You gave me the light bulb moment that solved the issue of OBD2.
I was wrong. All the rest of you who told me I didn't need it were right.
Here's were my mistake was. Jaguar V12 has a stand alone ignition system. Using a Chevy module to trigger the ignition.
Yank the ECM off and replace the EFI with carbs and it still runs.
I kept wondering how the system knew it was a 12 cylinder and not a V8. I had read many times it was batch fired. But how does the system know it's a 12 cylinder.
Finally it dawned on me. It doesn't, it just squirts a bunch of fuel and the valves open when it's their turn. The amount it squirts is based on input from the various sensors.
The light bulb moment was PaulVR6 said if there is something wrong it won't run. In my head my hypothetical was say the fuel pressure sensor went out. All I knew was the engine stopped running.
Paul VR6 said the data logger would have that information. Hook up the lap top see what information was off and go from there. Bingo !
Several had told me that earlier. But since I didn't ask the question, nobody explained it.
I kept going back to the idea of input from the OBD2 but you were right, it's displayed in the laptop. Hooking up the laptop takes about the same time/ effort as plugging in a reader.
Honestly, I figured you had a basic understanding of EFI when you started that thread. Most all OEMs started with a Bosch designed system. When I first started playing with EFI cars, I read the Bosch EFI book. Diagnosing, repairing and tuning will be much easier if you understand this book.
https://www.thriftbooks.com/w/bosch-fuel-injection-and-engine-management-bosch_charles-o-probst/400349/item/4525087/?gclid=CjwKCAiAo4OQBhBBEiwA5KWu_yL-6Xz7A2JT_rPXEgNzjWRHFl7StWZLc1b8VDB2g3uBOqgxuqGDbBoCBaAQAvD_BwE#idiq=4525087&edition=3629221
This is a way newer version than what I read, but I'm sure it still covers the basics and painful details.
AnthonyGS (Forum Supporter) said:
Honestly, I figured you had a basic understanding of EFI when you started that thread. Most all OEMs started with a Bosch designed system. When I first started playing with EFI cars, I read the Bosch EFI book. Diagnosing, repairing and tuning will be much easier if you understand this book.
https://www.thriftbooks.com/w/bosch-fuel-injection-and-engine-management-bosch_charles-o-probst/400349/item/4525087/?gclid=CjwKCAiAo4OQBhBBEiwA5KWu_yL-6Xz7A2JT_rPXEgNzjWRHFl7StWZLc1b8VDB2g3uBOqgxuqGDbBoCBaAQAvD_BwE#idiq=4525087&edition=3629221
This is a way newer version than what I read, but I'm sure it still covers the basics and painful details.
Yes I read and reread every book and magazine article I could get my hands on. I've got a whole crate of just EFI books. That are actually dog eared.
I guess I just learn different. In Navy Flight school everybody but me got done flying they went out. Me I stayed on base rereading and rereading the books assigned. The verbal test the next day I always did well because I had actually memorized word for word everything in the book.
I didn't know what it meant but I sure did well.
OBD2 has a lot of useful diagnostic capabilities - the catch is that it takes a team of factory calibration engineers to program in what conditions trigger these. Well and good if you're using it to tune the engine they set the OBD2 up to diagnose. A massive headache if you've tried to transplant the OBD2 system onto a completely different engine. You'll have an easier time looking at the raw sensor readings to see what is and isn't working.
Np frenchy. Obd2 even gets wigged out by modifications. Back in the dark ages we could tell we were on a run bc the ecu would be showing misfires on rapid accel bc the rate of change math was both ways and we could trigger it by revving too fast. A few passes in we would have to reset the ecu 
Hey thanks to everyone who tried to help me understand EFI. I'm sorry I failed to understand .
Please let's not make it a Frenchy problem
I know there are plenty of people willing to help others here. Let's try to keep this site open?
Post your questions, problems, thoughts, solutions, and guidance.
If you have a good experience with a company ( or bad) product or equipment talk about it.
Ask the site moderators if it can be done.
The wonderful thing about GRM is the community they have generated. I feel positive they will respond if sufficient interest is shown.
