Spring from the low pressure engine, you can see it stretched in the middle:
Spring from the good pressure engine:
Comparison between the 2:
Yesterday I wasn't able to remove the relief valve from the low pressure engine (goes in front of the spring), so decided to mess with it today and was able to take it out. As soon as I had it in my hands I know something was wrong as the 4 holes it has the edges had burr like if they had been drilled and all the edges of the relief valve were sharp, and it had scratches all over it so I sanded it with 2000 and 3000 grit and then using a file I eliminated the burr on the 4 holes. Installed it back and pressure went up to 40 psi, left the engine running and in 15 minutes, pressure was down to 15 psi.
Decided to remove the relief valve from the other engine and thats when I saw what had been done to the other one, the 4 holes had been drilled and also the piece had been cut.
Relief valve from the low pressure engine:
Relief valve from good engine:
The 3 differences between both relief valves are: the size of the holes, the distance between the holes and the lower part, the width of the lower part (has been cut).