[skunkwerks]

Originally Posted by John V.

HFR, my Data Plate shows 620419.

Is there a known decode for this?

I see patrick1234's is 620779.

skunkwerks, glad you jumped in. The Boss and I seem to have been the main skeptics. The partial VIN that Burgess posted does seem to eliminate the idea that it was a Pontiac Plant stamping. In particular, I note the "5" looks the same as on the '72 posted earlier and very different from the "5" seen on the subject ZC block. I'll accept your explanation as very plausible.

I think The Boss expresses a valid concern about possible grinding of what might have been a partial VIN. Worth a better look at that area. But if that checks out, I have no dispute.

The Bondo'd engine code area raises suspicion. But the fact that it was then marked as a XL code lends credence to the idea that whoever did it was led to believe the XL would be correct when in fact as a pre-March 15 Car Build, the XL is obviously incorrect.

And all signs indicate it should be a ZC, I am in full agreement on that point. But not a "rolling change" at all, not sure why you mentioned that. I now believe that all early year TAs and 455 Formulas produced for the Calif Market with auto trans and points Dist got the ZC as intended. The error is in the early year Engine Chart that failed to identify the ZC & ZA usage properly.

On the subject of the emissions decal, the Revision date on the drawing would have nothing to do with the Release Date for implementation of the changes. The drawing revision simply pre-dates the Engineering Release Date.

It is well established that the new Engine Codes entered production on March 15, 1973 (a Thursday) to comply with the EPA order. The PMD issued booklet that I mentioned earlier outlines this fact and a ton of other info about the related changes that were made.

The EUN breakpoint was 532727. The booklet also mentions that there were about 700 engines in inventory with EUNs below 532727 that were converted and confirms that they were to be repainted the darker blue engine color. Trans codes also changed. Even the Warranty Booklet and the Maintenance Schedule Folder were changed, all as explained in the 16 page "MID-YEAR EMISSION CHANGES" document sent out by the PMD Service Dept. that I have.

The Emission Label drawing Revision block shows that ZC & ZA were added on 8/9/72. I'm certain the ZC & ZA engines were released in time for the start of '73 Production. Perhaps they were designated late for F body use which might explain why the F body usage was not identified in the early Engine Chart. But it doesn't explain why the early Engine Chart failed to identify the ZC & ZA as California Only. Or why certain other codes weren't noted as "except California" on that same chart. That was surely a mistake.

I was surprised to learn that the ZC & ZA had a specific Emissions Label. That further establishes that patrick1234's TA was originally equipped with the ZC despite the fact the Shop Manual failed to show the F body application for it.

On 1/23/73, the drawing was revised again to reflect the March 15 engine codes, the ZC, ZA and all the rest of the early engine codes were removed from the drawing at that time.

The PK sticker continued in use for the late year XE, XL, XM, & X7. Curiously, the XA, XJ, XO, XT, & XY codes that appear in the late Engine Chart are NOT reflected on this Label Drawing.

I suspect there was a subsequent Revision to this drawing because I count about 15 new engine codes that are missing from the label drawing. Unless there was some consolidation of Engine Codes not reflected on the late Engine Chart, these missing codes needed to have a label associated with them.

The EGR change was NOT a rolling change. By all accounts, PMD continued building '73 cars with the original EGR equipped engines right to the EPA ordered cut-off date. This allowed PMD to use up as much inventory of Engine Assemblies as possible (to avoid having to convert them) but on March 15, by EPA order, they had to begin installing the new system.

What the label drawing does show is that PMD began the work to initiate the changes long before March 15. A LOT of engineering was involved before the change could be implemented in production. I'm sure PMD negotiated for as much time as they could. It would have been a pretty huge engineering task to reconfigure the emissions system and make all the changes that had to go along with that. I'm guessing EPA gave them about 90-120 days once the final order was issued and they had probably been in discussion and negotiation virtually from the start of '73 production as I'm guessing it didn't take long for EPA to realize what PMD had done and would have immediately called them on it to demand a change.

In fact, it wouldn't surprise me to learn that PMD might have stopped all production of '73s for a few days in order to prepare for the changeover of engines, trannies, etc. at all Final Plants to commence on Thursday March 15.

Regardless how it was executed, you can imagine the scramble that was involved. But I am convinced production of cars with the new EGR began on March 15 and not before.

John,
to clarify, rolling change on paperwork and documented book from GM. This was a clear oversight in some books as it was too expensive the change everything. Just saying.