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94 Chevy 2500 No power to fuel pump


sablawn
06-09-2011, 10:13 AM
Hi I see this post often but nobody ever says how they fix it they just say it's running now I just need help I have a 1994 Chevy 2500 350 engine auto 4x4 and I have no power going to the fuel pump fuse I replaced everything cpu, icm, new fuel pump, replaced ground straps on head & frame good ground at thermostat housing. If I run a hot wire to the fuel pump fuse the pump turns on same if I run the hot wire to the green wire on the fuel pump relay I can hear the fuel pump relay click and the fuel pump runs. But evan when I run the hot wire and crank it the injectors will not spray I have power going to the injectors and check them with 9 volt battery and they spray so something is just off and I can not fiqure it ou I just need help so if any one can help please let me know what to check

j cAT
06-09-2011, 05:17 PM
Hi I see this post often but nobody ever says how they fix it they just say it's running now I just need help I have a 1994 Chevy 2500 350 engine auto 4x4 and I have no power going to the fuel pump fuse I replaced everything cpu, icm, new fuel pump, replaced ground straps on head & frame good ground at thermostat housing. If I run a hot wire to the fuel pump fuse the pump turns on same if I run the hot wire to the green wire on the fuel pump relay I can hear the fuel pump relay click and the fuel pump runs. But evan when I run the hot wire and crank it the injectors will not spray I have power going to the injectors and check them with 9 volt battery and they spray so something is just off and I can not fiqure it ou I just need help so if any one can help please let me know what to check

with the key to ignition on, you should have 12 volts to the fuel pump relay contact...when first placing in the ignition on less than 2 sec does the relay energize?

if the relay does not energize this maybe the ignition switch.

the pump does run when you jump 12 volts to the fuel pump relay feed contact so the wires from there to the fuel pump are good.

the injectors always have 12volts to them ...the longer the injectors are grounded the more fuel is supplied..ecm controls this..

sablawn
06-09-2011, 10:22 PM
I replaced the ignition switch and the ecm. the fuel relay will not click when turning key on and the fuel pump fuse has no power going to it let me know if there is anything else I can check

MT-2500
06-10-2011, 07:07 AM
I replaced the ignition switch and the ecm. the fuel relay will not click when turning key on and the fuel pump fuse has no power going to it let me know if there is anything else I can check

Check for 12 volts power to relay and realy ground.
Then check for key on prime up sigal from VCM relay that turns on relay.

Also signal from VCM to relay engine cranking.

Got good spark craning.

What is pump pressure with pump jumpered?

j cAT
06-10-2011, 07:19 AM
I replaced the ignition switch and the ecm. the fuel relay will not click when turning key on and the fuel pump fuse has no power going to it let me know if there is anything else I can check

I think your vehicle has a oil pressure switch. this switch if defective will open the circuit if the oil has very low pressure or defective. I was going to post this last night but had a very long power failure here.

with the age of this good chance this is it ...injectors and fuel pump will be shutdown ...

MT-2500
06-10-2011, 01:05 PM
I think your vehicle has a oil pressure switch. this switch if defective will open the circuit if the oil has very low pressure or defective. I was going to post this last night but had a very long power failure here.

with the age of this good chance this is it ...injectors and fuel pump will be shutdown ...

The oil pressure switch is only a back for fuel pump in case the fuel pump relay fails.

JL Sargent
06-10-2011, 01:31 PM
I drove a '94 Chevy Diesel over 300K miles and when the fuel pump quit working the first thing I would do is replace the oil pressure switch. That truck, I know would shut down the fuel pump when the oil pressure switch went KAPUT! Happened 3 or 4 times over those miles.

MT-2500
06-10-2011, 02:48 PM
I drove a '94 Chevy Diesel over 300K miles and when the fuel pump quit working the first thing I would do is replace the oil pressure switch. That truck, I know would shut down the fuel pump when the oil pressure switch went KAPUT! Happened 3 or 4 times over those miles.

Oil pressure switch only supplies power to fuel pump if fuel pump relay fails. or is not working.

JL Sargent
06-10-2011, 06:58 PM
That's interesting. So my truck had a bad relay probably to start with. Then the oil pressure switch failed and killed the pump. I replaced oil pressure switch, truck runs fine again for 50K miles. All the while pump relay not working.

