89 Chevy 1500 Electrical Issues

[WCreighton]

Hi all,

 

I have an electrical issue and my fuel pump isn’t getting power. I checked the plug for the pump and it is reading plenty of power. What else could be wrong?

 

Thanks,

Will 

[Jsdirt]

Will the plug at the pump power a halogen headlamp? A test light or volt meter won't cut it. It needs to be able to handle a good load.

 

Most pumps pull between 6-8 Amps. A bad one can pull well into double-digits. Make sure that circuit can handle the load - test the power AND ground, separately, to rule out one or the other not being up to par.

[Doug_Scott]

On 6/4/2020 at 2:17 PM, WCreighton said:

Hi all,

 

I have an electrical issue and my fuel pump isn’t getting power. I checked the plug for the pump and it is reading plenty of power. What else could be wrong?

 

Thanks,

Will 

As Jsdirt said, check the ground side as well.  You will want to watch how you word your question.  You wrote that the pump was not getting power, then said it had "plenty of power" at the connector.  You can't have it both ways.  Please include what you used to check for power, and where you checked it.  The fuel pump will only run for a few seconds with the engine not running, are you seeing the power shut off after a few seconds?  Did the truck just quit running one day, or is it a truck that has been sitting for a long time not running?  How old is the pump?  How about the fuel filter?  You need to verify the voltage and ground first, and make sure that you do not hear the pump running for a few seconds and then stopping.

[WCreighton]

Sorry guys let me provide some background on the truck. It’s my buddies dads and a friend and I are fixing it up for him. We pulled it out of a barn with the knowledge “it has a bad fuel pump,” that was it. So we drop the tank and replace the pump with a brand new one. Before we put the tank back in we plugged the pump in to verify that it worked, and it did. We put everything back together but we still don’t get fuel to the engine. So we replaced the fuel filter, and still got nothing. So we figured we must’ve had the lines on wrong (we’re 17 year old kids who just wrench on stuff for fun and we’re learning) so we take all the lines off and gas runs out, but the pump still doesn’t work, even though it worked when we put it in. So I’m perplexed. Any ideas? 

[Jsdirt]

Sounds like you've got a blockage in the lines if I'm understanding correctly. Make sure the fuel filter is installed in the correct direction. "IN" is supposed to face the fuel tank, NOT the engine. You'd be surprised at how many people get this backwards, and are convinced they're right!

 

If that checks out ok, (and even if it doesn't ...) you'll need to disconnect the fuel line as close to the TBI unit as possible, disconnect the line from the pump, and blow compressed air through the line to make sure it's free and clear. There's a possibility the TBI unit itself might be plugged up with stale fuel deposits, or something failed up in there. I would disconnect the line at the TBI, and fire the pump up to see if you're actually getting fuel up there. If you are, it could just be plugged injectors, or the return line is plugged solid. Remember, the fuel in this vehicle was designed to circulate. Anything not used by the TBI would be sent right back to the tank. The return line flow is controlled by the fuel pressure regulator.

 

Just be aware of any fire hazards. Quite a bit of volume of fuel will come out that line during the 2-second pump prime cycle at "key on".

[WCreighton]

A blockage in the line could be possible, although the fuel filter is installed correctly and I’ve blown through the lines with air. My problem is my pump isn’t working at all, even though it’s brand new. When the turn the key it doesn’t pump. 

[davester]

Then it's testing if the pump is getting power & ground, then perhaps testing if directly applying power & ground makes the pump work.

[Jsdirt]

5 hours ago, WCreighton said:

A blockage in the line could be possible, although the fuel filter is installed correctly and I’ve blown through the lines with air. My problem is my pump isn’t working at all, even though it’s brand new. When the turn the key it doesn’t pump. 

Ahh, got it. The way you worded the previous post, it sounded like it was running but you were getting no fuel to the TBI.

 

Do you get the 2-second prime when initially turning the key on? If not, you need to start from the beginning. Battery, to fuse, through the oil pressure switch, and on from there. Also make sure both the power and ground can handle the load, like I mentioned previously.

 

Is a headlight bulb lighting when connected to pump power and grounded elsewhere? Is the light lighting on pump ground when connected to + elsewhere? If not, will the pump run if you bypass the relay by jumping the corresponding contacts for 87 & 30 in the junction box / fuse box? Is #'s 85 & 86 for the relay receiving power and ground?

[WCreighton]

So finally got around to testing the power from the truck. No power  Any ideas? What should we do next? 

[riverbanks]

Do you hear the relay click on firewall?and check the wiring connection at relay,red is power,grey is power to pump,2 seconds with key on, always while cranking and running