Dumb Question: Are Fuel Dampers adjustable?

[Zed Head]

4 hours ago, Muzez said:

When the car is running, fuel is only at ~25PSI

 

50 minutes ago, Muzez said:

I did a compression test last night. At the start of the test after sitting idle for about a week or two, the inline gauge was reading at 10PSI but jumped back up to ~35PSI at the conclusion of the test. Just checked in a few minutes ago and its back down to 25psi again. 

The fact that it hit 35 shows that the FPR is working.  It blocks fuel flow until the design pressure is reached.  The leak down to 25 isn't too bad, the systems always lose some pressure when the pump is not running. 

The 25 psi when the engine running is too low.  When you try the pump check test make note of how fast the pressure rises.  You might have just a weak pump or maybe a clogged filter.  Pressure should rise to 36.3 within just a few seconds.

[Muzez]

1 minute ago, Zed Head said:

 

The fact that it hit 35 shows that the FPR is working.  It blocks fuel flow until the design pressure is reached.  The leak down to 25 isn't too bad, the systems always lose some pressure when the pump is not running. 

The 25 psi when the engine running is too low.  When you try the pump check test make note of how fast the pressure rises.  You might have just a weak pump or maybe a clogged filter.  Pressure should rise to 36.3 within just a few seconds.

Will give this a try and report back. I think I have a spare fuel filter in the garage I can plug in to test that part asap. 

[Zed Head]

You could just disconnect the outlet of the filter and do a volume test.  That will tell you something.  There's a test described in the FSM.  Remove the hose, put it in a container, run the pump for a certain time, you'll have flow rate.  If it's low, replace the filter and try again.

I thought there was a rate test but there's not, that I can find.  Must have seen it somewhere else.  Anyway, when the flow is good, it's obvious, when it's not, it's obvious.

Edited October 29, 2021 by Zed Head

[Dave WM]

1 hour ago, Zed Head said:

You could just disconnect the outlet of the filter and do a volume test.  That will tell you something.  There's a test described in the FSM.  Remove the hose, put it in a container, run the pump for a certain time, you'll have flow rate.  If it's low, replace the filter and try again.

I thought there was a rate test but there's not, that I can find.  Must have seen it somewhere else.  Anyway, when the flow is good, it's obvious, when it's not, it's obvious.

I thought I read that same thing about the flow rate in the FSM. its got to be somewhere if we both remember the same procedure.

[Patcon]

I believe the mechanical pump has that procedure. I don't know about the efi pump

[EuroDat]

I don't know of any flow rate test in the FSM, but I made a simple write-up when I was having trouble with my EFI fuel system. There is a simple flow test in it. The document is in the Knowledgebase section on this site.

I haven't checked, but there could be something on the atlanticz site tech tips section. There is a lot of info on that site if you brouwse through it. It's easy to come across something and forget where you read it.

Looks like the OP has a Bosch 044 or similar aftermarket fuel pump. The 044 is a very good alternative to replace a defective original pump. It's also the pump Bosch reccomends since theis original pump is NLA

You can find them from €70 upwards. Back in 2017 I paid €35 * €4,95 shipping.🤔 That is inflation....

 

Edited October 30, 2021 by EuroDat
Added 044 fuel pump info

[cgsheen1]

 

On 10/29/2021 at 6:27 AM, Muzez said:

77 280z. Apologies for the crusty picture. Is the circled object at the top of the screen a damper or a regulator? And if its a damper, is it adjustable? 

Struggling with fuel pressure. I have an in-line gauge installed after the fuel filter. When the car is running, fuel is only at ~25PSI (compared to 34-36PSI expected). I took apart this whole section to remove some of the rust and replace the hoses, but I can't remember if I messed with the bolt on the top of the damper (and if it matters).  

 

The Fuel Pressure Regulator is supposed to maintain a fuel pressure differential of 2.5 Bar (~36.3PSI) between the fuel rail and Intake Manifold Pressure. So on a running EFI engine, fuel pressure is not a static value - it (constantly) changes with manifold pressure. If you have 10 PSI of vacuum, the FPR is going to pull 10 pounds of fuel pressure. Likewise if you're making 10 pounds of boost it's going to add 10 pounds of fuel pressure.

