1990 4x4 Burb, No power to fuel pump. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

m00n1957 · 12-15-2019, 10:12 PM

just purchased a 90 4x4 GMC Suburban 5.7, 700r4. previous owner claimed it needed fuel pump and had already purchased a new one. I installed new pump without disconnecting any wires from sending unit. I also replaced fuel pump relay and can hear it click when key is turned on but pump is silent and no fuel no start. you can prime engine and it starts fine. so I have a new pump and relay but no fuel, I totally new to TBI so any help is appreciated.

ChevyTech · 12-17-2019, 10:31 AM

Make sure there is power on the orange wire to the fuel pump relay. That is the supply.

The most common problem is the ground is lost for the fuel pump. Test the black wire with a white tracer on the to the fuel sending unit and make sure it is a good ground.

To power the pump there should be power to the fuel pump on either a gray wire or in may be light brown with a white tracer. The wire color changes with the model year and I can't remember the year it changed.

There will only be power for a couple seconds when you first turn the key on, then the power will shut off unless the engine is running or you are cranking the engine with the starter.

If you turn the key on and crawl under the truck to test it, the relay will have shut off the power before you get to the wires to test them.

1976gmc20 · 12-17-2019, 01:02 PM

You could run a long jumper wire from the battery to the connector just in front of the tank just to test out your new pump. That's what I did to discover that my pump ran but no fuel (the little short connecting hose had come off inside the tank

).

There should be an inline filter along the frame rail. That could be plugged up.

What about the module in the distributor? I believe that controls the TBI and ignition.

95 S_Trucker · 12-17-2019, 02:22 PM

Here is the diagram:

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speedygonzales · 12-18-2019, 09:28 AM

Pull the relay out of the socket.
Make a jumper wire with a spade connector on each end. Plug in one end on the "A" terminal of the relay socket and other end into "E" on the relay socket. Now try to crank the engine over. Based on what you have told us, I assume it doesn't start.

Now with Key On Engine Off, the relay is still out of the socket, remove the jumper wire you made and probe in "A" in the socket for the presence of +12V. If it's not there, you must trace the source on the orange wire. Check for the presence of an ECM B fuse, which should have been done long before this thread even got started.

Because you hear the relay click when the key is first turned on, we know that pin "D" is getting voltage and "F" has a good ground. You may need to come back to this later however, for the moment, move on.

If "A" has power, now check fuel pump fuse, which again, should have been done long ago.

If all that checks out and the fuel pump still doesn't come on, there is a break on the fuel pump wire that is either tan/white stripe or pink/black stripe. You could check the wire for continuity which would be hard to do or the easier method is probe it with the jumper in place from "A" to "E" like before and use a test light to locate where voltage is and where it is not.

A good place to start is the 2 sides of the bulkhead connector. Be sure it goes into one side and exits the other half of the connector.

You get the idea from here.

12-15-2019, 10:12 PM	#1
m00n1957 Registered User Join Date: Oct 2010 Location: blue mtn. ms Posts: 100	1990 4x4 Burb, No power to fuel pump. just purchased a 90 4x4 GMC Suburban 5.7, 700r4. previous owner claimed it needed fuel pump and had already purchased a new one. I installed new pump without disconnecting any wires from sending unit. I also replaced fuel pump relay and can hear it click when key is turned on but pump is silent and no fuel no start. you can prime engine and it starts fine. so I have a new pump and relay but no fuel, I totally new to TBI so any help is appreciated.

12-17-2019, 10:31 AM	#2
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: 1990 4x4 Burb, No power to fuel pump. Make sure there is power on the orange wire to the fuel pump relay. That is the supply. The most common problem is the ground is lost for the fuel pump. Test the black wire with a white tracer on the to the fuel sending unit and make sure it is a good ground. To power the pump there should be power to the fuel pump on either a gray wire or in may be light brown with a white tracer. The wire color changes with the model year and I can't remember the year it changed. There will only be power for a couple seconds when you first turn the key on, then the power will shut off unless the engine is running or you are cranking the engine with the starter. If you turn the key on and crawl under the truck to test it, the relay will have shut off the power before you get to the wires to test them. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too. Last edited by ChevyTech; 12-17-2019 at 10:32 AM. Reason: Add more

12-17-2019, 01:02 PM	#3
1976gmc20 Registered User Join Date: May 2015 Location: Montana Posts: 3,696	Re: 1990 4x4 Burb, No power to fuel pump. You could run a long jumper wire from the battery to the connector just in front of the tank just to test out your new pump. That's what I did to discover that my pump ran but no fuel (the little short connecting hose had come off inside the tank ). There should be an inline filter along the frame rail. That could be plugged up. What about the module in the distributor? I believe that controls the TBI and ignition. __________________ Current/past Chevy/GMC trucks: 1958 Chevy C-60; 1965 GMC C-50; 1965 Chevy C-10; 1971 Chevy K-10; 1973 Chevy K-20; 1976 GMC C-20; 1977 Chevy C-10 Suburban; 1980 Chevy K-10; 1989 Chevy K1500; 1991 GMC V1500 Suburban; 2016 Chevy K2500 HD Other vehicles: 1988 Jeep XJ; 2011 Toyota 4Runner

12-17-2019, 02:22 PM	#4
95 S_Trucker Registered User Join Date: Oct 2009 Location: . Posts: 2,178	Re: 1990 4x4 Burb, No power to fuel pump. Here is the diagram:

12-18-2019, 09:28 AM	#5
speedygonzales Registered User Join Date: Jan 2006 Location: Smithfield, VA Posts: 1,501	Time to look for voltage loss or breaks Pull the relay out of the socket. Make a jumper wire with a spade connector on each end. Plug in one end on the "A" terminal of the relay socket and other end into "E" on the relay socket. Now try to crank the engine over. Based on what you have told us, I assume it doesn't start. Now with Key On Engine Off, the relay is still out of the socket, remove the jumper wire you made and probe in "A" in the socket for the presence of +12V. If it's not there, you must trace the source on the orange wire. Check for the presence of an ECM B fuse, which should have been done long before this thread even got started. Because you hear the relay click when the key is first turned on, we know that pin "D" is getting voltage and "F" has a good ground. You may need to come back to this later however, for the moment, move on. If "A" has power, now check fuel pump fuse, which again, should have been done long ago. If all that checks out and the fuel pump still doesn't come on, there is a break on the fuel pump wire that is either tan/white stripe or pink/black stripe. You could check the wire for continuity which would be hard to do or the easier method is probe it with the jumper in place from "A" to "E" like before and use a test light to locate where voltage is and where it is not. A good place to start is the 2 sides of the bulkhead connector. Be sure it goes into one side and exits the other half of the connector. You get the idea from here. __________________ 99 Z71 (98 body style) Pride and joy



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