hi guys my 91 rs 305 tbi is gettin quite low gas mileage. or atleast i think so. 20 bucks gets me 4.5 gallons which only gets me about 60 miles incudling some freeway. i just switched the fuel filter and taht did not help. the only problems i know it has is that my fan is always running but besides that it seems to run fine. idk were to start with finding out what my problem is. car only has 162k miles

 

with the fan running all the time then that is the sendor in the passenger side head. as for gas mileage you might check the coolant temp sensor in the intake. loosen the coolant temp sensor with the car off and cool until it bleeds a tiny bit of either coolant or air and see if that helps.

 

If the fan is always running doesn't that mean it could be in limp home mode also? That kills fuel mileage.

Is your CEL on? When you turn key on it should come on, blink once fast then stay on till engine is started and go off.

 

as of right now im not throwing any lights. only thing is taht fans always on

 

Time for a Scan Tool or TunerPro and a cable to laptop.

 

the guy i bought it from said it had a bad switch i believe so he said he just put it so that it would always be on its not throwing any lights at all

 

Do a resestitence check on the coolant temp sensor at different temps.
Install a 195* t stat.
Check ign. timing & make sure it advances when you rev it.
Look at inj. spray pattern, no drips. Check the fuel pressure, 9-13psi. A restricted return line can cause high psi readings.

 

All the more reason for...

Specific data from each circut can tell you what is wrong. Just because it's not throwing an error code does not mean something is not wrong. The ECM is just an old dumb computer, does what it is told and can't do more then it is programmed for.

There is a pdf document that you should have to learn how to test each fault code, or circut of EFI if no fault code. Bottom of this link.
http://www.gearhead-efi.com/Fuel-Inj...-CEL-SES-Light

If O2 sensor is going bad it will reduce fuel milage and may not throw a code? Fuel pressure could be to high and again ECM has no way of knowing and may not do anything to throw a code. Vacuum leak, same thing? Timing, same...

 

and here's the measurements...

Coolant sensor approximate resistance specifications:
177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.
100700 ohms @ -40 deg. F. or - 40 deg. C.

 

coolant temp sensor is no good. they can be no good and the ECM won't throw a code because it just sees the car running hot or cold

 

your cat converter (if you still have one) could be clogged or an exhaust pipe pinched.

 

yeah, something is going on, stock these cars get 25 or better with the 305.