1995 GMC Jimmy Excessive Fuel Consumption

CFERRY1

MEMBER
1995 GMC JIMMY
6 CYL
4WD
AUTOMATIC
205,500 MILES

Upon the onset of noticing poor fuel economy in our
1995 Jimmy, we took it to our regular Mechanic for
a Tune-up. Our Mechanic performed the Standard
Tune-up and reported that we need to replace the
CPI or Fuel Injection Assembly. The Tune-up did
little to the Fuel consumption. On 3-05-08, I replaced
the Fuel Regulator. Fuel Pressure Test on 3-07-08 reads 62 psi key on / 59 psi engine running. Intake Manifold Vacuum Test on 3-06-08 reads 16-17 inches steady at startup idle. After some acceleration, vacuum will then decrease to 13 inches with slight needle fluctuations at idle. After the previous mentioned Tune-up another Test Facility read these two codes on their scanner: P0172 and P0304.
Presently running at 11 MPG Hwy. And City.
Can you suggest on what to test next? Try next?
Thank you

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

P0172 Typical symptoms of an engine that is running rich (too much fuel, not enough air) are poor fuel economy, elevated emissions (Carbon monoxide or CO), and engine may have rough idle or surge condition.

Possible causes include a bad O2 sensor, excessive fuel pressure (bad fuel pressure regulator or plugged return line), leaky fuel injectors, dirty air filter or restricted air inlet, or a defective coolant sensor that prevents the engine management system from going into closed loop mode.

P0304 Misfire at no. 4 cylinder-a misfire in a specific cylinder should lead you to check the spark plug, fuel injector and compression