I've unplugged my EGR solenoid and disabled EGR diagnostic in the PROM because my EGR was sticking and it's going to be eliminated by a Stealthram intake soon anyway. I get a steady knock retard of 3-7 (sometimes 10, eep) degrees during high load & WOT operation. I haven't changed the EGR enable temp.

I've heard that the ECM advances the timing when the EGR duty cycle comes up because it expects the combustion temperature to be low. Is this true and could this be (at least in part) causing my knock retard?

 

EGR cools the combustion chamber, so a lack of it could very well lead to knock. This (knock) happens on CCC Q-jet cars too, which have had EGR "eliminated" but not "unneeded."

 

Your EGR shouldn't be operating at high load or WOT. Sounds like you have too much timing in those areas. My max timing at WOT is 28 degrees, although I have good aluminum heads, an LT4 HOT cam, and 11.1 compression. I didn't make any more power with more timing (tried it on the dyno and the dragstrip).

After re-reading your message, you should either zero out the EGR duty cycle table or set the enable temp to something like 254 degrees. If you're still getting knock retard, then see above.

 

Thanks for the information. Instead of doing my Algebra homework, I was browsing anht_hac, and here's what I found.

- I can't find any reference to the EGR DC parameter in the timing routines. And since the EGR doesn't appear to have an enable flag to look for, I have to assume that timing isn't increased when the EGR kicks in.

- Disabling the EGR only by setting the enable temp to 255 looks to be sufficient to disable the EGR, the DC table can be left alone. Unless some other part of the code jumps directly to the table lookup routine (I didn't find any), it doesn't make it to the lookup code.

So it looks like I'll be disabling my EGR *and* adjusting my spark tables. After I get my knock counts down, I'll probably just disable the knock retard so I can adjust my spark tables better later.