So your thought is that the HPOP reservoir has to see pressure before the HPOP can make pressure? That is not making sense to me. Would it not gravity feed the HPOP? Why do guys that have a bad LPOP get the truck to run briefly when they refill the HPOP reservoir?
I an not disagring with a lot of what was posted just not in agreement on this point but interested in discussion on it.
If the lube oil system is functioning, then yes, the high pressure system can fire off of the non-pressurized oil in the reservoir and then run the truck long enough on the oil in the res for the lube oil pump to catch up and refill and pressurize the reservoir before the pump sucks it dry.
This is obviously not the case for this guy though, as he already stated the truck to fire up, then die a few moments later. That means that the reservoir is being pumped out by the high pressure pump and the lube oil pump is not replenishing it. The high pressure pump runs dry and the truck dies before the lube oil pump primes and refills the res.
Once this has happened the high pressure system is then rendered useless until you see lube oil pressure on the dash again, then while cranking usually within 1 to 2 seconds of finally seeing lube oil pressure you would see high pressure take off and the truck would fire and run ragged for 2 or 3 seconds before smoothing out again.
To re-itterate again...
On a properly functioning truck, with a filled reservoir... if you crank the truck the high pressure pump will begin pressurizing the heads and fire the truck before any pressure is acheived in the res by the lube oil pump, then a moment or so after the truck fires you will see lube oil pressure come up on the dash gauge.
In that case yes..... high pressure will happen without lube pressure, as the res is full and the high pressure pump will run off that volume while the lube pump primes.
However.... once the res is empty and the trucks dies out, the high pressure pump no longer has this option. It's running dry. At this point, there must first be lube oil pressure before high pressure. This is because the res will not fill slowly enough for the pump to pick up oil before pressure is reached in the res. Once the lube pump primes the lube oil will fill that res nearly immediately, and the pressure will come up before the high pressure system can refill itself and purge the air. As I said, usually takes 1 to 2 seconds after seeing lube oil before you see the high pressure gauge jump up and the truck fire off.
No different than what happens after an injector swap. Crank, crank, crank, crank, crank, crank then bing.... there goes lube oil.... then one-one-thousand, two-one-thou..... bing.... there goes high pressure and ROMP..... it comes to life.
