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.

 

[efnfast]

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

No difference

So far what I've found is that on cold and semi-cold starts there is no issue (fires up right away).

Once water temperature is around 100*ish or so, then it will just crank and no start. If I floor it while cranking it starts up immediately (initially thought this meant I was in clear flood mode, but I can't find any reference to a Gen 2 Viper having this feature).

I had Torrie adjust the startup tune (less fuel more air) and now when water temperature is 160* or above it starts up fine. However, it would still crank/no starts when temperatures are around 100-150ish unless I give the gas pedal a slight push (i.e., not to the floor, just a little push, like maybe 10% of the way down). Cut back a little bit more fuel and it starts up fine with no pedal action in this range. The amount of fuel cut back isn't abnormal/alarming to him for 80lb injectors.

I don't know what to make of this.

I don't think it is the IAC because it idles perfectly fine.

I don't think it's the fuel pumps because there's 2 of them and my fuel pressure is rock solid when cranking/engine running.

The regulator is not leaking fuel from the boost line (i.e., diagram issue)

It can't be a stuck/leaking injector because it idles/drives fine.

I can't be flooding my engine because the plugs looks fine and it responds to less fuel, either by tune modification or unplugging the fuel pump and cranking it.

This makes no sense - everything is perfectly fine for over a year, then one day it decides it has too much fuel on startup but everything checks out mechanically and nothing in log files suggests any issue.

 

[Goggles Pizano]

If you adjust the fuel in the tables that's your problem. Better to run rich then lean. Plus I bet there is a gap in the fuel table at that temperature range.

But then you contradict yourself that if you 10% the throttle it starts but if you adjust the tune and cut back on fuel it starts?

 

[efnfast]

If you adjust the fuel in the tables that's your problem. Better to run rich then lean. Plus I bet there is a gap in the fuel table at that temperature range.

But then you contradict yourself that if you 10% the throttle it starts but if you adjust the tune and cut back on fuel it starts?

I know - it's all very weird.

The initial adjustments Torrie made pulled back startup fuelling a little bit, which meant that instead of having to hold the pedal to the floor to restart it I could just feather it and it would start. He made additional startup fuelling adjustments and now it starts in all water temperature ranges without any pedal action, just like it used to.

I drove the car and STFT are +/- 5%, and LTFT is basically 0. No smoke, pulls hard, smooth idle, absolutely perfect to idle and drive.

So now I'm left with a quandry. It can't be electrical (e.g., bad ground) because electrical does not just impact startup. It can't be mechnical (e.g., leaking injector, dead IAC) because something would have to show up during driving. So how after a year of using my car on the old tune does the car go from starting perfectly all the time to one day decide it's being over-fueled only at startup to the point it will not start other than when the engine is basically cold.....

Unfortunately I've had weird tuning shit like this happen before. I have a built LS3 in one of my cars. Tuned it on the dyno. For 5 years it ran perfectly. Then one day after I started it it started spitting flames and blue smoke out of the exhaust and ran like absolute dogshit. Couldn't find anything mechanically wrong. Put it on the dyno and the fueling was absolute garabage. We re-tuned it and immediately the engine started working properly again and has been issue free for the the last 10 years. Nobody can explain that one - literally no changes were made to the car for 5yrs and overnight it went from being perfectly fine to the point I was certain the engine was finished, and the culprit was that its fueling requirement somehow decided to change itself.

 

[Goggles Pizano]

Corrupted tune file.

 

[efnfast]

Corrupted tune file.

then re-loading it would have fixed the issue (it didn't). With my new revised tune (reduced cranking fuel) cars starts up perfectly. If I re-load my original dyno tune from a year ago, it goes back to refusing to start. Re-load my new revised tune and it starts up perfectly.

 

[Viper Specialty]

Battery and/or battery related connections.

Crank fueling is both voltage offset and temperature based, and base offset reference and fueling are also pressure based, both fuel and atmospheric. Cranking voltage changes as battery ages. Very few tuners have the ability or knowledge base to properly set up voltage offsets. G3's tend to be very, very finicky on this because of how they opted to set up the voltage offsets and base tables. The fact you have 80lb injectors immediately tells me this is a possibility as proper information on these injectors is limited at best.

You *fixed* the issue, but chances are next time you change the battery out, it will create issues in other ranges instead.

*this* is why if anyone contacts me for tuning work, I wont take the job unless its based on stock injectors or exactly what type I tell them to install as I have the proper data.