paker

With a scanner EGR valveduty cycle was raised from 0 to 80%, but no change of rpm, no stumbling at all, no change of DPFE signal (stays at 0.9V). Where should I go from here? Tested with cold engine.

97 V6 4.2L

white89gt

Have you verified that the EGR valve is actually moving and holding vacuum?

paker

Vacuum tubing was removed from EGR valve and Mityvac hand vacuum was connected. Vacuum holds but engine idling doesn't change. Is it now narrrowed down to either EGR valve stuck closed or exhaust passage is blocked? Either way I have to remove EGR valve. Will report back

paker

Problem solved. The exhaust-to-EGR nut was loose and vented exhaust to air. This ties to high long term fuel trim. It was high but dropped to normal while cruising. This P0401 pointed me to the culprit. Now I should get a better gas mileage. Thank you.

Now a new but related question. How should I drive the vehicle for inspection? I remember reading so many miles at high speed and so many at low.

paker

Code returned. After tightening the exhaust nut, I connected Mityvac to EGR and pulled vacuum and engine stalled. So I thought problem was solved.

Changed EGR duty cycle to 80%. No change in engine idling. Apparently, vacuum didnt reach EGR valve. So EGR solenoid failed to send vacuum to EGR. Either EGR solenoid is bad or vacuum line has a hole.

Question: Can you feel engine vacuum sucking your finger at idling? I am not feeling anything from the vacuum hose connected to EGR vacuum solenoid.