‘97 5.7 build with 0411 swap fuel pressure issues…inline fuel pump questions

[97SWBCHEVY]

So I recently checked the fuel pressure on the truck and I was only getting 49-50 psi…and since the recommended pressure is 60 psi I changed the fuel filter and put a new fuel pump in the tank…checked the fuel pressure again and that changed nothing…the fuel pressure remained at the 49-50ish range… Upon doing some further investigating and following fuel lines I’ve discovered the truck also has an inline external fuel pump mounted between the regular fuel filter and the engine…just out of sight from the filter… This inline pump had apparently went out and was no longer working…I have no idea when it quit just know the pump is out…it’s an AIRTEX E8445 fuel pump that is supposed to push at 65 psi…
Question 1
With this pump being out and inline restrict the fuel pressure from the tank to the engine? Common sense says it could…but at the same time would it really though???
Question 2
Will an inline pump increase the pressure from the pump in the tank or will it basically be limited to the max pressure being pushed to it from the tank? (Does that make sense? lol)
Question 3
I’m going to put a new inline pump back on the truck since the truck is already plumbed for it and it’s done rather nicely. Any suggestions/thoughts/opinions/advice/preference on which brand to go with and what pressure rating would you suggest? I’m not looking to spend $400-500+ bucks on a pump when the spider has the basic upgraded spider with the regular size injectors…

Any suggestions would be greatly appreciated and thank in advance…
Shane

 

[GoToGuy]

Why install another pump? Too lazy to replace in tank pump? Recheck pressure from new intake pump. Before scab pump.
If in tank pump good check-out. Remove extra pump. Why have if OE system is up to spec? $$$ for something not needed or required. Your choice. But seems redundant.

 

[Amsterdamned96]

sounds like you have an mpfi or vortec with fuel-rail. the in-tank pump is a pick-up and the inline one suppllies the pressure. The in-tank pump strictly relieves the inline one from having to prime and allows it to operate at it’s listed capacity. you’ll need both for you injectors to atomize properly and also the fuel map might not like the low pressure very much.
I hope you’re careful when wrenching down there, i didn’t have the luxury of having a greasepit back then and when decoupling a fuel-bypass I doused myself in gasoline; poured it in my ear and all.

 

[97SWBCHEVY]

Why install another pump? Too lazy to replace in tank pump? Recheck pressure from new intake pump. Before scab pump.
If in tank pump good check-out. Remove extra pump. Why have if OE system is up to spec? $$$ for something not needed or required. Your choice. But seems redundant.

Sir I just put a brand new fuel pump in the truck less than a month ago…and a new fuel filter… The truck also has a Powerdyne Supercharger on it which I currently have bypassed because I’m needing to get a basic tune on the truck to get a good starting point…the build has E Tech heads and a cam…with the 0411 swap done… I’m assuming the inline fuel pump was installed when the supercharger was put on the truck…and at some point I plan on putting the supercharger replumbed and back in place…so I might as well do the inline pump now… Laziness ain’t got **** to do with anything! If I was lazy the truck would’ve been in shop a long time ago when I spun a main bearing in the original 5.7 and someone else would’ve turned all the wrenches that have been turned on the truck since then instead of me turning them… $$$ wise…why buy new factory OEM fuel lines to plum it the correct way which I would have to do if I removed the inline pump…if I wanted to save $$$ I would’ve just bought a used 350 and thrown that back in the truck in the first place!

 

[97SWBCHEVY]

sounds like you have an mpfi or vortec with fuel-rail. the in-tank pump is a pick-up and the inline one suppllies the pressure. The in-tank pump strictly relieves the inline one from having to prime and allows it to operate at it’s listed capacity. you’ll need both for you injectors to atomize properly and also the fuel map might not like the low pressure very much.
I hope you’re careful when wrenching down there, i didn’t have the luxury of having a greasepit back then and when decoupling a fuel-bypass I doused myself in gasoline; poured it in my ear and all.

