Heat, detonation, retune

[C4fan]

I had my 07 tuned last year and I thought maybe it could have been done a little better but the shop who did it has a very good reputation. The heat we've been having has started causing detonation (pinging) and the hotter it gets outside the worst it was getting. I spoke with the guy at the shop and he suggested new plugs (NGK TR55). I did and it improved but still was detonating quit a bit so I took it back to the shop. They were able to tune it out and I'm back running good again. One side effect was fuel mileage. I wasn't completely satisfied with the mileage from the first tune but it wasn't bad just not good. The best mileage we got was 25.5 mpg which was on a 450 mile trip we took a couple weeks ago. Today I hit 30.5 mpg as I was on my way home from Dallas. It backed off to 29.2 mpg and held once I got off the interstate and on back roads (not city).

[Peter Pan]

Seems your first tune was on the edge with lots of timing and this will cause what you experienced

[edcmat-l1]

Originally Posted by Peter Pan

Seems your first tune was on the edge with lots of timing and this will cause what you experienced

Sounds to me like either the knock sensors were de-sensitized too much, or the knock retard was decreased significantly, or both. Even if you crank a bunch of timing in the tune, the 07s and up (E38s) have very sensitive knock sensors, and should pull up to 10 degrees out of it if it's knocking. If you get to the point of hearing knock in a E38, there's something wrong.

[C4fan]

I'm afraid I'm pretty ignorant about how these cars computers work. They told me that when the car senses a knock it will fall back on a different set of tables but that they will only do so much. Yesterday I drove it the first time since getting back and it's running great at normal temps. The day of the re-tune the coolant temps were getting up to 230 and was knocking real bad until he got it tuned.