1998 6.5 Engine Runs Well at High RPM but Smokes at Lower RPM

Written by Bill Heath

Volume 2 Issue 3 - 6.2/6.5 Issues and Answers

Hi there. I love the magazine! I have a 1998 GMC 1500 Z71 Sierra extended cab 4x4 6.5 automatic. It has 170,000 miles on it. Engine codes are P0236,P1409,P1653,P0401,P400. I have installed new CDR valve, Vacuum pump, Wastegate Solenoid Valve and both EGR Solenoids. It bellows black smoke with no power until the rpms come up and the boost. Then it runs pretty good until I slow down . If I unplug the vacuum line to the EGR and cap it off it runs fine with no smoke at all but then the check engine light comes on. I have to get through emissions so I can keep my truck registered. Any help would be great, thanks. Kurt B. – CT

Proper EGR-system function is dependent on health of the