Check Valve? Fuel delivery . . .

Ricks911s · 05-01-2008, 04:30 PM

Is there a way to determine if the check valve has gone bad? Here's my thinking. I replaced my fuel pump and have completed several projects including some big oil leaks. In connected everything back up and checking whether the fuel delivery is working properly, here's what I did/double-checked.

(1) Replaced fuel pump and line between gas tank and fuel pump
(2) Removed injectors and placed in bottles (to check fuel flow)
(3) Lifted air sensor plate with injectors out . . . I hear the fuel pump working. But nothing coming to the back.

Thinking I've narrowed it down to the check valve . . . but when I disconnected the check valve side after completing (3) a little bit of gas was dripping out. So I know the fuel is going through the fuel pump. I don't think there is anything blocking the line . . . Totally confused as I see no other possible problem unless there's not enough pressure???? Will CIS pressure guages be able to determine this?

73 degrees here in Sacramento. Man, do I want to do some top off targa driving.

Thanks for help/advice if you have any.

911quest · 05-01-2008, 04:46 PM

What did you use for the fuel line between the tank and the pump? Could it be pinched?

Ricks911s · 05-01-2008, 04:51 PM

It's not pinched. Plus the fact I'm getting fuel on my check return valve reflects it's not pinched.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Ricks911s

Is there a way to determine if the check valve has gone bad? Here's my thinking. I replaced my fuel pump and have completed several projects including some big oil leaks. In connected everything back up and checking whether the fuel delivery is working properly, here's what I did/double-checked.

(1) Replaced fuel pump and line between gas tank and fuel pump
(2) Removed injectors and placed in bottles (to check fuel flow)
(3) Lifted air sensor plate with injectors out . . . I hear the fuel pump working. But nothing coming to the back.

Thinking I've narrowed it down to the check valve . . . but when I disconnected the check valve side after completing (3) a little bit of gas was dripping out. So I know the fuel is going through the fuel pump. I don't think there is anything blocking the line . . . Totally confused as I see no other possible problem unless there's not enough pressure???? Will CIS pressure guages be able to determine this?
73 degrees here in Sacramento. Man, do I want to do some top off targa driving.

Thanks for help/advice if you have any.

Rick,

You need a CIS fuel pressure gauge to help you diagnose your problem/s:

1). Check the residual pressure in the your fuel system. Fuel accumulator and check valve play a big role on this.
2). Measure the system pressure. Insufficient or low pressure could cause the injectors not to open or spray mist uniformly.
3). Determine the pump's flow rate (liter/min.) or pressure (65 - 75 psi).

Avoid guess work and it will save you a lot of aggravation and downtime. Good luck.

Tony

Ricks911s · 05-02-2008, 02:20 PM

Thanks Tony. I'll perform the CIS tests. Just to clarify . . .

To test pump's flow rate can I simply disconnect on the check valve side and "catch" the fuel in something where I can measure flow rate? Can you give some more advice on how to perform this test -- specifically how to test pressure AT pump? (Or is pressure taken with where CIS pressure checker thing is?).

Stanby for results. . .

Ricks911s · 05-02-2008, 02:41 PM

Okay . . sitting here on my laptop with gauges all hooked up. And results . .

NO PRESSURE

So with the help of Jim's CIS primer and working backwards my problem is somewhere between the Fuel Pump and Fuel Distributor. It crossed my mind that the control plunger might be stuck . . . but I think I stuck my small finger and felt it moving freely. Thoughts?

gtihop · gtihop's Garage

check the connectons on the pump- could it be wired backwards? also check the line from the tank to pump-make sure its not kinked or otherwise blocked.Can the check valve go in the pump backwards?

Ricks911s · 05-02-2008, 02:56 PM

Will triple-check electrical connections. But I hear it working when I jumpered pins 87a and 30 to check pressure. No kink in line from tank to pump as I replied to 911quest.

I'll activate pump and try to capture fuel over ~10-15 seconds to obtain liter/min reading.

I suppose a line between pump and fuel accumulator/filter could be blocked. But it was fine only a month ago. So that doesn't figure to me.

