Really need help with the last small issue with my 90

[Corvette95]

So this morning, new battery installed yesterday and trickled charged all night. Starting voltage was 13.35...started..cranked....same thing..DataCat shows all type of issues...restart fine, datacat fine...start....fine. This is what I tried this morning..because if its a ECM issue, why overnight sit? I unplugged battery, sit, rehooked battery, started fine Removed ECM, reinstalled , no change.started fine...WTH? The only thing else I know to do is let it sit again, and start tomorrow with alternator unplugged. I did check alternator voltage while running, no fluctuations..charging +/- 14.10 volts steady?

[Ccmano]

Does the car have headers as well as porting? Are there any other mods?
H

[Corvette95]

No headers. Catback only. I don't understand how it makes a difference to sit overnight and always do the same thing on first start, while unplugged the battery and ECM wont re-create the same issue? What happens on first cold start that doesn't happen after disconnecting battery and ecm and even letting it sit for a few hours? I know there is a lot of brain power here on the Registry. I have the ECM in the freezer right now..trying to figure out how to duplicate more than once a day.

[Ccmano]

Since you have owned it has it ever not had this problem?
H

[Corvette95]

I bought it in February, drove it 5 miles home then the virus hit so I went straight into the restore while the shutdown was going on and I had some help. The only known problem was an intermittent no crank. It just needed the starter relay added which I did, and the starter valley had never been cleaned and I replaced the starter...it fixed the no crank . So I never really drove it, the few times I cranked it before I took it apart I am sure it cranked and died and restarted fine..didn't think anything about it as I figured the full service, fixing vacuum leaks , and other would solve any hard start issues. It received a full by the numbers tune up , restoration, fluids, all. So when it became hard to start back assembled, I knew it wasn't right.there was no reason for it so I began the hunt. It had an aftermarket alarm and vats bypass on it that I removed. Everything is back to stock minus the starter relay.

[Corvette95]

Started fine this morning. Only difference was I unplugged the alternator before first start. Battery was full 13.35 volts. May or may not had anything to do with it. Of course, running like it just rolled off showroom floor right now. I am not going to start it again today and give it a 24 hour cool down.

[Ccmano]

Originally Posted by Corvette95

Started fine this morning. Only difference was I unplugged the alternator before first start. Battery was full 13.35 volts. May or may not had anything to do with it. Of course, running like it just rolled off showroom floor right now. I am not going to start it again today and give it a 24 hour cool down.

Was the cranking time any shorter? Mine starts within 2-3 seconds when cold right now.
H

[Corvette95]

Yes, it was 2-3 second crank with no issues.

[Corvette95]

I did having it running later last night than usual , about 6pm so the cool
Down period was a few hours shorter than the others .

[Ccmano]

That would be interesting if 'noise' from the Alternator was interfering with the crank and cam signals to the ECM at cold start.
H