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Fuel Pressure Question #1295022 09/01/12 11:51 AM 09/01/12 11:51 AM
Joined: Jan 2003 Posts: 5,443 Indiana Y YO7_A66 OP master
YO7_A66 OP master Y Joined: Jan 2003 Posts: 5,443 Indiana	I have a mechanical fuel pressure gage in line just before the carb. I am used to seeing the fuel gage showing pressure for several minutes (15+?) after I shut down the car. This morning I noticed that the fuel gage is dropping to zero after 15 seconds or so after the car is shut down. When the car was running, it was showing the proper 6+psi at idle, but I shut it down twice this morning while watching the fuel pressure and it dropped to 0 both times. Do you guys see the fuel pressure drop this quick after you shut your cars down? This is not typical for mine, so I am wondering if I am seeing the beginnings of a fuel pump (Carter mechanical) issue. Thanks 1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)

Re: Fuel Pressure Question [Re: YO7_A66] #1295023 09/01/12 01:30 PM 09/01/12 01:30 PM
Joined: Aug 2012 Posts: 28 B bb489ss member
bb489ss member B Joined: Aug 2012 Posts: 28	I have a carter on my 383 and it is 6 psi when running and when I shut it off it drops as well, but usually stays around 2-3 PSI. I'm sure someone smarter than me will chime in soon.

Re: Fuel Pressure Question [Re: bb489ss] #1295024 09/01/12 08:40 PM 09/01/12 08:40 PM
Joined: Jan 2003 Posts: 5,443 Indiana Y YO7_A66 OP master
YO7_A66 OP master Y Joined: Jan 2003 Posts: 5,443 Indiana	Thanks for your reply. I am just worried because I usually have to wait an hour or so or just crack open the carb to releive the pressure after a drive if I am making a tuning change. Today the pressure fell off as soon and I turned off the car and walked around to the engine to look at the gage. I also had some lean issues on my last drive that I could not explain. If the pump is going south, then my tuning issues would have an explanation. If not, then I need to keep searching. 1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)

Re: Fuel Pressure Question [Re: YO7_A66] #1295025 09/01/12 09:12 PM 09/01/12 09:12 PM
Joined: Apr 2010 Posts: 4,154 bethlehem pa M mikemee1331 master
mikemee1331 master M Joined: Apr 2010 Posts: 4,154 bethlehem pa	i would think with a mech pump the pressure would drop off slowly unless there is a leak. my electric drops off right away but thats because the pressure in the lines is relieved. but the leak down could be anywhere between the pump and the guage.

Re: Fuel Pressure Question [Re: mikemee1331] #1295026 09/01/12 09:37 PM 09/01/12 09:37 PM
Joined: Jun 2008 Posts: 3,916 usa L lewtot184 master
lewtot184 master L Joined: Jun 2008 Posts: 3,916 usa	if the pump maintains proper pressure when running i don't think i'd get over concerned. those pumps have 3 valves in them and maybe there is a little something letting one leak. they're fairly easy to take apart and inspect and do some upgrades to.

Re: Fuel Pressure Question [Re: lewtot184] #1295027 09/01/12 09:48 PM 09/01/12 09:48 PM
Joined: Apr 2010 Posts: 4,154 bethlehem pa M mikemee1331 master
mikemee1331 master M Joined: Apr 2010 Posts: 4,154 bethlehem pa	i didn't think that much leak down was a big deal either. the amount of air being drawn in while it's running would be tiny and his pressure hasn't changed. but the guage wouldn't care what it was reading, air pressure or fuel. maybe a peek at the float level would be in order.

Re: Fuel Pressure Question [Re: YO7_A66] #1295028 09/01/12 11:09 PM 09/01/12 11:09 PM
Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska	Quote: This is not typical for mine, so I am wondering if I am seeing the beginnings of a fuel pump (Carter mechanical) issue. That's a good question as you'd sure hate to have fuel leaking into the crankcase. A leaking needle/seat wouldn't be as bad but would need to be addressed and this DID happen all of a sudden. I think I'd toss on another pump even a cheap parts house airtex just to see if it goes back to holding pressure live every 24 hour block of time like it's your last day on earth

Re: Fuel Pressure Question [Re: RapidRobert] #1295029 09/01/12 11:15 PM 09/01/12 11:15 PM
Joined: Jun 2008 Posts: 3,916 usa L lewtot184 master
lewtot184 master L Joined: Jun 2008 Posts: 3,916 usa	Quote: Quote: This is not typical for mine, so I am wondering if I am seeing the beginnings of a fuel pump (Carter mechanical) issue. That's a good question as you'd sure hate to have fuel leaking into the crankcase. A leaking needle/seat wouldn't be as bad but would need to be addressed and this DID happen all of a sudden. I think I'd toss on another pump even a cheap parts house airtex just to see if it goes back to holding pressure i've had those pumps apart before. i think it would be difficult to get fuel in the crankcase with one. they have a relief hole in the top and the diaphragm has a seal at the top that the pressure spring holds in place.

Re: Fuel Pressure Question [Re: lewtot184] #1295030 09/01/12 11:24 PM 09/01/12 11:24 PM
Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska	Quote: i've had those pumps apart before. i think it would be difficult to get fuel in the crankcase with one. they have a relief hole in the top and the diaphragm has a seal at the top that the pressure spring holds in place. That's good news live every 24 hour block of time like it's your last day on earth

Re: Fuel Pressure Question [Re: RapidRobert] #1295031 09/02/12 12:03 AM 09/02/12 12:03 AM
Joined: Jan 2003 Posts: 5,443 Indiana Y YO7_A66 OP master
YO7_A66 OP master Y Joined: Jan 2003 Posts: 5,443 Indiana	The unit that I have is one of the "sealed" (cheaper) units. I can not open it up to repair it. It is about 3 years old and it has me worried since it stopped holding pressure after shut down and I had the weird lean issues on the last drive. Thank you all!! EDIT: I just checked and both bowls still show fuel in the sight glasses. It appears not to have any internal carb leaks. The unit is a Carter M6866. 7360977-M6866-3.png (30 downloads) Last edited by YO7_A66; 09/02/12 11:17 AM.

Re: Fuel Pressure Question [Re: YO7_A66] #1295032 09/02/12 10:20 AM 09/02/12 10:20 AM
Joined: Jun 2008 Posts: 3,916 usa L lewtot184 master
lewtot184 master L Joined: Jun 2008 Posts: 3,916 usa	Quote: The unit that I have is one of the "sealed" (cheaper) units. I can not open it up to repair it. It is about 3 years old and it has me worried since it stopped holding pressure after shut down and I had the weird lean issues on the last drive. Thank you all!! EDIT: I just checked and both bowls still show fuel in the sight glasses. It appears not to have any internal carb leaks. i don't care for those 2 valve pumps for performance.

Re: Fuel Pressure Question [Re: lewtot184] #1295033 09/02/12 11:18 AM 09/02/12 11:18 AM
Joined: Jan 2003 Posts: 5,443 Indiana Y YO7_A66 OP master
YO7_A66 OP master Y Joined: Jan 2003 Posts: 5,443 Indiana	Thank you for your reply. I am currently shopping for a new one and I have started a new thread on suggestions. Thanks 1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)

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