fuel check valve question - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
User Tag List

 
LinkBack Thread Tools
post #1 of 3 (permalink) Old 08-31-2019, 09:54 PM Thread Starter
Senior Member
 
Join Date: Nov 2001
Location: Middle TN
Posts: 5,418
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
(Thread Starter)
fuel check valve question

I'm getting the 78 back on the road and found a few things wrong. The PO had the wrong AFM installed so the pump ran whenever the key was on. I've corrected that by installing an AFM with the correct number of connections.


Fuel pressure goes to 40 psi when the fuel pump is forced to rwhen idling causes no change in FP. Clamping the return line causes 60 psi than settles to 55 psi. while the engine is off. Idle FP is only 30 while the FSM says it needs 36 and it drops to 0 when the engine is off. Applying vacuum to the pressure regulator


Is the fuel return line check valve in the fuel pressure regulator. Are there any other likely leak sources besides injectors and CSV? Those test good but the system doesn't hold pressure. I don't think the or CSV are leaking.

Anyone can drive a new car.
junkman is offline  
Sponsored Links
Advertisement
 
post #2 of 3 (permalink) Old 09-09-2019, 06:43 AM
Super Moderator
 
Tony D's Avatar
 
Join Date: Mar 1999
Location: The Island of Luzon
Posts: 40,999
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 300 Post(s)
fuel check valve is in the pump discharge.
The FPR has a soft seat that seals when the pressure drops and stops bypassing.

If you shut the car off and put a clamp on the return line under the FPR, and the pressure stays at 30 or whatever it was while running, then it's the FPR Seat that is weeping and losing pressure making for hard restarts.

If clamping the line doesn't stop it bleeding out to zero, then the fuel check valve in the discharge of the pump is leaking (or your internal bypass is not reseated after you lifted it at 60psi and showed it flowed deadheaded through the relief valve at 55 psi...)

If you need a pump discharge check valve, you can get them separately (not that go in the pump, they go in the line).

If it's the FPR seat, then you change the FPR.

Vice Grips, fuel pressure gauge, and a couple more starts will sort you out.

What has been will be again, what has been done will be done again; there is nothing new under the sun -- that means
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

If I throw a dog a bone, I don't want to know if it tastes good or not. -- Brick Top
Canadians don't get it. Period. End of discussion.
Tony D is offline  
post #3 of 3 (permalink) Old 09-09-2019, 08:23 AM
Senior Member
 
Join Date: Sep 2015
Location: Central FL
Posts: 943
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 218 Post(s)
Quote:
Originally Posted by junkman View Post
I'm getting the 78 back on the road and found a few things wrong. The PO had the wrong AFM installed so the pump ran whenever the key was on. I've corrected that by installing an AFM with the correct number of connections.


Fuel pressure goes to 40 psi when the fuel pump is forced to rwhen idling causes no change in FP. Clamping the return line causes 60 psi than settles to 55 psi. while the engine is off. Idle FP is only 30 while the FSM says it needs 36 and it drops to 0 when the engine is off. Applying vacuum to the pressure regulator


Is the fuel return line check valve in the fuel pressure regulator. Are there any other likely leak sources besides injectors and CSV? Those test good but the system doesn't hold pressure. I don't think the or CSV are leaking.
36 psi engine off pump on (no vacuum). Force the pump to run by disconnecting the start solenoid signal wire (spade), turn key to start. read while holding key in start position (engine will not turn over).


about 30 psi engine on idling pump on (normal vacuum while idling 16-20 inHg)


Dropping to zero is no big deal as long as it takes some time, like on hour. Yes it should hold put it does not really matter. If it drops in seconds then you have a problem.
Dave M is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in













Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome
 


Content Relevant URLs by vBSEO 3.6.1