Diagnosing Fuel Pump & Pressure
Thread Starter
1st Gear Member
Joined: Aug 2014
Posts: 80
From: New Jersey
Diagnosing Fuel Pump & Pressure
I have a '00 V6/Auto w/ 110k miles, stock.
I've been having intermittent starting issues and RPM based hesitation around 1200-1800 RPM under load which is pointing me towards the fuel pump.
Car has new battery, terminals, air/fuel filters, coil(x2)/plugs/wires.
I've hooked up my fuel pressure tester to the rail, initial KOEO after the car has sat overnight, the pressure barely registers on the gauge. After about 3-4x cycling the key and priming the pump up I can get it to finally peg around 40PSI. KOER tests show solid 30-32 PSI or 40-42 with vacuum line disconnected from FPRS. I've left the gauge connected overnight to see how much it bleeds off, and it will bleed off pressure after a few hours very slowly dropping to 0.
I've driven with a gauge connected and the pressure appears to be ok even during the hesitation/bucking I get. The car seems to buck pretty bad most noticeably on the hwy at 50-70MPH, and seems as though running the A/C makes it feel worse.
I changed the fuel filter last year, and it appeared to be the original with over 100k miles. It was full of black cruddy fluid of course, and I can imagine the fuel pump strainer can't look any better.
I'm about to just buy a fuel pump assy, knowing that my cranking issue as well as the fuel pressure bleeding off points me towards the pump. The spark plugs all look fine and I've ohm'd out the injectors and they all tick as they should.
I've been having intermittent starting issues and RPM based hesitation around 1200-1800 RPM under load which is pointing me towards the fuel pump.
Car has new battery, terminals, air/fuel filters, coil(x2)/plugs/wires.
I've hooked up my fuel pressure tester to the rail, initial KOEO after the car has sat overnight, the pressure barely registers on the gauge. After about 3-4x cycling the key and priming the pump up I can get it to finally peg around 40PSI. KOER tests show solid 30-32 PSI or 40-42 with vacuum line disconnected from FPRS. I've left the gauge connected overnight to see how much it bleeds off, and it will bleed off pressure after a few hours very slowly dropping to 0.
I've driven with a gauge connected and the pressure appears to be ok even during the hesitation/bucking I get. The car seems to buck pretty bad most noticeably on the hwy at 50-70MPH, and seems as though running the A/C makes it feel worse.
I changed the fuel filter last year, and it appeared to be the original with over 100k miles. It was full of black cruddy fluid of course, and I can imagine the fuel pump strainer can't look any better.
I'm about to just buy a fuel pump assy, knowing that my cranking issue as well as the fuel pressure bleeding off points me towards the pump. The spark plugs all look fine and I've ohm'd out the injectors and they all tick as they should.
1st Gear Member
Joined: Feb 2014
Posts: 90
From: FL
I have fixed a few mustangs with this same problem. 2 were worn out FP's and 1 was a corroded ground wire that would make better contact as the engine cranked. I will do voltage and ground tests first to make sure the pump is getting full juice. Next, I disconnect the inlet line to the fuel filter and do KOEO with fuel line in a coffee can (or whatever container I can squeeze up there) to observe fuel flow. Fuel flow should be a strong stream and plentiful. In the 2 cases, it was easy to see poor fuel flow from the pump. I like to make sure it is a FP problem before dropping the tank.
My usual rule of thumb - If the pump is over 10yrs old, I put a new pump in. It's always cheaper to repair in my garage then in some other shop in the middle of nowhere!
My usual rule of thumb - If the pump is over 10yrs old, I put a new pump in. It's always cheaper to repair in my garage then in some other shop in the middle of nowhere!
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