2002 Chevrolet Corvette Z06: Calling In The Pros
February 23, 2010
You're probably as tired of reading about our longterm 2002 Corvette Z06's ongoing detonation saga as we are dealing with it. Here's the latest.
This morning we brought it in to Bothwell Automotive in Torrance, CA. These guys are not Corvette specialists per se, but they do service about 20 'Vette customers and countless other makes and models. Oh, and they know plenty about how to go fast, too -- their lobby's trophy case is bursting with about a dozen and a half NHRA Wallys.
First, Steve Bothwell confirmed the detonation. Then he checked the fuel pressure to ensure that it doesn't have a bum fuel pump or clogged fuel filter. Fuel pressure checked out okay.
Then he hooked up the scan tool and checked the engine calibration to be doubly sure we didn't get snookered by the GM dealer. The calibration checked out too, so that's not the source of the problem, either.
With the scan tool, Steve observed the long-term fuel trims and noticed something that might be telling -- the fuel trim for the right bank of cylinders is +8%, and the left bank is +13%.
Basically, over time, the ECU has "learned" (based on feedback from the oxygen sensors) to compensate for a general lean condition by commanding the injectors of each bank to stay open longer than normal. Apparently the LS6 can only trim banks of cylinders and not individual cylinders. This is a 2002, after all.
Anyway, a lean condition is a prescription for detonation. An underachieving injector (or two) per bank is the leading candidate as the cause of the lean condition, but at this point there's no way to know exactly which injector(s) is the culprit.
His recommendation is to have the injectors flowed and cleaned, which might be enough to bring a lame injector(s) up to par. If not, we'll at least know which one(s) is frumpy and can replace them accordingly.
Why the ECU doesn't acknowledge and/or correct the plainly audible knock activity remains a mystery. For whatever reason, it thinks everything is just peachy -- no trouble codes, no knocksum on the scan tool. Go figure.
Jason Kavanagh, Engineering Editor