'71 Z28 LT1 fuel pump replacement?

Eric winkel

Member
Mar 3, 2021
50
Installed NOS service replacement AC Delco fuel pump today in 95 degrees
 

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hd_cat

Veteran Member
Sep 6, 2013
170
Cincinnati, Ohio
I tried several fuel pumps for the '79 Z/28 (3310 Holley), all of the "replacement" fuel pumps generate higher pressure than the Holley Carburetors can manage. The most manageable replacement fuel pump still generated about 10.5psi at peak, with the mechanical pump, the needle was always fluctuating, so it is more difficult to determine the actual psi range. I believe the combination of the sintered bronze filters and the dual line allowed the car to run properly with the higher pressure, thinking that the gauge reads higher than the pressure signal at the needles and seats. Recommendation: Have the original pump rebuilt, or buy one that is correctly numbered and built to generate 4 - 6psi.
 

Henry Albert

New Member
Oct 16, 2021
10
Carleton Place, ON, Canada
I put an old used pump that my buddy gave me on my rebuilt 350 and about a month later it leaked through the diaphram. Todays gas causes all kinds of issues on our old stuff. Also the gas ruined the pump on my HenryJ.
 

70lt1z28

Veteran Member
Gold Member
Oct 3, 1999
4,951
Beavercreek, Ohio, USA
I put an old used pump that my buddy gave me on my rebuilt 350 and about a month later it leaked through the diaphram. Todays gas causes all kinds of issues on our old stuff. Also the gas ruined the pump on my HenryJ.
One issue with a leaking diaphragm on replacement pumps is that many of them omit the small vent holes that were on the original pumps. When the diaphragm leaks, the gas has nowhere to go but into the engine instead of leaking out. If enough gas goes to the oil pan it can do two things, dilute the oil enough to take out the bearings or build up enough fumes to eventually combust and blow the pan or valve covers off.
 

Eric winkel

Member
Mar 3, 2021
50
Very interesting, I replaced my original pump (still have it) back in mid 90's with a Carter high flow and always had gas mixed with my oil thought it was a too big holley 750. Rebuilt the original 780 with stock jets, same issue. I wonder if it was the Carter pump all along? We'll see what the new NOS pump does or does not do
 

Henry Albert

New Member
Oct 16, 2021
10
Carleton Place, ON, Canada
M
One issue with a leaking diaphragm on replacement pumps is that many of them omit the small vent holes that were on the original pumps. When the diaphragm leaks, the gas has nowhere to go but into the engine instead of leaking out. If enough gas goes to the oil pan it can do two things, dilute the oil enough to take out the bearings or build up enough fumes to eventually combust and blow the pan or valve covers off.
My old pump has 2 vent holes above the diaphragm which is how I knew it was shot. The other old stock I put on also has the 2 vent holes, will see if it goes bad. Just finished putting in an electric near the tank just in case.
 




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