Fuel Pump Or something else ? Im lost
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Fuel Pump Or something else ? Im lost
I have a 1996 f350 crew cab 5.8 liter. It wont start the first time you turn it over but always on the second time ? The rear fuel pump works but when you give it gas it seems like its sluggish. When the front tank is selected it wont start the first time you crank it over but always the second time but runs like normal when you give it gas it runs great. Both fuel gauges work fine, new plugs, wires, cap and rotor, It never starts the first time but always the second time you cranks it over cold/hot. Any helpful tips thanks
Laughing Gas
Joined: Feb 2015
Posts: 765
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Welcome to FTE!
It's hard to diagnose just by symptoms alone. You need to run some tests to figure out if the basics to run the engine are present. Engines require fuel, spark and compression to run. If any of the three are absent/weak the engine will not run.
First thing to do is pull codes from the computer and see if there's anything relevant to point your testing in the right direction. If there are no codes stored then you have to start testing. Start with the least intrusive (taking parts off) things first.
If you don't have one, go to an auto parts store (O'Reilly, Autozone or NAPA) and rent a fuel pressure tester. Attach it to the fitting on your fuel rail (near the distributor) and cycle the key on, engine off. See if you are building fuel pressure. Seems like your front pump is having problems, make sure that one is selected when you perform the test. It should go from almost nothing to at least 35-40 psi instantly. If it builds slow/not at all then you have an issue with fuel delivery (probably the fuel pump itself).
Start with that and reply back with results.
It's hard to diagnose just by symptoms alone. You need to run some tests to figure out if the basics to run the engine are present. Engines require fuel, spark and compression to run. If any of the three are absent/weak the engine will not run.
First thing to do is pull codes from the computer and see if there's anything relevant to point your testing in the right direction. If there are no codes stored then you have to start testing. Start with the least intrusive (taking parts off) things first.
If you don't have one, go to an auto parts store (O'Reilly, Autozone or NAPA) and rent a fuel pressure tester. Attach it to the fitting on your fuel rail (near the distributor) and cycle the key on, engine off. See if you are building fuel pressure. Seems like your front pump is having problems, make sure that one is selected when you perform the test. It should go from almost nothing to at least 35-40 psi instantly. If it builds slow/not at all then you have an issue with fuel delivery (probably the fuel pump itself).
Start with that and reply back with results.
Cargo Master
Joined: Mar 2010
Posts: 3,328
Likes: 292
From: Laramie, WY
What happens if you cycle the key to ON but don't start (hold 1 second, or until you hear the fuel pump relay click off), turn it back to OFF, then ON, then start? This should pressurize the fuel system. It should remain pressurized as the truck sits, but a leaky injector or bad check valve in the FDM can bleed down pressure. A weak fuel pump or clogged filter don't help the situation. You could put a fuel pressure gauge on it, that's a good way to stop the guessing game.
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Well I believe i found the problem, rear fuel pump was only pressuring up to 30psi when key on and when running would drop to 27psi. The front pump is 32psi and when running drops to 29psi when running. Is it supposed to read over 40psi when key on then drop to 35psi ?
Cargo Master
Joined: Mar 2010
Posts: 3,328
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From: Laramie, WY
Pumps both sound weak. That's not enough pressure. I bet pressure falls way off when the truck is under load and consuming fuel faster than the pump can deliver it. When was the last fuel filter change?
Laughing Gas
Joined: Feb 2015
Posts: 765
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Yeah both fuel pumps should supply at least 35-40 PSI with the engine running. If you're dropping below 30 that would cause driveability problems but the truck would probably idle ok. If you experienced a pressure drop you're definitely losing fuel pressure somewhere. If both pumps dropped 3 PSI according to your test results then you might have a fuel leak somewhere between both pumps and the engine. I would check available voltage to the pumps (drop the tank and probe the fuel pump wires), then go through every fuel line and verify you don't have any fuel leaks. Also pull the spark plugs to make sure they aren't fuel fouled to rule out the injectors being leaky.
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New User
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Check the psi with the engine off and the self diagnostics port bridged for the fuel pump to run continuously, and also with the engine running. A chiltons or haynes manual will describe how to do those tests and others like the fuel pressure regulator etc, and what the psi should be under each condition.
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Today I installed two new/used pumps from a parts truck i had out back, now the truck runs great, starts first turn and lots of power ! These newer pumps are putting out 40psi and 37psi while running. Thanks for the leads to get this one fixed up !
Cargo Master
Joined: Mar 2010
Posts: 3,328
Likes: 292
From: Laramie, WY
Good deal! Make sure the filter is fresh so you don't roast the current pumps. I know the recommended filter change interval is pretty long, I replace them almost annually so the pumps are never over burdened. Cheap way to help the pumps last.
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matt2fan
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