LSx64Chevelle

I don't know if this is a stupid question, but I am looking for some input. I have a custom twin in tank setup for my Chevelle, one is a Walbro 255 and the other an Aeromotive 340. I was able to run 9psi on E85 with the single Walbro and in the pursuit of more boost bought and installed the 340. Now even under cruising my AFR will run normal and then shoot way lean and come back. My main question is are the dissimilar pumps causing this? And it goes lean under WOT, it pops coughs and runs like poop.

my setup:
5.3
tc78 with hopefully 18psi
80LB injectors
E85
holley Efi

Any input is appreciated

Majestic9C1

iTrader: (19)

do you run a hobbs switch and if so which one have you setup as your "secondary" pump?

LSx64Chevelle

No. They are both on all the time right now

samdogmx

iTrader: (14)

you have holley efi right? look at your data logs when it goes lean, are you dropping fuel pressure? Are your injectors maxed out? (imo 80s are not big enough on E)

if the holley isn't able to deliver the AFR you are commanding its something mechanical.

how are you pumps plumbed? series or parallel? what line size?

Old Geezer

iTrader: (3)

^^^^^What Sam said.......

LSx64Chevelle

Unfortunately I don't have a transducer to monitor fuel pressure, but even when cruising at 1500 rpm the afr will swing. The pumps I think would be series. I don't have much vertical room in my tank so one pump goes to a brass 90 into a tee and straight through to the hanger bulkhead. The second pump goes into the tee part of the tee and all said fittings are 5/16, if any of that makes sense. If not I can draw a picture and post.
I do think my plumbing could be an issue will lots of turns and such, but before I drop the tank and make 2 separate feed lines exit the tank before I Y them together I wanted to ask if any problem have been encountered by using 2 different pumps. Maybe depending on load or voltAge they produce a different fuel flow and fight each other some how.

LSx64Chevelle

The bluish line is -6 out side of the tank, black is 5/16 rubber, and yellow is 5/16 brass. I only have about 6" of vertical clearance.

Today I picked up a Y from the pneumatic dept. I am going to run 2 5/16 lines out of the tank, where it will then go to 3/8 into the Y and exit as 3/8. Hopefully I will get that done tomorrow night and this issue will be resolved.

samdogmx

iTrader: (14)

Im no expert but to me that looks like the stronger pump could be pushing fuel back through the other pump, unless, Do you have a check ball anywhere in the system?

After you switch the lines over to a Y, Id highly recommend getting a transducer hooked up. It is a hell of alot easier than guessing whats going on.....

samdogmx

iTrader: (14)

Im no expert but to me that looks like the stronger pump could be pushing fuel back through the other pump, unless, Do you have a check ball anywhere in the system?

After you switch the lines over to a Y, Id highly recommend getting a transducer hooked up. It is a hell of alot easier than guessing whats going on.....

realsquash

iTrader: (1)

There is no problem from using two different pumps at the same time, or your choice of T/Y fittings. I almost guarantee that your problem is fuel temperature. When you're cruising around in your nice 70 degree perfect weather (no jealousy there) both pumps running all the time are going to superheat the fuel. Next time it happens take a sample of fuel out of the tank and measure the temp (or just touch it). All pumps lose efficiency when the temp goes up, but that 340 will absolutely fall off a cliff. Then it will burn up the brushes. If you see black residue in the tank/filter/lines that's probably the brushes from that pump... 120-130F is the range where things go downhill fast.

Disable the 340 and cruise for a while and see what happens...

a-low

iTrader: (26)

I'm assuming there's no return line to the tank?
I have been told I have to have a return since I'll be
running 2walbros constantly that might be your issue?