TwinTurbo.NET: Nissan 300ZX forum - Almost done with plenum pull - caught dampener failure
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Subject Almost done with plenum pull - caught dampener failure
     
Posted by 300NASeattle on July 01, 2018 at 5:37 PM
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Message I pulled the plenum to replace the fuel rail isolators that were leaking air into the lower plenum. Cleaned a bunch of things,

deleted a lot of devices,
* EGR
* throttle body coolant hoses
* PRVR

replaced many things,
* isolators
* injector o-rings and pintle caps
* fuel lines and fuel filter
* intake compression bushings
* drivers side PCV valve - passenger done before
* all PCV hoses that were not easily reachable before plenum pull
* all vacuum hoses
* spark plugs even though the old ones looked fine
* Knock sensor harness to original location
* Coil Pack connectors - depinned most but had to crimp a few new wire connections
* FICD, AAC, passenger VTC connectors

and learned a lot more about the Z than I could just from reading tt.net posts. I was a little nervous about the way I replaced the fuel injector O-rings after reading a few places that talked about twisting the injectors side to side as you seat them into the fuel rail by hand (specifically from the Z32 Wiki). I put oil around the entire O-rings and then used a small 1/2" wooden brush handle to gently push the injector into the 1995 NA fuel rail by squeezing the the handle and the fuel rail on both sides of the injector. They mostly popped in except one that required a little more force for it to seat. This made me nervous after I read the statement,

"Do NOT try to force the injector in. It does take a bit of effort, but use only your hands (maybe a towel for better grip)--tools are not necessary and under NO circumstances should you try to "draw in" the injector by tighting the cap screws down on top of it. This will almost definitely cause an o-ring to pinch and cause a fuel leak."

This was after I had installed the plenum. Nothing in the FSM had mentioned this.

Since I was nervous about this I wanted to pressurize the fuel rail as soon as possible to see if I could smell any fuel. I didn't smell anything so continued to do the final reassembly and after getting the balance tube installed I did smell gas and thought I was going to have to order new injector o-rings and pull the plenum again to replace them. That was when I noticed the fuel leaking out of the vacuum hose of the fuel dampener that I had not connected yet. Thank god - just a bad fuel dampener :).

The bad thing is that if I had not been nervous during installation and pressurized the fuel lines I would have never found this or suspected that fuel could leak past the dampener's diaphragm and get pulled into the plenum.
The good thing is that with all the deletes I did, I could probably pull the plenum back off in under an hour. In fact, I had to double check that I wasn't missing something during reassembly because there seemed to be too few connections.

In the end it amazes me that the car only hesitated sometimes when warm, with extra fuel getting dumped in from the dampener, and air from the fuel rail isolators. I ordered a new fuel dampener and now need to wait another week to start it up. And now I am second guessing my decision to only purchase the dampener and not the regulator. I hate replacing good parts but if I didn't know about the dampener's ability to leak fuel into the plenum then what don't I know about the regulator? And with 150K miles, maybe it is time to replace it anyway ... ordering the fuel regulator as soon as I post this!

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