My 740 has been a work in progress over the last few months. A few weekends ago I tore into the engine and found that the head gasket was blown between cylinder two and three. This did not show up in the oil or coolant but rather during a leak down test you could feel the air passing between cylinder two and three.

After reassembling the engine I found that the fuel management system was having some trouble, something that probably pre-dated the blown head gasket. Around town the engine has plenty of power but once you take it out on the highway it surges and feels like its dropping a cylinder. I will make a list of what I know to help out in this process
- REX/Regina OBD 1 is reading off terminal 2, 2-2-2 Fuel Injector Relay, and 2-2-1 Lambda Sensor. When running test mode three all injectors click and the radio suppression relay clicks.
- Fuel pressure good (40psi at Idle, drops down to 35psi when open throttle body)
- Radio Suppression Relay connection cleaned and sealed.
- New Fuel Pump, Filter, Relay, Pressure Regulator
- Spark Confirmed with Timing Light, no codes on Terminal 6. New cap, rotor, plugs, and wires.
- Compression is good but not great (170 across all cylinders)
- No leak down test data, but can run this evening if desired.
- Replaced one injector with used, will swap back if necessary for testing.

As I continue to test this car it runs great up until about 2500 RPM and then surges and eventually trips the fuel pump relay and kills the fuel supply. This is a new twist to this project and would like to see if anyone else has faced this issue.

Thanks in advance for any wisdom!