To verify the correct fuel pressure on a running engine you need to know the value of both fuel rail pressure and MAP (manifold absolute pressure) at the same moment in time.

The fuel damper is installed to smooth the output of the stock fuel pump which squirts fuel in pulses rather than a steady even flow. Injectors work better with a steady even flow. Must be a little important, and nearly every modern EFI car has one too (probably much more critical with todays emissions engines than it was back in the day). That's if it's still working properly after 40+ years...

The stock FPR held fuel pressure even when the engine shuts down, so the fuel pump must also check fuel flow back to the tank. I've noticed that most aftermarket FPR's don't, and that also includes most adjustable FPR's.

Did you ever say why you think your fuel pressure is a problem?

[AZDatsun]

If you have an aftermarket fuel pressure regulator they supposedly have build in dampening I am specifically referring to aeromotive.  I am not sure how it compares to OEM though.  I would assume the diaghram on 40 year old ones would be close to shot but maybe not

[Muzez]

On 10/30/2021 at 4:14 PM, cgsheen1 said:

 

The Fuel Pressure Regulator is supposed to maintain a fuel pressure differential of 2.5 Bar (~36.3PSI) between the fuel rail and Intake Manifold Pressure. So on a running EFI engine, fuel pressure is not a static value - it (constantly) changes with manifold pressure. If you have 10 PSI of vacuum, the FPR is going to pull 10 pounds of fuel pressure. Likewise if you're making 10 pounds of boost it's going to add 10 pounds of fuel pressure.

To verify the correct fuel pressure on a running engine you need to know the value of both fuel rail pressure and MAP (manifold absolute pressure) at the same moment in time.

The fuel damper is installed to smooth the output of the stock fuel pump which squirts fuel in pulses rather than a steady even flow. Injectors work better with a steady even flow. Must be a little important, and nearly every modern EFI car has one too (probably much more critical with todays emissions engines than it was back in the day). That's if it's still working properly after 40+ years...

The stock FPR held fuel pressure even when the engine shuts down, so the fuel pump must also check fuel flow back to the tank. I've noticed that most aftermarket FPR's don't, and that also includes most adjustable FPR's.

Did you ever say why you think your fuel pressure is a problem?

@cgsheen1 I have been having issues with the car on start up (sputters at start) and when I get on the throttle over 3K RPM where it feels like it is running lean, like it wants to go faster but is held back. I checked the fuel pressure gauge at lunch today and it has some fluctuations and is running low (see below).

I drained the tank earlier this year to replace a hose between the tank and the pump, and there was a little sediment that came out of the tank. I am going to drop the tank this winter and see if it needs a recoat. In the meantime, I was trying to troubleshoot some of the other parts in the system. I was going to replace the filters in case there was build up in the filters and I need to make sure that there is no crimping in the hose that got replaced earlier this year (it was pretty tight to thread it through the bulkhead). 

 

[siteunseen]

I haven't read the whole thread but a trick I learned was to pinch the return line to the tank and see how it runs. I used some needle nosed vise grips with rubber sleeves over the grooves to not cut into the hose. Anyhow, my car ran better. That raises the psi on the fuel rail then to the injectors. Your injectors may need cleaning or the filters are clogged like you say. There's other things that could help.

If you haven't already, a clear filter right out of the tank before the high pressure pump will let you see sediment that could be in the tank. Here's a good write up on putting a Fram G3 before the pump.

https://www.atlanticz.ca/zclub/techtips/fuel/g3filter/index.htm

[siteunseen]

Oh yeah, another free and easy way to check the tank is remove the metal filter up front behind the radiator keep the fuel from draining out when you pull it, use your thumb or something on the bottom and sit it in a clear glass jar. Let it drain and see if the gas inside is all funky looking. Then tap it down on a white rag to see what comes out. 

"Shade tree mechanicus"