The revisions are expected to boost the level of GDP but not necessarily change the growth rate of GDP in recent years. "We're at 0.6 percent," for the second quarter, said Hatzius.
The revisions will include a new method to count research and development spending as a form of investment spending. Spending by entertainment and media companies on movies and certain other entertainment will now be considered investing in intellectual property. The revisions also include additional source data and recalculate seasonal adjustments.\
(Read more: White House: Health reform hasn't hurt jobs)
J.P. Morgan Chief U.S. Economist Michael Feroli said expects the Fed to be vague about the timing of its plans to taper back the $85 billion in monthly bond purchases. He expects the Fed to begin to move in September and start by cutting purchases by $20 billion a month in mortgage securities and Treasurys.
"To the extent we're right, that it is going to come in a very soft Q2 number, the Fed's known for a while. Even when Bernanke went before Congress and testified. He knew the Q2 print would be very bad and he didn't do anything to soften expectations for tapering later this year," said Feroli. J.P. Morgan expects second quarter growth of a half percent, but Feroli sees a pickup in the second half other year to 2.5 percent.
(Read more: What earnings season is saying about road ahead)
Feroli said the Fed could give a nod to the softer data. "I think they'll be able to ascribe some of it to transitory factors such as fiscal drag," he said.
There is some expectation the revised GDP data could help explain why GDP has been lagging other data for the last couple of quarters, especially the employment data. Other releases Wednesday include ADP's private sector payroll data at 8:15 a.m., and that number is expected to be around 183,000, down from 189,000 last time. That number is seen as a sort of precursor to Friday's July jobs report, expected to show 184,000 payrolls. The Treasury is also expected to announce the auction sizes for its next fiscal quarter at 8:30 a.m.
There is some talk the Fed may change its target of 6.5 percent unemployment for an area to begin to move short term rates, down to six percent. However, some economists think the Fed will wait for a later meeting to make any adjustments. Unemployment, at 7.6 percent last month, is expected to fall to 7.5 percent in July.
(Read more: US consumer confidence retreats, misses estimate)
"Our view is it's steady as she goes for a lot of things. Now is not the time for the Fed to be doing anything, but just clarifying stuff," Goncalves said. "If ADP is bad, and it's followed by weak GDP , they could sound very dovish for sure." He and others say the Fed could choose to taper back a smaller amount in September if the data does not pick up.
There is also a blast of early earnings news, including reports from AB Inbev, Comcast (CNBC's parent), Diageo, Honda, MasterCard, Energen, Talisman Energy, Southern Co, Humana, Delphia Automotive, Booze Allen Hamilton, Sodastream, Hudson City Bancorp, LPL Financial, Alcatel-Lucent, PG&E, Hess, Exelon and Garmin.
After the closing bell, reports are expected from Allstate, CBC, MetLife, Dreamworks Animation, Whole Foods, Marriott, Suncor Energy, Shutterfly, Trulia, Questar, Cabot, Murphy Oil, Lam Research and Yelp.