and purge valve next. Will this help? I also read on this site, the Fuel Pressure Regulator could be the culprit for the poor MPG. Is this a hard thing to replace or should I pay my mechanic to do it? I just wanna stop her from drinking up all the 93 so quickly....
    Thanks for taking the time to read this long post.

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    Ranger's Avatar
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    Re: '92 DeVille with Poor MPG's ? Help !!!!!!!!!!!!!

    12.6 for "mostly highway" is terrible. You should see at least 20.

    A dented tank will have no effect at all.

    A ruptured FPR is a definite possibility. Changing it is easy. Just do a search. It's been discussed many times.

    Also check the carboned EGR tubes down in the TB. Rod them out if clogged.

    Tank pressure should not cause poor mileage, but it is an indication of a problem. It tells me that your EVAP system is not working. You're on the right track with the purge valve, but also check the solenoid and vacuum lines.

  4. #3
    CadillacLuke24's Avatar
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    Re: '92 DeVille with Poor MPG's ? Help !!!!!!!!!!!!!

    OUCH. Those numbers hurt.

    I would find it hard to believe a dent in the gas tank would hurt your mileage.

    Did you hook up the rear struts again? Go find a new mechanic. If he does stuff like that he's no good.

    OK, for the fuel mileage issue. The FPR is a great place to start. It's on the top of the engine, I believe near the beginning of the fuel rail. More experienced members *COUGH dennis93coupe COUGH* have pics of the location. Do it yourself. Easy job.

    The whoosh from the gas tank doesn't sound good, but I have no idea on whether it would affect fuel economy.

    Good luck!

  5. #4
    CaddyDeville92's Avatar
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    Re: '92 DeVille with Poor MPG's ? Help !!!!!!!!!!!!!

    Thanks guys. Im off to the auto parts store to pick up a purge valve and FPR. As far as the rear struts. My mechanic disconnected the ELC compressor because it kept running and draining the battery. The struts were never touched. He advised me if I wanted to replace them with the original ones it would be pricey but instead go with Monroe passive ones. Hopefully I can get this problem under wraps. Would replacing the Vapor Canister help as well? Should I pick up a pack of vacuum hoses? Also what kind of hose is used for the "crankcase vent hose"?

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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: '92 DeVille with Poor MPG's ? Help !!!!!!!!!!!!!

    Rear struts should be less than $150 plus labor for Monroe Sensa-tracs. You just have to pull the hose off the FPR to check it; it should be dry in there. You could have some leaking injectors too. FWIW my Deville ran great on regular 87 fuel. I used to get 16-17 mpg on winter gas and over 20 mpg in the summer.

  7. #6
    CaddyDeville92's Avatar
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    Re: '92 DeVille with Poor MPG's ? Help !!!!!!!!!!!!!

    is it safe to run 87 on this year and model? does the car have to be running to pull the hose off the FPR to see if its bad?

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    Re: '92 DeVille with Poor MPG's

    Fwiw, I really wouldn't go so far as to say FPR replacement is easy... It LOOKS like it's right there for the picking on top of the engine, but it isn't. It comes out from the bottom of the fuel rail - which means the rail needs to be removed, which requires disassembling/moving other knick-knacks on the intake manifold, as well as the power steering pump. Relatively easy for the experienced, but a bit more involved than what's been portrayed in the above posts.

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    Ranger's Avatar
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    Re: '92 DeVille with Poor MPG's ? Help !!!!!!!!!!!!!

    Quote Originally Posted by CaddyDeville92 View Post
    The struts were never touched. He advised me if I wanted to replace them with the original ones it would be pricey but instead go with Monroe passive ones.
    You already have "passive" rear shocks.


    Quote Originally Posted by CaddyDeville92 View Post
    does the car have to be running to pull the hose off the FPR to see if its bad?
    Yes.

  10. #9
    dennis93coupe's Avatar
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    Re: '92 DeVille with Poor MPG's

    The FPR is on the bottom of the fuel rail, and it's the screws that are on the bottom that are hard to get in and out.

    CaddyDeville92 likes this.

  11. #10
    CaddyDeville92's Avatar
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    Re: '92 DeVille with Poor MPG's

    Thanks Dennis for the detail and photo. Ranger what would be the best route to solve the rear shock problem?

  12. #11
    Ranger's Avatar
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    Re: '92 DeVille with Poor MPG's

    If you need rear shocks I'd go with Monroe 71798 Sensa-Trac's. They should be pretty close to what you have now and a direct replacement.
    http://www.monroe.com/en-US/catalog/e-Catalog

    $62 http://www.autopartstomorrow.com/par...nsa-trac-strut

  13. #12
    aln92deville's Avatar
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    my 92 is having the same fuel issue but my FDC is at a whopping 13.2 and i can also smell fuel when i exit my car while running...also my fuel tank does the swoosh when cap is relived amd i also hear it expand and kinda pop after i turn my car off

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