5.3 Vapor Lock? or relay help

I completed my conversion in my 69 FJ40 a year and a half ago driving nearly 10,000 miles since complete. Last month while driving my engine just died. Temp outside was about 95, engine was at 195. Had it towed home pulled the Fuel Pressure Regulator to see if it was getting fuel. Yes fuel was being pumped. Put it back in and it started right up.

Yesterday while driving home from Denver it was about 95 or so degrees outside. Stop and go on interstate it just turned off again. Pulled the regulator again and put it back - no start. Ended up having it towed home. This time I put a battery tester on the EFI fuses and tested relays. After putting my relays back in, it started right up.

There are no errors or check engine light thrown. I was originally thinking it was vapor locking or something similar, but now thinking it might be a failing Relay cutting electricity to the coils.

Since it has ran so well for awhile without issue, any ideas on longevity of relays under the hood in high temp situation? I have a low mileage 2001 Chevy 5.3 engine.

Thanks for your guidance.

Hmmmm. Does your Fj have a vented gas cap or a sealed cap and dedicated vent port on the fuel tank? Oe fuel tank or AM fuel cell? In tank or inline pump.

Im just wondering about the possibility of a vent being clogged on your fuel tank. If so, a pump can only pull so much vacuum. Just a thought.

If you suspect a failing relay, just rig up a high impedance led light that you can watch while driving that is energized via fuel pump relay. If the light goes out when the engine shuts down, then all you have to do is verify that you still have V and G to the relay. If those are good, bad relay.

As far as I know, any relay should be unaffected by underhood engine temps. Correct me if im wrong here. Good luck!

You might just have a bad fuel pump, heat and vibration can cause enough pressure in the fuel tank to make it seem like fuel is flowing to the rails when you press the shraeder valve.

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Originally Posted by vortecyota

Hmmmm. Does your Fj have a vented gas cap or a sealed cap and dedicated vent port on the fuel tank? Oe fuel tank or AM fuel cell? In tank or inline pump.

Im just wondering about the possibility of a vent being clogged on your fuel tank. If so, a pump can only pull so much vacuum. Just a thought.

If you suspect a failing relay, just rig up a high impedance led light that you can watch while driving that is energized via fuel pump relay. If the light goes out when the engine shuts down, then all you have to do is verify that you still have V and G to the relay. If those are good, bad relay.

As far as I know, any relay should be unaffected by underhood engine temps. Correct me if im wrong here. Good luck!

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I have a non vented cap with the vent from the fuel cell going back to the filler neck of the stock filler. The fuel pump is mounted about 1 foot so outside of the cell mounted to the frame. I just went out and capped the vent outlet from the filler and vented the tank to above the bed area. Since relays are fairly inexpensive I bought some new ones on the way home just in case.

Thanks for your advice. I will drive with venting differently and see how this goes. A side note, when on the side of the road I did remove the gas cap to release any pressure. ?

Oh so you have already pulled the cap after it shutdown and it didn't restart? If so, I guess that eliminates that theory.

The cell will build pressure sitting in the heat with no vent, but once you have driven it for a while, I would expect the cell would be under vacuum. If that was it, it shoulda restarted when you pulled the cap. Oh well, on to the next!

check your fuel pressure sounds like a bad fuel pump . or low voltage at the fuel pump check your connections to

I will verify that the wires and ground are ok to the fuel pump. I am going to drive it for a few days in town to see if it happens again.