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Old 09-26-2018, 03:05 PM   #1
62step
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Cut wires on door - 1992 c1500

I got a 1992 chevy silverado C1500 extended cab shortbed with a 5.7L 2wd from a friend of mine. It was sitting for about 10 years before I got it, the motor was stuck and I got it unstuck (I was able to spin it freely). Before he let it sit he was prepping it for his diy paint job, well when he took the doors off, he cut the wires for all the power switches.


I've tried to start this thing for about a week, cranking, has spark has fuel, just cranks, doors still off with wires cut. Should I put the doors on and wire it up and see if that does something?

I'm not sure if there is a security or system thing that will not let me start the truck due to the wires being cut.

I know that I will probably need a rebuild on the motor due to it being stuck, but just wanted to know about the wires being cut.

Thanks!

Last edited by 62step; 09-26-2018 at 03:14 PM.
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Old 09-26-2018, 05:02 PM   #2
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Re: Cut wires on door - 1992 c1500

No many wires that go to the door, power windows or locks and maybe a light on the door. If it has a security system it would be tied into the door switch that should be on the side of the dash.
But you never know, I have seen people do crazy stuff to car I have purchased.

If it has spark and it has fuel, it may be to much fuel or out of time. Sometimes the coolant sensor fails and tells the engine its super cold or hot out and the fuel mixture is way out.
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Old 09-26-2018, 06:30 PM   #3
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Re: Cut wires on door - 1992 c1500

does your fuel pump only run for the prime when key turned ?

the oil pressure switch ( by distributor) is the switch that grounds the relay and allows the pump to continue to run.

you can by pass that by grounding, or use the tach feed wire to supply the ground.

the oil pressure switch is a nice fail safe if you ever loose oil pressure.
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Old 09-26-2018, 08:54 PM   #4
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Re: Cut wires on door - 1992 c1500

I've checked the timing and set it twice. I don't hear the fuel pump prime, I was spraying starting fluid into the throttle body, but still nothing. I will check that oil pressure switch by the distributor.
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Old 09-26-2018, 08:58 PM   #5
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Re: Cut wires on door - 1992 c1500

i belive your pump should prime for about 3 secs when the key is tuned to on...once the engine fires, the ecm continues the signal ( grounding) of the fuel pump by way of the oil pressure SWITCH to continue running.

there is also an oil pressure sender for the gauge, that is down by the filter.
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Old 09-26-2018, 09:10 PM   #6
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Re: Cut wires on door - 1992 c1500

The oil pressure switch is only a backup incase the fuel pump relay fails. In a properly operating system, the oil pressure switch does not supply power to the fuel pump.

Did the truck run when your buddy parked it? Or did it get parked because it didn’t run?

The fuel in the tank could have went sour and killed the pump. You need to drain the tank and put fresh gas in it anyways, so you might just throw a pump in while you have the tank out.

Double and triple check that your distributor is timed correctly.

Have you checked compression with a compression tester?

Do you see fuel being sprayed out of the injectors?
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Old 09-26-2018, 09:16 PM   #7
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Re: Cut wires on door - 1992 c1500

Quote:
Originally Posted by Stormin08 View Post
the oil pressure switch is a nice fail safe if you ever loose oil pressure.
That’s not true. GM would have a bunch of lawsuits if it was. An engine with zero oil pressure will still have the fuel pump running as long as the ecm receives an RPM signal from the distributor.

Imagine if your truck lost oil pressure at a redlight, your engine shuts off, the light turns green, and you get hit by a semi. GM would rather have an engine failure instead of a life failure.
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Old 09-26-2018, 09:53 PM   #8
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Re: Cut wires on door - 1992 c1500

The timing was checked 4 times by myself and a friend of mine. No fuel at injectors. Buddy said it was running one day and all of a sudden it shut off wouldn't come back. Put a fuel pump in it and it worked for about a week then it stopped again and wouldn't start. Put another new one and nothing.

