[Mudog715]

I split this out to a separate thread for clarity.

My original question:

"What happens when the EEC loses the CID sensor signal? Does it revert to batch-fire? It would have to, right, since it has no idea when it's on cyl 1? Or does it continue to sequentially fire the injectors, using the first TDC it sees as Cyl 1? Or does it "guess" at Cyl 1 based on the missing tooth from the CKP sensor, on the basis that it has a 50/50 shot of getting it right?"

Someone was kind enough to point me to the CDAN2 strategy doc. Here is what it says:

The CID_PROCESSING strategy is designed such that if the SYNC_CTR is
synchronized and the engine is in the run mode, the request to synchronize
fuel with PIP is issued.

[SYNC_CTR is apparently reset to 1 every time Cyl 1 is detected by the CID sensor and then increment by 1 on each successive TDC event (PIP signal)]

If the CID signal is lost, the value of SYNC_CTR will become greater than
NUMCYL after the engine cycle (720 degrees crank) is completed. The strategy
executed during the PIP interrupt checks if the CID signal is lost by
determining if SYNC_CTR is greater than NUMCYL. If a CID signal is not seen
for two cycles (1440 degrees) of the engine, the system will assume CID
failure and revert to injector on-edge timing at the nearest PIP edge.

Unfortunately, it does not seem to define what "injector on-edge timing" means. Does that mean it will go to batch fire or just stay sequential, chosing whatever cylinder happens to hit TDC next as "Cylinder 1"?

Anyone know for sure?

[Mudog715]

For the record the answer appears to be that it continues sequential injector timing, using the next PIP reference after the failure is detected as "Cyl 1" (which since it takes 2xNUMCYL to detect the failure, the PIP reference it will use will be (2xNUMCYL)+1 or 17 PIPs on a V8 after the loss of CID) and continues from there. So basically in the absence of a CID pulse, the EEC randomly chooses what will be cyl 1 and proceeds to fire the injectors according to the order set in the strategy. Apparently, batch-fire is only used during cranking and underspeed modes.