This weekend I've fought with what appears to be a vapor lock issue.

I tried to drive the car to southern California, and I was barely 30 minutes outside of town when it lost fuel pressure. I went under the car and by pinching the return line to the fuel tank (not the regulator return line) the pressure would come right back. Let go and pressure would go away.

Early troubleshooting actually made it seem like a pump cavitation issue, particularly with the lift pump. I had installed a higher pressure TBI pump (~22psi) for my lift pump when the universal one quit working. So I put a clamp on the fuel line and motor'd on. It hiccupped a couple times then I got a solid 80+ mile stretch without issue and thought I had it kicked, but then it cropped up again. So 155 miles into my 475 mile drive south I opted to turn around and head home, which it drove the 155 miles home without a single issue, ARRRGGHHH! My girlfriend is accusing the car of being a homebody, lol.

So at that point, I figured it was a cavitation issue and the TBI pump needed some pressure to push against, so I made a restrictor tube from a piece of steel tubing with a 1/4" chunk of barbed brass fitting in the middle and installed it in the middle of the fuel tank return line, and the next day I drove out to Bonneville for a day trip test drive. It's ~130-140 miles each way and it was due to be 97F there to test for heat (and it was hot!), as it doesn't quite get warm enough here for proper testing. Well I made it out there, purr'ing like a kitten, drove to the end of the road at the Salt Flats, went back ate lunch, then as I was heading home I didn't even make it out of Wendover before it lost fuel pressure again. This time I tried pinching the lines and it wasn't coming back. So it is likely a vapor lock issue of some sort and my restrictor tube made it so when it vapor locks it vapor locks hard. Frick.

So the suggestions were to re-do the fuel system again to a "best practices" set up with the regulator at the end of the fuel rail and the return all the way back. In my mind though, I cannot see how this will make the fuel stay cooler as it would then take heat picked up in the fuel rail and bring it back to the tank as well as if I use the OE fuel line it crosses within and inch of the exhaust at the rear of the car to pick up more heat.

So I made two changes to the existing system. The first is I welded together a larger surge tank. Similar design but almost twice as tall. I put the high pressure pickup at the bottom with around 4" of distance before the next inlet. I've ran the inlet for the lift pump next inline, so the return from the regulator is above the lift pump inlet to try and push the returned fuel upwards and back towards the fuel tank return. Then I welded three "cooling" fins to the side of it. They hang off the side of the panel, past the gas tank and should pickup quite a bit of airflow. Theoretically helping cool the fuel in the surge tank. Then the other change I made was I installed a low pressure lift pump (essentially the same model pump that was on it to begin with) to reduce the pressure loading of the fuel (though I don't think 22psi adds much compressive heat).

The OHC purred like a kitten, still appears to be getting around 20mpg, oil pressure while cruising is now with 10w-40 oil is at the regulator spring limit of 55-60psi. It gets a little warmer than I'd like, but coolant temps didn't crest 195F and that is livable. The front crank seal appears to be leaking some oil, it doesn't have the blow by it had before (doesn't puff smoke out the oil fill tube with the cap off), the evac pump still pulls a fair amount of oil, so the baffles haven't changed a whole lot and I probably still need to work on getting the oil cap and dipstick tube sealed.

The smoke from the wild fires in Washington made the salt flats too hazy for a really great picture.



Edited by TheSilverBuick (07/21/14 09:09 AM)
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Rebuilding an OHC Pontiac 250 with EFI and a Turbo