Home  |  Forums  |  914 Info  |  Blogs
 
914World.com - The fastest growing online 914 community!
 
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG. This site is not affiliated with Porsche in any way.
Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners.
 

Welcome Guest ( Log In | Register )

> Fuel pump vapor locking
jims914
post Mar 30 2023, 02:30 PM
Post #1


Member
**

Group: Members
Posts: 123
Joined: 11-March 11
From: Tempe,AZ
Member No.: 12,816
Region Association: Southwest Region



Anyone have a problem with vaporing with a three port pump ?
Any solutions ?

Thanks Jim
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
 
Reply to this topicStart new topic
Replies(1 - 12)
Rrrockhound
post Mar 30 2023, 06:13 PM
Post #2


Member
**

Group: Members
Posts: 192
Joined: 30-November 05
From: Delaware, OH
Member No.: 5,213
Region Association: None



QUOTE(jims914 @ Mar 30 2023, 04:30 PM) *

Anyone have a problem with vaporing with a three port pump ?
Any solutions ?

Thanks Jim


I cut out a piece of aluminum-backed heat shielding and tuck it between the pump and the heater valve and never have a problem anymore.

Similar to this:

Heat shielding
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
emerygt350
post Mar 30 2023, 07:35 PM
Post #3


Advanced Member
****

Group: Members
Posts: 2,025
Joined: 20-July 21
From: Upstate, NY
Member No.: 25,740
Region Association: North East States



As the original slime insulation falls off the fuel line from the firewall you may want to replace it with dei insulation. That and the shield does wonders. Instead of a shield I put an extension on the heat valve as described in the service bulletin. No problems since the dei and extension.
User is online!Profile CardPM
Go to the top of the page
+Quote Post
wonkipop
post Mar 31 2023, 01:39 AM
Post #4


Advanced Member
****

Group: Members
Posts: 4,159
Joined: 6-May 20
From: north antarctica
Member No.: 24,231
Region Association: NineFourteenerVille



QUOTE(jims914 @ Mar 30 2023, 02:30 PM) *

Anyone have a problem with vaporing with a three port pump ?
Any solutions ?

Thanks Jim


where is it.
in the original spot?

if it is in original spot its not the pumps problem.
the pump is a fabulous design with no faults.
its that cast magnesium fan shroud.
its a heat sink.
all the heat in the engine just conducts to the magnesium.
........and radiates. after you shut down.
as deborah harry would say!

and boils the fuel in the line feeding the pump.
and maybe even the pump itself.

you either put up with it for the sake of originality like i do.
or move it up front.

User is offlineProfile CardPM
Go to the top of the page
+Quote Post
brant
post Mar 31 2023, 07:26 AM
Post #5


914 Wizard
**********

Group: Members
Posts: 11,584
Joined: 30-December 02
From: Colorado
Member No.: 47
Region Association: Rocky Mountains



It’s not the pumps fault
Just the location

Move it
User is online!Profile CardPM
Go to the top of the page
+Quote Post
PCH
post Mar 31 2023, 05:10 PM
Post #6


Member
**

Group: Members
Posts: 140
Joined: 3-January 19
From: Santa Barbara
Member No.: 22,772
Region Association: Southern California



The vapor lock problem disappeared after I went to carbs.

When I had the FI, it would vapor lock fairly regularly, especially after a short stop. I started to carry cans of cold (off hand I don't remember what they were called) and cool the fuel lines and pump when it vapor locked. That worked every time to get me back on the road.

