I work on these Volvo's everyday,And more and more I'm hearing Gas mileage
from my customers.Start with the basics.The first thing is spark plugs,do you have the correct one for your 240 are do you have those high dollar platinum's
that the coil can't handle.If you haven't done so replace all vacumn lines
check the line that goes to the tank under the dash this is the one that gets over looked all the time,what about the tank it's self I'm finding more of these with dry rot cracks in them and it's just enough to cause a problem.Gas today is junk lets face it the gas company's have us right where they want us.
If you don't believe it then crank up your car and watch the water come out the exhaust,all of that's not condensation.Take the pipe off between the AMM and the throttle body and check for cracks and oil build up,Give it a good cleaning
especialy at the two necks you will be suprise of the vacumn leaks that I find
at these two places.Check the grounds on the fuel rail,have you cleaned these grounds what about a meter to check for resistance to the computer,I try to holed a Omh of 1.6 are less.the more resistance you have the more fuel the computer is going to put to the injectors.One thing that I do on this is to cut the eyes on the grounds off and install new ones with soilder ends.I also get the grounds off of the turbo's that have two ground leads and attach one to the valve cover the other to the fuel rail back bolt , the ground lead that you take off of your 240 attach to the two bolts on the fuel rail this will give you a complete ground to the fire wall.Check the bolt to the fire wall is it clean and does it have the ground washers on it.I had a customer aweek are so ago say that she was getting bad mileage but then also admitted that she sat in the drive way the other day and let the car run for 30 minutes while she was on the cell phone.One thing that I'm going to do is to replace the injectors on my 85/240 with the ones that are being sold on Ebay for $70.00 plus shipping they have a four hole spray pattern and are matched up with new screen filters.I believe that this will help out on the fuel mileage.The other thing that I do is too install a small vacumn check valve on the drivers side of the vacumn tank.This helps to holed vacumn in the tank at nite and at stop lights when you have a air horn leaking down.If you have a 88 are older check the engine timing
try to get it set what Volvo says.There are plenty of things that you can do to get better mileage just start with the basics and keep going,check your mileage every week make changes,if it makes it worse then go back the other way with what you have done.One other thing to look at is the old Cat. has it come apart and stopped up part way in the neck at the rear exhaust and is not letting the engine breath.I can go on and on,For those of you that are getting 26MPG and better around town then laugh all the way to the bank and take care of that car because you are doing something that the other people aren't and that is having to make that car payment every month.
Take care
Rodney