Fuel check valve and the 3port fuel pump Options

[brant]

I think there must be a check valve built into the 3 port djet pump

I believe mine is not working
(Hard starting symptoms)

Has anyone pulled theirs apart?

Pictures or a thread?

I'm also wondering if adding an in line check valve would work?

[sixnotfour]

its a pressure bypass , not a check valve

Remember the pump runs a few seconds to pressurize the system before cranking..

whats your hurry man, relax.. (IMG:style_emoticons/default/smoke.gif) let it work

[brant]

Ok it's just a bypass

So has anyone ever added a check valve?
I imagine it adds some restriction to the system
What would be the other reasons this is a bad idea?

I'm having a hard start situation
If I turn the key it is a 25 second crank before it starts

If I turn the key off/on about 5 times and let the pump prime
Then it will start instantly

So I'm loosing pressure
I figure it's either a bad/leaky injector or a situation where the system s draining back to the tank

I will test fuel pressure and injectors when I get home
But might also test the drain-back by adding a check valve?

[sixnotfour]

Ok it's just a bypass

So has anyone ever added a check valve?
I imagine it adds some restriction to the system
What would be the other reasons this is a bad idea?

I'm having a hard start situation
If I turn the key it is a 25 second crank before it starts

If I turn the key off/on about 5 times and let the pump prime
Then it will start instantly

So I'm loosing pressure
I figure it's either a bad/leaky injector or a situation where the system s draining back to the tank

I will test fuel pressure and injectors when I get home
But might also test the drain-back by adding a check valve?

filters dirty or pumps bad , use a 2port later pump..relax

[Dave_Darling]

The pump itself acts as a check valve, at least to some extent. There is no specific check valve built in. There is a spring-loaded valve, but its intent is to bleed off overly high pressure from inside the pump back to the tank.

--DD

[brant]

The pump itself acts as a check valve, at least to some extent. There is no specific check valve built in. There is a spring-loaded valve, but its intent is to bleed off overly high pressure from inside the pump back to the tank.

--DD

Dave,

I'm having a Djet problem where after the car has set for one minute (or even over night) it is hard to restart

cranking the starter for approximately 30 seconds works, and everything runs fine
turning the key on about 4 times, to prime the fuel system yields a totally normal quick start

(I can hear the pump run for the 1 second activation when the key is turned prior to engaging the starter)

Prior to this problem starting up, I had tested/rebuilt all of the injectors and verified fuel pressure

obviously I need to check the injectors again for a possible leak/failure and check the fuel pressure again

the only winter modifications in the induction system were new hoses and relocating the pump from the front belly pan area, to the just below the tank area (a la 1975 style)... so the pump moved about 10 inches higher into the chassis and I suppose that could effect the bleed back a little?

I was never boiling fuel or having a hard to start problem before
I verified fuel pressure after the fuel pump slight relocation

I'm wondering if a failed fuel pressure (stock style) regulator could fail and allow all of the sitting fuel pressure to bleed off down the return line too.

my current working theory is that
1) pressure is bleeding out an injector (although it doesn't seem rich when it starts)
2) pressure is bleeding out through the feed line or pump
3) pressure is bleeding out through the return line or stock style pressure regulator

I have not tested yet.
I will be able to test this weekend to verify that the pressure is bleeding off
but during the 1 second pump prime with the key on, I can hear the pump change tone as if it is re-pressurizing the system and this is what led me to the de-pressurized-system theory.

gas mileage is still 30 -34mpg on the highway so I doubt the injectors are leaking but need to verify.

thus my thoughts about a check valve.

brant

[John]

My suggestion would be to recheck the lines under the tank.

If you are using a 75 style pump (inlet one end, outlet opposite end) then one of the two lines typically makes a 180 bend. My solution to having a kinked line under the tank is to take a piece of Stainless tubing and make a smooth 180 in that and use that for the supply side from the tank to the pump. I only use enough hard line to make a "U" so that I can get that out the access hole into the front trunk. With that in mind, I think I prefer them mounted just above the gravel pan next to the steering rack.

Since you are using a old 3-port pump, I would suggest that you double check to make sure you are using the correct ports to pressurize the fuel ring and return to tank.

Good luck.

[Eric_Shea]

Time for one of these:

(IMG:http://www.914world.com/bbs2/uploads_offsite/i.ebayimg.com-1110-1473700341.1.jpg)

Any of the Denver crew have a fuel pump you could try?

