Fuel pressure... pre/post heads

Mdub707 · Apr 3, 2013

I know this has been brought up from time to time, and in my circle of WVO burning buddies, it's talked about even more. Thanks to Dave @ veggiegarage.com I'm going to be running two 0-100psi EV2 fuel pressure gauges. One is going to be hooked in the factory fuel bowl of my 6.0, and the other will be in the manifold of my vegistroke. For those that are not familiar the vegistroke is basically a copy of the factory fuel system, except it feeds in from the back of the heads and hits check valves in the front. So when I'm on diesel, diesel is run through like normal, up to the fuel bowl, down to the heads, through the heads and out the back to a check valve on the vegistroke manifold. It basically creates a x-over line for the heads. The vegistroke is just the opposite, feeds into the back of the heads and hits check valves in the front, keeping the WVO and diesel separate. We run the diesel farther back to ensure that no oil is trapped there for the next time we switch over.

If this all sounds like chinese to you, don't worry. The whole point of this is I'm going to run two fuel pressure gauges, one reading at the fuel bowl, one reading behind the heads and we can now watch the difference in fuel pressure readings in front of, or behind the injectors. Should be interesting. I have a feeling many guys who read at the fuel bowl are going to be a little more nervous when they see what pressure looks like past injectors 7 and 8. :rockon:

01PSD · Apr 3, 2013

If you have an Aeromotive regulator setup after the heads, and you have your fuel pressure gauge hooked up to that and it's maintained at a constant 58 PSI.. then the pressure throughout the heads (before and after) is 58 correct?

Mdub707 · Apr 3, 2013

As long as your pump can keep the volume flowing. Theoretically in a sealed system, pressure should be constant throughout, though I doubt it actually is in this case. I bet pressure is substantially less after the injectors than it is at the fuel bowl. Honestly I think the fuel bowl is one of the worst options for placing a fuel pressure sender.

Guys running a big pump with a RR probably wont have these issues. There are guys out there running say 155's or 175's with a stock pump and no RR. It's more aimed at those guys. Some guys read pressure at the fuel bowl and think they're ok with fuel pressure. I'm going to to attempt to prove that thought one way or the other.

I was originally reading fuel pressure down on my vegistroke manifold for a while (behind the heads) and on diesel, new OEM pump, stock injectors, blue spring upgrade, and old style fuel filters, on a MILD street tune I could easily drop fuel pressure back there down to 25psi or so.

amarillo250 · Apr 3, 2013

I changed the location of the sensor after MPD installed the RR and I am with Mdub707 on this one 100%. My readings before the switch have been constant 58psi with the AD2, when it was still in there and working LOL. but after the switch I noticed that the pressure dropped on hard acceleration from 64psi to 62psi. With the pressure sens. at the fuel bowl it never dropped a bit no matter what.
Long story short, You get a better and more accurate reading after the heads.

Mdub707 · Apr 3, 2013

My truck had an idle fuel pressure of 65ish on #2, with 1/2 throttle that would drop to about 45ish, with WOT, 25ish or less.... on nothing more than a street tune. This was reading behind the heads.

I just moved my pressure sender to my fuel bowl to try again this weekend to see what's up. Regardless, I will have 2 gauges side by side in the future to actually record and show everyone exactly what's happening.

amarillo250 · Apr 3, 2013

good subject and gives lots of younger guy's a good idea what to do before wasting money

bboteler · Apr 3, 2013

opcorn:

Mdub707 · Apr 5, 2013

Drove the truck to work this morning with the fuel pressure gauge hooked up at the fuel bowl. Idle pressure is around 65psi, under WOT it never drops below 55psi. When it was back down on the vegistroke manifold behind the heads, it was dipping to 25psi on the same tune. This is preliminary. I have the vegistroke manifold off of the truck right now, going to clean the thing inside and out to ensure there is no amount of blockage inside to skew pressure readings. My 2nd gauge setup is on the way, so I will have side by side fuel pressure gauges to physically show the difference. I'll keep you guys posted, as it may not happen for a few weeks.

lenzhotrod · Apr 5, 2013

Are you aware that those check valves do have built in bleeds, they are not a true check valve.

Mdub707 · Apr 6, 2013

My check valves are not the same ones that come factory...mine are true check valves and also outflow factory "check valves."

Lassie · Apr 8, 2013

Ford doesn't know the definition of "check valve" or "snubber". The "check valves" in the fuel supply lines and the HPO standpipes are actually snubbers. Full flow one direction and reduced flow in the other. Used to dampen or attenuate noise in fluid systems from actuator disturbances..i.e. - injection event.