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Fuel Problem? Pump?

raceace73

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July 27, 2008
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City, State
PITT.,PA
Year, Model & Trim Level
97 EXPLORER
Hello everyone. I am having trouble with my 94 4.0 ohv ranger. I think it's the fuel pump but im not sure. Sometimes it will run ok but then it will start to cut out. I'll be going along and it will loose power. I can put my foot to the floor and go about 25. It will get a little gas but it wil buck like a bronco(horse not suv) until I can get it off of the road. It will usually start but sometimes it wont even do that. I switched out the fuel pump relay and thought it fixed it but I was wrong. Does anyone know what might be causing this? I just wanted to make sure that I am getting the right thing before I drop $100+ on a fuel pump.

Also, if it is the fuel pump, is there a aftermarket fuel pump that isnt quite as pricey as the OEM? I know where there is a cheap holley pump but I am used to old carb engines and I dont know how that would work with the computer.

Any help is appriciated.

Thanks,
 



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A couple of tests I would suggest:

1) Fuel pressure. Arguable the best test to see if the pump is good or bad is to put a fuel pressure gauge on it (when it is acting up). Normal fuel pressure should be ~40 psi with no vacuum to the fuel pressure regulator down to ~30 psi with vacuum applied to the regulator. My own, non-scientific tests indicate that the engine will start to stumble and stall if the pressure drops below 20-25 psi. If the engine is stumbling/stalling/won't start and the pressure is above 30 psi, the fuel pump is probably fine. If the fuel pressure stays below 20, then the fuel pump might be indicated.

2) Pull codes. the PCM monitors the fuel pump circuit for electrical faults. If you get fuel pump codes (specifically 543 or 542), that could indicate some electrical fault in the fuel pump circuit. Of course, additional diagnosis will be required to determine if the fault is in the pump or elsewhere in the circuit.
 






Pcm?

Thanks. I have a couple of quetions.

In relation to #1, what do I need to do to put a fuel pressure gauge on it (before or after the vaccum)? Would it just be an in line piece with adapters or would I need to run a whole new line?

In relation to #2,I have a 94 Ranger which I believe id OBD1? Would reading the codes tell me if I have a fuel problem on this year truck? I know that OBD1 dosent tell you much.

Thanks again!
 






In relation to #1, what do I need to do to put a fuel pressure gauge on it (before or after the vaccum)? Would it just be an in line piece with adapters or would I need to run a whole new line?
The test port is already built in to your fuel rail. It looks like a tire valve sticking out of the passenger side of the fuel rail. My fuel pressure tester came with an adapter that allows it to attach to this port. I would expect that most fuel pressure testers will have the correct adapter (if needed) to attach to this port.

In relation to #2,I have a 94 Ranger which I believe id OBD1? Would reading the codes tell me if I have a fuel problem on this year truck? I know that OBD1 dosent tell you much.
How much information depends on the specific problem it has. IMO, pulling codes only takes a few minutes. If there is no information in the codes, then you aren't out much. If you do find a fuel pump code (542 or 543), that will tell you that there is some kind of wiring fault in the fuel pump circuit, which could save you chasing other things. I guess in the end, it will take as much time and energy trying to argue whether pulling codes is useful as it will to just go out and pull codes.
 






Thanks Again.

Another question I have is regarding aftermarket fuel pumps. If my codes read that my pump was bad would it be a bad Idea to go aftermarket. I know a buddy who has a Holley Blue electric fuel pump and regulator he will take $35.oo for. Is this a good idea? Bad Idea? Would I have to do somthing to bypass the fuel pump relay?

Sorry for all of the questions. I am kind of a rookie.
 






I haven't got anything against aftermarket pumps in general. I don't know anything about the Holley pump you mention. I know that I usually associate Holley with carb's, though, so I would check the specs on that pump carefully. A carb pump only needs to generate 10-20 psi of pressure. Your Explorers EFI system runs continuously at 40 psi, and the OEM pump's max pressure is supposed to be something like 80-100 psi. As long as the pump meets or exceeds the OEM specs for volume and pressure, it should be fine.
 






I know someone who has a fuel pump for a 90 Ranger. Would this be comparable or would that most likley be carbureted?

Thanks
 






Do you know which engine? I'm somewhat sure that all the Ranger engines in '90 would use a similar pump to the one for your '94 Explorer, but I can't be completely certain. You'd still want to be certain that the replacement pump puts out enough pressure/flow for the 4.0 L engine.
 






Psi?

I am looking at some external universal pumps. I know I need 40PSI minimum. What would the maximum be?

Thanks
 






In terms of pressure, I doubt there is a spec for max pressure. The way the fuel system is designed, any excess pressure/volume delivered to the engine is returned to the tank. As long as your pump doesn't completely overwhelm the fuel system (in terms of volume flow), you shouldn't need to worry about a max pressure spec.
 






Flow

Any I idea how much flow would overwhelm the system? I would have just gone for the most GPH/LPH not knowing what was too much.
 






I don't have any idea.
 






Well since I havent got a code reader and cant get it to Advance, let alone find the time to trace the wiring harness. Does anyone have any other ideas of what it might be? Could it still be the fuel pump even though it starts sometimes when you turn the key and it runs better with the MAF unplugged?
 






Well since I havent got a code reader and cant get it to Advance,
FWIW, a paper clip or anything else that looks/acts like a small jumper wire is all you need for a code reader. We have tutorials (and even a few sample videos) here, or you can find tutorials all across the internet. Any good repair manual (Chiltons + Haynes together is what I used the first time I did it) should have test instructions, too.
 






If you replace the fuel pump, I just did mine, my trusted mechanic told me that the OEM pump is actually a Carter manufacture. I got the replacement piece, (pump, strainer and float) from Rockauto, a site vender. There was a 5% discount, search the site. With shipping it was like $110.
 






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