Car will not start unless fuel pump unplugged first

[efnfast]

2001 viper w/ built engine and paxton. Fuel system is double RSI in-tank (2x walbro 267), external Weldon regulator, 80lb bosch injectors. Car was dyno tuned by Torrie ~2yrs ago (HP Tuners + stock ecu) and has run flawlessly since but today decided to "break".

If I try to start the car it cranks, sometimes sputters like it almost wants to start, but will not start.

If I remove the fuses for both fuel pumps, the car will start immediately, idle for a second, then die.

If I then put the fuses back in (either 1 or both pumps), the car will immediately start, idle fine and drive fine. Going WOT runs like a ***** ape and does not blow up. However, when I stop the car and turn it off, when I try to restart it it will not start unless i remove the fuses for the fuel pump, start it, let it die, then plug the fuses back in. It does not matter if, once it starts up, if I drive the car for 5 minutes, idle it for 5 minutes, or quickly turn it back off .... as soon as i key off it will not restart until I first run it briefly with the fuel pumps disconnected.

Regulator shows 56psi with vacuum hoses disconnected (exactly where I set it years ago) when cranking or idling. When I key on the pumps turn on (audible), regulator goes to 56psi, then back to 0 when the pumps shut off 1-2 seconds later.

It almost feels like the manifold/fuel rail is flooded with fuel, but that doesn't make sense because then the car wouldn't idle or drive fine once it starts, and when I can get it to start in that above sequence of events it does so immediately without any issues (e.g., coughing, hesitation, etc.).

edit: I also can't see it being something in the tune because it's been perfectly fine for 2 years, and if the tune were flooding it with fuel on start, then when I plug the fuel pumps back in it would re-flood.

edit 2: If i leave the car sit for ~2hrs it will start up on the first crank and idle fine. If I turn it off and immediately back on, it will go back to just cranking and coughing, until I unplug the fuel pump, let it fire up and idle for a second to clean the rails out, die, then plug the fuel pump back in and it will start up immediately. I suppose a solution is to put the fuel-pump-on wire on an off/on switch and first start the engine with it off then on, but that still leaves me wondering *** is going on

 

[99RT10GTS]

Thinking ground issue or possibly a vacuum leak?

 

[efnfast]

It idles fine and fuel trims look fine so I don't think it's a vaccum leak. Last times I've had vacuum leaks either the idle was super high and/or short-term fuel trims were really off (like +/-25%). And all hoses are connected and visually look fine

Ground doesn't make sense because the symptoms occur like clockwork in an exact sequence.

It's almost like the intake manifold is getting flooded with fuel when I shut the car off, so it has to get drained out (either by time, starting w/o fuel pump, etc.) before it will work again, but that doesn't make any sense because one would think the car would be running like crap then

 

[efnfast]

Does a gen 2 viper have a clear flood mode? I.e., press the gas pedal to the floor and the injectors won't fire when cranking the car?

 

[daveg]

If you let the car sit for a few days and you still have to unplug the fuse, chances are the Manifold is NOT gas saturated as it will have dried up by then

 

[efnfast]

Some progress today, I'm just not sure what it means.

Car sat overnight. Started up on first crank, idled fine. I did on/off several times, no issues.

Drove it up/down my driveway then off/on several times, no issues.

I let it warm up to just before the fans turned on, no issues.

However, once it warmed up to the point where the high speed fan turned on, then when I keyed off it would not restart. It would just crank and sputter but no start.

If I floored the gas pedal (i.e., entered flood mode) it immediately started up on first crank. It would idle hang slightly high - ~1,500 rpm - for a second or two, then drop down to 750.

I looked at three plugs and they were fine (i.e., not fouled or smelling of fuel).

So when the car is warm, when starting either I'm getting too much fuel, or not enough air. Given I have no issues when the car is cold, I want to lean towards fuel because I image a cold engine loves lots of fuel and a hot engine doesn't.

I can't see tune because how could it be fine for a year and not act up? But I also can't see mechanical like leaking injector because it idles and drives perfectly fine.

 

[Goggles Pizano]

Next time turn to key on/off to run the pumps 2 or 3 times then try to crank it.