i have a 84 gsl-se and am getting 11mpg on normal driving. i have read it should be about 17ish. i read a post saying bad compression could be responsible, but i have passed emmision tests. i would think the emessions would be bad? is a rebuild the answer?

 

not always. start by doing a complete tuneup. dont forget to chang your fuel filter and air filter as well. that should be a good start. it also depends on how you drive. if you are always lauching the car hard or getting up to speed quickly, your gas mileage will suffer.

 

have you done a compression test?

worn motor could be a factor, but not that much...

 

i did a full tune up exept fuel filter when i bought the car as it was sitting for 3.5 years.i put my foot into it once and a while but not all the time. i ran injector cleaner through it , should i get them cleaned properly. any other things from sitting that long?

 

do the MMO treatment if it sat a long time..

 

Check the coolant temp sensor located on the back of the water pump housing.
This is for the ecu and tells the computer how cold or warm the coolant is for fuel delivery. One of the most common problems on the se when it comes to Mpg loss.

 

I used to think my car got crappy gas mileage because of the fuel pump, until everyone told me that I drove agressive! Roar!

 

Good call Doc.... (as usual)

 

Brand new in 1984 as per the window sticker, SE's got 16-23 mpg. I still pull 13.8 mpg on my '85 SE and thats with mods. Also, yeah Doc thats a good place to start along with the aforementioned fuel filter and air filter. ALWAYS let your car warm up to temp before driving it. ALWAYS, and don't overlook the importance of an oil and filter change. Plug wires will degrade over time, if you havent yet changed yours it might be worth looking into(magnecore wires are the best I've found so far and are all I use, go to their website for some really straight-forward info about spark-plug wires) Picking up some electrical contact-cleaner for your connections in the engine bay couldn't hurt either.
HTH

 

whats MMO?

what should the reading be on the coolant temp sensor?

 

MMO stands for marvel mystery oil. Do not believe this is factor in your issue. The only test i do for the CTS or WAter thermo sensor is at the back of the ECU that is located under the passenger side front carpet. You are looking for a voltage reading at pin # c which is the left connector and is the 2nd one over from the left. The voltage on a warm engine is supposed to be within 1-2 volts.
You will take more time doing the test than just putting a new one in. For your info if you do not know where it is located. It is at the back of the water pump housing.
It is easiest replaced by removing the alternator which takes about 5 minutes to
to remove. Unplug the connector and remove with socket or wrench. Don't forget
to do this after the engine cools down. You will lose some coolant but release the cap to vent the pressure. Also don't forget to remove the ground cable on the battery when you remove the alternator.

 

To take another approach, are your brake calipers binding? Tire pressure? Any issues with the drive line? Its not always engine related when you get bad mileage. Just something else to check in addition to the engine.

 

That is true. What about tire size. If you have a different tire sizew you speedo will be incorrect and figuring milage is difficult.