Fuel pump shuts off when warm

Hi everybody. I have something that is driving me a bit crazy. I have a 77 308 GTB, so a carb car. I am having a very annoying and strange issue. It would seem that when the car is fully warmed up that the fuel pump shuts off. This only seems to happen when fully warm and when actually going down the road. I can let the car sit and run in the garage for an hour or more without any issues at all. It is also always fine from cold, until the oil temp gauge moves off of its peg. I have already replaced the fuel pump with a Hardy unit, as I thought that was the issue, but to no avail. It seems to be electrical of some sort, but I have checked at the fuse panel, and there at least seems to be power through the fuse when this is happening. The fuse panel is a replacement Birdman unit by the way. Could it be a broken wire to the pump that only has an issue when it gets warm? Definitely a real head scratcher and something quite hard to diagnose since it won't pop up its head when the car is stationary in the garage.

 

The other thing I was thinking was possibly vapor lock. I am not able to hear the Hardy pump click when this happens so I guess there is a chance it could be vapor lock. The fuel return from the carb to the passenger tank is blocked as it was recommended by the folks at Hardy to run this without a return so that it would build proper pressure. Please let me know your thoughts.


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Steve thanks for your help. The Hardy pump I installed was model 8812-3. The spec sheet for it is here:

https://www.hardi-automotive.com/wp-content/uploads/DB8812-3.pdf

I tried installing it with the fuel return hooked up but it only was generating about 2psi and the pump ran continuously. I reached out to the folks at Hardy and the recommended dead heading the pump and thus resulted in 5psi and the pump turning off once it built pressure. I wonder if I’m getting boiling in the lines, building pressure and causing the pump not to run? I wonder if I connect the return if 2psi is enough pressure. I thought the carbs needed 3-5psi. Also in terms of plumbing is the pump supposed to come directly from the tank or should I the tank go to the fuel filter then the pump? I have seen suggestions both ways and I have a feeling having this incorrect would pose issues as well.

The seat switch bypass is a good idea. Mine is indeed bypassed and I checked it when I redid my interior and it was all good at that time but doesn’t hurt to give it another look.


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Thanks for the confirmation. It sounds like I do indeed have everything hooked up correctly. I had triple checked all the diagrams I had seen but it is good to hear confirmation on this. I currently do not have the factory rollover check valve in the return line. So I thought I might try hooking the return back up and putting in a check valve with a 3psi spring. Hopefully this will allow flow but bring pressure up from the 2psi that the Hardy was running at with the return completely open. From everything I had read 2psi seemed too low but I actually never tried to drive it that way. I immediately reached out to Hardy and they recommended the dead head configuration which on a mid engine car like the 308 probably would end up with too much heat and having vapor lock. I will report back after giving it a try. The check valve comes tomorrow supposedly.


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Thanks! I looked at the specs of the pump you are using and they look to be identical to the one I bought. Only difference looks to be the orientation of the inlet and outlet. Your part number looks to have them 180 degrees out while mine is 90 out. So it looks like mine should work just fine without any regulator and with the return hooked up. I hooked up the return this weekend, just haven’t had a chance to drive it yet and see. I will keep everyone posted. If it’s all down to the return I’ll feel really dumb but I was following the advice that the folks from Hardy gave me. Maybe wasn’t the right advice for a 308 with four carbs and all that mid engine heat lol.


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I know before it warmed all the way up with oil temp up to snuff it didn’t have any issues. I could take it to 5k with no fuel starvation at all. Didn’t want to push it farther without good oil temp and that’s when the issues started. I hooked up the return but haven’t had a chance to drive it yet. I will keep everyone posted.


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It’s good to know that 2psi is ok. With the return hooked up I was measuring 2.5psi. I was concerned as I was reading a minimum of 3psi was ideal. I’ll try running it without any check valve at all and see how it goes. No reason to add in more complexity if it’s not needed. Thanks for the help.


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Interesting. The part number I purchased has them fixed 90 degrees from each other and are moveable. All of the pump specs seem the same. Hardy makes way too many part numbers. I’m guessing the inlet/outlet have to be the difference but we will see. I tried running it in the garage with the return hooked up and it ran totally fine. Haven’t had time for a good road test as of yet but maybe this weekend. We shall see.


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