LPG operated usually fine but drops pressure after a couple of hours continous use in our coffee van. Pressure will rise again after 10 mins or so. How do we stop this from happening? Jan

I would take a look at what is different in the morning than at night. Is there some type of environmental factor (Food, activity or stress)? Is there a medication that you are taking that is affecting your blood pressure? Is that medicine wearing off or are you taking too much? This should be considered as well. You can try performing some detective work yourself or set up an appointment with your primary care physician. Good Luck.

Not real familiar with your engine, but generally you have two coolant temp sensors. One just runs the dash gauge. the other speaks to the computer and acts sort of like a choke. If the computer thinks the engine temp is hotter or cooler than it actually is, fuel metering will be wrong. The more likely culprit is the low fuel pressure. I have even seen a bad fuel cap cause something like this, as these systems operate under pressure I believe.

You have to let the system run for a while for the suction pressure to stabilize, if the metering device is a TXV pressure will rise and fall as the valve opens and closes. If this is R22 you need to get the suction pressure up

Have you put a pressure gauge on and then drive to see if pressure drops. If it does it is likely the pump. Sometimes these problems lead to it being the computer.

I know you said new fuel pump and filter but I would recheck the fuel pressure. Drive the vehicle with the fuel pressure gauge on it and see if the pressure drops after 10 minutes.

Sounds like there may be a fuel filter problem, try replacing the fuel filter. Specially if you have not done it over a while.

Replace the fuel pump relay, it's easy and cheap.

is oil filter clogged???

POSS FUEL PRESSURE LEAKING INTO INTAKE VIA FUEL PRESSURE REGULATOR

your engine needs flushed .what is going on is idle has less pressure than driving and the sump is picking up dirt and debris but when you turn off or idle the debris falls off the sump.