Intake pop/flap sound

[rcb280z]

Do the vacuum test again on a warm engine at idle. No Throttling, just let it idle. I think its going to be fine but want to see the results at idle while not disturbing it.

[siteunseen]

If you pull the oil fill cap on the valve cover and there is no change in idle then you have a vacuum leak. If it stumbles and wants to die then your engine more than likely has "good" vacuum. A vacuum gauge is a good tool also.

 

 

That's how I found one of the dumbest things I've done, so far. 

 

After a simple valve adjustment my car ran worse.  I unscrewed the oil cap and nothing happened.  Did the yogurt cup test, when I blew into the brake booster bung my hair parted from the air coming out from under the valve cover.  I had put the valve cover gasket on upside down, 

they have a straight side and the off-set side.

[Zed Head]

There are several potential air leak paths in to the intake system, from split vacuum hoses, PCV hoses, the EGR tube, gaskets like site mentioned, and more.  Could also be a low fuel pressure, as noted.  But, considering that you've put seven years worth of work into it already, maybe the coolant temperature sensor circuit tweak would be worthwhile.  It will allow you to add fuel to the fuel-air mixture and see if the popping is due to a lean mixture.  Sometimes you can fix everything on the engine and still have a lean mixture, due to 39 year old old parts and/or today's fuel.

 

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

 

Do not adjust your AFM.

[urbtsx]

So we turned the distributor cap clockwise until timing was 18 which is high, but until the pressure reading on the vac gauge was 16.5-17 which apparently is nominal operating psi. Here's a vid with idle and throttling and it seems ok. We've reduced and or eliminated the pop in the afm...not sure if we've solved the issue or not ...?

One website I went to said "on throttle, hitting 0 and then up to 23 is diluted oil or worn rings"

Secondchancegarage.com

https://vimeo.com/142011619

EDIT: forgot to mention we have smelled unburnt gas always when driving it or idling. And now that we've done all this we STILL smell unburnt gas

EDIT 2: we retarded the timing back to where it was before all this, and we got the pop sound. It was only eliminated with advanced timing...

Edited October 10, 2015 by urbtsx

[Zed Head]

As Fastwoman has often noted, a lean miss will leave unburned fuel in the exhaust system.

 

You have made no mention of driving the car (oops, sorry, you did mention driving in the post above.  My mistake).  No offense but that's what really matters.  You don't want to decide that the engine needs rebuilding off of a vacuum gauge reading or some popping in the intake manifold.

 

Not really clear what you're trying to do.  Are you trying to make it sound good so that you can sell it, or does the popping just bother you when you start it to keep things lubricated?  Kind of sounds like you're storing the car as a "survivor" type car.  7800 miles can be put on car in about 6 months, on average.  You're obviously not using the car.

 

The timing adjustment could probably cover a lean mixture.  I'd put that coolant circuit tweak and see what happens.  It only costs about $3 and some time, and is completely reversible.  No wiring cutting needed.

Edited October 10, 2015 by Zed Head

[urbtsx]

If I sound happy it's because we're making progress. We are by no means mechanics, but have general knowledge and passion for this car. It's my dad's and I'm helping him so we can get it running - it drives well, just the sputtering and dying issues I mentioned above; so I can drive for my wedding next year.

Yes it has 7800 miles, it is rarely driven because it can't be enjoyed because of the issues.

Sent from my Commodore 64 using Tap and Talk

Edited October 10, 2015 by urbtsx

[Zed Head]

Have you had the valve cover off?  Inspect the cam lobs and verify that the notch and groove match the zero mark on the pulley.  When you can't find the simple solution you need to go back to the basics.

[Zed Head]

Considering all, it really shouldn't be dying if it's the lean AFM problem.  I've had that issue and the engine will sit and idle forever, and drive with the intake popping, but it doesn't sputter and die.  It just won't accelerate.

 

Even seven years ago the car was 30 years old.  Could have a rusty tank, or even old fuel if you haven't been ablt to drive it enough to cycle through a tank.  You need to confirm that you have good consistent fuel pressure.  It's critical to the EFI system operation.  Build the basic information, like fuel pressure, correct timing, intact cam lobes, notch - groove - timing mark aligned, etc.  

 

It might even be an ignition module problem.  What does the tachometer do while it's popping and sputtering?  It gets its signal from the coil, and gives clues about what's happening there.

 

Gotta measure and record those basics though.  Get them all in one place for a good review.

[siteunseen]

Before I did the coolant tweak my would pop and stumble until 2500 RPMs then pull like normal.  

 

Try partially clamping the return line to build more fuel pressure, making it richer.

[urbtsx]

Quick note- we ran the car for about 5 mins and after shutting off there was pressure in the gas tank - upon opening the gas cap air flowed out quickly.

Sent from my Commodore 64 using Tap and Talk

[Zed Head]

Some people say that a little bit of pressure is normal on the newer 280Z's, like yours.

 

You're focusing on the simple obvious stuff though.  Noises and smells.  They won't tell you enough to solve the problem

[Zed Head]

Didn't mean to demean with the above post.  But many many people have been here trying to solve their EFI problems and they always end up taking the measurements that need to be taken.  There are so many interconnected pieces, and often someone will adjust one to try to help the problem (like your timing adjustment), and end up hiding the true cause.  Volt/ohm meter, fuel pressure gauge, and timing light and you can get the engine to where it should run right.  You might find something off on the way.