Sir I just want to thank you for one thing…second thing is where the hell were you at yesterday!! lol I’m by no means a certified kickass mechanic but I can usually do some shade tree wrenching on things with the best of em… Unfortunately yesterday I learned firsthand just how painful getting gas in your ear is!!! I had propped the fuel line up inside the frame rail and at the worst time ever while sliding out from under the truck said fuel line shifted and gas ran directly in my ear…and I can honestly say I haven’t felt pain like that in years…and I couldn’t get away from the pain trying to get it flushed out wasn’t that easy and it’s still a lil uncomfortable right now…24 hours later!!!

 

[GoToGuy]

So you have a highly modified truck. And you asked a question based on a stock setup? Ever heard of the context of the question determines the answer? Ha Ha

 

[97SWBCHEVY]

Well as of right now I wouldn’t consider it to be a highly modified truck…the supercharger is bypassed…it’s just a 5.7 build with heads, a cam, and a 0411 swap…it’s just not a stock rebuilt 5.7 with a black box…lol

 

[L31MaxExpress]

Why install another pump? Too lazy to replace in tank pump? Recheck pressure from new intake pump. Before scab pump.
If in tank pump good check-out. Remove extra pump. Why have if OE system is up to spec? $$$ for something not needed or required. Your choice. But seems redundant.

~20 years ago I worked on a bunch of GM fleet trucks and vans that had a Ford in-line pump added to the frame. The logic was simple as to why when I started asking questions. The older GM pumps would start to lose pressure long before they quit working entirely. The Ford pump for some reason lived a lot longer the way they were built. The Ford pumps did not like pulling fuel. The Ford pump took some of the stress off the in-tank pump allowing it to live a much longer life. The Ford pump was easy to access and change. It was a 10 minute replacement vs dropping the tank. My 1983 G20 van is still setup the same way. EP381 in the tank and a Ford pump on the frame rail. It was 100% reliable for 8 years of driving.

The newer GM replacement Delphi pumps seem to live well now so it is really not needed unless like the OP the system needs to run at as much as 80-90 PSI while the engine is in boost with a supercharger. Some of those older supercharger kits had a rising rate FMU, for every 1 psi of boost, fuel pressure was increased at either a 2:1 or 4:1 ratio. A 4:1 ratio on an engine making 10 psi of boost would put the fuel pressure at 98 psi if the base pressure was 58 psi and a 2:1 would be 78 psi. Even with a stock regulator the fuel pressure is going to increase 1:1 with boost pressure. An old factory style spider ran at 66 psi, 10 psi of boost would have the fuel system running at 76 psi. The volume of the stock replacement in tank pump would drastically fall off at that pressure without the in-line booster pump.

 

[GoToGuy]

Yeah I'm aware, and got the books on turbo, super, turbo compound, and such. Was not aware of a " pony " fuel pump application. If it keeps the fleet in-service longer, it's an earned investment.
Is this practice localized or is there a service bulletin on this?

 

[L31MaxExpress]

Yeah I'm aware, and got the books on turbo, super, turbo compound, and such. Was not aware of a " pony " fuel pump application. If it keeps the fleet in-service longer, it's an earned investment.
Is this practice localized or is there a service bulletin on this?

I think it was a localized thing I saw and mostly 1 fleet although another fleet that I know of did the same thing on the Express van cutaway chassis short buses. 1project2many goes into more detail than I even knew on it just a week ago on gearhead-efi. This guy is smart when it comes to GM EFI as well. He has a Suburban with a 302 Vortec in it, interesting build. L99 4.3l crank and rods in a L31 block. He has also done some 7395' cams in a few of those buses. Gave me a lot of tips to make my brake system work better and easier to maintain in my Express too based off his experiencw with the buses.

Edit-If it was an older TSB, I have never seen a copy of it. My best guess is the mechanics maintaining fleet vehicles just realized the Ford frame pumps were lasting better and started adding them in-line.

You must be registered for see images attach