No power to fuel pump relay.
 

I have a 01 2500 hd 6.0 auto. For the last few months I noticed that if I hopped in and tried to start it immediately it would crank for aces seconds 5-10 before it started. If I turned the key to the run position for about 3-5 seconds until the bunger went off then it would immediately start. I would drive it about 1 mile to the local 7-11 for coffee and **** it off. When I would return it would crank over on the first turn of the key.. I wasn't to concerned since it runs great any other time. Well this morning came I same routine.. Turn key.. Wait and fired right up. Stopped for coffee came back out and it started right up. Now here's where my issue comes in. I get let off work early so I can take my wife on a date.. Come out the the top floor of the parking garage in the rain (trucks to long to park any where else) go to start it and she just cranks.. Popped the hood, depressed the valve on the fuel rail and nothing.. Little bit of gas just trickled out of it. Luckily from my current jeep wiring project I have my test light (no multi meter tho) so I get to probing fuses.. With the key on all fuses under dash and hood check out good. I pulled the f/pump relay and swapped it with the horn relay. When the horn relay was placed into the fuse block with the ignition on it never clicked.. Swapped it back into the horn spot and it worked fine. So to me it sounds like and issue between the computer and the relay.

I then cut a piece of wire and jammed it into the relay sockets one at a time and used the light to check power and with the ignition on only on socket lit up.

Knowing the little bit about a relay that I know I assumed there would be 2 prongs that would be hot. The hot from the battery and the source wire from the comp.. The other 2 should be relay ground and power out the accessory.

I'm broke so I can't take it to the dealer. Any info would be great.. Hope I explained the problem well enough.

check both the crank fuse located in the I/p and the underhood fuse block ign A fuse

Crank fuse is getting power only when cranking and ignition fuse is good.. Any thing else? I'm hoping to borrow a buddies scan tool to try and see if it's thrown a code.

Any other ideas?

to clarify: the truck cranks but doesn't start....or won't crank?


You initial long crank is due to a leaking check valve in the fuel pump. The fuel is draining back to the tank when the pump shuts off.

if the truck is cranking but you have no fuel pressure, you probably need a fuel pump. Can you hear the pump prime for 2 seconds when turned to the run position?

Yeah it cranks great. I don't hear the fuel pump kick on. When I pull the fuel pump relay and re-insert it it doesn't click. So I figured I wasn't getting power to the relay

ok, I been giving you wrong info them.

I'll correct this for you after gsp kicks some ass in his title defence.

assuming you do not have the dual tank set-up

at the fuel pump relay:

Power side of the relay
-one terminal should have battery voltage at all times. It is fed by the ecm b fuse

-one terminal feeds the fuel pump and should have 12 volts when the relay closes. if you power this terminal the fuel pump should run

Control side of the relay
-one terminal will have voltage for 2sec to prime the fuel pump when the key is turned to run. It is supplied power by the ecm. Once the ecm detects a rpm signal, the ecm will keep this voltage on.

-one terminal should have constant grd.

Are you checking the relay ecm feed terminal at the relay within the 2second prime cycle?

Got it fixed.. Yeah I called a mechanic buddy and he said the same thing about the relay. Pulled the bed, swapped in a new airtek unit (I know they are not the greatest) and viola.. Truck runs and my fuel gauge works.. Like a Christmas miracle!!