duowing

Alright, I need to pressurize my intake or something so I can try and find out where or if I have a leak so I can try and fix my idle. I'm wondering is there any thing that you can make to pressurize the intake, or is there something special I can buy? I really want to track down this leak, although I have a hunch it's coming from my intake manifold.

snwbrderphat540

you got a boost guage with vac reading right? if so whats your VAC read at idle once teh car is warmed up?

duowing

Well I did this, I took a vacuum line, put a valve stem I cut from an old bike inner tube into it, clamped it into the vacuum line. Now I'll just block off the intake part by my MAF and the other vacuum lines, and I got an air compressor so I'll try it out.

While idling and while warmed up my vacuum generally sits around 17-18, but it varies from 20-17. While cold vacuum is way lower than it used to be, and for some reason my vacuum seems to vary alot more now, I'm wondering if maybe I just have a leak from where the MAF meets the turbo inlet hose or something. Since it's smaller, it might be that the hose isn't sitting flush, because my vacuum started being weird right after I switched the ECU/AFM to Z31 setup. I'm also wondering if the AAC valve would make a difference, if there was a vacuum leak before, maybe the AAC was staying open and evening out the vacuum?

hoov100

fire it up and get some starting fluid and spray around vacuum ports, it doesnt seem to work on small ones, but it works on the big ones,

duowing

Alright so I plugged off a bunch of hoses and things, removed my MAF and plugged that part, then I just pulled a vacuum line from the manifold and used my air compressor to start pumping air into the manifold, and you can hear the air leaking out. It was hard to pinpoint exactly where as it was kind of loud and a lot of it from what I could tell, but it wasn't coming from any other vacuum ports, and sounded definitely like it was coming from the manifold mating surface. So I'm pretty sure it's leaking, and that's causing my rough idle, which got rougher with the MAF switch, as the AAC valve would have helped more with the 280ZX AFM/ECU combo.

Anyway when you pressurize the intake should it hold that air, if it doesn't leak? Or would it still gradually leak out through the exhaust or something?

snwbrderphat540

dont do that.... an aircompressor can blow ****. dude, with those vacumme readings you DONT have a leak. give this vac leak thing a rest dude. your fine. stop being paranoid. my car would sit the same way when it ran good tehn when it warmed up it have more vac. thats cause of the air regulator that closes up the warmer it gets out. ur fine. ur fine. ur fine. and w/e vac leak there is, the turbo will make up for it. that possible 1 inHG you have is nothing the turbo cant make up for by just keeping the wastegate a little more closed. dude, ur fine. ur fine. ur fine!!!!! drop it. if the car seems to be running a little wierd look some where else. cause THIS ISNT THE PROBLEM!
ill bet you any money on it.

duowing

I was doing low amounts of pressure, such as about 2-3psi. Anyway I'm mainly trying to figure out why I can't get my car to idle correctly, I know that with the air regulator open that vacuum is alot lower, but it's reading like 10inHG if not less with the air regulator open, with the AFM/ECU setup it'd read around 15inHG when the air regulator is open. It's possible that it's not a leak at the manifolds, but I've replaced so many things with still not seeing improvements.

CHTS, Fuel Injectors, Plugs, Wires, Cap, Rotor, O2 Sensor, Fuel Pressure Regulator, the CAS has been replaced, many vacuum lines, PCV valve, put on a new J-pipe as I messed up my old one when pulling the manifolds, plugged the pop-off valve, swapped to Z31 MAF/ECU, battery cables, battery, alternator, checked/cleaned wiring, and other things I'm forgetting, all of which have never seemed to straighten out the idle or anything.

snwbrderphat540

all engines run crappy when cold. is it really that bad? let teh car warm up before you drive it. driveability wasnt affected so its not that big of a deal. with the swap if its now down to 10 in HG from the original and pretty normal 15 in HG then its just the air regulator. it open causing a good vacumme leak through the intake system and a sped up idle. not much you can do about it but attempt to eliminate it... but then it will run kinda crappy all around anyways when cold.

drr280zx

did you try spraying soapy water on the piping? spray the piping with the engine tunning and producing a little boost. if it bubbles then that is where ur leak is double check anything that is hard to get at and any ribbed piping. other then that just go over every hose clamp in the intake.

and hoov spraying starting fluid works only on a N/A setup with a vacuume leak. with a boost leak you've got too much fuel and not enough air

snwbrderphat540

well he is talking about an idle problem, so thats vacumme and boost prob. but he hits boost fine i garuntee it. and as for vacumme its only abnormally low when cold. try retorquing your mani bolts and if nothing, its something to do with the swap... cause 15-17 in HG at idle is normal when cold. however. my car im having probs with all around... i so angry now.

