Anybody here ever hook a gauge up to see just how hard the CP3 is working to get fuel from the tank in a non-lift pump situation? I've noticed quite a bit of difference in the amount of smoke my truck makes with a tune from a clean filter to a dirty filter and a full tank of fuel to an empty one.

I just got a Autometer 4301 boost/vacuum gauge to see how well a fuel pressure/vacuum gauge can work to let me know when it's time to change filters or how badly I need a lift pump. :)

Granted the gauge I have is not designed for fuel and I was hard pressed to find one that is for a similar price tag, so I plan on filling the 1/8" line 1/2 full of fuel and the rest air so as not to draw air into the CP3 or fuel into the gauge. I routed it under the hood to keep the fuel on the fuel end, and the air from bubbling back towards the filter assembly. For the hookup I tapped into the composite bleed screw on the filter since that's the last connection before the CP3 as far as I could tell, and now I'm just waiting for the adhesive to dry (don't wanna suck that into the pump). Hopefully in the morning when I get it hooked up the rest of the way it will work as planned. If anybody else has tried something like this, let me know! I'd be curious to see how you went about it.

Well, I just got done hooking everything up a little while ago and went for a ride to try it out. I filled the fuel tank up after the install. At idle, the truck is drawing about 5" Hg (vacuum) at the pump and at 55 mph it's drawing about 8-9" Hg. It's been about 4 months since changing my Cat filter down by the fuel tank, and next week I'll change that and see what difference it makes. Anybody know how much vacuum there is on the fuel supply with just an OEM filter that's clean?

Here's some pics finally!

At idle with an outside air temp of 34 degrees F. Cold fuel in the tank which is at empty according to my fuel gauge.
http://farm4.static.flickr.com/3385/3276829329_f736c2cd49.jpg?v=0

Here are the lines under the hood. Gotta love zip-ties!

http://farm4.static.flickr.com/3398/3277649932_ba72613c2e.jpg?v=0

Finally the hobo connection at the filter assembly:

http://farm4.static.flickr.com/3391/3277649988_06220abd67.jpg?v=0


I hooked up the pressure line to the bleed cap on the top of the OEM filter assembly (pic 3) and just drilled it to the right size then put some high temp fuel resistant silicone to seal it. Should have drilled and tapped it to use the proper connections, but I was lazy and just wanted to see if it worked.

I then primed the filter assembly without the gauge hooked up to flood the line with fuel to decrease pressure variables from having it full of air as well as to keep air from entering the CP3 when drawing a good vacuum at the pump.

I looped the gauge line around like in picture 2 to isolate the remaining air in the line when under load to the top of the loop to prevent air from getting into the CP3 as well.

I'd be worried that eventually the RTV'd hose connection will loosen, and a vacuum leak will leave you stranded.
Greg @ Lube Specialist sells filter vents that include an adapter, which adapts the metric straight threads of the vent hole to a female 1/8" NPT. You can now install a compression fitting on hose with a compression to 1/8" NPT adapter, and it won't leak.
You could loosen the compression nut when priming a new filter.
I don't know if he sells the adapter alone.
Here's a link:
http://lubricationspecialist.com/front/shop.aspx?catid=10&parentid=0&curr_page=2

But this wouldnt work with a lift pump correct? It would be pushing fuel into the gauge wouldnt it? I'm still a little confused on the install, as far as air and fuel in the same line?

But this wouldnt work with a lift pump correct? It would be pushing fuel into the gauge wouldnt it? I'm still a little confused on the install, as far as air and fuel in the same line?

His compound gauge would work with a lift pump, (30 IN HG - 0 - 20 PSI), however most would recommend NOT installing this type of michanical gauge, because flammable fuel will be in lines, through firewall and into cab. If used, the air could be purged before connecting to gauge, but with the pressure tap off the top of the filter, air may continue to collect in tubing. Assuming lift pump pressures of 6-10 PSI, air with the fuel will affect gauge accuracy slightly.
Autometer makes an electronic gauge that has an electronic transducer mounted directly to fuel system, and it sends an electrinic signal to the gauge.

I totally agree that I need a more reliable hookup on the filter assembly, RTV is NOT the best way by a long shot, but it works at the moment and I've got a spare threaded fitting to block it off in the event the RTV method goes south so I'm not stranded.

If I'm not mistaken, the inside parts of the gauge are made out of bent brass or copper, right? In that case, the line could be flooded completely with fuel. If the gauge does fail, I'm not overly concerned about 10psi of fuel spraying in the truck with a lift pump. The commercial truck I drive has a gauge in the cab that's connected to a 3,000 psi hydraulic pump (and yes it came that way from the factory brand new in 2006) that much pressure makes me nervous.

I totally agree that I need a more reliable hookup on the filter assembly, RTV is NOT the best way by a long shot, but it works at the moment and I've got a spare threaded fitting to block it off in the event the RTV method goes south so I'm not stranded.

If I'm not mistaken, the inside parts of the gauge are made out of bent brass or copper, right? In that case, the line could be flooded completely with fuel. If the gauge does fail, I'm not overly concerned about 10psi of fuel spraying in the truck with a lift pump. The commercial truck I drive has a gauge in the cab that's connected to a 3,000 psi hydraulic pump (and yes it came that way from the factory brand new in 2006) that much pressure makes me nervous.


3,000PSI:eek:

The hydraulics aren't in use when you are in the truck though , are they?

Still I wouldn't want fuel all over the inside of my truck, and I'm sure you wouldn't either.

The gauge typically reads 1500-2500 psi but I've seen it over 3000 a few times, and yes the truck's running while I'm in it. The gauge is about 2 feet from my head in the overhead console in the concrete truck. If that ever blew, it'd suck. And yes, I'd rather not have fuel all over in my pickup either. I did it this way more as a proof of concept and when I get around to a lift pump, I'll get a sending unit type gauge to avoid the fuel in my truck hazard. :)

I've got a spare threaded fitting to block it off in the event the RTV method goes south so I'm not stranded.

If I'm not mistaken, the inside parts of the gauge are made out of bent brass or copper, right? In that case, the line could be flooded completely with fuel. If the gauge does fail, I'm not overly concerned about 10psi of fuel spraying in the truck with a lift pump.

Good thinking with the spare filter vent plug as a back-up.
The bent tube in the gauge is called a bourdon tube, which should be reliable, and burst pressure is probably 3 or 4 times the max. gauge reading.
The plastic tubing will be the most likely thing to fail, if anything.