Fuel pump not working

Tiny
SOONERBILLS
  • 1992 CHEVROLET TRUCK

1500 model six cylinder 4.3 engine two wheel drive automatic 115,000 miles.

I cannot get this truck to start. When I put gas down the TB the truck will start right up and run until the fuel burns off. When the key is turned on the fuel pump does not come on. I pulled the pump and bench tested it and works perfect, good motor speed and pumps plenty. Reinstalled pump after inspecting all connection at tank and up stream wiring.
I then checked the fuses and found nothing there wrong. I replaced the engine bay fuse, fuel pump relay. I hot wired the circuit at the fuse and the pump runs then. Tried to start it and there is no fuel through the injectors. I assume no power to the injectors as well. I have since replaced the ECM, oil pressure switch as well as the ignition module in the distributor. All this and still no success. I am at my wits end! Can anyone help me please?
Thanks

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Sunday, September 28th, 2008 AT 1:24 PM

10 Replies

Tiny
RASMATAZ
  • MEMBER

When i put gas down the TB the truck will start right up and run until the fuel burns off

This one here it tells you the ignition system is working otherwise I do not think it will fire up if its no good.

Lets concentrate on the fuel system. Do you hear the fuel pump come On with all these items replaced-if so double check the fuel pressure making sure its within specs. Fuel pressure okay. Now we check for injection pulses.

Here are some wiring diagrams (below) for the engine and fuel pump along with a guide to help you do some testing:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

Please run some tests and get back to us we are interested to see what it is.

Cheers

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Monday, September 29th, 2008 AT 6:14 PM
Tiny
SOONERBILLS
  • MEMBER

Thanks for helping!
This truck has the TBI system.
I have never gotten a peep out of the pump even after replacing all the above mentioned parts. As mentioned I can get the pump to come on if I hot wire (jump) the fuel fuse on the firewall next to the fuel pump relay. I can only get the pump to fire in this manner by using a separate power source I.E. A jumper wire from the positive battery terminal. This is the fuse wired to the relay and ECM with a gray wire. With this I assume the wiring to the pump is sound.
But even with the pump running like that, the injectors are not cycling or spraying any fuel when I have the ignition on.
I am not up on how to properly test whether power is being supplied to the ECM and whether power is coming from the ECM to the relay. I have used a meter on some of the wires and some show hot though I do not remember which.
I am in training at a distance from the house right now so I won't be able to work on the truck until Friday, but any help in sending me in the right direction is really appreciated.
Thanks.

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+4
Tuesday, September 30th, 2008 AT 12:24 PM
Tiny
SOONERBILLS
  • MEMBER

Okay, I have had a chance to check some things. I rechecked the pump and it fires good and pressure is +55 at the TB. It still will not come on with the key/ignition and the wiring checks out when I hot wire from the fuse plug near the relay. I checked power to the relay and the orange input power wire from the ECM is hot with the key on but no other coming out from the relay. Checked for good ground there/okay.
So still no power to pump! Power in to relay but none out and it is a new relay!
Checked power to injectors and the hot wires are hot when key is on and when the other side is grounded they will fire. I hot wired the pump and grounded the injectors one at a time and they sprayed fuel big time and the engine would start. But without manual grounding the injectors will not fire or pulse. Well I am closer but no closer if you know what I mean. I am still at a loss as to what the problem is. Why will the pump not come on and why will the injectors not fire? Please help!

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+6
Friday, October 3rd, 2008 AT 8:25 PM
Tiny
RASMATAZ
  • MEMBER

Sounds like a computer problem it grounds the injectors and also the fuel pump relay.

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Sunday, October 5th, 2008 AT 5:54 PM
Tiny
BEVO995
  • MEMBER

Soonerbills, my truck is fixed. It was the fuel pump but once I changed it, I had to ground a contact on the test connector that specifically tells the ECM to close the fuel relay. Once the pump ran, I removed the ground and started the truck. Without doing that, the ECM did not power the relay. Go look at my post
1993 Chevy Truck No fuel to TBI.
There is a real good information that Merlin2021 provided and the answer may be that simple. The ECM gets it reference pulses from the ignition module to operate the fuel relay to keep it working and will shut down the fuel pump after two seconds if you stop trying to start the vehicle or there are no reference pulses. I think this will help you. Send me a post when you have success!