Anyway back to this guys question. SO, with a failed relay and a good oil pressure switch pump should be working?

j cAT
06-10-2011, 08:30 PM
That's interesting. So my truck had a bad relay probably to start with. Then the oil pressure switch failed and killed the pump. I replaced oil pressure switch, truck runs fine again for 50K miles. All the while pump relay not working.

Anyway back to this guys question. SO, with a failed relay and a good oil pressure switch pump should be working?

according to the wiring diagrams I have reviewed ,,,the oil pressure switch failure , will screw up the injectors and the fuel pump..

hopefully he will respond to this issue with the details on correcting ..

MT-2500
06-11-2011, 06:26 AM
That's interesting. So my truck had a bad relay probably to start with. Then the oil pressure switch failed and killed the pump. I replaced oil pressure switch, truck runs fine again for 50K miles. All the while pump relay not working.

Anyway back to this guys question. SO, with a failed relay and a good oil pressure switch pump should be working?

The 6.5 wiring is a little different but basic the same as the 350 on oil pressure switch and fuel pump relay.

Yes fuel pump should/will run off of oil pressure swith if relay fails.
But engine has to be cranked until oil pressure comes up.

The relay out put power and oil pressure switch output on the gray wire from both is connected together to fuel pump power feed.
So either on can run/turn on/or power up the fuel pump.
The oil pressure switch was put on them and designed to power the fuel pump in case the fuel pump relay or relay circuit fails.

IF relay is working as should.
And has good fused power to it and turn on signal from computer.
It will power fuel pump for 2 second prime up and then on engine cranking and engine running.

A good test is to unplug fuel pump relay with engine running.
If engine still runs the oil pressure switch is working ok.

MT-2500
06-11-2011, 06:32 AM
according to the wiring diagrams I have reviewed ,,,the oil pressure switch failure , will screw up the injectors and the fuel pump..

hopefully he will respond to this issue with the details on correcting ..

J cAT
On the wiring diagrams from Mitchell/All Data I do not see any connection to the injectors threw the relay or oil pressure switch.
What brand wiring diagrams are you using?

All of my wiring shows the out power feed gray wire from fuel pump relay and oil switch tied together so either one can power/run the fuel pump.

j cAT
06-11-2011, 10:22 AM
J cAT
On the wiring diagrams from Mitchell/All Data I do not see any connection to the injectors threw the relay or oil pressure switch.
What brand wiring diagrams are you using?

All of my wiring shows the out power feed gray wire from fuel pump relay and oil switch tied together so either one can power/run the fuel pump.

The diagrams are not helms/oem ,,,thats why I was not sure if this applied to this members vehicle.

I know that the use of oil pressure is/was used as a safety device to kill fuel delivery if the engine is not running ...which could occur like in a vehicle being in a collision etc..

MT-2500
06-11-2011, 11:25 AM
The diagrams are not helms/OEM ,,,thats why I was not sure if this applied to this members vehicle.

I know that the use of oil pressure is/was used as a safety device to kill fuel delivery if the engine is not running ...which could occur like in a vehicle being in a collision etc..

The oil pressure switch is not a safety or kill switch but the other way around.
It will keep the fuel pump running if relay fails.

In a collision on GM the fuel pump will not shut down until engine quits running.
Ford has a enertsa switch that is designed to kill fuel pump on impact.

sablawn
06-13-2011, 01:46 PM
Hi thanks for the reply I'm not sure what the VCM is. The truck starts when I dump some gas down the carb. As far as the oil pressure switch I can replace it but when I'm cranking the oil pressure gose up on the gauge But I will replace it and let you know what happens

MT-2500
06-13-2011, 03:31 PM
Hi thanks for the reply I'm not sure what the VCM is. The truck starts when I dump some gas down the carb. As far as the oil pressure switch I can replace it but when I'm cranking the oil pressure gose up on the gauge But I will replace it and let you know what happens

VCM 0r PCM = Engine Computer.

The oil pressure is not going to fix it.

Check fuel pump relay.
Like fused 12 power to to and check it for switchig 12 volts to gray fuel pump run wire.

Fuel pump has to have 12 volts to it and good ground to run.

If it no run with power and ground check fuel pump.

4x4junkie
06-13-2011, 08:16 PM
its quite possible a bad plug or corroded plug at the fuel pump relay could be of issue for him as well....... corrosion in any plug is always bad news, even with a new relay a bad connection can cause just enough voltage drop that it wont engage the coil of the relay to close the contact which can prevent it from running.

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