The bed is unbolted so I might try and tackle the pump this weekend, but I did a compression test and it read 90psi with oil in it... so I'm thinking the rings busted when I broke loose the engine or something. I would think with at least that much psi it would try to start since it had spark and fuel (from throttle with starting fluid).
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Old 09-26-2018, 11:31 PM   #9
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Re: Cut wires on door - 1992 c1500

Ya, the truck will run with a bad ring. I drove my TBI 305 1000 miles smoking with a bad ring and it would still start every 6 months for fresh gas.
Have you checked the fuel pump fuse? You can run a jumper on the oil pressure switch between the white and orange wire, should here the pump kit on, if not you have a power issue. You also have a brake out around the steering column. It is the harness going to the fuel pump, good spot to check for power. I have also found this plug unplugged causing failed fuel pump symptoms.
Oil pressure switch should activate around 4psi +/- a little.
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Old 09-27-2018, 06:47 AM   #10
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Re: Cut wires on door - 1992 c1500

The fuel pump will prime for 2 seconds, then the ECM/PCM will provide a ground for the fuel pump relay.

Can we stop telling the op that the oil pressure switch supplies power to the fuel pump? It is a back up only when the relay fails!
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Old 09-27-2018, 06:50 AM   #11
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Re: Cut wires on door - 1992 c1500

Electrical diagram:

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Old 09-27-2018, 08:27 AM   #12
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Re: Cut wires on door - 1992 c1500

Quote:
Originally Posted by 95 S_Trucker View Post
The fuel pump will prime for 2 seconds, then the ECM/PCM will provide a ground for the fuel pump relay.

Can we stop telling the op that the oil pressure switch supplies power to the fuel pump? It is a back up only when the relay fails!
It was simply a way of testing operation, put in the jump wire and check operation. Not blaming the switch.

The ECM will provide a ground sooner than the switch, but ether can be used on start up once oil pressure is reached. Electricity’s will take the path of least resistance, if the oil pressure is reached before the ECM grounds the relay than the fuel pump will have power.
All backed by the diagram posted.

Still would start with checking for power to your fuel pump.

Last edited by mikebte; 09-27-2018 at 08:32 AM. Reason: Spelling
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Old 09-27-2018, 10:02 AM   #13
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Re: Cut wires on door - 1992 c1500

Thanks for the diagram, I do not hear the fuel pump prime, I just hear what sounds like a fuel pump priming in the passenger side of the dash.. (Heard it does that heater core or something, I don't know) After I did the compression test and it being 90 psi when it's supposed to be near 180 (?) I'm thinking the engine is done.

I will try and tilt the bed up probably friday night and see if all the connections are good, see if the tank needs to replaced or just drained. I also need to find the bolt size for the bed.

I appreciate everyone's responses.
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Old 09-27-2018, 10:26 AM   #14
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Re: Cut wires on door - 1992 c1500

Quote:
Originally Posted by 62step View Post
Thanks for the diagram, I do not hear the fuel pump prime, I just hear what sounds like a fuel pump priming in the passenger side of the dash.. (Heard it does that heater core or something, I don't know) After I did the compression test and it being 90 psi when it's supposed to be near 180 (?) I'm thinking the engine is done.

I will try and tilt the bed up probably friday night and see if all the connections are good, see if the tank needs to replaced or just drained. I also need to find the bolt size for the bed.

I appreciate everyone's responses.
That is a tad low. The minimum spec is 100PSI, and they should all be within 20%.

I would check for power at the fuel pump fuse and relay. You can power the test terminal(it may be at the ALDL, terminal G) and see if the pump runs. If you decide to do that, you should use a fused jumper wire with a 20A fuse.

The bolt heads for the bed bolts are 18mm.
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Old 09-28-2018, 12:17 AM   #15
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Re: Cut wires on door - 1992 c1500

so,hopefully not totally derailing the OP's thread...

S trucker...enlighten me, as i have been told and it appears in the diagram ( yours and some that i have)...if the oil pressure switch opens, ground is not complete...engine dies from fuel pump loosing power.

reason i ask....this saturday i am planning on finishing my engine install (removing factory tbi and wiring), using a fitech unit.

i was under the impression that i need to run a ground to my fuel pump relay in lue of the pressure switch. the tach signal can provide this, but i like the idea of the switch ????
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Old 09-28-2018, 05:50 AM   #16
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Re: Cut wires on door - 1992 c1500

Quote:
Originally Posted by Stormin08 View Post
so,hopefully not totally derailing the OP's thread...

