My setup: 1978 Caprice. Stock 5.3/4L60. Single line truck intake. Corvette regulator/filter. Stock gas tank from 1994 Caprice with OEM fuel sender assembly. Walbro 250 pump. Upgraded Racetronic pump-bulkhead harness.

My car wouldn't start one day. It would crank, but no start. After a little cranking it started. It happened again a week or so later. Then one day wouldn't start at all. I couldn't hear the fuel pump pumping, so I replaced it. Also installed new fuel sender, pump, all new harness from pump to tank bulkhead. All wiring from the pigtail that plugs into the tank back is new. Car just left me stranded again. This morning it cranked with no start. After 3 tries it started. Then left me stranded at work. After almost running the battery down, it did start again. Once it's running, it doesn't ever die. If I leave it sitting, sometimes it won't start (sometimes it does). Have used a test light and the pigtail at the pump is getting power for 5 seconds prime. Pump and harness all work properly when bench testing with 12v. I can push the schrader valve on the fuel rail when it won't start and no fuel comes out. No amount of hitting the tank causes it to begin working. I have had the tank out 3 times now and all wires, connectors, etc are new and functional. I cannot understand this intermittent no-start/no fuel pressure. It seems to be electrical in nature, but I've checked everything. I've checked the relay, and it's working properly. I've checked all the fuses, they're working properly. I am unsure what to do next? This is my daily driver, and has left me stranded now three times and I've had to haul it home. I would appreciate your input.

Thanks,
Brandon

 

What gauge wiring did you use when replacing the wiring? My truck was doing that at one point and it ended up being that the wiring that comes in the factory wiring harness was too small. I ended up running a 10g wire to the alternator for power supply and ran a 10g ground wire to the frame and it stopped.

 

Did you change the filter?? I was having a problem similar and found after changing fuel filter that there is something loose inside the filter rattling around. I havnt had any random no start conditions since replacing... but am knocking on wood now that I said that.

 

Thanks for the response. I just came back because I forgot two things. One: I built this car 5 years ago and it's been a daily driver ever since and never had any issues until a month ago. Also, I used a Tech II to toggle the fuel pump relay on and off. Sometimes the pump will pump, sometimes it will not, so it definitely seem electrical, but I can't understand what's going on since I've tested and replaced all the components.

 

That makes it sound an awfully lot like a sticking relay. Although a corroded connection in some wiring could cause the same symptom.

 

Run a test light off your fuel pump hot wire from the relay socket.

 

Probably the relay or connection to it

 

I did previously run a test light at the pigtail where it plugs into the fuel tank, which is right behind the relay. Every time I've checked it, I have someone turn the key on and the light comes on for about 5 seconds then goes off. When I cycle the the key on and off, or when i triggered it with the Tech II, I can hear the relay kick on and off also. Is it possible that it's working enough for a test light, but may be low voltage?

 

Being the problem is intermittent could have just not been occurring while you tested it... you need to test during the no start condition

You could wire a bulb in parallel to the fuel pump after the relay and place it somewhere you can see for testing purposes... if the car no starts and the bulb doesn't light then the relay isn't closing

 

I had a similar issue with my TA several years ago. It ended up being an intermittent ignition relay.

 

Since its lighting up the bulb with the relay in place, Id say that circuit is most likely okay. You could ohm out the wire and see if there is voltage drop there, but I wouldn't expect it. The pump does only cycle for a few seconds to prime the system before starting. Id throw a new relay at it and see how it does.

 

I jacked the car up. On jack stands, no fuel pump. I moved the wires around the relay / harness and the fuel pump began to work. I couldn't get it to fail again (wife in car cycling key on and off). I pulled the relay and noticed the hot wire looks like it had gotten pretty hot. I have 10 gauge wire run all the way to the battery. It's run through a Waytech fusebox with a 25a fuse. The relay itself is a 40amp. It seems Racetronix printing their own part number on it. I hoping I can find a regular part number that will fit into the same harness connector. Given the burn marks on the connector, I'm going to replace the relay. The wires themselves don't seem to have any problems that I can detect.

 

That relay socket ( connector ) is ROASTED.
You NEED to replace BOTH the Relay and the socket. You'll probably find the wires leading up TO the socket have been hot, and are shitty as well.

 

With 10 gauge wire all the way back and fused, what could have caused the socket to overheat like that?

 

Poor pin contact will do that

 

OK, thanks. I'll cut out the RaceT stuff and splice in new things. The problem I'm having is that RaceT puts their own part number on the relay so I can't go find the part somewhere else. I called Waytek and they weren't able to find it either. I'll start a separate thread for this question to increase visibility, but I'll also ask it here. Does anyone have a manufacturer part number for the Relay and connector below:


This relay is used in most current-production Racetronix harnesses.) FEATURES:

• Plastic dust cover, shrouded, steel mounting bracket, epoxy sealed
• Supression resistor = safe for use with solid-state drivers
• P.B.T. Polyester enclosure
• ISO/TS 16949, ISO9001, ISO 14000
• Tested in accordance with SAE J2544

COIL DATA:

• Configuartion: S.P.S.T. 4-Terminal (1 Form A)
• Voltage DC: 12
• Resistance Ohms: 109 (+/- 10%)
• Suppression Resistor: 680 Ohms, 1/2 Watt
• Combined Resistance Ohms: 93.9

CONTACT DATA:

• Material: Silver tin oxide
• Max. switched power: 560 W (SPST), 560 W (N.O.), 420 W (N.C.)
• Max. switched current: 40 A (SPST), 40 A (N.O.), 30 A (N.C.)

Ambient Temperature (Operating): -55°C (-67°F) to 125°C (257°F)
Terminals:Tinned copper alloy

Life Expectancy (Minimum operations):

• Mechanical 1 x 107
• Electrical 1 x 105 at 40 A 14 VDC Res.

 

Honestly any 12V relay with the right amperage rating would work. Just have to wire it appropriately. I'd be tempted to use a standard "bosch" relay and socket.

 

Search delphi mp 280 sealed relay

 

looks an awful lot like this inline relay setup that seems to be in every gmt800 vehicle that i've parted out:




happy to send you one for the cost of shipping if it helps, i've got a bunch kicking around.

 

Yea those are delphi metri-pack 280 5 way connectors