Fuel Pump Challenges

[XJSteve]

Hi Everyone, just want to pick your brains on an electrical problem I'm having. I have a Cobra kit car I just picked-up with a Ford 5.0 V8 engine 1990-93. It started to back fire and lose power especially over large bumps in the road. Eventually it would idle well but backfire and grunt whenever the clutch was engaged.

I don't have a formal fuel pressure measurement tool but tried to release pressure at the (?)Schrader valve on the fuel rail and no spray came out. I thought it was likely the fuel filter or pump. I dropped the fuel tank, replaced the pump and filter and hooked it all back up. When I tried to start the engine, it would turn over but no run. The pump could be heard priming and I primed it 5-6 times but still no pressure at the fuel rail. I then dropped the fuel line at the fuel filter input port and tried to prime again, still no fuel. Then dropped the tank again and pulled the pump and placed it into a container of fuel and still no fuel output. I then measured the voltage to the connection to the pump and it was 6.75 when both grounded to the connector ground and a chassis ground. I believe this means that the fuel pump ground it not an issue? So, I then spliced in a second line to the hot side of the pump and ran it directly to the positive side of the battery and still the pump would run but no fuel. I even measured the voltage directly on the wires in the pump as it ran and got about 12 volts when connected directly to the battery. So, I then took the pump back to the shop I bought it from thinking it was a mechanically faulty new pump. They took it apart to confirm I wasn't a dolt and left some sort of plug present. They then ran a bench test using solvent and Voila, it produced solvent. So.....what the heck is going on and what do I do next? Could it be that I have volts but insufficient amps (don't know how to test that)? I would think I would have sufficient amps if running directly off of the battery with measured 12 v. Should I run a new ground directly to the battery? If that works, I could splice a temporary manual switch to turn the fuel pump on and off. It has to be my electrical connections as the pump has been proven to work!!

signed, I would like to check the fuel level in the tank with a lighter right now ,

Stevejavascript:void(0);

[Marco]

I fought with a fuel pump one time for a long time before i discovered it wouldnt run because of the coil    i would throw some fuel or spray down the carb/throttle body and turn it over a few times to see if its fuel it actually needs. just a thought

[XJSteve]

Hi Guys/gals,

Here's the update. This car is obviously a summer only machine so instead of spending my whole summer trying to figure it out, I elected to go redneck style. I got the pump going with independent wires directly to the battery and it actually produced fuel! So, today I'm going to wire the whole thing with 10g, an inline 30 amp fuse and toggle switch under the dash. The fuel system will be manual on and off which is a bit of a pain but will likely cut down on theft at any rate!!

Steve

[Mr Tim]

You should have more than 6.75 volts at the connector. i know you said your just going to wire it direct, but if you want to check the supplied voltage with your meter grounded directly to the battery, if you get 12ish volts then there is a ground problem, if you still get 6.75 you likely have a bad power wire/ connection somewhere.

[XJSteve]

Marco, I had a look at the engine. Couldn't find any type of relationship between the coil and the fuel pump. Not sure if the Jeep engines are an exception in this department.

Mr. Tim, I never did place my test ground to the battery itself but rather picked a thick piece of chassis to ground to and got the same 6.75 volts. I actually ran the independent line directly to the battery and got fuel pressure and obviously a running fuel pump but the damned car still wouldn't start. Already replaced the coil, dist cap, rotor, wires and plugs. Running VERY lean on all cylinders but number 8 when the old plugs were pulled. Probably reflects the poor voltage of the fuel pump just hanging on by a thread in terms of output.

Steve

[Marco]

hey steve, sorry i meant to just throw some fuel in it to make sure thats what it was missing to start- sounds like it was. if your planning on running a new wire with a switch i would guess then the pump is running while the car is on, why not just run a new wire and tap off the ignition side of your key instaed of a manual switch? or am i missing something completly here?

[esi]

Your fuel pump wires should start at a relay. find the relay and checkk the voltage there. It should be 10-12 volts and 14 while running. If you don't have full voltage at teh relay try swapping it out. If you have full vooltage at the relay you probably have crappy wires in between relay and the tank. Run a jumper set of wires from the relay to the pump.

[vantagetes]

Your fuel pump wires should start at a relay. find the relay and checkk the voltage there. It should be 10-12 volts and 14 while running. If you don't have full voltage at teh relay try swapping it out. If you have full vooltage at the relay you probably have crappy wires in between relay and the tank. Run a jumper set of wires from the relay to the pump.

This.

[XJSteve]

Thanks for all the replies guys! I figured out what the problem was. Who knew that the red wire on the pump was the ground and the black wire on the pump was the hot in order to make the pump actually pump fuel. Got that sorted out and replaced a connection in the loom. The challenge with this vehicle is that although the wiring itself is 1990 Ford 302, the locations of the relays etc. does not match the original car at all. Sounds like a minor problem but when two relays go "click" when you power on the ignition, it means you have to pull one and see if the pump still primes in order to narrow it down. I guess if it was straight forward, we'd call it a Honda, drive it everyday without any breakdowns and fall asleep at the wheel with boredom!! May the challenges continue!!

Steve

[JackstandJohnny]

hondas make great RTI ramps..................................

[TL-Iguana]

Isnt honda an acronym for Had One Never Do Again?