Vacuum??

[sjbsuperman1425]

So I am pulling TERRIBLE vacuum lately.. Sometimes It will be around 18-19" and others (like 10 minutes ago) it is struggling to get 15". I tightened some hoses down, checked for crack hoses, listened for them and nothing. Everything seems to be in order.

I did put RTV on the throttle body and the rear manifold (w/ the brake booster and FPR connector) and have RTV on the turbo elbow that connects to the hotpipe and has three bolts. Everything seems to be ok. It has trouble starting up but once it gets going it runs great, boost 10psi fine and pulls hard.

I did replace the head gasket (as some may know), but I doubt that if the head studs were loose (retorqued like 3 times) it would cause this problem, since I'm not burning coolant, oil, or mixing the two. There isn't anything other than a vacuum or boost leak that can cause this correct? I replaced my intake gaskets as well but i doubt those are leaking, as If i disconnect the nipple on the IC pipe, the car wont even idle..

Any ideas? This is driving me crazy. I'm thinking of just redoing the RTV with High Temp silicone thats sensor safe on the throttle body, back of manifold, and the turbo elbow. Thoughts, because I'm out of them..

[boost_boy]

It's not your T-body. What did you do with the vacuum nipple under the T-body? Did you plug it or did you let it just be tinking it doesn't do anything? The CA doesn't have many vacuum outlets, so it should be fairly simple to source a vacuum leak. The only other way your vacuum drops is if you've cracked some pistons.

[ca18detgabby]

spray some carb/choke cleaner on your vac connections and listen........

Have you checked to make sure your IACV isnt dirty?

[sjbsuperman1425]

i dont think I've put the engine through enough abuse to have the pistons be cracked..

I've been using starter fluid to check some of the vacuum lines, the throttle body gaskets and things like that. Someone suggested I leak test the intercooler. As for the port on the TB, that is plugged off and not leaking. I adjusted the TPS a bit and it helped quite a bit with the driveability, but vacuum is still around 15-16", which isnt' bad, but isn't what I would like i guess.

Im going to redo the gasket on the turbo elbow that connects to the Hotpipe and see if that helps, then clean the IACV from there. I think I'm going to bump the fuel pressure up a bit as well since my plugs are a tad bit white.. But the car runs great other than crappy vacuum..

[sjbsuperman1425]

well the turbo elbow to hotpipe had a good seal. So i put more RTV on it and put it on. I did notice the air filter was slightly coming off the MAF which is ghetto rigged by electrical tape.."re-taped" that up. I'm going to fire it up when I get home from an interview and see what happens. I'm thinkign I may take the IACV off, clean it, and then put RTV on that as well. Im going to check the vacuum lines for the boost gauge and such for more cracks or something "logded" in them, since the car seems to idle and drive great, but with low readings..its very odd..

[boost_boy]

It doesn't take massive boost or heavy abuse to crack pistons, but we'll avoid that subject for now and in your case. I would also chack the gauge itself. I've experienced this on an autometer gauge on a customers car. The dang thing said the car was only seeing 2psi of boost inder fool throttle, but the engine was fuel cutting like crazy. Turns out, the gauge was faulty and when replaced, the car was running 18psi of boost on a freshly bult engine .

[sjbsuperman1425]

the gauge corresponds with my HKS boost controller reading..so i'm guessing its pretty good. I got it to idle better now, still not the same. I did a compression test and got 90psi across the board, but this was with a "loan a tool" tester from Autozone for $40. also did a leakdown test which turned out very good and the car still has tons of power when boosting.

What i did find out is that I am running a bit lean and am burning quite a bit of oil, most likely from a blown turbo..It comes and goes so i'll keep an eye on this.

Would a vacuum leak cause a lean condition?

[sjbsuperman1425]

well last night I went on a drift expedition to relieve my stresses and it boost and go sideways just fine. But after doing this, I developed an exhaust leak from between the manifold and turbo..POS eBay flimsy gaskets and hardware. I also noticed there are only like 3 bolts holding it on! So I'm not gonna drive it much until I get this fixed..

As for the vacuum, its still at 15-16" on cold start, which my cold start is a POS..I'm going to turn up the fuel pressure a tad bit while I'm doing the turbo gasket and also redo the IACV with some RTV sensor safe silicone.. I've had that thing off alot and never changed the gaskets so this very well could be it even tho the carb cleaner trick test clear on it..

[sjbsuperman1425]

could any of the idle components either leaking or not working properly cause a low idle with an idle hunt and bad vacuum?

[boost_boy]

Find a competent compression tester and re-test that puppy. 90psi across the board sounds tired and hopefully the rings were put on correctly.

[sjbsuperman1425]

i never touched the bottom end. I've only done the head gasket and ARP's. 90psi sounded low to me, but i did it when the engine was cold and I think that might be the reason for the low readings.

[sjbsuperman1425]

well after adjusting my idling and fixing my turbo-manifold gasket, my vacuum seems to have returned to normal..for now. I'll update with a Video (i've know i've been promising one for awhile lol) asap.

[davidricardo86]

the gauge corresponds with my HKS boost controller reading..so i'm guessing its pretty good. I got it to idle better now, still not the same. I did a compression test and got 90psi across the board, but this was with a "loan a tool" tester from Autozone for $40. also did a leakdown test which turned out very good and the car still has tons of power when boosting.

What i did find out is that I am running a bit lean and am burning quite a bit of oil, most likely from a blown turbo..It comes and goes so i'll keep an eye on this.

Would a vacuum leak cause a lean condition?

I'm sure we've all seen this before but for a few of those that haven't, here's what affects idle on the stock setup.



Those compression numbers seem awfully low, try a different gauge.

Vacuum leaks in a Mass Airflow electronic fuel injection system will have a greater affect on overall driveability versus a speed density system (lucky me, i still have my stock setup). A vacuum leak will cause a lean condition. A vacuum leak can also cause the Idle Air Control Valve to close, resulting in a idle drop or idle hunt. If the IACV is malfunctioning, idle quality will suffer.


My idle does a similar thing on cold starts though. The very first time i start the engine, idle goes to 700-800rpm, it drops and suffers to fast idle, then finally it just shuts off. I then start it a second time and fast idle works perfectly, slowly the rpms drop to normal idle and everything works fine. Occasionally, at a stop light, stop sign, or going through a corner with the brakes applied, idle will drop so low and hunt, causing the engine to shut off while going through the corner (very annoying) or while I'm waiting for the light to turn green. I haven't tried replacing my IACV but i did clean and resistance tested it when i rebuilt the engine (i wish i could test it dynamically). I want to buy a new one to test this theory, otherwise I'm suspecting my idle problem could be vacuum related as well.