Sullair 375 air compressor ( CAT engine)

[senpai01]

We have a sullair air compressor that has high rpm issues at our shop. The SSAM flashes 4 times saying uts underspeed.

So a CAt tech came and said it was an ecu issue, which was replaced (quite some penny for the client). Found out it wasn't the issue so we went through the rabbit hole.

Thought it was the tac signal from the alternator, checked and it was alright (7.5-8.0 VAC and 315-330hz). Checked continuity from the alternator to the SSAM, it was good.
Replaced the electronic speed controller and the pressure sensor, still nothing. Heck we even cranked up the psi as stated by a sullair tech service provider.
What could be the issue, as I'm stuck

 

[Vetech63]

Have you verified the loaded speed of the engine? How long will it run before it shuts down?

 

[senpai01]

Within a minute it will shut down if we are at high rpm. But when we unplug the relay it will run but still at low rpm.
at load speed it should hit 2200 from what the sullair tech guy stated

Have you verified the loaded speed of the engine? How long will it run before it shuts down?

 

[Vetech63]

What relay are you unplugging?

 

[senpai01]

The one that shuts off the machine when it runs at low rpm on load. I was told to unplug to check if its an engine related

What relay are you unplugging?

 

[senpai01]

Update on the machine:

after talking back and forth with Sullair tech support, we took the machine to CAT to deal with the engine underspeed. Sure enough they fixed it, as Sullair stated if there was underspeed issue and they put the wrong program it wouldn't kick high throttle.

even on our end with the CAT software from another heavy duty tech, he could not bump up the rpm (as if it was locked)