To the D15Z1 guys - EGR maintenance eliminates detonation

[greasemonkee]

After a year-long battle I've finally arrived at a conclusion. My D15Z1 liked 93 octane, any less and it had terrible detonation. On hot days even 93 octane fuel would detonate severely during throttle tip-in and about 5 seconds afterward. Only once in a blue moon an intermittent MIL would come up for the EGR sytem, but with the half dead O2 sensor it was hard to trace down. At the point where I threw my hands up and decided to tune the engine myself, ditch the entire EGR system, and eliminate leanburn limitations I noticed this -

There is no vacuum on the EGR valve while driving under any condition. ...but why no MIL? I proceeded with the Helms troubleshooting procedure and discovered the EGR lift sensor was stuck in the full open position. This explains why the ECU was adding a ridiculous amount of timing creating tremendous detonation.

The solution is rather simple and free:

-Remove EGR valve from the engine
-Unclamp the sensor from the valve
-Carefully pry upwards on the three corners of the sensor where it mates to the valve. The plastic keepers will break off in the diaphragm housing.
-Remove the broken plastic from the diaphragm housing
-Clean the movable shaft in the sensor with WD-40 or equivalent to remove the hardened grease. Work the shaft through its range of motion until there is minimal resistance.
-It may be worth adding a minimal amount of grease on the very end of the shaft where it contacts the diaphragm and on the shaft (high temp of course).
-Align sensor to its original position and reclamp.
-Clean the soot from the base of valve and around valve/orifice to ensure proper flow.


Over the past year I've wasted approximately $500 on 93 octane fuel - school of hard knocks. Hope this helps anyone who is having unexplainable detonation issues.

I'll try to add a couple of pics later