Fuel

AZFORDFREEEEK

MEMBER
1988 GMC C3500
V8
2WD
AUTOMATIC
97,000 MILES

I have A 1988 gmc R3500 it has the 7.4L fuel injected it is running extremely rich and I can not figure out why there is no check engine light and I have already replaced the temperature sending unit that is right by the thermostat housing I cant afford to just start replacing sensors without knowing whether they are bad like the mapp, throttle positioning, or the o2 sensors is there A way to test these without replacing or will this pull A code on a scan tool even though there is no check engine light on? Thanks

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

Probable causes of an engine running rich are as follows:

1. Excessive fuel pressure can be cause by restricted fuel return line
2. Defective Oxygen Sensors.
3. Leaking injectors and fuel pressure regulator.
4. Coolant temperature sensor out of calibration.
5. Restricted air intake system.