Official test results of fuel inlet presure/timing

[BrandonMag]

Thanks for the information, Mel.

When I start my truck up in the morning, I turn my Facet pump on just before I start cranking (after the WTS light goes out). I've noticed in the past couple of weeks that if I turn the pump off, the engine gets noticeably quieter. I thought it may have had something to do with the increased fuel pressure, and now I know for sure.

 

[Clb]

So @Agnem
Does the extra pressure acording to this when causing retarded timing ,

1 Permanently across the range ...idle to governor retard internal availability,

or 2 just the static point of the event( ex. Its knocked back 1 deg from 9.5 to 8.5, reset to 9.5 and all is as normal?

Edit
For pulling loads, if the loss is internal, and it ( guessing here) would be a detriment to the power curve, them would putting a regulator in front of the ip cure the issue?

Thanx cb

 

[laserjock]

Just to ask it another way, for the average Joe, will it even matter so long as the timing is set at 2000 RPM? At that point you are pretty much in the middle of the band so it should be reasonably linear to either side I would think right or am I misunderstanding that? When you reference the advance in timing at idle is that from where it was set at 2000 rpm? I picked up the 9-11.5 psi version of the facet pump figuring that with the fuel filter in there, chances are pretty good the running pressure would be in and around 7-9 psi. That should help with some of the starvation issues I've seen folks have (like at WOT). Yes pressure and flow are different but the filter being a restriction, delivering the same volume at a slightly higher pressure should be beneficial at times of high demand. Given Mel said about 0.25 degrees advance at idle per psi over 5, even at 10 psi you should be a little over a degree advanced at idle. Probably not a big deal but something to definitely be aware of.

 

[Agnem]

Look at it this way... you will have about 10.5 to 12 degrees of internal pump advance. Too much inlet pressure will start to amputate the range at the top, so now instead of 11 degrees lets say, now you only have 8, or 6.... this will affect your lower RPM power under load as well as cut off your cruising timing. You cannot compensate externally by changing the way you rotate the pump body. You can always set the timing to 8.5 as long as the pump body slots will allow it. The range is the range... it has nothing to do with where you set the pump.

 

[raydav]

So, is fuel pressure induced timing change a good thing?

I can add another data point to this subject. And that is the observed performance difference between 5-7 pounds and zero.

My supply pump is on the frame at about the mid point of the vehicle. Thru a switch, I have the choice of the pump running either when there is oil pressure, all the time, or not at all; off. Several times I have driven off with the the pump in the off position, and didn't notice any difference. The IP pulled fuel from the tank, thru the supply pump.

 

[gandalf]

Thanks for re-posting this, Mel. It's something we should all be aware of. I have this one bookmarked.

 

[teletech]

I hadn't seen this before, interesting.
I've got an '85 that has the original mechanical lift pump. I've been tempted to change to an electric system, but as long as the system stays tight it always has seemed to work OK. This timing data makes me ponder how the fuel pressure varies with load and RPM due to the mechanical fuel pump. I guess a drive with a pressure gauge hooked up would provide interesting data.

 

[Macrobb]

You probably want to upgrade your mechanical pump due to it's age.

That being said, with a /good/ mechanical pump on my '93 and it's big IP, I'm pushing 4 at idle, 3 at WOT. It *might* drop to 2.5 worst-case, but generally it's within a 1-psi range(I have a mechanical 0-15 psi gauge).
This is measured after the fuel-filter as well.

Going back to the original topic, I wonder what the test bench would show in the 0-5 psi range. Does the timing curve expand(more range)?

 

[Clb]

Ok obie whan...

Mel
With this discussing - primer I have an issue to run past ya.

93 in my sig 47k on truck new bb codes from your standyne supply???? Or delphi's???
I have one of the carrier group buy pumps on the frame rail under cab.

Spooled up with 5 k on the hitch pin(5er) new filter (fuel) the filter idiot light comes on.

Could the pump seriously be under flowing\supplying the ip?

Lines are clear, fsv flushed and I shot air thru it, 2 fresh fuel filters,timmed, air filter good, fuel tanks full.

 

[Macrobb]

Ok obie whan...

Mel
With this discussing - primer I have an issue to run past ya.

93 in my sig 47k on truck new bb codes from your standyne supply???? Or delphi's???
I have one of the carrier group buy pumps on the frame rail under cab.

Spooled up with 5 k on the hitch pin(5er) new filter (fuel) the filter idiot light comes on.

Could the pump seriously be under flowing\supplying the ip?

Lines are clear, fsv flushed and I shot air thru it, 2 fresh fuel filters,timmed, air filter good, fuel tanks full.

Not that I'm an expert, but that filter light comes on for one of two reasons - either the wire is loose and shorting to ground, or you aren't getting fuel pressure through the filter. Get a mechanical gauge and check it.

 

[hesutton]

Yeah, gotta check your fuel pressure after the filter. On my IDI's I run a fuel pressure gauge in the cab so I know what it's doing all the time. The Autometer sender is in the filter head where the factory filter light sender would go on both my rigs.

Heath

 

[Clb]

Bumping this back up to the top for
@tbrumm