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Monday, October 6th, 2008 AT 6:46 PM
Tiny
BEVO995
  • MEMBER

Soonerbills,
I forgot to mention this. In your post you mentioned the fuel relay having power on the orange wire but nothing else. Your trucks diagram probably is the same as mine. You mentioned jumping power to the fuel pump wire. If it is a gray wire, then you probably have a green/white wire that the ECM energizes the relay coil with. I use a sewing pin to pierce the wire to read the voltage when you can not get to a contact. You already changed the relay and I bet it's the ECM that is not providing voltage to power the relay because the ECM is shut down and not broke.

Do not know the electrical diagram for your truck but on mine, the coil winding is grounded on one end the the ECM applies power to energize the relay coil. When you turn the key on, 12 vdc is applies to one of the relay contacts and only when the ECM applies voltage to the coil does the contacts close and feed voltage to the fuel pump.

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Monday, October 6th, 2008 AT 7:15 PM
Tiny
SOONERBILLS
  • MEMBER

The truck is now running!
Turned out that a cut wire (green/white) to the relay was the culprit. Previous owner chopped off the o2 wires, ran a straight exhaust and cut through the harness in the process, nailing the relay wire. This fried the ECM and after replacing the harness I was able to get the truck started.
Now I have find out why it is rough running and stalling at idle.

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Monday, October 13th, 2008 AT 12:37 PM
Tiny
BEVO995
  • MEMBER

Soonerbills, success feels great now that you fixed your truck. Bummer that one spends so much effort but I can definitely tell you this site saved me some time and I have learned from it. I appreciate the reply that you have it working. Hoped the information I sent helped.

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Monday, October 13th, 2008 AT 7:52 PM
Tiny
WAYNE MOORE2
  • MEMBER

Need help please badly. 1992 Chevrolet c1500 4.3 truck. Put in new fuel pump. TBI, fuel pump coming on when key on. Turns over with it. Injector working but right one does not work when trying to start engine.

Question I have to be sure. Should motor not start if only one injector is working? Know it would only run half the six cylinder engine but should it not start?
Then I could be more sure I have just a bad injector the problem?
Is it certain if fuel relay is cutting on fuel pump when turning key on its okay?
If injector on right. Checks out okay when I do the transistor battery test on the not working fuel injector on right. Side and its good where do I go then?
I have power to left side injector.

Okay to make better sense. If truck should crank and run on one injector working I am lost.
Also if right injector is good I am really lost.
Hope people understand where iam at. Please give me all your thoughts what I may be missing. Thanks to all.

Again need help I am six two years old, on disability with no money pay get fixed. Please read above. It is old truck but all I have. Need help so badly.
Someone please tell me what to check and test next in detail. I need my truck get to doctors and food.

You are nice people here knowing it is the fourth all with there families as they should be. Mine are grown. Not out to help me anymore.

Way it goes with many older people. All enjoy your holiday and family. It is so important to have a close net family.

I do not have that. Sorry to bother you with my problems. Sit at home and wait for help. One day I did not needed help as now. If broke I worked on it until I found problem.
Now I need help to find the problem. Again you please write in.

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Monday, July 3rd, 2017 AT 1:04 AM
Tiny
2CARPROS KEN
  • ADMIN
  • 9,439 POSTS

Hello and welcome to the site,

Yes, lets get this problem fixed for you. It sounds like the ignition module and gone out which is a common problem with these trucks.

To confirm lets check for spark.

Here is a guide to help you get started:

https://www.2carpros.com/articles/how-to-test-an-ignition-system

Please run this test and get back to us we are interested to see what it is.

Cheers, Ken

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Wednesday, July 5th, 2017 AT 1:46 PM

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