User is offlineProfile CardPM
Go to the top of the page
+Quote Post
emerygt350
post Mar 31 2023, 06:27 PM
Post #7


Advanced Member
****

Group: Members
Posts: 2,025
Joined: 20-July 21
From: Upstate, NY
Member No.: 25,740
Region Association: North East States



You don't have to redesign the car and send high pressure fuel 6 feet through the tunnel to fix this.
User is online!Profile CardPM
Go to the top of the page
+Quote Post
brubou
post Mar 31 2023, 06:46 PM
Post #8


Bruce Bouchard
**

Group: Members
Posts: 92
Joined: 29-February 16
From: West Bradford, PA
Member No.: 19,716
Region Association: MidAtlantic Region



Pressurized fuel is going through the tunnel either way, pump in front or pump in back, the system is 29psi.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
wonkipop
post Mar 31 2023, 07:25 PM
Post #9


Advanced Member
****

Group: Members
Posts: 4,159
Joined: 6-May 20
From: north antarctica
Member No.: 24,231
Region Association: NineFourteenerVille



QUOTE(brubou @ Mar 31 2023, 06:46 PM) *

Pressurized fuel is going through the tunnel either way, pump in front or pump in back, the system is 29psi.


not strictly correct.

the fuel circuit from the pump to the fuel pressure regulator is pressurized in the pre 75 stock pump scenario. that is restricted to the ring from the pump near the engine to the fpr in the engine bay. the rest of the lines are at lower pressure.
the feed line is more or less just weaker suction/gravity feed. flow rather than pressure. the return line is the bleed out of the relief valve in the pump and the fpr. thats why they are two different diameters. the feed line is larger diam by 2mm.

different matter in the 75 cars. the feed line from the pump up front to the fpr is at full pressure right through the car. it was also made of an entirely different material. a high pressure nylon plastic.

(IMG:style_emoticons/default/beerchug.gif)

in the case of a healthy 1.8 L jet the fuel pressure is at 35 lbs. drops to 28 at idle and off throttle. slightly higher than the D jets.


User is offlineProfile CardPM
Go to the top of the page
+Quote Post
jims914
post Mar 31 2023, 07:28 PM
Post #10


Member
**

Group: Members
Posts: 123
Joined: 11-March 11
From: Tempe,AZ
Member No.: 12,816
Region Association: Southwest Region



Thanks everyone for your input.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
brubou
post Mar 31 2023, 08:09 PM
Post #11


Bruce Bouchard
**

Group: Members
Posts: 92
Joined: 29-February 16
From: West Bradford, PA
Member No.: 19,716
Region Association: MidAtlantic Region



QUOTE(wonkipop @ Mar 31 2023, 09:25 PM) *

QUOTE(brubou @ Mar 31 2023, 06:46 PM) *

Pressurized fuel is going through the tunnel either way, pump in front or pump in back, the system is 29psi.


not strictly correct.

the fuel circuit from the pump to the fuel pressure regulator is pressurized in the pre 75 stock pump scenario. that is restricted to the ring from the pump near the engine to the fpr in the engine bay. the rest of the lines are at lower pressure.
the feed line is more or less just weaker suction/gravity feed. flow rather than pressure. the return line is the bleed out of the relief valve in the pump and the fpr. thats why they are two different diameters. the feed line is larger diam by 2mm.

different matter in the 75 cars. the feed line from the pump up front to the fpr is at full pressure right through the car. it was also made of an entirely different material. a high pressure nylon plastic.

(IMG:style_emoticons/default/beerchug.gif)

in the case of a healthy 1.8 L jet the fuel pressure is at 35 lbs. drops to 28 at idle and off throttle. slightly higher than the D jets.


No kidding. TIL

As far as two port pumps go; if in the engine bay the supply line thru the tunnel is gravity (lower pressure) to the pump, and the return line is pressurized?

However, if the two port pump is up front, both the supply and return are pressurized?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
JeffBowlsby
post Mar 31 2023, 09:52 PM
Post #12


914 Wiring Harnesses
*****

Group: Members
Posts: 8,438
Joined: 7-January 03
From: San Ramon CA
Member No.: 104
Region Association: None



Factory fix: https://bowlsby.net/914/Classic/zSB_1973-10-06_P213.pdf
User is online!Profile CardPM
Go to the top of the page
+Quote Post
wonkipop
post Apr 1 2023, 12:55 AM
Post #13


Advanced Member
****

Group: Members
Posts: 4,159
Joined: 6-May 20
From: north antarctica
Member No.: 24,231
Region Association: NineFourteenerVille



