Fuel check valve and the 3port fuel pump Options

[BeatNavy]

◦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.

Brant - I have similar experience on an otherwise generally well-running 2056 D-Jet. I've wondered the same thing about a check valve. I bought my fuel pump rebuilt from AA a couple of years ago, but I'm thinking about changing to that Bosch 2 port unit.

Can someone confirm: should the fuel pressure in the system STAY ~29 psi even when the pump is off (or maybe bleed down slowly)? Mine does not. It bleeds off right away. My other symptoms:

1. Takes me about 5 seconds of cranking to start when it's cold, and I ALWAYS have to feather it once or twice during the first 10 seconds of running or it will die one time. If it does die, it will immediately fire up with turn of key and stay started.

2. If I kill engine and IMMEDIATELY restart, it fires up with no problem.

3. If stop briefly for a few minutes, e.g., to fill up gas or run quickly into a store, it may take 5 to 15 seconds of cranking and then will idle so low for 20 or 30 seconds that I normally have to feather it to keep running. After that, idle picks up and all good. It doesn't seem like it's that "warm start over-enrichment" issue, because the head temp is still high, and my O2 is showing more like 14+ at that point.

This morning after a 20 minute doctors appointment. I started the car with accelerator depressed, and it did seem to help it start more quickly and stay started.

Maybe I'll put replacing the fuel pump on my to-do list and see if that helps.

Also, I've tried to go to that P914fan.net link before hoping to get answers, only to find a "fitness fan blog." And Brad's fuel pump page isn't working the way it's supposed to anymore (I think it may not be compatible with modern browsers). I know he's been active here recently - I don't know if he's got the time to update it or not, but it would be appreciated (IMG:style_emoticons/default/pray.gif)

[87m491]

I don't know D-jet at all compared to my CIS cars but I think it would stand to reason that residual pressure might bleed off but not drop to zero like flipping a switch.

5 Seconds to start from cold could be almost anything, then feathering might point to another tuning issue as the whole purpose of F.I. is to preclude this issue. Most of what I have read and experienced on D Jet is a high initial idle with a drop towards normal once warm.

Killing and re-firing instantly doesn't sound too surprising with everything else, pressure may be bleeding off but every turn off the key on fires off the pump with a short prime pulse giving you back "full" pressure after the quick shut down.

Your short stop scenario is like classic CIS vapor lock or pressure bleed down via a bad check valve. Since after the initial prime the pump won't run unless it senses the engine running and of course the engine won't run without higher fuel pressure. Many will hard wire the pump to run with the ignition on circumventing the speed sensor, and causing a safety hazard.

If you can't find a source for the "pressure leaks" I'd say get the new 2 port pump and be done with it.

Brant - I have similar experience on an otherwise generally well-running 2056 D-Jet. I've wondered the same thing about a check valve. I bought my fuel pump rebuilt from AA a couple of years ago, but I'm thinking about changing to that Bosch 2 port unit.

Can someone confirm: should the fuel pressure in the system STAY ~29 psi even when the pump is off (or maybe bleed down slowly)? Mine does not. It bleeds off right away. My other symptoms:

1. Takes me about 5 seconds of cranking to start when it's cold, and I ALWAYS have to feather it once or twice during the first 10 seconds of running or it will die one time. If it does die, it will immediately fire up with turn of key and stay started.

2. If I kill engine and IMMEDIATELY restart, it fires up with no problem.

3. If stop briefly for a few minutes, e.g., to fill up gas or run quickly into a store, it may take 5 to 15 seconds of cranking and then will idle so low for 20 or 30 seconds that I normally have to feather it to keep running. After that, idle picks up and all good. It doesn't seem like it's that "warm start over-enrichment" issue, because the head temp is still high, and my O2 is showing more like 14+ at that point.

This morning after a 20 minute doctors appointment. I started the car with accelerator depressed, and it did seem to help it start more quickly and stay started.

Maybe I'll put replacing the fuel pump on my to-do list and see if that helps.

