EFI Pump and welding the Tank, Engine shaking?

[FoMoCo]

Hey all,
I've logged about 10,000 mile since adding the EFI 300 to my 69. Zero problems and gets about 18 mpg on the highway. Currently the truck has a low pressure diaphram pump followed by a high pressure Walbro GSL pump. Both pumps are mounted above the spare tire under the back of the bed. All fittings are 6AN. I was hauling a golf cart yesterday and the engine seemed to loose power and shake. I pulled over and the highpressure pump was very hot. The fuel filter was removed while I was pulled over and found it very dirty. The filter is the little summit racing aluminum filter, they type that's about 4 iches long. I ditched the screen and the truck was running better but still a little jerky. However, the fuel pump was cool to the touch after an hour of driving.
I put a bottle of STP FI system cleaner in before fetching the golf cart(about a 3 hour highway round trip) I guess it really loosend up more garbage than the filter would hold. I'll be replacing the filter with something more substantial this week.
My question: Can/should I lose the low pressure pump and weld an AN fitting to the bottom of the tank? Where should I weld the fitting? I'm sure the highpressure pump demands more volume than the low pressure puts out. The bottle neck in the system is the filter and the return side of the fuel rail. These help by creating a little back pressure, but big pump still pushes more than the little pump pulls. I think a gravity fed high pressure pump would perform better. BTW If I started over it be a carb 300 all the way.

NIck

[FoMoCo]

I agree, the fuel line is too big. I unhooked the return line and let the pumps fill some empty gas cans. I'd say there was little to no PSI. The truck stuggled to navigate my flat driveway today. I think the bad filter over heated and killed the high pressure pump. I'm still going to tig a fitting on the bottom corner of the tank. The gravity feed method and single high pressure pump should be the ticket.

Nick

[Dragon]

Drop the mechanical pump EFI does not use that restriction.

Well if you want a carb 300 I will go get one and take your efi in trade. The carb one won't get but 15 at best most days.

[averagef250]

He doesn't have a mechanical pump, He knows what he's doing by his description.

I've run carb and EFI 300's in the same truck and got the same freeway mileage from both, low to mid 20's in an F100 2wd. The carb was on an EFI engine with EFI manifolds and duraspark. It ran pisspoor cold and had a part throttle miss (carb), but made the same HP. The EFI was far more driveable. Fire up and go, much more mid range and off-idle torque.

[scott123]

I have exactly the same setup on my EFI 302 and dont have any issues. After I first made the swap and was trying to isolate some drivability issues I bypassed the low pressure pump with fuel line and it ran the same with or without.

I am currently running 2 pumps, a low pressure feeding a high pressure and it runs great.

I believe the only time you would need the low pressure is if you sucked the system dry and couldnt get prime.

[averagef250]

It actually depends entirely on the high pressure pump you are using. Some will self feed and prime, many will not. The bosch pumps I've found work find standalone.

[Dragon]

You are blowing high pressure through the low pressure pump. Not a good thing.

[averagef250]

You are blowing high pressure through the low pressure pump. Not a good thing.

I think you are reading this all wrong. He has an EFI 300, the complete full meal deal installed in his 69. There is absolutely, positively, zero chance of any mechanical pump here.

[scott123]

You are blowing high pressure through the low pressure pump. Not a good thing.

As well the series is like this

Tank---LPP----HPP-----Injectors----Pressure regulator----Tank

[FoMoCo]

Everything's back and running. I replaced the pump with a single Walbro GSL 392 mounted the rear most crossmember, replaced the filter with a big fram paper element unit, and tig welded a 6AN fitting to the front-middle part of the tank. I ended up putting the return line on the original tank feed line. With gravity feeding the pump it sounds much better (the pump). I'll try to get some pics up this Saturday.

Nick