I have a 46 Ford PU that I put a 300-325 horse, 350 Chevy in. I am running a Rochester Quadra-jet that has been rebuilt and set up by a guy that knows Quadra-jets. I also built and placed a 2nd fuel tank at the rear of the frame. So I now have the original tank under the seat and a second tank in the rear. The second tank has about 8 feet of line before getting to the fuel pump. The current electric fuel pump is a Carter in-line, solenoid type pump that is suppose to put out up to 14psi with an adequate flow rate for that engine. There isn't enough room for a mechanical pump. The electric pump is under the truck 3 to 4 inches above the exhaust and maybe 2 feet from the front tank. The tanks go into an electric switching valve. Then I have a filter before the pump and another after a Holley 12-803 regulator. After driving for 30 minutes or more, and/or getting on the throttle a little heavy, I am getting large fluctuations in the fuel pressure and the truck starts running like crap. Sometimes it dies just going down the road at 35 mph. I've changed the regulator once and currently have the new one sitting at 5.5 psi. The pressure seems to hold steady when I first start it. It does not matter which fuel tank I have the engine running on. When it starts acting up the pressure can fluctuate from zero to 8 psi. My next thought is to change the fuel pump and mount the new one in a different location. I am also wondering about putting a booster of some kind near the rear tank. If so what would that need to look like? So are there any thoughts on what might be going on? Is the pump having a thermal reaction and breaking down? Is there a different electric pump I should be using? I am at a loss.
Sounds like the filter before the pump is possibly restricting the fuel flow to the pump. The line from the pump to the carb is most likely running near dry and the prefilter is keeping the pump from getting a full flow of fresh fuel....hence the pressure fluctuation and crappy running engine.
Thanks guys. I was lying under the truck on a creeper, pondering life as I know it. I wondered, with the fuel pump and about 6 or 8 inches of fuel line 3" above the exhaust could I be having some kind of vapor lock going on. Happens mostly after getting on it or climbing a hill. Doesn't go away until everything cools down? I am going to take your advice and remove the pre-pump filter and I am also going to undertake moving the fuel pump and lines to a better position. (No small task). I'll let you know.
I know, I have a '46 PU with a Carter pump also. It's mounted on the right frame rail, just forward of the factory tank I liken building this thing to building a motorcycle. There's not much room to get things located. I have an added cross member for the T-400 trans also, so between those two things being in the way there's even less room. Good luck!
Yes, I think you are experiencing vapor lock. Also, the pump bypasses fuel within itself when there is not enough fuel flowing into the carb to keep itself cool. That tends to make it heat up too. Try to mount the pump far away from the exhaust as you can. Carry a spray bottle of water with you for those times when it acts up. As far as the rear tank needing a lift pump, it should draw the fuel from a long distance. I have the same pump setup on my motor home feeding a BBC and it sucks the fuel from the rear tank which is about 20 ft. No lift pump. I know that breaks the laws of physics, but hey, it works.
Electric pumps don't suck...well a lot of people on the HAMB probably think they do but what I mean to say is electric pumps are designed to push fuel, they don't suck it. That is, at least not efficiently. Add the heat from the exhaust and you have the recipe for delivery issues. 2 pumps, located immediately adjacent to their respective tanks, wired so each works in conjunction with that electric switching valve, insulated from the heat and flowing into that Holley regulator ought to do the trick. I had a jet boat with 2 saddle tanks and each had an electric pump and a valve like you describe. Should work the same way right? That's a lot of fuel capacity, you running shine?
Unless you changed them, you have 1/4 inch fuel lines. That is NOT big enough for a late model OHV engine. Electric pumps do not like to suck fuel very far. They should be mounted as close to the tank as possible and AWAY from heat sources.
Mount away from heat, Better to push fuel 8’ than try to suck it 8’ so mount the fuel pump closer to the tank. Make sure it has a big enough wire feeding it power and keep that away from heat as well. Make sure it’s not sucking air and the tank is vented. Each tank should have its own pump. Watch for restrictive fittings in the line. That filter before the pump is a good idea and should not be restricting unless you’ve plugged it with dirt already.
Are you sure we aren't the same person maybe from different dimensions. That is where my pump is located. I Have a T400 tranny and the pump is mounted to the remains of the old crossmember, just forward of the main fuel tank. To funny.
A couple things stand out. Is the pump mounted with the inlet fitting at/below the bottom of the lowest tank? 3-4" inches is not enough distance for an unshielded fuel line, and I'm assuming that's hardline NOT 8' of hose. I've never had much luck with the inexpensive deadhead regulators, might consider a bypass regulator looped back into the inlet. I found silicone fuel line insulation that works REAL well in keeping radiant heat out of the line. A bit expensive but if space is at a premium (has to be close to heat source), it's a good alternative.
Anytime I shortcut, I regret it later. Inline fuel pumps aren't as good as intank pumps. The prepump filter protects your pump from tank debris. Problems always rear their heads at the worst times. I would remove the truck bed so you can get to most everything easily and then do the job right. Don't understand the need for two gas tanks, and I would get the one behind the seat and remove it. I have found that the late 90s S10 Blazers (2 door only) have some nice size square tanks. The fuel pump hole in the tank varies somewhat depending on the year of the tank and you need to get the correct pump for the year of the tank. I think they went from a low pressure pump to a high pressure and changed the size of the hole. Anyway, they are almost square tanks and you can then use a factory in tank pump. Pickups and four door blazers have a side mounted tank. Install a 3/8 line to the regulator and on to the carb. Then put a 5/16 return line to the tank along with a vent tube. The pump will furnish plenty of fuel and bypass the excess back to the tank. No vapor lock. Its better to just buy a new tank online for about $125 than to find a used one. You said the second tank was in the "rear". Don't know exactly where you are saying it is , but in my installation its really in the rear...behind the rear end.
Removed the filter that was inline before the pump. Re-positioned the fuel line and pump. So far so good. First test drive was a success.
Hopefully this has cured your problems. Carry a can of aerosol "Freeze Spray" around for any roadside vapor lock remedies.
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