Strange vacuum leak sound

[TomoHawk]

Higuys,

On my 78 280Z, I can hear what sounds like a small vacuum leak or hiss from the area around or under the throttle body, but I am having trouble pinpointing it. The hissing could be coming from the BCDD area under the throttlebody but I prefer not to take the whole thing apart unless it's necessary, and thought that someone has had a similar experience with a solution. AFAIK, there aren't any vacuum taps under there.

thx

[geezer]

I had an old toy stepthescope (did I spell that right?) with a length of 1/4" hose on it that was great for finding vacuum leaks. You could just bring it to someone who will gas check it.

[justaZcarguy]

Tomohawk, this is going to sound like a dumb question, but have you tried the starter fluid / carb cleaner trick?

~Brian

[TomoHawk]

Nope, I didn't try spraying flammable liquids on the engine near the coil & dizzy. :eek: with the fan blowing like crazy.

Since I want to service the fan clutch, I could listen with the fan removed. that should give me a minute or two to listen for the leak.

thx

[justaZcarguy]

Oh Tomo, where is your sense of adventure????

Plus, you forgot to mention the headers dangit.

I've always been leary of that same thing, but have never had a problem. If you have arc outside the cap, them that is another issue. But still, better safe than fire marshall Bill.

I can't say that I have had that vac leak in that same area, but I guess that I would try the steth idea, is it running rough at all?

[twsutt]

I hate to sound stupid, but couldn't a cracked rubber air intake hose (either before or after the AFM) make a sucking sound?

[geezer]

Go to a tire shop who uses nitrogen instead of air and have them direct a narrow stream of gas over the suspected area. Make up your own adapter & hose and have a vacuum gauge setup in plain view under the hood. Makes quick, safe vacuum leak detection a breeze.

[sblake01]

I hate to sound stupid, but couldn't a cracked rubber air intake hose (either before or after the AFM) make a sucking sound?

Not stupid at all. In fact it's a very common problem with this nearly 30 year old rubber to crack in between the folds. I replaced mine about 8 years ago that is the one right in front of the throttle body but I don't think Nissan has them anymore.

[twsutt]

I know that it's possible for them to crack between the folds, I just don't know if the engine pulls air in strong enough to make the mentioned hissing noise that Tomo is talking about. Besides, I'm sure that was the first thing that TomoHawk checked. Right?

[TomoHawk]

I put on new rubber hoses about a year ago. Maybe there is a small leak if the hose isn't sealed up perfectly.

[=Enigma=]

Disconnect the fan belt, find a smoker, bum a cigarette, light it and hold it near the suspected area. If there's a leak you will see the smoke gravitate towards that area. Works for me.

Oh yeah, Aloha from Oahu!!!

[DatsunZsRule]

Not stupid at all. In fact it's a very common problem with this nearly 30 year old rubber to crack in between the folds. I replaced mine about 8 years ago that is the one right in front of the throttle body but I don't think Nissan has them anymore.

The A.F.M. Boots are still available through Nissan. I had to replace mine last year and they had them