Code 37 is usually the temperature circuit that will not let the transmission go into overdrive until the transmission is warm. I have by passed that circuit a lot of time.
The 5.9 is usually a bullet prove old proven engine and I do not understand what could be happening. I wish I was there looking at the engine.
Let's try one more thing Take out number one plug and hand bring the cylinder to TDC. (Number one is the cylinder head that sticks out the farthest). I put a long screw driver in the plug hole and feel the piston at the top. Check your front pulley timing mark and make sure it is exactly on TDC.
Make sure the rotor points to number one cyl in the distributer cap.
I want to eliminate all timing issues. Let me know!
Tuesday, December 15th, 2020 AT 2:52 PM