Found a GM smog pump with stamped number 7801149, another stamped number D13, and a casting number of 247, all on the cast rear cover. On the housing, there is a stamped number 09991S. Can anyone decipher this?

7801149=part # of the rear pump cover which wasn't available as a separate part, this cover was on the 7806686, 7801512, 7802609, 7803948, 7803947, and probably other AIR pumps.
I'm not certain of the other numbers; my pump has a D24 and 166 on it, the pump date code is 283 7 (Oct 10, '67) for a 3rd week October car build.
The date code on AIR pumps was stamped on a rear cover bolt boss on the aluminum pump housing and is a Julian date. 099 9=May 9, 1969. 1S, I don't know, mine is stamped 1Y.
BillL

Mines has the same number on a 11A built 69. Here's a pic. Looks like a 270 and a D6 also. Bill, should I have an 8 somewhere around the 270?

http://i44.photobucket.com/albums/f26/ccarney69/69%20Chevelle/Smog%20Pump/P1010104.jpg

Chris, I don't think so. IF the 270 number is the Julian date of the casting, then it would go from 001 to 365, or 366 if it's a leap year. I'm wondering if the "D" numbers could signify a casting die.:confused:
Here are two pics of the pump date code to make it easier for you to find and a pic of my pump's rear cover
BillL

http://i113.photobucket.com/albums/n219/pvpatriot1/Smog%20pump/Smogpump004.jpg

http://i113.photobucket.com/albums/n219/pvpatriot1/Smog%20pump/Smogpump002.jpg

http://i113.photobucket.com/albums/n219/pvpatriot1/Smog%20pump/Smogpump003.jpg

Thanks guys for your input. Attached are pics of mine, came off my 05A Baltimore built 396-350. However, believe the 09991S code should be April 9th, not May 9th, maybe "S" is Saginaw plant 1st shift? Could the D13 be a date (Apr 13th?). Just got it back from rebuild and restoring.

You're right, April 9. I can't count. :clonk:
The pumps were built by Rochester, so I don't think the "S" would be for Saginaw.

As for "D" being a date code-it's a bit odd that cars built in May, October, and November with smog pumps dated April, '69, October, '67, and what ever Chris's is dated (I'm guessing October or November, '68) would all have rear covers built in April. If the other numbers on the cover are casting dates (and I believe they are), then the covers were cast on June 15 for a Oct 10 pump, Sept 27 for a (guess)Oct or Nov pump, and Sept 4 for an April 9 pump.
Again, I don't know for sure.;)
We need some more guys with '68 and '69 pumps to chime in with the numbers off of their pumps.:)
BillL