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TBI fuel pump problem

Tiny
MLINTON2
  • MEMBER
  • 1992 CHEVROLET SILVERADO
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
Hi Everyone,

I bought the truck listed above k1500 with a throttle body.
I put a new fuel pump in it and the pump does not run with the key in the on position, engine not running. It fires right off with 15lbs. Psi. And runs good when I start it.
Does it hurt the pump or anything to just drive the pickup that way? Will it leave me stranded or anything because of it? I'm going to be switching it over to carburetor a little later on and I don't think I need the pre prime for carburetor, do I?

I have 8.7 volts at the center wire at the pump, which I think is for the prime. I'm going to try to find the problem and fix that to, but if it won't hurt the pump to run it like it is then I can go ahead and us the pickup while I'm trying to find the problem. If you have any ideas on what could be wrong I would appreciate the help.

Thanks a lot for the help. You are all great.
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Thursday, April 4th, 2019 AT 10:52 AM

17 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon,

You need battery voltage to the pump. 8.7 may be the gauge wire.

What color was the wire?

As far as your jumper, yes yo can run it like that but I would not do it for long.

Did you check the relay? Verify your fuses are good by testing for power on both sides.

Roy
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Thursday, April 4th, 2019 AT 12:21 PM
Tiny
MLINTON2
  • MEMBER
  • 15 POSTS
It was a purple wire, in the center of the plug.
Then there is a gray wire and a black with white stripe wire.
The fuses and relay are good.
I was just out checking voltage again and the purple wire has 8.4 with key on, and 15.6 with key off. Shouldn't the voltage with the key off be 0?
I ran a jumper wire from the battery with 12.6 volts and touched it to the Purple wire and the pump still didn't run.

The pickup will start and run fine without using a jumper wire. Just plugged in to the harness. So if it runs good without using a jumper wire is it okay just to run it however long I need to?

Thanks a lot for the help.
Michael
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Thursday, April 4th, 2019 AT 1:02 PM
Tiny
ASEMASTER6371
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Got it.

The gray wire is the fuel pump wire.

By jumping the purple, it may have fries the gauge unit.

Try jumping the gray wire.

Is there a wire at the battery positive cable taped to it? If there is, it is a primer wire directly to the fuel pump.

Roy
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Thursday, April 4th, 2019 AT 1:08 PM
Tiny
MLINTON2
  • MEMBER
  • 15 POSTS
There is a fairly large black wire that is molded right into the Positive battery cable and it looks like it may have an inline fuse.

The fuel gauge seems to be working alright.

So if I unplug the pump from the harness and touch a jumper from the battery to the gray wire on the pump harness tjhe pump should run, is that right?
I want to be sure I'm getting the right wire so I don't burn somthing up. I tried it earlier and didn't here the pump and I was right at the pump.
I got sparks when I first touched it so I didn't leave it touching very long.

Could the problem be the ignition switch?
I don't know why with the key off that I get 15+ volts on the gray wire.
And, when I turn the key on I only have 8.4 volts.
When I turn the key on it starts buzzing and when I wiggle the key the buzzer goes on and off.

Thanks,
Michael
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Thursday, April 4th, 2019 AT 1:48 PM
Tiny
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You told me before you were testing the purple wire. You said nothing of the gray wire at all.

Can you please clarify?

Roy
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Thursday, April 4th, 2019 AT 1:50 PM
Tiny
MLINTON2
  • MEMBER
  • 15 POSTS
I did tell you that I jumped the purple wire. And you told me that I may have fried the gauge unit and that the grey wire is the fuel pump and to try jumping the grey wire.

Sorry I didn't mentioned jumping the grey wire earlier. I new it got power when cranking it over and the pickup would start, so I figured that it was ok and that the grey wire was for when you started the engine and maybe the purple wire was just for doing the prime. My mistake.

So I jumped the grey wire from the battery and it runs the pump.

But, when I start the pickup it isn't by using a jumper wire from the battery. It is with the wire harness for the pump plugged into the factory wire harness coming from the front of the pickup.
That's why I was wondering if it would be alright to run it that way. Not by using a jumper wire.

Sorry for the mishap,
Thanks for your help,
Michael
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Thursday, April 4th, 2019 AT 4:15 PM
Tiny
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Yes it 3.

Roy
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Thursday, April 4th, 2019 AT 4:23 PM
Tiny
MLINTON2
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Not sure what you mean by "Yes it 3"
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Thursday, April 4th, 2019 AT 6:04 PM
Tiny
ASEMASTER6371
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Wow, senior moment.

I meant yes, it is. Sorry. Long day.

Roy
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Thursday, April 4th, 2019 AT 6:06 PM
Tiny
MLINTON2
  • MEMBER
  • 15 POSTS
Got looking and saw where there were yes and no on the answers that I should have checked. I think that is what you were getting at with "yes it 3".
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Thursday, April 4th, 2019 AT 6:09 PM
Tiny
MLINTON2
  • MEMBER
  • 15 POSTS
I think I have something wrong in the ignition switch. I went out and started wiggling the key around and now I am getting pressure reading with key on engine off of 15psi. And with engine running of 15psi.

Could the ignition switch cause the problem?
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Thursday, April 4th, 2019 AT 6:16 PM
Tiny
ASEMASTER6371
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No worries. We are good.

Roy
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Thursday, April 4th, 2019 AT 6:24 PM
Tiny
ASEMASTER6371
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Key off is good. It should retain pressure when off.

Roy
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Thursday, April 4th, 2019 AT 6:25 PM
Tiny
MLINTON2
  • MEMBER
  • 15 POSTS
My pressure drops back off after relay quits.
Does the TBI retain pressure?
I thought I read somewhere that they don't hold pressure like the multi-port injections do. But, you can't always believe what you read either.

Thanks for all the help Roy. Much appreciated.
Michael
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Thursday, April 4th, 2019 AT 7:33 PM
Tiny
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Don't believe much on the internet. It is full of inaccurate information.

Yes, it retains pressure. The pump is what keeps the pressure in the lines.

Roy
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Friday, April 5th, 2019 AT 5:28 AM
Tiny
MLINTON2
  • MEMBER
  • 15 POSTS
Thanks Roy for all the help. I'll check and see if I have an injector leaking or something that lets the pressure go back to 0 when the relay clicks.

I think we figure out the pump. I ordered a new ignition switch and key cylinder.

You have a good weekend.
And again Thanks a lot.

Michael
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Friday, April 5th, 2019 AT 8:45 AM
Tiny
ASEMASTER6371
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You are welcome.

Always glad to help.

Roy
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Friday, April 5th, 2019 AT 10:46 AM

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