flatbed

Help,
Every now and then truck has trouble restarting if motor is hot. Typically I unplug EFI fuse let it sit 30sec and then it's all good.

Today it sputtered out, back fired and stalled while driving. With IG on I opened flap on VAF (volume air flow meter) and here circuit opening relay click and fuel pump kick on, but no start. That means my EFI main relay and circuit opening relays are working? Let truck sit for about 10 minutes then it fired up and drove home.

Truck has EGR delete, PAIR delte, and all three VSV's unhooked with vaccum line from intake straight to fuel regulator. Has ran great like this for about 6 months. Until Now. Getting ready to drive from Ga to Vt in two days.
thanks

scope103

Warmer now than in the last 6 months?

One of the VSVs you unhooked is probably the Fuel Pressure-up. You might have vapor lock, which is what the FPU is designed to address (it raises the fuel pressure slightly until it starts).

wallytoo

iTrader: (1)

misread it. yes, with the vacuum line directly connected from the FPR to the plenum, you'll get lower pressure during start-up.

if the FPR vacuum is not connected at all (and the plenum connection is capped), you'll get max pressure all the time (around 40 to 45 psi).

wally

flatbed

Vacuum and fuel pressure move inversely, correct? My direct connection to plenum allows full vacuum causing pressure regulator to return more fuel and drop pressure.

flatbed

Next time it cuts out, will unscrewing the fuel cap to release vacuum get rid of vapor lock? I want to have a few tests ready to eliminate variables.

When it cut out driving today it sputtered then backfired, would backfiring be more of an ignition/coil igniter problem or could fuel loss cause backfire on an EFI?

thanks, I appreciate the help

wallytoo

iTrader: (1)

i'd suspect excess fuel for whatever condition is resulting in backfire, rather than less fuel.


i don't believe unscrewing the cap will have an effect on vapor lock.


you could always try to get max fuel pressure next time it cuts out, and just disconnect the FPR vacuum line (and cap the line so no leak to the plenum). rather than 28-30 psi at startup, you'd get 35-40 psi.

wally

scope103

The fuel pressure regulator is to assure that the pressure ACROSS the injectors is constant. So as the pressure in the plenum DECREASES (which could be said: vacuum INCREASES), the fuel pressure decreases. Note that pressure in the plenum is at minimum when idling. If you disconnect the FPR vacuum line and expose it to the higher-pressure ambient air (this is what the FPU does), the fuel pressure increases to push the vapor bubble (vapor lock) through the system. If you connect the FPR vacuum line direct to the plenum, the truck will run fine, except for FPU.

There is NEVER vacuum in the fuel tank, only pressure (occasionally). The fuel cap allows air in as the pump pushes fuel out (otherwise the fuel pump could crush the tank!), but never allows fuel vapors out (which are generated sitting there on a hot day). The fuel vapor gets squeezed into the evap canister.

wallytoo is correct; vapor lock has nothing to do with the fuel cap.

crawler85

I had similar symptoms when my igniter went bad.

Would drive it around for a while, it would die, crank but no start unless I waited about 15 minutes for it to cool down.

There is a check for the igniter that involves using a AA battery.

scope103

Interesting. Any idea what it is?

https://www.yotatech.com/forums/f116...gniter-287857/