Does anyone know the max IP inlet pressure? I'm running a duralift e-pump that is putting about 7psi at idle. It drops about 1psi for every 1000 RPM's. I read that IP inlet pressure can affect timing.

 

 

I don't get the thing about timing either, but I wanted to ask.

A long time ago, I forgot to turn my duralift pump on, and I drove for 5 miles with 0 pressure. I didn't notice any timing change from 7psi to 0psi.

 

factory calls for 7 psi at idle.

 

It's kinda like the Duramax;s that dont use a lift pump, the CP3 sucks the fuel right from the tank, witch is why the duramax eats injectors and pumps. Guy's add a fass or air dog system to stop that. as long as you have a tight fuel system it will run with no lift pump, but that is only if you have a tight system.

 

What's really important is a consistent fuel pressure. It can be 0, as long as it's 0 at idle and 0 at WOT. You could probably get away with 9, as long as it's consistent.
Varying pressures will definitely affect timing, more than enough to be noticable - lower pressures = more retarded, so you'd see it as a quieter engine under heavy throttle, and perhaps white/gray/blue smoke.
Personally, my mechanical pump on my '93 puts out 4 PSI at idle, 3 at WOT, driving a RD2-110 IP.

I recently swapped a 'new' engine in and ended up with an older filter head(and filter attached to it)... the filter was partially clogged, evidently, because it triggered the fuel filter light(vacuum sensor on fuel filter) at WOT.
That made a massive difference when I swapped a new one on it, even at idle - I ended up adjusting the engine 3+ degrees from where I had adjusted it, just going to a new, non-clogged filter.

So, yes, a few PSI does make a difference in timing.

 

I'm not really convinced fuel pressure affects timing. Here's why: I have two fuel circuits that have a selector valve on the inlet to the IP. I have a fuel pressure gauge on that section of hose from my selector valve to the IP inlet. When I run my IDI on the stock diesel circuit, I get around 6-7psi. My timing is at 4.5 deg BTDC. I had a friend switch it to the other biofuel circuit, which due to all the heat exchangers, different filter head, and different fuel pump, gets about 3-4 psi at the IP. My timing strobe never showed any deviation from the 4.5 deg BTDC when my friend flipped between the 4psi system and the 6psi system.

But then again, I was testing that on a what I now know is a busted IP, so maybe that affected it.

 

The lift pump force feeds the tranfers pump which is a vane pump nice postive pressure into the ip. So when the injection cycle starts the plungers are preloaded with higher pressure so when peak pressure is reached injection happens at an earlier point. Now you need quite a pressure change to make a big difference but it can happen.

 

The next time I time my engine, I'm going to time it with the e-pump on, then while the engine is revving at 2000 RPMs, I'll flip off the e-pump and see what happens. I'll post a video of what I find. My piezo clamp should read a slightly earlier injection pressure if the pressure is higher.