Really need help with the last small issue with my 90

[Corvette95]

OK, so this morning...I do have video of fuel pressure but that is not the issue. Today I started it while recording with DataCat. While Tech1A shows no codes, no RPM drop etc. All HELL breaks loose on first start...I am not sure I can post the video file from the DataCat, but I can post screen shots. First one is from the first start of the day..looks at all the data drops and errors, even no rpms...then look at longer view with multiple restarts, after first start, no errors, no crazy readings. I am not sure to look at crank sensor, cam sensor, DIS or ECM...gotta think about this???

[Ccmano]

Originally Posted by Corvette95

OK, so this morning...I do have video of fuel pressure but that is not the issue. Today I started it while recording with DataCat. While Tech1A shows no codes, no RPM drop etc. All HELL breaks loose on first start...I am not sure I can post the video file from the DataCat, but I can post screen shots. First one is from the first start of the day..looks at all the data drops and errors, even no rpms...then look at longer view with multiple restarts, after first start, no errors, no crazy readings. I am not sure to look at crank sensor, cam sensor, DIS or ECM...gotta think about this???

Not sure what I'm looking at? What signals are those? The problem here is you have no basis of comparison. For all we know this could be normal.
H

[Corvette95]

If you look at first photo, that is a screen shot of the first minute of running. The parameters and colors are in the boxes up top that correspond to the graphing lines...It shows RPM count goes to zero multiple times, DIS signal failure several times, Cam sensor signal lost (Green line) (all momentarily) . This is all happening while its running, even though it is idling, the crank reference signal drops to zero (RPM's are the blue line). Basically every major sensor is spiking way up and way down, DIS reference volts there, then gone. This has to be ECM, DIS . I just checked (the best I could) the DIS connection for tightness.... Then the next screen is the restart..all normal, no errors, no spikes in ANYTHING.

[Corvette95]

Here are some more simplified examples...these shows all sensor inputs waaay on and off and out of range .this is again the first start of the day....The lines correspond to the checked boxes above. RPM is Blue.

[Corvette95]

This is second start after cutting ignition off and immediately restarting..every fine and normal.

[Ccmano]

All true, but until I can see similar data from another car that is operating normally we don't know if this is abnormal. Did you start the car as I previously requested, if so what was the result? The other thing that strikes me is the battery voltage. It is suspiciously on the low side of normal at 12.2 to 12.3. I would prefer to see a resting voltage of 12.5 to 12.7. I know it doesn't seem like much but I've seen these cars do very strange things with low battery voltage. When the car is running it should be 13+volts.
H

[Corvette95]

Originally Posted by Ccmano

All true, but until I can see similar data from another car that is operating normally we don't know if this is abnormal. Did you start the car as I previously requested, if so what was the result? The other thing that strikes me is the battery voltage. It is suspiciously on the low side of normal at 12.2 to 12.3. I would prefer to see a resting voltage of 12.5 to 12.7. I know it doesn't seem like much but I've seen these cars do very strange things with low battery voltage. When the car is running it should be 13+volts.
H

Yes, here is the video you requested from this morning. It did not stall today... but this is when the datacat was running that you see on the prior posts. https://vimeo.com/449330176

[Ccmano]

Originally Posted by Corvette95

Yes, here is the video you requested from this morning. It did not stall today... but this is when the datacat was running that you see on the prior posts. https://vimeo.com/449330176

So it started without the stumble and die out when you let the pumps run. It still cranks a very long time before starting. The long cranking may be related to your readings. What is the battery voltage without the ignition on and once it's running?
H

[Corvette95]

Originally Posted by Ccmano

So it started without the stumble and die out when you let the pumps run. It still cranks a very long time before starting. The long cranking may be related to your readings. What is the battery voltage without the ignition on and once it's running?
H

Well, I honestly have done that exact same thing for the past few weeks, even have it past videos posted here. Today was a fluke that it didn't die but I have been watching fuel pressure each time.....I tightened the DIS plug about 1 1/2 revolutions on the 1/4 inch bolt. The voltage ignition off engine off is 12.85 and 14.3 running. Measured with volt meter. I have been keeping a battery tender n it every night. I have a new AC Delco battery here that I am going to swap out and slow charge tonight (just to be sure even though it is brand new) and see how cold start goes in the morning. You are right about possibly voltage related, if not battery itself maybe noise from alternator. Will post again at my regular time tomorrow. Thanks!

[Corvette95]

As I wait for tomorrows cold start, I am leaning (and hoping) this is a bad alternator regulator (was just rebuilt - zero miles on it) or bad new AC Delco battery..it tested good at parts store but still suspect. Here is the first moments of the cold start cycle....