Re: Need Help Diagnosing a Fuel Delivery Problem
Thanks everyone for your input and suggestions. Iíll try to answer everyoneís questions:
Vapor lock Ė The car had a square-bore Edelbrock (I forget the model) installed when I bought it, and that would get hot enough to boil the gas after a long drive. I put a 1/2 inch phenolic spacer under it, and that solved the boiling gas problem. It didnít solve the WOT issue. I had been running the 1/4 inch carb gasket recommended by SMI under the current Q-jet. I replaced that with a 1/4 inch phenolic spacer when I reinstalled the engine last month. It didnít seem like it made any difference.
Fuel lines near something hot Ė There is a header pipe about an inch away from the hard fuel line thatís bolted to the frame. I donít know if thatís close enough to be a concern. I was running stock exhaust manifolds and exhaust pipes on the previous engines, and they were several inches away from the fuel line. I was experiencing the same problem with the stock exhaust system.
Distributor or ignition problem Ė The car had a large-body Accel HEI distributor when I purchased the car. That was being fed about eight volts through the stock resistor wire. I rewired the ignition to get 12 volts to the distributor and figured that would solve the WOT problem. It didnít. Iím currently using a new Accel street billet magnetic pickup HEI distributor thatís fed 12 volts from the horn relay through a 40 amp relay (I got the idea for the upgrade on this site somewhere). Coil is a 45,000 volt Pertronix.
Monitor the fuel pressure Ė Iíve considered that before, and probably should. Iím using a stainless version of the 3/8 inch fuel line between the pump and carb, and donít want to cut it. I probably have enough spare fuel connectors lying around to rig up something to temporarily monitor the fuel pressure.
Here are a couple other possible causes that Iíve thought about:
Fuel tank not venting properly Ė Iím wondering if the gas cap may not be allowing enough air into the tank. Maybe after about a half hour the tank is under vacuum, and the pump is working against the vacuum to supply the engine. Iíve drilled a small hole in my old gas cap to try out that theory.
Tank pickup not oriented properly Ė Is it possible the tank pickup isnít oriented where it needs to be in order to pick up gas when the car is under heavy acceleration? Or maybe it doesnít go down into the tank far enough. I have had the pickup out of the tank before, but didnít pay much attention to how it was oriented or how far down the tank the pickup went.
Thanks again everyone for your suggestions. Keep them coming!!
69 RS, Hugger orange/black, Deluxe interior, Sony AM/FM/XM/CD, PS & PB. 355, forged pistons, Eagle rods, balanced, Iron Eagles, 9.4:1 CR, .038 quench, XR270HR Cam, Z28 intake, FAST-EZ EFI 2.0, Thorley Tri-Ys, TCI 700R4, 2400 stall, 3.42 posi