Also, I've tried to go to that P914fan.net link before hoping to get answers, only to find a "fitness fan blog." And Brad's fuel pump page isn't working the way it's supposed to anymore (I think it may not be compatible with modern browsers). I know he's been active here recently - I don't know if he's got the time to update it or not, but it would be appreciated (IMG:style_emoticons/default/pray.gif)

[brant]

◦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.

Brant - I have similar experience on an otherwise generally well-running 2056 D-Jet. I've wondered the same thing about a check valve. I bought my fuel pump rebuilt from AA a couple of years ago, but I'm thinking about changing to that Bosch 2 port unit.

Can someone confirm: should the fuel pressure in the system STAY ~29 psi even when the pump is off (or maybe bleed down slowly)? Mine does not. It bleeds off right away. My other symptoms:

1. Takes me about 5 seconds of cranking to start when it's cold, and I ALWAYS have to feather it once or twice during the first 10 seconds of running or it will die one time. If it does die, it will immediately fire up with turn of key and stay started.

2. If I kill engine and IMMEDIATELY restart, it fires up with no problem.

3. If stop briefly for a few minutes, e.g., to fill up gas or run quickly into a store, it may take 5 to 15 seconds of cranking and then will idle so low for 20 or 30 seconds that I normally have to feather it to keep running. After that, idle picks up and all good. It doesn't seem like it's that "warm start over-enrichment" issue, because the head temp is still high, and my O2 is showing more like 14+ at that point.

This morning after a 20 minute doctors appointment. I started the car with accelerator depressed, and it did seem to help it start more quickly and stay started.

Maybe I'll put replacing the fuel pump on my to-do list and see if that helps.

Also, I've tried to go to that P914fan.net link before hoping to get answers, only to find a "fitness fan blog." And Brad's fuel pump page isn't working the way it's supposed to anymore (I think it may not be compatible with modern browsers). I know he's been active here recently - I don't know if he's got the time to update it or not, but it would be appreciated (IMG:style_emoticons/default/pray.gif)

That sounds like exactly the same symptoms
I too would love to know if a stock djet system maintains some pressure when shut off
Mine maintains zero pressure within 1-2 seconds

I will let you know soon what my findings are from removing/testing/and perhaps beating my pump with a hammer. I intend to remove the spring loaded return over flow valve and examine it

If I don't find anything out. I intend to get a 2 port pump and test it also

[BeatNavy]

That sounds like exactly the same symptoms
I too would love to know if a stock djet system maintains some pressure when shut off
Mine maintains zero pressure within 1-2 seconds

I will let you know soon what my findings are from removing/testing/and perhaps beating my pump with a hammer. I intend to remove the spring loaded return over flow valve and examine it

If I don't find anything out. I intend to get a 2 port pump and test it also

Brant - that would be awesome. If somehow I get around to swapping pumps before you do I'll make sure to post an update. It's a small but annoying behavior that does sometime impact my driving -- so I want to get it fixed (IMG:style_emoticons/default/smile.gif)

Thanks!

[Dave_Darling]

I too would love to know if a stock djet system maintains some pressure when shut off
Mine maintains zero pressure within 1-2 seconds

My system bleeds down to ~10 PSI relatively quickly, over the course of a minute or so, and then much slower down to zero. Dropping to zero within seconds tells me something is leaking.

There is no check valve inside the three-port pump. The rollers and rotor in the pump serve as a check to reverse flow, that's it. The valve in there is only a pressure bleed-off to dump overly high-pressure fuel back to the tank; it is not a one-way check-valve.

I would suspect your pressure regulator may be leaking, or possibly an injector is stuck open.

--DD

[brant]

I too would love to know if a stock djet system maintains some pressure when shut off
Mine maintains zero pressure within 1-2 seconds

My system bleeds down to ~10 PSI relatively quickly, over the course of a minute or so, and then much slower down to zero. Dropping to zero within seconds tells me something is leaking.

There is no check valve inside the three-port pump. The rollers and rotor in the pump serve as a check to reverse flow, that's it. The valve in there is only a pressure bleed-off to dump overly high-pressure fuel back to the tank; it is not a one-way check-valve.