[Elliot Cannon]

I had an issue like that with a '79 911. It would crank for some time before starting. My Porsche guy said it was a check valve that maintains pressure in the system when the engine isn't running. When the pressure bleeds down it take some cranking so the pump can get the pressure back up. Don't you carry a couple spare fuel pumps in your trunk? (IMG:style_emoticons/default/biggrin.gif)

[brant]

I can easily pull the pump this weekend.
I added a 75 style fuel door to the passenger side of the front trunk
I really don't think I have any kinked lines, but can verify easily by opening the door and shinning a flash light


oddly I've put a few thousand miles on the car since the new fuel lines were added 5/16 and this is a new problem

but I do have a brand new spare pump that I can install
(after I verify pressure and injectors)

I really do think my fuel pressure is bleeding down somewhere
I don't think a kinked line would cause that... and once running everything is fine
(400miles yesterday and it ran like a top, getting over 30mpg the whole time)


Yes....
I need to restore it
I just need to pay off one more race motor and strip it down... then its definitely time

[John]

From what I recall (this is from memory) on the 3 port pumps, if one had the supply line from the tank hooked up correctly and had the other two ports swapped (pressure port from pump "Teed" into the return line to the tank) and the return port from pump feeding the fuel ring, that it might build enough back pressure through the smaller return tube to the tank that the car would eventually start and run. These stock 4-cyl engines really don't consume that much fuel, so I believe that once enough pressure built up, the car might run fine, but I believe it would take time to build enough pressure in the first place.

It can't hurt to check the ports on the pump just to make sure.

There is no check valve in the fuel circuit in a stock 4-cyl 914 that I am aware of (just the pressure relief on the 3-port pump).

[Dave_Darling]

Definitely check the pressure. You're only speculating until you see what the pressure actually does.

You might also want to check that the four-pin connector on the relay board is fully seated. One of the pins there carries the starting signal to the ECU, which in part uses it to tell the fuel pump to run.

--DD

[rhodyguy]

Have you looked down the fill opening and glaced at the filter sock recently?

[brant]

Have you looked down the fill opening and glaced at the filter sock recently?

when I had the tank out last april-ish

but it runs great
I had it to about 115mph sustained on sunday for approximately 5 miles
no fuel starvation while running

just no fuel to start for about 20-30 seconds while it primes up.

[John]

Just for giggles, you might want to check pressures. Also as a test, pinch off the return line (after the pressure regulator) and see if you get a faster start.

[sixnotfour]

put a 2 port pump in,, problem gone..the roller vane pump needs to be lower for feed ..total restoration not necessary at this point ..drive it like you stole it...


you are correct..like it needs a check valve ,,really you need the proper pump for where you put it..


In fact I send you one free ..I don't do type 4sale anymore....LMK

[brant]

put a 2 port pump in,, problem gone..the roller vane pump needs to be lower for feed ..total restoration not necessary at this point ..drive it like you stole it...


you are correct..like it needs a check valve ,,really you need the proper pump for where you put it..


In fact I send you one free ..I don't do type 4sale anymore....LMK

I will buy one from you if you have a spare..
I'm thinking the relocation is part of my problem

[sixnotfour]

put a 2 port pump in,, problem gone..the roller vane pump needs to be lower for feed ..total restoration not necessary at this point ..drive it like you stole it...


you are correct..like it needs a check valve ,,really you need the proper pump for where you put it..


In fact I send you one free ..I don't do type 4sale anymore....LMK

I will buy one from you if you have a spare..
I'm thinking the relocation is part of my problem

pm me address

[brant]

Question

I know the injectors fire in pairs
When I pull the injectors and turn the key on I get the 1 second of pump running without turning the motor over

2 of the injectors spray for that 1 second
If I unplug their electrical feed none spray
Does this mean that the distributor has stopped on the pair that are firing?
None leak with those two electrical connections unplugged

Pressure gauge builds up for that one second then bleeds down just as quickly as it built up

[brant]

So Brad Anders website indicates their is a check valve in the fuel pump and that there have been instances of them failing...

unfortunately the URL's on his page are not working:
Fuel Pump •Function: Supplies fuel to the injectors and cold start valve.
•Failure Modes ◦No pressure/inoperative: Can be due to electrical or mechanical failure. The engine will not run in this condition. See the URL below for a test procedure.
◦Improper fuel line hookup: Very odd problems in maintaining pressure, with odd drivability problems. Check the factory workshop manual for the correct hookup.
◦Clogged return line: I had this happen when I converted back from carburetors, my return line was clogged at the tank. High fuel pressure and rich, possible gas contamination of oil. If you can't regulate the pressure, this may be your problem.
◦Failed Check Valve: The check valve keeps the pressure to the injectors and CSV up after the fuel pump is shut off to prevent vapor voids from forming and speed up starting. A failed check valve may cause some hot starting problems. There has been one report of a failed check valve causing the fuel pump to return all fuel to the tank, with no supply to the injectors. See the URL below for a test procedure.

•Notes: Detailed procedures on checking the fuel pump are documented in the Factory Workshop Manual. The electrical plug, contacts, and boot are often in poor condition due to exposure to heat, battery acid, and the environment. Contact failures are a common cause of a sudden shut-off of your car while driving. You should hear the fuel pump run for 1.5 seconds after turning the key to the "on" position. If you don't hear the pump run, check the fuel pump relay on the relay board, and the connection plug to the fuel pump. I keep a cheap Radio Shack multi-meter in my car just for this problem.
•More: There is an excellent reference on debugging fuel pump problems at the URL below:


http://www.914fan.net/fuelpump.html

I also have created a series of flow charts for diagnosing the fuel pump circuit and relays:

http://members.rennlist.com/pbanders/FPChecklist.htm