Fuel Pressure Regulator Question - Page 3 - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #21 of 25 (permalink) Old 06-21-2018, 09:14 AM
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if the diaphragm is ok (can hold up with finger on nub) that only confirms the action to open and close the valve.
the valve can get carboned up and not seal well, that is one failure point, also the vacuum supply to operate it can become defective that is another.
Realize that all this EGR may have nothing to do with your idle issue, its just that sometimes it gets overlooked. If you cleaned it well and applied new gaskets and can confirm there is NO vacuum applied at idle, then its prob not the problem.


I would then move on to other checks of the EFI like the temp sensor, and TPS. The assumption being a A/F mixture issue.
also check ign timing with a timing light, IIRC 10 degrees BTDC is a correct starting point at idle.
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post #22 of 25 (permalink) Old 07-07-2018, 01:52 PM
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I sort have the same issues, popping sounds when pressing the gas pedal and hesitating when accelerating. My fuel pressure at idle is 29 psi and hardly rises when rpm increases, when a put a clamp on the fuel return hose and let the pressure rise to 40 psi the car runs oke. I checked all vacuum lines, everything seems oke, except it doesn't hold vacuum on the vacuum advance. Vacuum is constant at 15Hg. I blocked of the EGR valve, but it didn't help. Next thing I'm going to do is clean the injectors and try to fix the vacuum advance.
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post #23 of 25 (permalink) Old 07-07-2018, 05:48 PM
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Could be a vacuum leak.
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post #24 of 25 (permalink) Old 07-11-2018, 12:48 AM
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Had a nagging problem like this on two previous Z cars. On the first (280z) everything seemed to check out but rough idle and popping on decel sometimes. When I pretty much ran through the list of everything else, I finally bit the bullet and replaced the manifold gasket(s). Problem solved! On the second car (280ZXT) the guy was selling because HE couldn't get the dang thing to idle right. So replaced those gaskets again right off - problem solved. It's a pain, but . . . just sayin'
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post #25 of 25 (permalink) Old 07-11-2018, 01:09 AM
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Quote:
Originally Posted by 6shutr View Post
Had a nagging problem like this on two previous Z cars. On the first (280z) everything seemed to check out but rough idle and popping on decel sometimes. When I pretty much ran through the list of everything else, I finally bit the bullet and replaced the manifold gasket(s). Problem solved! On the second car (280ZXT) the guy was selling because HE couldn't get the dang thing to idle right. So replaced those gaskets again right off - problem solved. It's a pain, but . . . just sayin'
This makes a lot of sense for sure. OP - grab some starter fluid and spray around there to see if there is indeed a vacuum leak there and if there is 6shutr has solved your prob

1978 280z - stock L28 engine - Dallas, TX
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