Been working on a friends new Hess and Eisenhardt. It’s got a neat trick… gas pours out of the filler cap if you open it after driving. I drove it maybe 40 miles and the tank was pouring gas out after stopping and opening the filler. It did this several times, and has at least 75 mile on this tank of gas… so it’s gotta be 3-4 gallons down from full at least.
My understanding of how this all works is the lower tank is constantly pumped into the upper tank, and then excess from upper tank backflows to the lower tank. Has anyone had a similar problem? I’m guessing either the lower has a clogged vent, not allowing gas from upper tank back in, or the hose from upper to lower tank is blocked?
After overflowing it continued to bubble for quite a while.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
2
It’s a complicated system. Besides the upper and lower tanks you describe, there is also a surge tank. Fuel is pumped from the surge tank to the engine, and excess is returned to the upper tank.
There is a popular modification to the H&E that involves feeding the output of the pump in the lower tank directly into the drain from the upper tank to the surge tank.
I concur, what you describe is probably a vent problem. The carbon canister arrangement was modified by a recall, and some models were modified incorrectly – I don’t recall which, but it might have been the H&E. Whatever, you might start your diagnosis by ripping out the panel in front of the LF wheel and looking at the vapor collection system. There should be a “Rochester valve” with three connections, one to the vapor separator at the rear, one to the carbon canister, and one to intake manifold vacuum. Rochester valves fail all the time, sometimes due to dirt or carbon granules jamming the internal passages. I always recommend installing inline fuel filters on either side of the Rochester valve to keep crud out. I also suggest installing a solenoid vacuum valve to bypass it when the engine is running, just to ensure the vent is wide open during operation.
There should also be two purge valves which connect the carbon canister to the PCV system. One purge valve is opened by a signal from a throttle edge tapping on the LH throttle body. The other is similar but a separate throttle edge tapping (they may open at different throttle settings, I dunno) and also has a vacuum delay valve in the line. Frankly, not likely either is your problem unless they were plumbed incorrectly during the recall.
The carbon canister itself was originally vented to atmosphere via a hose out the bottom of the car. The recall did away with this hose, venting the canister into the bodywork. It also flipped the canister upside down for some reason.