89dieselkong

Have questions on the FP reading that I am getting from my lift pump. Installed a Raptor 100 a couple months ago. At idle it reads 15-16psi, but then drops to 8-10psi while cruising, and when I get on it I can bury the needle on 0 psi. I am curious why I am able to pull my fuel pressure down running the Raptor. The engine is bored .40 over, has 50HP Scheid Injectors, and I am running a Smarty Jr. on SW1. For filtration I have the factory filter plus a GDP 2-micron kit in between that and the CP3. I am running the standard fuel lines that come with the kits (nothing oversized) Filters were changed today. I know what the Raptor 100 can flow, and the GDP kit says it flows 100GPH. I am using a fuel snubber on the CP3 to prevent fuel spikes to the FP gauge. Leads to a few conclusions:

1. The fuel lines are too small and I am draining the system
2. The gauge is broken
3. The snubber fitting is causing the readings to be off
4. The Raptor is bad out of the box.
5. I am actually draining the system (didn't think possible with what I have for fuel mods) I am guessing I am in 400HP range and figured the Raptor 100 was enough
6. This is just normal...

Any and all advice is appreciated!

C Schomer

FWIW, my gdp walbro 391 idles at 17 and wot is 15, measured at the cp3. I check mine every summer with a temporary test gauge and no snubber, on the dash, and I'm about to go put it in. You have something wrong. I'd start by trying another gauge. Craig

jforce

The Raptors are pure overpriced junk. Mine never made the pressure they claimed,like yours,then quit. I had a 150. Biggest waste of money ever. Perfectly clean inside when I took it off. JUNK! Looked like a cheap seal failed. Oh and they refuse to warranty mine. It's scrap metal.

89dieselkong

So I put a new Raptor pump on and still have the same issues. Went the length of the fuel line and no pinches or restrictions that I can see. Only thing I can think of now is either the gauge is bad (Isspro EV2), that running the sender through a fuel snubber is causing to to read bad. or that the lines on the GDP 2-micron kit is too small causing a restriction and I need a big line kit. Thoughts?

BigIron70

Are you using a draw straw? T into suction side of pump install vac gauge if suction restriction of more than approximately 100 MM Hg or (4.0 inch Hg)
Then you have a pickup screen blocked or debri in tank blocking pickup. I have seen many pickup screens become completely plugged causing fuel pressure problems under WOT or heavy loads while towing.

89dieselkong

No I have a liberty canister mod. It has been like this since I installed the fuel pressure gauge. It read the same on my stock LP before the Raptor and liberty mod. That is what has me thinking it is either a bad gauge (electric gauge) or the lines with the GDP Filter are too small. It isn't an all of a sudden type thing.