Comon vacuum leaks?

[ericem]

I want people to tell me what common vacuum leaks they have found with there car? I am pretty sure my car has a vacuum leak somewhere still... Checked a few hoses and sprayed Intake cleaner around various areas with no luck. Idle still has slight fluctuation and the engine shudders.

[log1call]

Well is you really mean shudder, not surge, it may be a missfire. Could be an electrical, a fuel, or a compression induced missfire.

If you put a vacumm gauge on it, it will be low but fairly steady if you have a leak, it will perhaps follow a surging idle but still be mainly steady. If you have a missfire it will flicker quite quickly.

There are some quite good web pages about describing how to read a vacumm gauge.

vacumm leaks you may not find with cleaner would be PCV valve and brake booster.

[ericem]

well lets say my hg is like between 17-18 and the gauge moves steady between that gap.

[mexicanzero]

sure sounds like an air leak check your intake gaskets (manifold, throttlebody, iac...) as well as all the beather tubing going from the valve cover gaskets through under the manifold and then up to the intake.

and i'd recommend using carb or sombustion chamber cleaner and listening for the idle dropping indicating a leak. intake and brake clean is very flammable and dangerous near very hot parts.

-Alex

[ericem]

That breather that goes under the intake manifold can cause a air leak? There is definitely a leak at the driver side I replaced the U hose in the middle which fixed my oil leak on the block and the passenger side hose was replaced, now I need to do the driver side hoses I guess, I only replaced all the hoses on the passenger side valve covers. Have already done NGK wires, plugs gapped at .40, lots of intake cleaner and seafoam. I will probably just do the IAC gasket when I remove the turbo. Ill think about the TB and manifold. They don't appear to be leaking, but sounds common now after reading your thread and asc_up.

Another thing I figure you should know, getting low voltage at idle. Thinking I should change my ground wire and maybe the positive wire. Any input on that? I have gone over every single ground on the car and added grounds to the manifold, shock towers etc, but only with 12 guage wire. Already tried another alternator as well!

[mexicanzero]

all the breathers are connected together and if you follow the rear breather tube on the drivers side valve cover you'll see it goes to the intake after the maf. soooo if one of the hoses or plastic lines is cracked in the end you will be sucking in a bit of unmetered air... like having a tiny vac leak. which along with other stuff can cause issues.

as for the low voltage... what voltage are you getting? check at the battery terminals aaannddd at the alt terminal grounding through the case of the alt. so positive terminal of voltmeter on alt terminal and negative touching the case of the alt. the readings should be very close. what is your idle at? low/rough idle can cause low voltage.

as for the ground/power wire mods i used 4 gauge. if your gona do it might as well do it right. no such thing as overkill. i sounds like your grounds are in the right places (you didnt mention alt bracket! it should be grounded) as for power i used a short piece of 4 gauge going direct from the alt to the batery positive.

-Alex

[ericem]

yup compared right at the terminals. The issue is when the engine bay is very hot the voltage goes as low as 11.7v especially with lights on in d. Rpm is around 700 25+ -. I also grounded the alternator. I like the idea of a positive cable right to the battery but did you fuse it ? Anyway to replace the stock wire going to the fuse box ?

[mexicanzero]

woah 11.2 is waay low does it go up with rpm? my car sat at 14.1v last time i checked (week ago) at 700 rpm. it used to sit around 13.6 when my car was idling really low/rough. either way at 700ish rpm it shouldnt be much lower than 14 v.
how long ago did you change the alternator? does the car die on you when driving at all? i think spec is at 2000rpm with eng warmed up voltage should be like 14.3v-15v or something in the neighborhood of that.

there is a temperture sensitive diode in the internal regulators of these alternators so that when very cold and the car is idling higher and richer the alternator produces a bit more voltage to keep up with demands. once the engine warms up voltage goes back to normal.

you said the issue is when the engine bay is very hot... what voltage does it sit at with the engine cold? and your engine isnt over heating right?

the stock wiring to the fuse box can be replaced, anything can be replaced but the fuse box and i think the drivers fender or at least fender liner have to come off. i didnt fuse my power wire from the alt to battery been running it over 1.5 years with no issues.

-Alex

[ericem]

well lets say i rev to 900 i can get low 13s tried another alternator out of curiousity and voltages acted exactly the same. I think ill try a wire from the alternator right to the positive. Did you still use the original wire as well ?

[mexicanzero]

yep i nevr touched the original wire just installed the second one as well. but if the voltage at the batt positive and the alt positive is the same then the added wire will do nothing.

[ericem]

like I said though its when the engine bay is hot so never really compared. I figure might as well just try it out its pretty simple as well as a thick ground going to the original locations and leave existing and see if there is any change but ill add one thing at a time.