5v at fuel pump

[BCMTNKJ]

Recently purchased an 02’ liberty with the 3.7l v6. Was driving on the road a few days ago, the engine sputtered then died. When cranking it to start it would grab to 200-300rpm for a half second then drop down to zero while still cranking. Never started completely. Got it home, tried to crank again now there is no rpm jump at all, just cranking. Tested the fuel rail and got 0psi. Tried jumping the relay and got 0psi. Put a voltmeter on the harness at the pump and am only getting 5volts. From reading on this forum I have gathered it should be a full 12 volts.

In the am...
1) I’m going to jump the relay then measure the volts at the harness

2) I’m going to jump 12v to the pump itself to make sure the pump actually works

3) Jump a new ground to the harness

Anyone have any insights or tips on where else to look?

 

[Billwill]

Is the battery in good shape?
Should not drop below about 10 volts while cranking.

Definitely check the main grounding points.
Both battery connections must be clean and tight.
The negative battery lead going to chassis/ground must be clean and tight there.
The two grounding straps coming off the rear of the heads going to the Firewall must be clean and tight all ends.

 

[BCMTNKJ]

Is the battery in good shape?
Should not drop below about 10 volts while cranking.

Definitely check the main grounding points.
Both battery connections must be clean and tight.
The negative battery lead going to chassis/ground must be clean and tight there.
The two grounding straps coming off the rear of the heads going to the Firewall must be clean and

Is the battery in good shape?
Should not drop below about 10 volts while cranking.

Definitely check the main grounding points.
Both battery connections must be clean and tight.
The negative battery lead going to chassis/ground must be clean and tight there.
The two grounding straps coming off the rear of the heads going to the Firewall must be clean and tight all ends.

Thanks for your reply. I got a lot of my information for investigating this problem from another thread you commented on in August about voltage drop at the pump. Very informative in regards to how to follow manual. Thank you.

I went out this morning under fresh light and a new cup of coffee. I realized I was testing the wrong wire to get 5 volts. Was testing the sensor. So here is the new list of readings.

battery - 12.03
With ignition on - 12.02 at pin 30 on fuel pump relay
With ignition on - 0 at pump module
Cranking - 10.5 at pump module
If jump relay - 12.02 on dark green/white wire

With relay jumped I can **** start the pump but only get 7psi at rail so I’m gonna order a new pump. Install and check psi at rail and running volts at the pump. I’m curious as to why I’m not get a full 12 plus at cranking

 

[BCMTNKJ]

Thanks for your reply. I got a lot of my information for investigating this problem from another thread you commented on in August about voltage drop at the pump. Very informative in regards to how to follow manual. Thank you.

I went out this morning under fresh light and a new cup of coffee. I realized I was testing the wrong wire to get 5 volts. Was testing the sensor. So here is the new list of readings.

battery - 12.03
With ignition on - 12.02 at pin 30 on fuel pump relay
With ignition on - 0 at pump module
Cranking - 10.5 at pump module
If jump relay - 12.02 on dark green/white wire

With relay jumped I can **** start the pump but only get 7psi at rail so I’m gonna order a new pump. Install and check psi at rail and running volts at the pump. I’m curious as to why I’m not get a full 12 plus at cranking

Thinking about it again though... the battery volts will drop while cranking so I tested cranking volts at battery and pin 30 on relay. They all match at around 10v. All seems normal. I’ll get the new pump in the next few days.

 

[lfhoward]

The battery sitting at 12.0 volts seems low. 12.6-12.8 would be full at rest, and 13.5-14 would be what it should read when charging (motor running). Unless it is not charging when running (bad alternator?).

 

[BCMTNKJ]

The battery sitting at 12.0 volts seems low. 12.6-12.8 would be full at rest, and 13.5-14 would be what it should read when charging (motor running). Unless it is not charging when running (bad alternator?).

Vehicle doesn’t run right now so can’t test charging volts but I’m gonna put a charger on it anyways as I’m have been draining it pretty good the last few days while diagnosing the fuel pump issue

 

[JeepJeepster]

What pump did you go with? You going to try to use the access panel in the back or drop the tank?

 

[BCMTNKJ]

What pump did you go with? You going to try to use the access panel in the back or drop the tank?

I ordered the Delphi pump off rockauto and then got a filter as well. As far as I’m aware Delphi is a gm supplier. I didn’t want to go with value brand as it’s my hunting vehicle so break downs can end up being pretty inconvenient. I popped the access panel to do the testing of the fuel pump module so I’ll get it out that way as well

 

[Noclutch]

did the new fuel pump end up fixing your problem?