| EFI Excessive Fuel Pressure at shut off [message #288872] |
Fri, 16 October 2015 20:06  |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma:
|
Senior Member |
|
|
I posted this same question to the google EFI group. Posting it here in case anyone here has experience similar to this.
So, here's one for ya....figure this one out. I have a batch fire port injection system on my Cad 500 that is controlled by Dynamic EFI software. Since I first installed it, 4 or 5 yrs ago, I've had issues with fuel heating up as it passed through the fuel rails and returning to the tanks hot, eventually (especially in warm weather) bringing the fuel in the tanks to the boiling point (vapor lock in the tanks.) So, I changed the system so that it is (my term) "dead headed" to the fuel rails. I moved the fuel pressure regulator back to the tanks and put the pumps in the tanks. Fuel now comes out of the tank, and can flow directly to the fuel rails (no return at the rails) with the excess fuel being diverted at a "T" (back at the tanks) to the FP regulator and back to the tank. The regulator is located on the frame directly in front of the forward tank, with gas returning to the tank through the drain plug hole. By running 52 lbs of pressure, I figured, that kind of pressure would keep the fuel in the rails at a liquid state. So now when the motor heats up to normal operating temperature, and I shut the motor off to....say...fill the tanks on a gas stop, fuel pressure builds in the system to over 100lbs. At this point, there is so much pressure in the system that the injectors are unable to open which keeps the engine from restarting. Turns over with spark, but no start. If I then pull the cap off of the Schroeder valve on the fuel rail and release the pressure, it will start immediately and run normally. It takes about 5 minutes for this pressure to build. So today I decided to observe this first hand by putting a FP gauge on the rails and observe the pressure to verify excessive heat is causing the fuel to vaporize and build pressure. I was surprised to find that when the pressure exceeded 100lbs and engine would not start, that the fuel rails, injectors, the one hose leading to the rails, and fuel filter were actually cold to the touch. If I allow the engine to cool, the pressure drops and the engine will start normally. I have checked the fuel pumps and they are NOT running when the pressure is building at key off.
What the hell is happening here? What is causing the fuel pressure to rise to such pressures, and what is the solution? I am considering putting another FP regulator in at the fuel rail and setting it at say 65lbs, so that regulator would bleed off the rising pressures back to the tank and allow for normal hot restarts.
ANY IDEAS??
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
