Python (502) high pressure fuel pump

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   I am going through the fuel system on my ‘99 Python 502 (8.2L). Was thinking it may be wise to replace the high pressure fuel pump while I had the FCC apart. Documentation on the Python is fairly thin, so curious if any others have gone down this road.

Some good information from GaryS, Don, Paul and others, trying to figure out what was used on the FCC GT40’s (link).  Here is what I think I have pieced together:

RA080025A = hpp for GT40/Apex/Excal. No confirmation on the Walbro equivalent part number 

RA080027A = hpp for 6.0 and 8.1 Python. Gary’s was marked GSS439 on the pump itself.

Gary was intending to try the Walbro GSS340 on his GT40, this is sometimes referred to as a “high pressure” pump in Mustang circles (rated at 67gph /255lph at 40psi, and 112psi max). Especially when compared to a GSS307, which is a similar bodied Walbro and what I found in my 502 Python’s FCC (guessing it’s original but who knows for sure). That’s rated at 67gph/255lph at 40psi, with a 50psi max. Gary’s 6.0/8.1 FCC came with a GSS439, which may be a proprietary pump for PCM as no specs are online. It’s been speculated that the GSS350G3 (92gph at 40psi, 112psi max) might be a suitable replacement for that set up.

I called Richard at SkiDIM/NP, and he guessed they might’ve put the bigger pump in the 99-02 502’s (contrary to what I found in mine), and regardless, is what he’d recommend putting back in.

So I guess my plan is to order the GSS350G3 (quite a bit cheaper than the PCM RA080027A) and give it a shot. Will report back later this spring with any findings.

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TRBenj Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21186	Post Options Post Reply Quote TRBenj Report Post Thanks(1) Quote Reply Topic: Python (502) high pressure fuel pump Posted: March-27-2024 at 3:50pm
	I am going through the fuel system on my ‘99 Python 502 (8.2L). Was thinking it may be wise to replace the high pressure fuel pump while I had the FCC apart. Documentation on the Python is fairly thin, so curious if any others have gone down this road. Some good information from GaryS, Don, Paul and others, trying to figure out what was used on the FCC GT40’s (link). Here is what I think I have pieced together: RA080025A = hpp for GT40/Apex/Excal. No confirmation on the Walbro equivalent part number RA080027A = hpp for 6.0 and 8.1 Python. Gary’s was marked GSS439 on the pump itself. Gary was intending to try the Walbro GSS340 on his GT40, this is sometimes referred to as a “high pressure” pump in Mustang circles (rated at 67gph /255lph at 40psi, and 112psi max). Especially when compared to a GSS307, which is a similar bodied Walbro and what I found in my 502 Python’s FCC (guessing it’s original but who knows for sure). That’s rated at 67gph/255lph at 40psi, with a 50psi max. Gary’s 6.0/8.1 FCC came with a GSS439, which may be a proprietary pump for PCM as no specs are online. It’s been speculated that the GSS350G3 (92gph at 40psi, 112psi max) might be a suitable replacement for that set up. I called Richard at SkiDIM/NP, and he guessed they might’ve put the bigger pump in the 99-02 502’s (contrary to what I found in mine), and regardless, is what he’d recommend putting back in. So I guess my plan is to order the GSS350G3 (quite a bit cheaper than the PCM RA080027A) and give it a shot. Will report back later this spring with any findings.

MrMcD Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3749	Post Options Post Reply Quote MrMcD Report Post Thanks(0) Quote Reply Posted: March-27-2024 at 9:35pm
	Tim, I would start with your injectors and see what pressure GM recommends for the injector. My memory says the GM injectors are more prone to not work right if the pressure is not dead on. I just worked on a 1999 350 with the Vortec injection system. The pump had 60 PSI while cranking but dropped to 52 PSI once started and the pressure relief valve took over. A blip of the throttle would jump the pressure to 60 again as vacuum fell off. What I had read on this engine was the injectors would not function below 46 PSI? I worked on a newer 8.1L and it had the new style injectors with a fuel rail set up and they sit outside the manifold while the early design were inside the intake manifold they called those the Spider design. When searching for your new pump make sure the pressure capability is well over the running pressure. Dead Head pressure might be listed as high as 100 PSI even when the system regulates pressure to 60 PSI.

TRBenj Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21186	Post Options Post Reply Quote TRBenj Report Post Thanks(0) Quote Reply Posted: March-28-2024 at 7:30am
	These are not standard injectors, they don’t cross to anything off the shelf. I believe they are the same ones used on 502 Mercs of the same era (500efi, etc used the same intake manifold). Reading on OSO, should be regulated to 38psi or so. This PCM set up is externally regulated, and has the return to the FCC- so not sure if getting a hpp pump with the exact pressure characteristics is critical (just want to make sure it’s not deficient). I guess that is part of my question. I had the injectors rebuilt and tested this winter as part of this same fuel system cleaning/overhaul. The boat had old/contaminated fuel in it when I bought it.

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11112	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: March-28-2024 at 7:58am
	Nautique Jeff seems to have a couple of boats with 502's that are in some stage of restoration. You'd think that a restoration would involve at least a fuel filter change along with the little discharge hose on the fuel pump, and he or one of his helpers or the people he deals with at PCM should know if the pumps inside his FCC's match yours. A check with him might tell you something

63 Skier Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: October-06-2006 Location: Concord, NH Status: Offline Points: 4269	Post Options Post Reply Quote 63 Skier Report Post Thanks(0) Quote Reply Posted: March-28-2024 at 8:47am
	Tim, what boat is the '99 Python in?
	'63 American Skier - '98 Sport Nautique

MrMcD Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3749	Post Options Post Reply Quote MrMcD Report Post Thanks(0) Quote Reply Posted: March-28-2024 at 12:02pm
	Sounds familiar Tim, the 8.1 I repaired was in a Cobalt that had sat for 5 years and the gas was very bad. The 8.1L and 502 are very similar, both big block Chevy’s with slightly different bore and stroke. When I got it I could make it run but only on 3 cylinders, 5 injectors were plugged up. I actually cleaned all 8 in my garage till I had good spray patterns in all 8 and re installed. I hooked up an alternate fuel supply to the fuel pump and flushed it and the lines to the injection and fuel rails before hooking up the fuel line and starting the engine. It ran like brand new. The hardest part was draining the 44 gallons of bad gas and getting rid of it. Have you flushed the FCC with fresh gas, that might get it running again. These pumps are flow through, the gas runs over the motor to cool it and lubricate it as it works. The old fuel might be gel like and stop it from working?

Python (502) high pressure fuel pump

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