I have a GMC C4500 at work throwing the P01093 code and I was gonna shim the relief valve and see if that solved the problem.

Thanks Brett

The 4500 is sorely in need of a fuel lift pump setup and THIS is what you should really do first. Chassis length, ft of head between engine and tank etc all add up...

As for the shim mod, I would do a bottle test to verify first but a 4mm washer typically handles this. 2ea.


Post should be in Fuel/air systems forum.

Thanks for the info