https://vimeo.com/141010856

Anyone have any input on this sound. I'm not sure if it's the afm flap, or if it has to do with running lean/rich. It's been idling weird. We've replaced the spark plugs, wires, cap, the injectors are all working (I felt the vibration).

Any input greatly appreciated!

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Usually when they pop through the throttle body or AFM, you have a vacuum leak causing it to run leaner.  Check the accordian boot that connects the two, it could be cracked or on crooked.  Look for any other cracked or disconnected vacuum hoses.  If you don't see something obvious, search for "yogurt cup test".  You shove a cup into the opening of that accordian boot where the AFM connects to the throttle body, sealing up the system.  Then you can pull the brake booster hose off and blow into that bung.  Listen for hissing sounds.  

That's hard to identify by the microphone in the Cell phone. It kinda sounds like a " Clack " to me rather than a " Pop " . It almost sounds as if it may be the check valve in the Charcoal Canister. A defective CC valve could make that noise and may cause a vacuum leak that could explain your rough running. Could also be the BCDD valve snapping shut. I don't have one on my car ( TWM Throttle Body ) so I'm not familiar with the noise they make.

 

If you have some time available the weekend we could meet up somewhere and I could have a closer listen. I can bring my Stethoscope and a few other things. I have a 1976 280Z so we can compare the two cars together. Sometimes it's easier to find strange noises with two people listening in different areas.  PM me if you want my contact info.

 

Regarding AFM. It is possible could be sticking and then snapping shut. May need a cleaning with a spray cleaner. CRC makes a MAF and AFM cleaner that works very well. Certainly wouldn't hurt to clean the AFM. You can get it at Lordco, NAPA or Canadian Tire etc.

 

Richard

 

Edit: Had a second listen after reading Cliff's post ( We were replying at the same time... but my Insomnia is way worse than his. It's 2:41 AM on the West Coast!! ) Now I'm not as sure as to what I'm hearing... Cellphone microphones are not as good as human ears. Do check out that AFM to TB connector boot as Cliff suggested. I have a spare one if your's is the pre-1977-78 type.

Edited October 1, 20159 yr by Chickenman

Definitely sounds like AFM pop. Take another video next to the AFM so we can verify thats were its coming from. What ever you do, DO NOT start adjusting on the AFM to attempt to fix the popping. I was guilty of this many years ago and by the time I repaired the real problem I had destroyed my AFM. As mentioned above, look for a vacuum leak. cracked hoses, split AFM to intake boot, etc. Then try the yogurt cup test. Post another video first if you can.

Thanks for the input everyone. I'll get another vid of the engine and see if that helps. I'll check the hoses and I'm searching for the yogurt cup test after I post this.

Thanks!!

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From Fastwoman's post in a thread I found,

"There's a quick way to test for vacuum leaks. When you get your new AFM and boots, first connect up just the boot that goes to the throttle. Then stuff something (I use a yogurt cup) inside the boot opening to block the air. Pull off the vacuum hose to the brake power booster, and attach a hose to the manifold that you can stand to put in your mouth. Then blow into the manifold like you're inflating a balloon. The pressure will build, until you can't blow anymore. Just hold the pressure there, and see how long it takes to dissipate. It should take probably 15 sec or more for most of the air to leak back out. Then pull off the little vacuum hose beside the brake booster hose, and repeat the test. You'll see/hear/feel lots of air coming out through that little nipple, and the air pressure should leak down MUCH, MUCH faster. If there is a dramatic difference between the two, your intake and engine are tight. If the difference isn't very dramatic, you have a leak somewhere."

Here's an updated vid closer to the intake.

https://vimeo.com/141864898

We're going to try the AFM cleaner - as it's the easiest solution so far. If that doesn't help we'll try the yogurt cup test.

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It actually sounds a little worse that plain old lean running from an AFM issue.  Hate to say camshaft lobe but that's a possibility.

 

You didn't give much information, like can the car be driven, is this a new problem, is this car new to you, stuff like that.  That would help a lot.

 

If it's a camshaft lobe it should go away when you disconnect that cylinder's injector.  No more fuel to pop.  Disconnect one injector at a time, rev it up and listen for the pop.  If it's isolated to one cylinder you know where the problem is.  The injector pug clips take some finesse to remove.

 

The video was better, now tell a story about the car.

The car is a 1977 with 7800 original miles. Everything is completely original on the car, except fuel filter, inline fuel filter, spark plugs and wires, distributor cap head.

We've tried adjusting timing. We've searched for vacuum leaks with water spray but found nothing. The gas tank seems to have no rust in it.

It's been an issue since we bought the Z in 2008. It runs well, but as it heats up it idles rough, the intake pop happens, it back fires, sputters and dies sometimes. Sometimes it idles nicely at startup. Pressure builds up in the gas tank and you have to release it through the gas cap and it helps to run smoother.

I hope that helps. Those are the main problems.

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The car is a 1977 with 7800 original miles. Everything is completely original on the car, except fuel filter, inline fuel filter, spark plugs and wires, distributor cap head.

We've tried adjusting timing. We've searched for vacuum leaks with water spray but found nothing. The gas tank seems to have no rust in it.

It's been an issue since we bought the Z in 2008. It runs well, but as it heats up it idles rough, the intake pop happens, it back fires, sputters and dies sometimes. Sometimes it idles nicely at startup. Pressure builds up in the gas tank and you have to release it through the gas cap and it helps to run smoother.

I hope that helps. Those are the main problems.

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That does help.  The pressure buildup in the tank and the symptoms you describe don't fit together though.  Are you sure that it's pressure and not vacuum?  Because the popping and dying could be caused by fuel starvation.  But that wouldn't be caused by pressure in the tank.  What's happens if you just let it run with the cap off?

 

You didn't say anything about actually driving the car either.  And 2008 was a long time ago.  Have you been living with this for seven years?

 

Also, "adjusting timing" doesn't tell where it ended up.  What was the number?  Sorry, but devil, details, all that stuff.

It still sounds like an intake backfire to me. Its exactly how mine sounded when it was lean.What is your fuel pressure? Check it at idle and throttling it.

 

Pull the gas cap like ZedHead says to see if it changes anything. Did this start all of a sudden? Or has it gradually gotten this way? And when you say backfire are you talking through the intake or exhaust? How do the plugs look? Has anyone messed with the AFM in any manor?

 

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.

 

Run the tests everyone wants you to run and post back. Hopefully it shows its ugly face soon. Check your pcv hose and valve too. Could have a vacuum leak there.

Edited October 9, 20159 yr by rcb280z

Just ran a vac test. Will try to get more this weekend. Getting the fuel pressure test kit tomorrow.

Removing the gas cap does nothing at idle.

Sorry for the hasty response. Managed to grab this before heading out.

Here's the result of the vac test.

https://vimeo.com/141966956

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Edited October 10, 20159 yr by urbtsx