1993 Nissian PU 2.4L

[paulsharvey]

Son just picked up a 93 Nissian Hardbody, king cab (i think the one with the suicide seats), allegedly rebuild engine, fairly good body, heavily molested wiring. After replacing battery, we got it to start and run for maybe 45 seconds. Fuel pump comes on with key on, and shuts off after about 13 seconds, so it builds fuel. When it acts like it's gonna die, you can keep it running with a hit of starter fluid.

So, any ideas on hunting down the fuel problem? I down loaded and sent him a 96 page electric diagram, but like I said, it's been molested. They deleted the passenger seat, some emissions stuff, and power steering pump, they cut the belt. Point is, there are about a dozen wires going no where, and many on the ones that go somewhere aren't original.

My thought, air leaking into a fuel line, possibly at the pump/tank ring, but I'd rather not pull the bed if there are smarter places to look.

It does have a brand new fuel regulator (last guy). The line going to it was really dry rotted, so I spit on it, and it ran longer than usual, so he replaced that line, and no improvement, so I don't know if that was the issue or no.

 

[paulsharvey]

We know it needs stuff, it's got an electric fan with alligator clamp for the fan motor... but before throwing parts cannon, at everything, want to get it running.

Clutch is good enough to load on trailer, and it appears to have most or all gears.

Brand new Goodyear all terrain tires too, and new rear drum break shoes

 

[flyerdan]

Search or ask over at Ratsun, that's where all the Datsun people ended up.

 

[kf4uda]

Just for kicks I fed your 1st post into ChatGPT and here was its response. Maybe it will help:

Primary Suspects​

1. Fuel Pump Control / Relay Issue
   • You mentioned the pump primes with key-on but doesn’t seem to stay running. Many older Nissans rely on the ECU to keep the fuel pump running after the initial prime. If the ECU isn’t getting a valid RPM signal (crank angle sensor, distributor signal, etc.), it may be cutting power to the pump.
   • Test: Jumper the fuel pump relay (bypass it) to see if it stays running.
   • Check ECU codes (even if the wiring is a mess, if the ECU works, it might still throw a relevant code).
2. Fuel Pressure Issue
   • It’s possible the pump is weak, the fuel filter is clogged, or the pressure regulator isn’t holding.
   • Test: Check fuel pressure at the rail with a gauge.
   • Quick and dirty test: Spray some starter fluid while it’s dying. If it revives momentarily, fuel starvation is the issue.
3. Injector Power / Grounding Issue
   • If the pump is running but injectors aren’t firing, you’d get a similar symptom. With the "molested" wiring, the injector power circuit or ground could be damaged.
   • Test: Use a noid light to check if injectors are getting a signal while cranking.
   • Check injector fuse and relay. (Nissans often have an injector relay separate from the fuel pump relay.)

Potential Fuel System Leaks / Air Intrusion​

You mentioned a possible air leak at the pump/tank ring. While that's possible, unless the pump is externally mounted (which I doubt on this truck), it shouldn’t pull air into the system unless there’s a break in the pickup line inside the tank.

Smarter places to check before pulling the bed:

• Inspect all rubber fuel lines for cracks, especially near clamps and fittings. If there’s a small vacuum leak before the pump, it could be sucking in air and losing prime.
• If the return line is clogged or the pressure regulator is bad, fuel may not be maintaining enough pressure at the rail.
• If you can hear the pump struggling or getting louder when it starts dying, that might indicate fuel starvation.

Quick Steps to Diagnose​

1. Jumper the fuel pump relay to keep the pump running and see if that fixes it.
2. Check fuel pressure at the rail to confirm whether it's a pump or regulator issue.
3. Check injector pulse with a noid light.
4. If all else fails, bypass the factory fuel system by feeding fuel directly from a jerry can through a test pump to eliminate the tank/pickup as a suspect.

With the hacked-up wiring, I’d bet on a fuel pump control issue rather than an air leak in the fuel line.

 

[paulsharvey]

Just for kicks I fed your 1st post into ChatGPT and here was its response. Maybe it will help:

Primary Suspects​

1. Fuel Pump Control / Relay Issue
   • You mentioned the pump primes with key-on but doesn’t seem to stay running. Many older Nissans rely on the ECU to keep the fuel pump running after the initial prime. If the ECU isn’t getting a valid RPM signal (crank angle sensor, distributor signal, etc.), it may be cutting power to the pump.
   • Test: Jumper the fuel pump relay (bypass it) to see if it stays running.
   • Check ECU codes (even if the wiring is a mess, if the ECU works, it might still throw a relevant code).
2. Fuel Pressure Issue
   • It’s possible the pump is weak, the fuel filter is clogged, or the pressure regulator isn’t holding.
   • Test: Check fuel pressure at the rail with a gauge.
   • Quick and dirty test: Spray some starter fluid while it’s dying. If it revives momentarily, fuel starvation is the issue.
3. Injector Power / Grounding Issue
   • If the pump is running but injectors aren’t firing, you’d get a similar symptom. With the "molested" wiring, the injector power circuit or ground could be damaged.
   • Test: Use a noid light to check if injectors are getting a signal while cranking.
   • Check injector fuse and relay. (Nissans often have an injector relay separate from the fuel pump relay.)

Potential Fuel System Leaks / Air Intrusion​

You mentioned a possible air leak at the pump/tank ring. While that's possible, unless the pump is externally mounted (which I doubt on this truck), it shouldn’t pull air into the system unless there’s a break in the pickup line inside the tank.

Smarter places to check before pulling the bed:

• Inspect all rubber fuel lines for cracks, especially near clamps and fittings. If there’s a small vacuum leak before the pump, it could be sucking in air and losing prime.
• If the return line is clogged or the pressure regulator is bad, fuel may not be maintaining enough pressure at the rail.
• If you can hear the pump struggling or getting louder when it starts dying, that might indicate fuel starvation.

Quick Steps to Diagnose​

1. Jumper the fuel pump relay to keep the pump running and see if that fixes it.
2. Check fuel pressure at the rail to confirm whether it's a pump or regulator issue.
3. Check injector pulse with a noid light.
4. If all else fails, bypass the factory fuel system by feeding fuel directly from a jerry can through a test pump to eliminate the tank/pickup as a suspect.

With the hacked-up wiring, I’d bet on a fuel pump control issue rather than an air leak in the fuel line.

That sounds possible. Someone removed a lot, and there are multiple wires running to nothing.

That info about the ECM controlling the pump once running might be the critical link.

It does stay running on starter fluid.

 

[paulsharvey]

Off topic, but maybe I need to play with some of the AI things. I assumed it was way more generic, but that prompt is kinda interesting, and has actual info