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| 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: 10
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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.
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| Re: [GMCnet] EFI Excessive Fuel Pressure at shut off [message #288880 is a reply to message #288872] |
Fri, 16 October 2015 21:36  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Hmm. Verrrry interesting. Only way you could experience a pressure rise
like that is to heat the vessel the fuel is contained in or to reduce the
size of the vessel. But, your description accounts for temp rise. Do you
have check valves in the system anywhere besides where you have mentioned?
Or perhaps a pressure accumulator? Just a S.W.A.G. on my part.
Jim Hupy
On Oct 16, 2015 6:06 PM, "Larry" wrote:
> 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.
>
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| Re: EFI Excessive Fuel Pressure at shut off [message #288882 is a reply to message #288872] |
Fri, 16 October 2015 21:45 |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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Senior Member |
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Not familiar with that particular system, but is the regulator vacuum /boost referenced?
If it isnt seeing vacuum,the pressure would go up.Probably not that much though - id expect 14-15 # maybe.
Other though is that being a deadhead system without a bleed off, the gasoline may be expanding in the line even if not vaporizing since it is under pressure
76 Glenbrook
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| Re: EFI Excessive Fuel Pressure at shut off [message #288883 is a reply to message #288872] |
Fri, 16 October 2015 21:56 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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If the fuel line crosses over the exhaust anywhere, that area might get hot when the air stops moving after the engine stops.
If you release the pressure after it reaches max pressure, does the pressure come back up?
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: EFI Excessive Fuel Pressure at shut off [message #288884 is a reply to message #288872] |
Fri, 16 October 2015 22:12 |
George B.
Messages: 213
Registered: February 2012
Karma: 1
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Senior Member |
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I ask in advance for the right to stink! This is really an out-there idea so please be kind.
Perhaps the "Dead End" in the rails is acting somewhat like a water-hammer arrester coupled with air somehow getting into the fuel lines allowing a pressure build up in the arrester like area of the rails.
But wait, that might cause some erratic pressure changes but should not account for the build up upon shut down??? Did the added pressure gauge on the rails actually read 52 with the engine running?
George Butts
Las Vegas Nevada
73 "Custom 26' Q" & 76 23' Birchaven
71 Honda 600 Coupe & 01 Tracker Toads
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| Re: EFI Excessive Fuel Pressure at shut off [message #288886 is a reply to message #288872] |
Fri, 16 October 2015 22:49 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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Senior Member |
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Larry wrote on Fri, 16 October 2015 18:06I 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.
Larry,
Most interesting, and for me informative.
First, I also have "thought" that gas in a return system eventually will heat the gas in the tanks. I am glad that at least someone, besides me, has seen this unfortunate situation. With my first coach, with a bum separator valve, I had to be very careful when opening the cap. And yet, with CA ethanol, it never "vapor locked".
Second, I am pretty sure we are seeing gas in a pressure cooker. It heats and at least expands... we know that can happen and increases the pressure. I agree it is not boiling at 100 lbs. Letting it pop off in the engine compartment is not a good solution and having to open the hatch just because you got gas is not good either.
I think the second regulator in the system is spot on. I don't know how accurately they can be set, but if it were as you say set to 65 lbs, it would then let the rails bleed off fuel. I suppose the trick is to figure out what the magic "too much pressure" amount is for the injectors. I would think the closer to 52 the better. It can't be good for injectors to try to force open under that much resistance. The moment the first injector opens, all should be well, I would think.
Alex, at GMCMI had a fuel cooler on his Atomic EFI. He was so busy fixing steering for everyone that I didn't get a chance to ask if he was deadheading or returning. Atomic gives you the choice. I would not think that even coolish or cooler fuel would prevent it from super-heating when the engine is shut down. I imagine temps really climb on top of the engine at shut down.
Most interesting. Make sure to tell all here and on EFI what your final solution might be.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: EFI Excessive Fuel Pressure at shut off [message #288890 is a reply to message #288872] |
Sat, 17 October 2015 00:02 |
Adrien G.
Messages: 474
Registered: May 2008
Location: Burns Flat, OK 73624
Karma: 1
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Senior Member |
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Larry,
It sounds like the FP has a check valve to hold pressure.
So, either change FP to not hold pressure when stopped, or yes a second PReg
and that can be installed downstream of the FP, not necessarily right at the rail.
The 100 lbs at the rail will also be at the FP outlet.
Anyway to shield and/or insulate the fuel line to slow the heat absorption?
Adrien & Jenny Genesoto
75 Glenbrook (26-3) Mods LS3.70 FD / Reaction Sys / 80mm Front&Intermidiate / Hydroboost / 16" Tires / Frame Rebuild / Interior Rebuild
Yuba City,Ca. Text 530-nine-3-three-3-nine-nine-6
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| Re: [GMCnet] EFI Excessive Fuel Pressure at shut off [message #288900 is a reply to message #288898] |
Sat, 17 October 2015 09:36 |
GMC.LES
Messages: 505
Registered: April 2014
Karma: -2
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Senior Member |
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I would think that the addition of an accumulator to absorb the apparent expansion would solve(or camouflage) the problem. Many FI systems use them, so finding a suitable unit shouldn't be difficult.
Good luck finding the cause and solution.
Les Burt
Montreal
'75 Eleganza 26'
The EWIP (Eternal Work In Progress)
> On Oct 17, 2015, at 9:40 AM, Matt Colie wrote:
>
> Larry,
>
> After reading this through about four (maybe more) times, I think I know what is going on.
