Aloha,
Anyone know the relationship between leaking EVAP purge valves & short term fuel trim. I have consistantly lean Long & short term trims (-6 to -7) & know if I pinch the purge vapor hose, the stft will return to normal parameters if the valve is leaking.
My question is...would a leaking purge valve cause the motor to run rich or lean ?.
Mahalo

 

The ECU will sense the air leak (O2 sensor readings) and compensate by changing Long Term Fuel Trim (LTFT) which will be negative. If LTFT exceeds a lmiit, perhaps 35-40%), then Check Engine Light is set on. Probably obd1 code 43 for fuel supply is set.

good luck

 

Thanks Tex,
Ended up being the hose between the Purge Valve & the manifold. Fuel trims fine now. I wanted to fix it before I replaced the cat.