911quest · 05-02-2008, 03:32 PM

Rick I have personally on a few occasions had a fuel line that didn't look pinched but was just enough to allow a trickle of fuel thru the pump. With that being said I would remove the line from the tank to the pump and make sure gas runs out. It is also possible that the tank outlet is clogged did you drain all the gas before you put the pump on? Maybe all the crud is in the bottom of the tank now. Just throwing out some suggestions.

Ricks911s · 05-02-2008, 04:02 PM

Thanks 911quest. If I came across as blunt, I apologize. Not being able to drive in this 75 degree weather is shortening my nerves. This stuff is suppose to happen in the winter.

Took your advice and pulled line from tank to pump. My tools took a short swim in the gas that POURED out for a couple minutes till it evaporated.

Disconnected hard line that runs from pump to fuel filter/accumulator to test that fuel was running through pump. Jumpered and activated pump. Nothing.

Re-installed pump (without check valve) to check if fuel going through pump and check valve was the issue. No fuel still. Problem not check valve.

Electrical connections okay.

Took out fuel pump and inspected for any other issues. None found.

Looks like I'll have to order a new pump unless anyone can give advice on how to bench test. Bleh. These little cars get expensive.

911quest · 05-02-2008, 04:05 PM

Rick I had a new bosch pump do this to me once on a 77 brand new out of the box nothing the thing was no good.

boyt911sc · boyt911sc's Garage

Rick,

My suggestion is not to replace CIS component/s unless verified to be defective. If I were you, I'll do the following:

1). Remove the FP from the car and bench test it. Apply 12 volts to FP. I would also measure flow rate or delivery pressure of the FP. You will need a simple set-up to perform this test. The results will tell you whether the FP is good or defective. NO guess work.

2). If the FP pass the tests, install it back and proceed for additional testing. Draw gasoline from the tank using your newly tested FP and measure the pressure or flowrate before the fuel accumulator. If you cannot get the values you obtained from step #1, two possible causes: (a). There is pinch point or restriction along the fuel line;(b). There is insufficient flow of fuel to the FP.

If you don't have the patience and time to do this tedious work, replace your FP. But if your problem is flow of fuel from the tank, buying a new FP will not solve your problem. Investigate the root cause of the problem not the symptoms.

Tony

Ricks911s · 05-05-2008, 09:21 AM

Thanks for the reply Tony. I test things as far as I know how to . . . so I'd appreciate an elaboration on your suggestions.

With respect to (1) how does one apply 12V to bench test the FP? I've already jumpered pins 87a and 30 and hear that power is getting to the FP while it's in. So if it's a simple question of whether or not the FP is getting power, I think I can safely deduce that yes, it is. If it's a question of how much power, or something more specific, I'm unsure how to proceed. Second, I'm unsure how one would measure "flow rate" or "delivery pressure". As I mentioned, fuel is not passing through the pump. This obsevation coupled with my belief that 12V is getting to the pump leads me to believe I have an issue with the pump "pumping" sufficient pressure. In fact, it appears there is no pressure (at least at the fuel distributor as CIS cold pressure check indicates). Phew . . . okay so let me back up with a series of logical steps/deductions to reflect where I am.

1) Replaced fuel pump (FP)
2) Replaced fuel line from tank to FP
3) Pushed up on AFS (air flow sensor) with injectors pulled so I could verify fuel was getting to the back . . . there was NONE
4) Posted here . . . thought maybe check valve was the problem as this pump worked before I pulled it out.
5) Jumpered pins 87a and 30 to verify CIS control pressure(s) were within spec before firing the car up . . . Results -- NO PRESSURE
6) "Listened" (I know, not very scientific) to FP while brother-in-law activated jumpered FP relay swith. . . .Results -- Could hear whine of fuel pump as if it was trying to work.
7) Checked line between tank and FP . . . gas came POURING OUT. Looks like I'm okay there.
8) Pulled line on the other side of the FP to see if fuel was getting through the pump. Results . . . fuel wasn't getting through. Not a drop.
9) Pulled check valve to see if fuel could get through without the check valve. Still no fuel.

So you see, I just don't see how the problem could be anything other than the fuel pump. Now if there is a way to test it to make ABSOLUTELY sure, I'm more than open on doing that.

Thanks Tony or anyone else that can help.