S trucker...enlighten me, as i have been told and it appears in the diagram ( yours and some that i have)...if the oil pressure switch opens, ground is not complete...engine dies from fuel pump loosing power.

reason i ask....this saturday i am planning on finishing my engine install (removing factory tbi and wiring), using a fitech unit.

i was under the impression that i need to run a ground to my fuel pump relay in lue of the pressure switch. the tach signal can provide this, but i like the idea of the switch ????
95 S_Trucker is correct that the oil pressure sender will not disconnect power to the fuel pump on these TBI trucks. GM did build trucks that way in the past, but that was before TBI.

The next correction I want to make is the fuel pump relay and the oil sender are on the power supply side of the fuel pump circuit and not the ground side.

The truck has a fuel pump relay that supplies power to the fuel pump when:
- Anytime the ECM receives a distributor reference pulse. (Engine running / engine cranking)
- The key is turned on engine not cranking – relay applied for 2 to 20 seconds (most trucks 2 seconds), depending on emissions equipment. Trucks over 8500 GVW and some other vehicles have and electronic Fuel timer module that allows the pump to run up to 20 seconds.
The key must be turned off for a certain amount of time before it will prime the system again when turned back on.

The ECM should store a code 54 if the fuel pump relay fails.

When the engine has oil pressure a redundant circuit supplies power to the fuel pump. This circuit goes through an oil pressure sensor/sender. This circuit is independent of the fuel pump relay.

If you remove the fuel pump relay, the engine will have to crank until it gets oil pressure, and then the fuel pump will get power.

Once the engine has oil pressure the fuel pump should get power even if the relay has failed.

If you pull the fuel pump relay while the engine is running it should keep running. If it dies the oil sender or its wiring is bad or the engine lacks oil pressure.

If you unplug the oil sender while it is running it should keep running also. If it dies the fuel pump relay or its circuit is bad.

Keep in mind there is a redundant circuit (two circuits) supplying power to the fuel pump when the truck is driving down the road.
1 – The oil pressure sender
2 – The fuel pump relay
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Old 12-04-2018, 10:12 AM   #17
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Re: Cut wires on door - 1992 c1500

I appreciate all the help. I currently have the motor torn apart, cleaning all the pistons and everything. The rings were definitely stuck on about 6 pistons. I don't want to put a battery in the engine bay and connect the cable with nothing plugged in, so I might try and jump the fuel pump just to see if it runs somehow.

Thanks again, I will keep you updated!
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Old 12-12-2018, 11:51 AM   #18
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Re: Cut wires on door - 1992 c1500

I tried jumping the Gray and orage wires from the fuel pump relay connector with no luck of hearing the fuel pump come on. (Ignition key ON)

Also, everything is unplugged, but I figured I would try and jump it just to see if it works. Do I need to jump wires on the oil pressure switch also?

Thanks!


P.S. Engine is getting bored out 30 over due to rust pitting in cylinder walls.
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Old 12-12-2018, 01:07 PM   #19
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Re: Cut wires on door - 1992 c1500

the fuel pump harness has a 2 wire connector right below the brake booster, just above the frame...
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Old 12-13-2018, 11:08 AM   #20
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Re: Cut wires on door - 1992 c1500

Ok, I guess I just need to jump those two wires? I know the connector near the fuel tank is 3 or 4 wire connector for the fuel sending unit/pump..
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Old 12-13-2018, 11:11 AM   #21
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Re: Cut wires on door - 1992 c1500

i supplied power to ORANGE (?) if i recall, and grounded the other (black or brown).

i have removed all factory TBI wiring and computer. my EFI unit has a relay for the fuel pump internally, i did reuse the factory plug for that location.
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Old 12-13-2018, 11:14 AM   #22
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Re: Cut wires on door - 1992 c1500

Ok, I'll check it out later today, 2 wire connector beneath the brake booster, correct?
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Old 12-13-2018, 11:35 AM   #23
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Re: Cut wires on door - 1992 c1500

yep, right above frame rail.
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Old 12-13-2018, 12:30 PM   #24
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Re: Cut wires on door - 1992 c1500

Thank you!

I guess it's time to see if I need a pump or not!
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Old 12-14-2018, 03:35 PM   #25
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Re: Cut wires on door - 1992 c1500

I jumped that connector (gray wire and black) I put voltage to the gray wire with the key in on position and I head the pump!
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