Hello everyone. may have a slight issue. ive got a ls2 with l92 heads and truck intake. I noticed yesterday that while idling or giving it some rpm, the center of the intake is getting sucked in. Ive got the pcv hooked up right from the left valve cover to top of the intake. but the only thing I can think of that might be wrong is that I have the right valve cover pcv blocked off since I don't have a inlet on my cai yet. not sure if that could be the issue or not though. Thoughts?

 

 

ill get a video tonight, but all I know is the damn thing was moving

 

It sure as hell is possible. Usually they flex the other way, outward under pressure. But if it can flex out, it can flex in. It's nylon, after all. Even a sheet metal intake can do that. Wasn't there someone recently on this forum complaining about a sheet metal intake "vibrating" with perceived pressure (or vacuum) pulses?

OP, it would be good to monitor MAP. Do you have a scanner tool? May even be able to check on a handheld at Autozone.

 

yeah I work at a gm dealer so I have a tech 2, but the map sensor was I believe around 74kpa at idle, I'm going to double check that number tonight and use a vacuum gause also.

 

Agreed. Engine vacuum isn't going to suck in an intake manifold.

Now I've seen video of some cheap *** intake tubes sucking in, because they're **** material..

So OP are you talking about the intake MANIFOLD or intake tube? If you're talking about the tube then I'm guessing it's a cheap setup that has a rubber tube instead of plastic or metal.




Completely and totally different, sheet metal flexes easy.

 

its the center if the intake. I guess I forgot to mention that its an l92 truck intake

 

I gotta see this. Something is way off here and I think seeing it may help.

 

no modifications and the center of the intake on top by where the pcv from the left valve cover plugs into. I tried unplugging it with no change, but I have the right side valve cover temporarily plugged in front, the one that goes to the intake tube

 

Post video

Anyone around you have a vacuum gauge you could hook up? Or a vacuum pump, those usually have a gauge

 

 

at idle vacuum is at around 8-10in hg

 

Nothing wrong with that and 8-10 is fine. Hook up the PCV system and forget about it.

 

 

When I was revving, vacuum was going to around 20in hg but that’s what I was thinking, usually cars I work on vacuum idles around 17in, so why is the intake flexing

 

Because it's thin plastic

20 in hg on decel is no big deal either.

Other intakes may do it also but people don't normally stare at the intake and look for flex, if it's a problem it'll crack and you'll have a vacuum leak. So either forget about it or put a different intake on it.

 

 

I would man, when I had a turbo car with a boost gauge my vacuum was always 12-17, sometimes it would spike closer to 20 on hard decel with the throttle closed. I bet all of those intakes do that and nobody notices.

It is super weird though and now the next time I have a truck in the shop that has one of those intakes I'm gonna watch it for doing that if I can remember by the next time one comes in. If that intake was as common as all the other truck intakes we probably would of heard about that flexing by now, you may have started something here..

I kept picturing the more common ls intakes, most are curved on top and wouldn't flex, that one being flat on top isn't as strong, so now I'm a believer in it flexing, thanks for the video.