VERY weird vacuum issues

[RipperXX]

Ok so I FINALLY got to go home on leave with the intent of bringing it back to Oklahoma, (car was sitting in Georgia). Anyway sometimes I will start the car and it is pretty much near perfect, idle around 18-19inches of vacuum and hit 20-21 inches on deceleration. Then other times, I will start it and it will have at worst I have seen around 6inches and idle rough, sometimes improve to about 10inches, but even during deceleration it wont go but maybe to 11. It varies with each time I start her up but stays fairly consistent while driving it, however I think once did go from crap to near perfect.


It's got me completely stumped whatever it is, I boost tested the car to 21psi at which point my stock 1G BOV started to open. I can post a log of some of my LTFT tuning if anyone wants to see it cause theres something I thought a bit odd anyway when comparing the 50hz sliders to the rest. the 50hz is pretty far positive while all the others are a little negative.



I also considered the MAP sensor for the boost gauge being bad but considering it actually idles worse the lower the reading I figure it is fine. Oh and I am still on stock cams.

 

[Boost92awd]

How many times has it done this? What was the weather like when this happened? Have you looked for vaccum leaks when it does this?

 

[habitatguy187]

Mine does something very similar to this, although at worst it will idle -12-14. I haven't found anything really, maybe a check valve of some sort?

 

[RipperXX]

Would the check valve from the brake line do this if it were stuck open?



it seems to have better vacuum most of the time when I first start it when it's completely cool then gets worse as I drive it more. And as far as how many times it has done it... pretty much always it's just that
I thought it was related to something else so I didn't post about it. but since I fixed the other problems and boost leaks and it's still doing it. I have no idea what to even look at to fix it. I did boost checks out the butt and found even a little one at my FPR, fixed them all and still doing it so I have no idea.

 

[habitatguy187]

Yeah I had a tiny boost leak on my fpr too, swapped mine out with a buddies and same thing so I figure it's ok as tiny as it is. My car is the opposite though, it will only do it when I first start it, then get normal as I drive it around.

 

[boyd0069]

could be a number of things i currently have a 27 lb vaccum with a 95 lb compression in all cylinders figure that out w/blown turbo but my mitsu made it 700 miles with a bad engine thank you 4g63t

 

[anteversion]

this is probably not a vaccuum issue like you think it is. Im sur that is probably and mecanical/electrical problem, so when the problem occurs, the engine is running badly and then the vaccuum drop

 

[RipperXX]

See I was thinking it might be timing related, BUT if that were the case then how could it be about where it should to be to basicly perfect?

And if the ignition timing was off I would think I would have detonation like crazy going WOT. (if it were to advanced anyway) And I don't understand how anything electric could cause it. Unless it was something like the ISC valve stuck open? That is seriously the only thing I can think of.







Edit: Also about the idea it being electrical, I added some grounds of which I even soldered the connections and all the factory grounds minus the exhaust ground are still on the car and fine as far as I know. So anyone else think the ISC COULD even do something like this?

 

[RipperXX]

Yeah I had a tiny boost leak on my fpr too, swapped mine out with a buddies and same thing so I figure it's ok as tiny as it is. My car is the opposite though, it will only do it when I first start it, then get normal as I drive it around.

I fixed that leak by unscrewing the vacuum fitting and putting a little pipe dope around the threads, screw it back in and yay! Worked for me anyway, might try it.

 

[habitatguy187]

As far as it being something electrical I was pretty much thinking the same thing, like maybe the car is just running too rich and bogging a little causing the vacuum to drop. It just sucks testing the ignition system.

 

[RipperXX]

If it were a problem with the ignition system being weak, wouldn't I have problems with mis firing from the spark being blown out at WOT? (20-21psi)

 

[srumel]

Not necessarily. I would check the coil's resistance and the plug wires. Failing that, it could be that the EGR is sticking open. Try blocking it off or just unplugging the vacuum hoses from it, and of course plugging the disconnected hoses.

 

[RipperXX]

Not necessarily. I would check the coil's resistance and the plug wires. Failing that, it could be that the EGR is sticking open. Try blocking it off or just unplugging the vacuum hoses from it, and of course plugging the disconnected hoses.

EGR has been blocked off for about two years now. I will check the resistance on the coil packs though.

 

[Defiant]

Look for the kink in your vac sensing line that's sucking itself closed.

 

[RipperXX]

The vacuum line is that hard nylon tubing, and it's a short stright shot from the source to the MAP sensor. Good idea though

 

[RipperXX]

Well I boost tested it again and thought I found a decent boost leak around the EGR block off plate so I removed it and put high temp copper RTV on the plate and put it back on, let it sit half a day, started the car and no better.


I felt a decent amount of air for no louder than the leak was, so it may have only ben a hair from the EGR and I thought for a moment at least the leak was from the bottom of the TB. So I guess once I get to Oklahoma I will boost test it again this weekend or something assuming all goes well and see.