Just picked up an 85 vette. When cold, car will not start until oil pressure builds up to 45-55 pounds. It will start firing when pressure reaches 45-55 and finally starts. You cannot hear fuel pump running when you turn the key.
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A couple things that I failed to make clear....
The oil pressure sender is way off.... Building 55 lbs or even 30 with the starter is just not gonna happen. 5 to 10 maybe, but not much more. The starter can't spin the engine fast enough to build more pressure. If the engine idle (700 rpm) gets a real 15-20 psi oil pressure, then 60 rpm while cranking ain;t gonna build more than 10.
The oil press sender wire section is cheesy at best,. and its not uncommon for people to see 30 to 60 lbs with the key ON and engine OFF. Or it'll show 80 when you're idling and less with rpm increase. The harness has factory splices that corrode and start to come apart and the poor connections or broken connections effect the resistance values of the oil pressure sender. Its a pretty sensitive signal to the digital dash display.
I just bought a new oil pressure wire section with plugs on Flea-Bay. Everybody buys a new sender first,. then when things don't get better they end up having to address the wire rot or they just drive around thinking they have 70 or 80 psi oil pressure....they don't. A mechanical oil pressure gauge will demonstrate whats really going on...
The low oil pressure switch only requires around 4-6 psi to close and complete the power circuit to bypass a bad fuel pump relay. Most auto parts stores will have a new fuel pump relay. Filters are a bit more and pumps with new tank screens are closer to $100.
There is no point in buying
ANY parts until you do a fuel pressure test with a good gauge.
If starting when hot or warmed up and there
is fuel pressure, go back and test the fuel pressure while cranking warm and driving. The gauge should be pretty steady around 40 psi. If the needle flickers around and dives and takes a second or 2 to recover thats the sign of a plugged tank screen or filter. The system might build pressure but it cannot flow very much thru the clogged filter. Thats what the flickering needle in the fuel pressure gauge is saying.
After the car sits for a while the pressure will bleed off and the trash settles in the filter and will then let some fuel pass again. As soon as the engine runs again and moves the fuel it also moves the trash back into the filter and fills the last open space in the filter. I've seen this a hundred times.
It Dies in traffic or won;t start again after sitting for 3 minutes....starts fine when stone cold OR after sitting for an hour and letting the fuel pressure drop off to zero.
Its not so much the temp, its the pressure in the fuel line that keeps junk stuffed into the filter screens. As soon as the pressure drops so does the trash and fuel can flow again, for a few minutes until the trash fills the filter screens again.
