Random Poor Running/Stalling

Bandit723

Veteran Member
Oct 1, 2016
4,257
Waupaca WI
Well again what does your voltmeter show when in the low RPM's. Not sure how you wired in the electric fuel pump. two things come to mind either low voltage or the pump wiring is reversed. I did bring up crud in the fuel bowl but i am sure you have ruled that out.
 

Ratty_81

Veteran Member
Nov 13, 2020
401
@G72Zed
I know that pump is not the best and my mounting could be compounding the problem, butthe previous owner daily drove the car for 3 years this way. Unfortunately, I have a late model block without fuel pump provisions.
I’m assuming the pick up is 3/8”, but I suppose it could be smaller. It’s just a stock replacement from one of the parts houses.
@CorkyE
Appreciate the offer. Pump is not PWM, it’s just a smart controller with built in relay that uses the tach signal to the keep the pump running. I installed it for safety in case of a crash. I have it wired directly to the battery and am using it’s internal relay to fire another relay, so it’s not even carrying pump current. I’m still suspicious of it randomly cutting out though.
@Bandit723
I plan to monitor fuel pressure and voltage on the coil hot wire.
On vacation at the moment and probably won’t get to it until week after next.
 
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G72Zed

Veteran Member
Sep 8, 2015
4,057
Canada
OK, from the sounds of it, it could be a combination of mounting location/pickup and/or electrical/relay issues.

I've been down this road so many times decades ago with electric pumps.....just went back to the "KISS" way of doing things.

A good investment is an AFR gauge, that may in fact point you in the right direction just as quick as the fuel pressure gauge.
 

2ndGenCrazy

Veteran Member
Aug 18, 2011
892
Upstate New York
I had this same issue many years ago. I'm not saying this is your issue, but you could try it and see what happens. I removed the fuel line connections at the fuel tank outlet and fuel pump inlet, then blew it out with compressed air into a paper towel. I had a large amount of rust and crud that came out. Problem went away.
 

Ratty_81

Veteran Member
Nov 13, 2020
401
So it looks like I have a fuel delivery problem. Put a camera on my FP gage and went for a ride. Under hard acceleration, pressure drops to nearly zero. Just cruising around town it’s under 4. Pic is a screenshot of the video I took under 3/4 throttle acceleration. Thinking of putting in an aeromotive tank and pump or a Holley in tank retrofit pump. Thoughts?
 

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Ratty_81

Veteran Member
Nov 13, 2020
401
After a bit of research, I think my return line is also contributing to the problem. I have it reduced from 3/8 to 5/16 to attach to the factory vapor return line. Sounds like it’s a bad idea to undersize the return. With a not so powerful pump mounted in a less than ideal spot, I’m shooting myself in the foot. PO had a 3/8 barb to 1/4 npt 90 threaded into the front of the tank for the return.
I need to find a proper bulkhead fitting and see if I can get my or my daughters arm in the tank to get the nut on it…
 

Ratty_81

Veteran Member
Nov 13, 2020
401
Ok, I'm really stumped now. Relocated the carter pump to the front of the fuel tank level/below with fuel level. Pump started out with 6psi at the carb then slowly dropped off to around 3psi after a 15 minute drive. Pressure still dipped under acceleration. Figured the pump must be going bad, so I installed a new Holley blue pump last night. Started out at 7psi and was down to zero after a 10 minute drive. Stalled on me couple times and I barely made it home. Also dipped under acceleration. I connected the pump directly to 12V and still zero. I'm started to think the pick up in the tank is screwed up or something. I just cant understand how it could go from bad to worse with a new pump unless the pump has failed already???
1660909748531.png
 

CorkyE

Veteran Member
Lifetime Gold Member
Nov 4, 2004
11,772
Ringgold, GA
Did you install a new pickup/sock with the new tank? Something is still restricting, could be a line collapsing. Try taking the filter out of the equation. You could, but I don't think you have a voltage drop to the pump. If you still have that safety relay, wire around it just to test.
I've ran that same setup with no issues.
 




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