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I have a ZTR mower that had a failed Kohler engine. Replaced it with Vanguard EFI 28 hp. Changed the pin orientation of the Molex connector on the ZTR to match the Vanguard motor. I have no safety switch issues that would stop fuel pump from being energized. The engine cranks, I have spark, but no start.
The vacuum operated fuel pump is working. I have fuel at the pressure test port, but no high pressure. The high pressure fuel pump is not receiving the negative from the ECM for the pump to run. I do have the positive from the MPR when the switch is turned to the run position.
I know a safety switch in the wrong position stops starting by way of the ECM not sending negative to the fuel pump, but I do not have this problem. I do not know what other conditions would cause this situation.
I have read through the repair manual and made many voltage checks coming to the ECM. All inputs I checked have been good.
I have searched for some kind of logic flow chart or something to become more familiar with how the system works as a whole.
A new engine should not have this issue.
Any suggestions would be greatly appreciated.

Mechanic Mark you must be the bravest one out there! No one else wants to touch this. I appreciate you response. I have poured over all this information and read through the troubleshooting in the repair manual as well. I need to understand how the ECM manages the high pressure fuel pump, but a complete understanding of the this system is not readily available to me. I was hoping to find a logic flow chart or some in depth description of how it works. The repair manual does not touch on the information I feel I need to figure out the root issue. I also do not have any experience with the Briggs EFI, but I was able to figure out on my own that the high pressure fuel pump was not working. I mean, you still have to have the basic requirements to make an engine run, right? Even if you now have some electronic box doling out some of the required stuff just when it wants! It just took a lot of reading to find out why I was missing the negative to make the high pressure pump run. I don't have a MIL hooked up yet. I am going to hook up an miniature LED bulb tomorrow and see if I can read any codes. Maybe that electronic box will have a nice blinking conversation with me and I'll find some other component to test.

First do you have a copy of the EFI-ETC Diagnosis and Repair manual? If not DL from the following link. Also not the EFI test software from Briggs no longer works on systems not using WIN10 or greater.

https://drive.google.com/file/d/1KIoo8INyRfo3gpAhsEeNttl3eGc99C0r/view?usp=drive_link

Second here is a note from that manual. OF course your not going have a ground signal after 2 seconds of initial turn on; unless, the engine is running or cranking.

Mr Fixit. said:

Changed the pin orientation of the Molex connector on the ZTR to match the Vanguard motor.

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I don't think anything in this connector would be causing the issue but to be sure, have you double checked that you got the correct pin orientation?

The other thing I would check, and maybe you already have, is continuity from the ground at the fuel pump plug to the corresponding pin in the ECU connector. In other words, make sure the ground at the fuel pump is connected to the ECU.

Mr Fixit. said:

A new engine should not have this issue.

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Agreed

I don’t know if this service bulletin will help you out, but I thought I would pass it on. https://www.lawnsite.com/threads/37-hp-efi-vanguard-on-72-ferris-starting-issue.505229/
Also this service manual is available if you want to subscribe. https://www.scribd.com/document/538854661/vanguard-37-efi-repair-manual

StarTech said:

First do you have a copy of the EFI-ETC Diagnosis and Repair manual? If not DL from the following link. Also not the EFI test software from Briggs no longer works on systems not using WIN10 or greater.

https://drive.google.com/file/d/1KIoo8INyRfo3gpAhsEeNttl3eGc99C0r/view?usp=drive_link

Second here is a note from that manual. OF course your not going have a ground signal after 2 seconds of initial turn on; unless, the engine is running or cranking.

View attachment 68799

Click to expand...

I appreciate the repair manual. The one I found was from 2014 and was lacking. The 2021 version you have provided appears to have a lot more information and hopefully will provide the information I need to figure this out.
As far as the negative return from the EMC, there is never a time that there is a negative return to run the high pressure pump. Safety switch input to the ECM will keep the negative return from reaching the high pressure pump, but I have not discovered any other condition that would. Do you know the conditions that must be met in order for the EMC to provide the negative return.
Thanks

Thanks to everyone for the input and information. I finally got time to install the MIL late this evening to see if I could read any DTCs. Once I installed the MIL and turned the key on, the high pressure fuel pump ran for the first time. I turned the key off and back on and started it right up. I was aggravated with myself for thinking that I didn't really need a MIL. It is now very obvious that this engine will not run without that necessary MIL.
I am still working on the BB wiring diagram to bring it into the 21st century.