I Have Just Had Major Tune Up New Plugs, Wires, Distributor Cap, Rotor, Air Cleaner, Pvc Valve, And Now The Car Gets Worse Gas Milleage Than Before?? Anybody Have An Idea What Else I Can Do.

Willard Winn

Wear a lighter shoe.

O2 sensors may be an idea , they can fail so slowly that they dont trigger the check engine lamp from what ive heard OBD1 computer is not as senstive on changes to the O2 sensor like the OBD2 system in later cars

Perhaps a new fuel filter will allow the computer to make beatter adjustments on fuel pressure

how bad of milage are we talking ? im ususly between 17.9 and 25.6

:banghead: I HAD NEW 02 SENSORS AND EGR VALVE PUT IN ALSO..IT HAS BEEN A WHILE FOR THE FUEL FILTER. WILL TRY AND SEE WHAT HAPPENS. FUEL MILEAGE IS DOWN TO AROUND 17 ON THE HIGHWAY.THANKS FOR YOUR HELP.

WILLARD WINN

oh i almost forgot , make sure you check the fuel pressure regulator for leakage , take the vac line off the regualtor and plug that line with something then with engine running ensure fuel doesnt drip out of the nipple on the regulator (curtsy bbob)

also chack for vac leaks , i knocked a few loose dureing my tune up

Anybody Have An Idea What Else I Can Do.

I agree with stoneage about making sure you have no vacuum leaks.

One misfiring plug can drop your mileage. Make sure your new wires are fully on the plugs & in the distributor. Are the wires run through the wire looms & properly spaced?

What plugs did you get? If everything else checks out OK & you didn't get the original AC Delco plugs, I would definitely recommend using those. It won't cost much & may solve the problem.

Any codes in the computer now?

How's your wheel alignment?

i wouldnt say your mileage "sucks"

its a pretty old car, that never claimed to be fuel friendly to begin with. dont expect numbers to be so great.

for the records, my 4.5 gets 18-20mpg averages. computer says ~22 usually. highway numbers arent much higher at all.

last year my car agot 17mpg around town and 26mpg on the highway, now I am getting 14/20 (if that)

my car also stalls sometimes when at idel (stop after moving)

someimtes the idels is rough to wear the car vibrates

some power seems to be lost

there is a rattling from under the car that is annoying....

... what do we think? the inside of the cat is broken off... solution? cat is coming off, stright pipe going in with an exhaust cutout :lildevil:

I have a 94 Sedan Deville with 52,000 miles on it. I keep a fuel logbook and since April 15, 2004, my overall mileage has averaged 17.88 MPG. The lowest mileage I have recorded is 11.60 and the highest is 23.36. Around town, it does guzzle around 13 MPG, but on the highway, I can get in the low 20s. EPA is 17/26, so I'm recording around normal. To close, when engineers design a Cadillac, fuel economy is not one of their top five concerns, so why let it be one of yours? Enjoy the ride.

i dont think he is concred with milage totaly here . i think he has had the car for awhile , perfomred regular manitenace on it and saw a drop in fuel economy from what the 4.9 was getting before maintenace

now me on the other hand , i was upset after the first 3 weeks of ownership , but i was spoiled by 10 years of japanese 4cyl cars , it took awhile and some insight from bbob to turn me around , now im happy with it , esp comapred to what dad gets with his silverado

the deville for what it is gets awesome milage on the highway ,only the buick lesabre is more impressive when we talk about size and mileage but at a loss in power

wonder what a 1994 Deville Concuorse got EPA wise? im gonna go check...edit! 16/25 vs our 4.9s 16/26 , not much diffrence there

undefinedI BOUGHT THE CAR NEW AND RAN GREAT AND THE GAS MILEAGE WAS A LOT BETTER AND AFTER THIS TUNE UP THE MOTOR RUNS GREAT NO PINGS OR MISSES BUT THE MILEAGE WENT DOWN. I WILL CHECK THE LINES LIKE YOU SUGGESTED, THANKS FOR THE HELP TO EVERYONE.. OH BY THE WAY THIS IS NOT MY 1ST CADDY..

WILLARD WINN

Just came back from a 700 km trip, averaged 25 mpg with my newly fixed AC on, and up to 30 mpg without. I'm happy. Saskatchewan is flat, no hills!

damn , i need to get mine out on a good road trip , every long distance ive been on has been filled with so much damn traffic i cant keep cruise locked on one speed

damn , i need to get mine out on a good road trip , every long distance ive been on has been filled with so much damn traffic i cant keep cruise locked on one speed

LOL! Too many slow moving seniors down there slowing you up, eh? :D One thing about where I am, you can drive for an hour or so and never see a town or city. You break down, you'd better have a good cell phone.

My gas mileage just went way down also about 2 weeks after changing out my wires and plugs. My check engine light came on and thanks to this website and my fellow cadillac owners I was able to figure out the code that caused the light to come on. It was a P027 code which is an "open throttle signal switch". I'm going to call a cadillac dealership to see how much it will cost to fix that. I think it may have something to do with either my muffler (which I am replacing in about 2 weeks) or my a/c (which I just had a new compressor put a couple of days ago) which still doesn't blow cold air. :hmm:

LOL! Too many slow moving seniors down there slowing you up, eh? :D One thing about where I am, you can drive for an hour or so and never see a town or city. You break down, you'd better have a good cell phone.

haha , i know those areas well , the cellphone i had at the time always worked in those area too . down here i have a cellphone so bad i cant make a call unless i am standing directly under a cell tower . The company i have has a mascott in the form of a dork that goes around on his phone saying "can you hear me now?" apprently he is makeing sure i cant get a signal ...

its a sad day when cell phone service in fairbanks alaska is beatter than a major metropolitan area in florida (tampa)

btw ,og dude , that switch may very well inhibit the A/C , it does indeed shut off the compressor at WOT perhaps the computer is seeing WOT all the time keeping the compressor shut off

Hey thanks for the info. I got my mileage problem fixed though at the dealership. Apparently my throttle had all kinds of gunk in it and it couldn't open and close properly. Mileage is back up to 30mpg city. Also replaced the fuel motor?(maybe relay or switch). Wasn't paying too much to the mechanic like I should have.