QUOTE(brubou @ Mar 31 2023, 08:09 PM) *

QUOTE(wonkipop @ Mar 31 2023, 09:25 PM) *

QUOTE(brubou @ Mar 31 2023, 06:46 PM) *

Pressurized fuel is going through the tunnel either way, pump in front or pump in back, the system is 29psi.


not strictly correct.

the fuel circuit from the pump to the fuel pressure regulator is pressurized in the pre 75 stock pump scenario. that is restricted to the ring from the pump near the engine to the fpr in the engine bay. the rest of the lines are at lower pressure.
the feed line is more or less just weaker suction/gravity feed. flow rather than pressure. the return line is the bleed out of the relief valve in the pump and the fpr. thats why they are two different diameters. the feed line is larger diam by 2mm.

different matter in the 75 cars. the feed line from the pump up front to the fpr is at full pressure right through the car. it was also made of an entirely different material. a high pressure nylon plastic.

(IMG:style_emoticons/default/beerchug.gif)

in the case of a healthy 1.8 L jet the fuel pressure is at 35 lbs. drops to 28 at idle and off throttle. slightly higher than the D jets.


No kidding. TIL

As far as two port pumps go; if in the engine bay the supply line thru the tunnel is gravity (lower pressure) to the pump, and the return line is pressurized?

However, if the two port pump is up front, both the supply and return are pressurized?


ok mate

what would i know? (IMG:style_emoticons/default/biggrin.gif)
you must have a pressurised fuel tank as well. (IMG:style_emoticons/default/bootyshake.gif) (IMG:style_emoticons/default/beer.gif)
you probably do. mine isn't.
think about it and get back to me.
who knows. american mind set. no better than average aussie mind set?
the chinese will do you if you don't up the game?
they are most certainly doing us!

flow yes.
pressure no.
there is a difference.
you build pressure with a "dam".
thats what the fuel pressure regulator does.
the fuel pump doesn't actually do pressure. it does flow. primarily.
and it supplies the flow against the dam wall to build pressure.
and once the resistance builds against the dam wall it blows it out the side via the check valve - should the fuel pressure regulator fail to do its job and jamb up.

(IMG:style_emoticons/default/beer.gif)

thats why there is 2 tests for a fuel pump?
there is a flow test - volume in prescribed time.
and a pressure test, where you apply resistance and see if it can build pressure before it blows the relief valve.
not trying to pick a dumbo internet fight.
just trying to be helpful.
but then again just a dumb aussie so what would i know? (IMG:style_emoticons/default/beer.gif)

think about it. its fluid mechanics. there is flow, and there is pressure.
i can assure you there is very little pressure in the return line. but maybe quite a bit of flow.
same in the supply line. with a pre 75 set up.

post 74 there is a longer pressure line between the fuel pump up front and the fuel pressure regulator in the engine bay. thats the pressurized section of line.

but believe what you want to believe and do what you want to do to your car.
its your car. (IMG:style_emoticons/default/beer3.gif)


the point is @emerygt350 is correct. i'll put a 1000 aussie pesos on his opinion as a mere wager.
after all he is a ford man. he thinks like henry. the great american engineer.
maybe even superior to ferdinand porsche?
gives him real cred in my book. go ford. (IMG:style_emoticons/default/biggrin.gif)

and......two port fuel pumps relieve pressure by blowing it back through the supply line.
thats where the pressure relief valve is.
they do not need a third port.
its a very smart simplification.
i think mercedes in league with bosch worked that one out around about 1975.
its a long time ago.
and everyone in the USA making fuel pumps has benefited from their thinking since.
because lets face it, the US car manufactures were not even doing fuel injection in mass market cars back then, with high pressure fuel circuits, they were still frigging about with vacuum choked carbies.

i've rebuilt 3 original 3 port fuel pumps.
and a slightly later 2 port bosch pump off a merc.
i've seen what is in the guts of these things and got my tiny antipodean mind around it.
they are brilliant pieces of german engineering.
and they arrived at it long before the rest of the automotive world.

one word. physics. understand it and move ahead.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



- Lo-Fi Version Time is now: 28th March 2024 - 10:56 AM