I would suspect your pressure regulator may be leaking, or possibly an injector is stuck open.

--DD

How do test the pressure regulator?
It sits at 29psi when turning over and 29psi while running

I pulled the injectors and they are not leaking

Brad Anders site confused me by claiming there is a check valve in the pump

[BeatNavy]

How do test the pressure regulator?
It sits at 29psi when turning over and 29psi while running

I pulled the injectors and they are not leaking

Brad Anders site confused me by claiming there is a check valve in the pump

Brant, did you test the injectors for leaking while cranking or with the system pressurized? I probably need to do the same, I found a pretty decent write up of some injector tests on this thread:

http://www.914world.com/bbs2/index.php?s=&...st&p=958085

Curiously, he mentions a "check valve" in the pump too. Somehow there's a notion of a check valve, or some function that maintains pressure in the system, inside our stock pumps.

[Dave_Darling]

I think the references to "check valve" either misinterpret the over-pressure valve, or are references to the fuel not being able to flow backwards through the pump stage.

To test the regulator, you can get an extra piece of fuel hose and run it from the regulator outlet to a good-sized container. Run the fuel pump until you get to 29 PSI, then stop. If a lot of fuel keeps coming out of the regulator outlet while the pressure drops, the regulator is probably letting the pressure out.

If no fuel comes out, and the pressure drops, pull the injectors off of the engine while leaving them connected to the fuel lines. Check for leaks. Ditto the cold-start valve.

--DD

[brant]

I think the references to "check valve" either misinterpret the over-pressure valve, or are references to the fuel not being able to flow backwards through the pump stage.

To test the regulator, you can get an extra piece of fuel hose and run it from the regulator outlet to a good-sized container. Run the fuel pump until you get to 29 PSI, then stop. If a lot of fuel keeps coming out of the regulator outlet while the pressure drops, the regulator is probably letting the pressure out.

If no fuel comes out, and the pressure drops, pull the injectors off of the engine while leaving them connected to the fuel lines. Check for leaks. Ditto the cold-start valve.

--DD

Already tested the injectors but will test the regulator next

Also is it confirmed that the regulator should hold fuel pressure when working correctly?

[brant]

I fixed it

Will keep testing after it cools down for a couple of days... But 2 seperate tests of 30 minutes show good results.

An open fuel pressure blow off valve seems to offer a pathway to bleed off the lines and bypass the pump rollers. Causing the hard start

Not a check valve but fails in the same way as a check valve

My valve failed. There is a piece of rubber holding it together, allowing it to work correctly...

[BeatNavy]

Did you have to break open the pump to get to that pressure relief valve? And you were able to either reseat the rubber or replace it with something?

Good info! I may try to find my "spare" pump...

[brant]

Some details
I may get a better picture when I get home

So on the 3 port pump there is a pressure blow off valve that opens a pathway for the pressurized fuel to bypass the output "D" fitting on the pump. I assume the original designers figure that when the hose feeding the injectors was already fully pressured to 29psi (built to that pressure by the regulator) that the pump was pushing against that head pressure and possibly running under load needlessly (wear to the pump gears?)

What ever their original logic was, they created a blow off valve for the fuel to bypass that out put path and divert to the tank return pathway

when the valve is open and doesn't get pushed by its 2springs back to the closed position, and the car/pump is turned off..... The residual fuel in the lines is sitting At 29psi and runs backwards in the circuit to drain through this open valve when sitting at rest

There is a crimp cap on the pump
Under the cap is:
a cap gasket
A large spring
A spring plate/divider
A small spring
A rubber snapped into the piston (40 years old)
And a piston

My rubber broke (a bad pregnancy joke)

The one end of the rubber creates the seal for the closed piston
With the rubber missing the piston doesn't close and leaves this alternative pathway for fuel to drain backwards in the circuit when the pump/key is turned off

You can pry the aluminum cap off of the pump and expose all of these parts

I will look for replacement part alternatives when I get back home
Out of town right now working on the racecar