Hi Pro,
This is not a viable option because the VSM (vehicle systems manager) on the trucks would not allow it. However there have recently been multiple service grams put out by NACCO pertaining to flash upgrades for the ECU, Regulator, and VSM that should help your problems.

Is it possible to copy the old ecm and reload it into the newer style to make the system run richer? I do not have any problems with the old style trucks that have no pressure sensor on the fuel rail.

Pro, You cannot enrich the mixture without getting a code. The tolerances for the rich and lean are so tight that the slightest adjustment will give you codes. When Yale made the switch to the emission controlled engines all the programing was set to tight. You might be able to get an after market ECU that would allow you a wider range of adjustment. I have not tried this and not sure it would work or if it would be compatible with the current system. Good Luck.

Garland thank you for the information. I think I better try the newer version of this head. I don't understand why the older fuel system has had no failures while the one with the pressure sensor on the rail has had 5 failures this far.
Steponmebbboom I have used this machinist for twenty plus years. Never had a problem, until these heads. He said this was an automotive engine converted to use propane and was not designed for it. I do understand that he has no knowledge of propane use on a forklift. The old 3.0 yale and hyster used was a marine engine. There are several others that have also used automotive style engines in forklifts with no problems. I do not accept his answer as the gospel. I am wondering about running them to lean with excessive combustion chamber heat. will this cause the seats to recess into the head? How can you richen up this style lift without getting a code?

Can these issues be addressed by a competent rebuilder? I have had heads cut before for nickel seats.

Pro, Yale has replaced the 2.4 cylinder heads with new and improved, part number 582002516. The original heads did have problems with the valves and seats. Not sure how good the new head is as this is the second update for the 2.4. The new cylinder head features hardened seats with higher contents of chrome, molybdenum, cobalt, and nickel, and nitrided valves. Hope this helps.

Just had a glco50 with the Mazda engine and impco fuel system at same customer start missing and it proved to be #1 valve lash to tight. Suspect valve recessing in head on this one too. Any ideal what causes this? Truck had 9600 hrs on it.