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Message: [QUOTE="IHPowerstroke7.3, post: 1282633, member: 7642"] The change in pulse width from 3rd to 4th yes, but its not like the pump is driven by the engine, so RPM has no direct effect on fuel pressure. On a obs using the in valley pump yes that would affect it. Only in tank mod it had done was a 5/8" pick up, with a 5/8" line that was reduced to 3/8" (or whatever stock is) to factory pump. He was told to put it back to stock and replace the stock pump with another. So that is what I did, blew out the factory line and re connected the line to the pump (it was capped off) Problem was there with the 5/8" pickup and when the stock line hooked up its the same. As far as the low ICP causing low fuel pressure, I have a basic understanding of everything that happens inside a heui injector. Way I understand it is like this. Lets say ICP is supposed to be 3000 psi, fuel pressure is 60 psi and pulse width is 3.0 ms (using random numbers so don't read into it.) If the hpop drops pressure, lets say to 2500 psi, the injector is not going to inject the same amount of fuel into the cylinder as it would if icp was 3000 psi at 3.0ms. If the IPR is already maxed out, only other thing the PCM could do is increase pulse width to say 4.0 ms, holding it open longer to inject the desired amount of fuel into the cylinder to meet the mass fuel desired. Obviously the fuel pressure is going to drop a lot more than normal if all 8 injectors are draining more fuel than they normally would (if that makes sense) I'm using random numbers, tomorrow I plan to go out and log some data and see what is actually happening. Without knowing the tune, I can't say what pulse width the PCM is calling for under normal circumstances. But if I see ICP dropping off and I see a stupid number for Pulse width after the drop in ICP, then it may be the issue. Sorry for my stubbornness when it comes to the line size, restrictions on all of that. But if there wasn't a problem with the truck before, I can't see something that can't physically change (line size) being an issue now. Restrictions such as a fuel pickup, yes, but changing the pickup did not have any effect on it. Changed the regulator, says the filter is new, i'll confirm that first thing tomorrow. [/QUOTE]