Fuel pump issues

[Clone TIE Pilot]

This is for the 87 Regal in my sig with the 305 swap. I have been having a strange rich issue combined with nozzle drip at idle. After checking float height, needle valve, and other adjustments, I checked the fuel pump. I am running a stock return style mechanical fuel pump, the book says output should be 5.5 to 6.5 psi. I disconnected the fuel line to the carb, attached my vacuum gauge to it and got 8 to 10 psi! At the same time my fuel gauge is reading a quarter tank high. Not sure if I have a bad sending unit that may have a restricted return or the pump has issues too. I blew compressed air through the return line no improvement.

 

[MontesbyE]

This is for the 87 Regal in my sig with the 305 swap. I have been having a strange rich issue combined with nozzle drip at idle. After checking float height, needle valve, and other adjustments, I checked the fuel pump. I am running a stock return style mechanical fuel pump, the book says output should be 5.5 to 6.5 psi. I disconnected the fuel line to the carb, attached my vacuum gauge to it and got 8 to 10 psi! At the same time my fuel gauge is reading a quarter tank high. Not sure if I have a bad sending unit that may have a restricted return or the pump has issues too. I blew compressed air through the return line no improvement.

1981-1983 CCC (Computer Control Carburetor) Videos

https://gbodyforum.com/threads/gm-ccc-service-videos.76761/ (The discussion tab should point to this thread. )

gbodyforum.com

Its got a lot of good info on the CCC Quad, Open loop/closed loop ect. If your fuel pump is pumping, Id look elsewhere.

 

[Clone TIE Pilot]

1981-1983 CCC (Computer Control Carburetor) Videos

https://gbodyforum.com/threads/gm-ccc-service-videos.76761/ (The discussion tab should point to this thread. )

gbodyforum.com

Its got a lot of good info on the CCC Quad, Open loop/closed loop ect. If your fuel pump is pumping, Id look elsewhere.

I know since I am the one who created that thread and linked those videos. A fuel pump that puts out too much fuel can force the needle valve open and cause rich conditions and nozzle drip. Looked over at Cliffs forum and he says that many replacement mechanical pumps are higher psi than originals.

Currently I have my base ignition timing at 12 degrees BTDC, float height at 11/32. With the idle fuel screws set at 3 and 3/8 turns I have nozzle drip at 600 rpm and the dwell is fixed at 45 degrees in closed loop. If I turn the screws out to 4.5 turns the dripping stops but the dwell is still stuck at 45 degrees which is full lean command. The engine is pulling 20 hg so it is not a vacuum leak.

 

[MontesbyE]

I know since I am the one who created that thread and linked those videos. A fuel pump that puts out too much fuel can force the needle valve open and cause rich conditions and nozzle drip. Looked over at Cliffs forum and he says that many replacement mechanical pumps are higher psi than originals.

Currently I have my base ignition timing at 12 degrees BTDC, float height at 11/32. With the idle fuel screws set at 3 and 3/8 turns I have nozzle drip at 6 rpm and the dwell is fixed at 45 degrees in closed loop. If I turn the screws out to 4.5 turns the dripping stops but the dwell is still stuck at 45 degrees which is full lean command. The engine is pulling 20 hg so it is not a vacuum leak.

well alright then, didn't put 2 and 2 together. Thanks for the vids

 

[pontiacgp]

I think you found the problem, try another fuel pump or get an adjustable regulator

 

[Clone TIE Pilot]

There are conflicting specs concerning fuel pump pressure. One manual says 305 fuel pressure be 7.5 to 9 psi, while another says 5.5 to 6.5 psi. Either way, my pump ranges from 8 to 10 psi at least as my gauge only goes to 10 psi and its pegging the needle so its likely higher than 10 psi.

Some bad news is that GM no longer makes replacement fuel pumps for MCs, I am forced to go aftermarket. Airtex and Spectra have pumps with 7.5 min psi and 9 max psi. The stock mechanical pumps for this cars are 3 port return systems. They only pump fuel to the carb when it needs it, similar to a return style EFI system.

 

[lilbowtie]

Regulator

 

[Clone TIE Pilot]

The stock pumps have built in regulators as they circulate fuel to the pump and back to the tank. Not sure how you can add a second regulator into an already regulated fuel system.

 

[olds307 and 403]

This seems to be a common issue with fuel pumps these days. I have ran multiple Carter Muscle car pumps in both the two and 3 line versions with 0 issues on my Olds both with Qjets. One guy had issues like you are having, the rest are very positive. The pic looks right, one guy has a pic with 3 lines installed on his van. https://www.summitracing.com/parts/crt-m6626

 

[Clone TIE Pilot]

Doing some research, its not uncommon for mechanical fuel pumps to begin to push out too much psi as they begin to fail, enspecially with E10 or higher gas. Springs can corrode and no longer compress right, valves can become sticky, passageways can become blocked, etc. Since mostmechanical fuel pumps are climped together, you can't take them apart for repairs or cleaning.