fuel pump relay bypass


ChuckT121
01-16-2007, 11:59 AM
ok , I have read about 100 or so posts about the fuel pump on a 98 blazer (give or take a couple years). :banghead: I am wondering about this fabled wire that is supposed to be near the firewall. I have looked for it and had 3 others looking for it. none of us can find it.:disappoin Is there another place that it may be? is it possible that the 98 doesn't have one? Is there another way to bypass the relays? Thanks for any input.

DelCoch
01-16-2007, 03:14 PM
The red fuel pump test wire will be on the left inside fender about 10 inches from the firewall, hanging from a wire loom; among the large group of wires next to the eletrical junction box/fuse panel on the driver's side fender. From what I've read from others on this board, I'm almost sure the '98 has it.

Let us know if you find the test wire.

To test the relay: The fuel pump relay is usually next to another relay with the same part number and you can swap them out to see it makes any difference. I think the fuel pump relay on a '98 may be located under the hood on the firewall - either that or inside the golve compartment.

A repair manual should give the location for the relay.

jdl
01-16-2007, 03:31 PM
If your talking about the fuel pump prime connector? Some GM vehicles have it and some don't. I looked at a fuel pump wiring diagram for a 98 s10 blazer. It doesn't show a prime connector for that vehicle.

On A lot of GM vehicles, there is a gray wire that carries voltage from the pump relay to the pump, when the relay is energized.

I believe there is an oil pressure switch in your fuel pump circuit. When you crank it enough to build oil pressure, there should be voltage on the gray wire.

I started to tell you how to use a jumper to run the pump, but, I'm not sure I was looking at the correct diagram. I think I'll just stop here.

ChuckT121
01-16-2007, 05:00 PM
I have checked everywhere for that red wire and can't find it. I hav3e also hade others check and they can't find it either. I swapped relays in the box under the hood and replaced the relay on the firewall. no luck.

Perhaps I should start with all that has happened and what has been done. I have a 98 with the vortec engine(obvoius I know but bear with me). It wasn't running right and seemed starved for gas on hills. I stated with replacing the filter (something I learned about from my fords). In doing that the line needed to be replaced as well. Took it to a shop and they said the tank was leaking and wouldn't pass inspection.It ran a bit better for a while and quit. No sound from the pump. When I put gas or starting fluid in it would run until it burned off. OK sounds like a whipped pump. I replaced the pump unit with a Delco and replaced the canister valve as that broke removing the tank. Still no luck with the pump priming.( no sound and runs with gas added) . I checked relays before and after. the one in the box clicks the other didn't. Both were replaced. Now I have anew tank, new canister valve, new line new filter, new relays and no working pump. Everything I have read seems to point to that red wire to test. I can't find it. Any other ideas short of another trip to the shop would be helpful. :newburn:

DelCoch
01-17-2007, 12:42 AM
When you turn the on key, do the instrument panel service lights light up, i.e., SES light, Brake light, etc? If not, check the ECM fuses with a test light. The fuel pump won't run if these service lights don't light up.

First order of business is to check the battery with a load type tester. AutoZone and some other auto parts stores will do it for free. A weak battery will not allow the fuel pump to build up the necessary pressure (61 psi) to start the engine.

Then you need to determine if you have current at the gray fuel pump wire at the wire connector located on the top of the gas tank where it hooks to the fuel pump connector. Disconnect the connector and check the gray wire coming from the engine with a test light, make sure you have a good ground. If you have current, then use the black wire in the connector for a ground. If this checks out, check the gray wire with a multimeter to see if it has 12+ Volts. Should read between 12 & 13.5 or something greater than 12 volts.

Keep in mind - current is only applied to the gray wire for 2 seconds when the key is turned on. Then the key must be off for 10 seconds before you get another 2 seconds to the pump. This is with the key on - engine off.

If you have 12+ volts going into the fuel pump, the pump should run for those 2 seconds and you should get a fuel pressure reading at the shrader valve. If not, I would say the pump is toast.

jdl
01-17-2007, 09:45 AM
I have checked everywhere for that red wire and can't find it. I hav3e also hade others check and they can't find it either. I swapped relays in the box under the hood and replaced the relay on the firewall. no luck.

Perhaps I should start with all that has happened and what has been done. I have a 98 with the vortec engine(obvoius I know but bear with me). It wasn't running right and seemed starved for gas on hills. I stated with replacing the filter (something I learned about from my fords). In doing that the line needed to be replaced as well. Took it to a shop and they said the tank was leaking and wouldn't pass inspection.It ran a bit better for a while and quit. No sound from the pump. When I put gas or starting fluid in it would run until it burned off. OK sounds like a whipped pump. I replaced the pump unit with a Delco and replaced the canister valve as that broke removing the tank. Still no luck with the pump priming.( no sound and runs with gas added) . I checked relays before and after. the one in the box clicks the other didn't. Both were replaced. Now I have anew tank, new canister valve, new line new filter, new relays and no working pump. Everything I have read seems to point to that red wire to test. I can't find it. Any other ideas short of another trip to the shop would be helpful. :newburn:

Do you know which relay is the fuel pump relay? My info doesn't show a power distribution center for the relay, if there is, there should be a lid, the underside of the lid has labels for the relays, tells you which one is which. If it is just a single relay with a connector plugged in, look at the color of the wiring going to the relay. My info shows, gray--black--dark green with a white tracer--orange. You find the relay that has those color wires going to it and I think you found it.

The wiring diagram I was looking at for a 98 s10 blazer, doesn't show a prime connector. Maybe that is why you can't find it. If there is red wire that comes off the pump relay connector, follow it through the wiring harness.
Usually on a rwd GM vehicle that has a prime connector, it is right by the fuel pump relay, you can't miss it. On the vehicles I've seen with a prime connector, it is always on the same side of the engine compartment as the battery.

Most relays have a diagram on top, it will show control and load circuits. Is it a regular ISO relay, if it is the terminals are numbered. Is there an 87 terminal?

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