what can cause my mpg to go from 18 to 15 on a 85 Caprice classic?

J

James

New member
i just had rotor,coil,and ignition module replaced. Plus it idles real high. i had it looked at cause it wouldnt start, could they have tried adjusting the carb but since that wasnt the problem now its outta tune? I used to get 18mpg city, now its about 15mpg. Oil is good, Trans fluid is good, and it has a new air filter. Also my tires are 205/75/15, but i had to get a used tire to replace a flat on the back passenger side and all i could get is a 205/70/15. Could that 1 smaller size tire throw it off too?
 
Engine timing is the problem,to high it will fast idle ,and lose fuel mileage to low it will rough idle and idle to slow & waste fuel-lose mileage ,these cars need to be mag timed,if you can find garage that has one they are a hand held unit with digital read out,I,m the only one in my area that has one,and it sets the timing pin point perfect like GM did at factory hope this helps my friend
 
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