duowing

I'm also saying too though, that I don't think I should be able to hear the air leaking out as loud as I was. You also have to realize boost will read correctly even with a leak at the manifold. As the gauge is placed before the mating surface the gauge will receive the pressure reading before the air leaks out at the manifold.

snwbrderphat540

no it wont ^^^ if it reads boost thats what its reading. if theres a leak any where it will read it. its how stuff is pressurized. thats like saying if you pressurized a can and stuck a guage at one end and put a leak at the other it would read the same... it wont. it will show its leaking. thats just how air works, now mabey it would be different with some sort of viscous liquid

duowing

My main thing is that after reading threads and crap, I've seen that it's common to have boost leaks that will rob you of power, but a gauge and stuff will not display it because it's a small leak. My main concern is the fact though that when I pressurize the intake is that it sounds like there's a lot leaking around the intake manifold. Now I know air will leak out of the exhaust through the turbo, but the intake I'd think should be able to build up more pressure as well. I mean I messed up my valve cover gasket a little bit the first time I put it on, and it had itself a nice little oil leak occurring, so I'm pretty sure the mating surface getting all scraped up on my intake gasket would cause a problem.

I read a thread on HybridZ about the intake/exhaust gasket. The guy said the gasket with the metal backing around the exhaust ports would have been reusable had it not gotten banged up when removing it. The gasket looked very similar to how mine looked when I couldn't get the intake manifold to line up properly.

snwbrderphat540

you wont be able to get that to work i wouldnt think... you have valves that are open remember those things that open and close to let air in and out.... well maybe, plus, if you put teh gasked on right, its probably not leaking. its more than likely a hose or a small leak since it wont always be air tight, its also going to leak out the TB so that method your using, i really dont think is going to work. you can try starter fluid at idle... spray it around the mani and stuff, if it sucks in the motor should speed up. or brakleen then teh motor will slow down

lww

There are too many ways for the air to escape the intake system on a ZX (or any car for that matter) for a pressure test to be usefull. The open valves, the air bypass on the TB, etc.

duowing

Well mainly I'm thinking that it shouldn't be so loud around the manifold, but who knows. I've replaced so many things and can't get it to idle correctly. I mean it could be a leak somewhere else, I did hear of one guy who's vacuum dropped after he did the swap and it turned out to be the AAC valve I believe was leaking, and got vacuum back after removing and plugging that. I'll give it a try, soon put in my mallory ignition and blaster coil and see if that makes any difference, and eventually redo the intake manifold gasket just to be sure. Although I'll check the torque on it all before I do that.

I've tried that spraying brakleen many times on the manifold and never pulled any results, although then I realized that a lot of it burns out white through the exhaust, so I'll have to buy a new can and spray around the manifold and see if I get any white exhaust.

snwbrderphat540

yup, or use seafoam. only problem is, if it falls on the hot exhaust manifold, it will make white smoke to making you think u found a leak in teh intake and exhaust

duowing

if there's an intake leak, would the seafoam actually leak out through the intake manifold mating surfaces? Or you're just saying to use seafoam in the same way that you'd use brakleen?

snwbrderphat540

yes use seafoam in area's you think u have leaks. its burns whiter than an albino. super smokey, better than brakleen ive used both.... and more. im saying be careful not to spill/drip any onto the exhaust manifold because it will create an illusion of a leak by allowing the seafoam to burn up on the exhaust manifold... which is also bright white.

duowing

Ok, so I've narrowed my issues down. The only problems the car seems to have are hesitation/running lean(at least I think lean) during cold, when fully warm if I turn the car off and let it sit for 5-10+ minutes the car will have a really crappy jumpy idle for a few moments, until I start driving or keep the revs up for like 10 seconds or so and my idle is generally crappy.

One thing I've noticed is that the car starts up fine from a cold start, and my vacuum reading will sit around 13-15inHG which seems about right since the air regular is open. The car will drive and go with no problem from a cold start as well. After a few moments, I'll come to a stop and I'll notice the vacuum has dropped to about 11inHG, this is when I notice that even though the air regulator is still open the idle also drops to a little below 1000. Now it gets a little random, as sometimes the car goes fine and other times I get a hesitation, or sometimes real bad hesitation which seems like the car is running real lean for a few moments. After a little longer, I'll feel when the air regulator finally closes and the throttle gets more responsive, and then I'll have no problem, but my vacuum will vary about 2-3inHG every time I slow down to a stop. I'm thinking maybe my AAC or VCV could be the cause of this? Maybe the vacuum line I have directly connected to the AAC is collapsing and allowing it to open, I'm not really sure. I'm gonna soon plug off everything, and leave the air regulator, but if you guys have any suggestions let me know.

I'd assume it's probably not a manifold leak, also considering every so often I get out the Brakleen and spray it all over the manifold with no change in speed.

Also quick question: How or what does the vacuum check valve do? I know there's one on the line that goes from the intake to the VCM.