>
> You have two separate issues. They are in cahoots just to make your life interesting.
> The first is that your pressure regulator is not functioning. It is were, it would relieve the pressure just as you have done at the pressure test
> port.
> The second, and this only matters because of the first, is that the block coefficient of aluminum (the rails) is actually higher than that of the
> typical components of "gasoline" as you get it at the pump.
>
> What is "Gasoline"??
> It is a collection of distillates that come off crude oil between about 150 and 300°F. It is comprised of an alphabet soup of stuff and the only
> thing that is really certified is the vapor pressure and the hydrogen/carbon ratio. But is all has about the same thermal expansion rate.
>
> I hope something here is actually a help.
>
> Matt
> --
> Matt & Mary Colie - Members GMCMI, GMCES
> '73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: [GMCnet] EFI Excessive Fuel Pressure at shut off [message #288901 is a reply to message #288900] |
Sat, 17 October 2015 09:54 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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VW Rabbits, Dashers, Audi Fox's, Saab, and many others used a common
Germany Bosch all mechanical fuel injection system know as CIS. That stood
for continuous injection system. The injectors were not timed, but sprayed
a continuous stream, the volume of which varied by a plate in the center of
a venturi connected via fulcrum and lever to a stainless steel diaphragm in
the fuel distributor body. They would experience hot starting problems like
you describe. The first fix was an accumulator in the high pressure supply.
Later fixes were solenoid controlled electrical valves. The accumulator
received fuel from the tank mounted high pressure pump, and acted as a
buffering agent to both smooth out pump pulsing as well as limiting
pressure when hot shut down occurred. They were just about bullet proof.
Should still be some around in salvage yards and aftermarket sources. Just
something to think about.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Oct 17, 2015 7:36 AM, "Les Burt" wrote:
> I would think that the addition of an accumulator to absorb the apparent
> expansion would solve(or camouflage) the problem. Many FI systems use them,
> so finding a suitable unit shouldn't be difficult.
>
> Good luck finding the cause and solution.
>
> Les Burt
> Montreal
> '75 Eleganza 26'
> The EWIP (Eternal Work In Progress)
>
>
>> On Oct 17, 2015, at 9:40 AM, Matt Colie wrote:
>>
>> Larry,
>>
>> After reading this through about four (maybe more) times, I think I know
> what is going on.
>>
>> You have two separate issues. They are in cahoots just to make your
> life interesting.
>> The first is that your pressure regulator is not functioning. It is
> were, it would relieve the pressure just as you have done at the pressure
> test
>> port.
>> The second, and this only matters because of the first, is that the
> block coefficient of aluminum (the rails) is actually higher than that of
> the
>> typical components of "gasoline" as you get it at the pump.
>>
>> What is "Gasoline"??
>> It is a collection of distillates that come off crude oil between about
> 150 and 300°F. It is comprised of an alphabet soup of stuff and the only
>> thing that is really certified is the vapor pressure and the
> hydrogen/carbon ratio. But is all has about the same thermal expansion
> rate.
>>
>> I hope something here is actually a help.
>>
>> Matt
>> --
>> Matt & Mary Colie - Members GMCMI, GMCES
>> '73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control
> Arms
>> SE Michigan - Twixt A2 and Detroit
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: EFI Excessive Fuel Pressure at shut off [message #288936 is a reply to message #288872] |
Sun, 18 October 2015 08:48 |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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Senior Member |
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First, thanks for all of the thoughts and suggestions.
It has been suggested that the regulator goes to max at "0" vacuum, this is has not been my experience...that at "0" vacuum, the pressure goes to MAX. I am using this regulator. An Aeromotive 13105 compact EFI Bypass Regulator.
When I first set this up, I pulled the wires from the Oil pressure sending unit and tied them together so that the fuel pump would run continuously at key on. That allowed me to get a PSI setting for the first startup of this new EFI system. With key on, the pump ran continuous and I made initial pressure settings of 42lbs. I thought that initial setting would remain after startup. On startup...engine running, pressure dropped a full 10lbs, so I had to up the pressure some more so the motor would run under power, and eventually settled on 52lbs running. It should be noted, that the regulator does continue to "regulate" without vacuum, and does not go to MAX as suggested. It appears that the regulator delivers about another 10lbs at 0 vacuum.
One little tidbit that I forgot to mention... when I moved the pumps into the tanks and put the regulator back at the tank for a "dead head" system, I found that apparently one or both of the checks in the pumps were leaking back, dropping pressure at hot shutoff to "0" , allowing vaporization of gas in the fuel rails and making for a hard restart. So I put a check valve in the system between the regulator and the fuel rails. This then allowed pressure to drop from the regulator back, but held pressure in the fuel rails...apparently to well.
After reading all of the thoughts and suggestions, I am going to try another regulator at fuel rails to regulate excess pressure build-up at hot key off. I will set the pressure at 65lbs and see what happens. My thought is that this second regulator will not be a factor in running regulation, the other regulator at the tanks will control that. Only when the pressure at the fuel rails reaches 65lbs on hot shutoff, will it then activate and bleed pressure off a little at a time as it reaches the set pressure.
Just what I'm thinking now. Any other thoughts?
Larry
Larry
78 Royale w/500 Caddy
Menomonie, WI.
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