Vacuum drop after PI Swap

SFC.Kill · Apr 20, 2009

My gauge was reading 12hg at idle before Full PI Swap. Now it is reading 6hg is that because of the increased compression ratio? I noticed to after swap my car idles at 1000, was at 700 before swap do I got a problem somewhere. Pulled off IAC connector and no change in idle. I drilled and tapped the PI intake so I have both coolant sensors. Also my idle hangs too. Might have to do IAC mod.

the98stang · Apr 20, 2009

It's pulling in air somewhere from a vacuum leak. Use a butane torch to find the leak (butane will cause a rise in RPM once the leak it found). Check all vacuum hoses, especially the ones you removed for the swap.

bhuff30 · Apr 20, 2009

Yup, definately a vacuum leak somewhere. Even 12" Hg seems a bit low. Another trick is to use starter fluid and spray in various places you suspect. If the idle speed increases, you found the leak.

SFC.Kill · Apr 20, 2009

Cool, will check it out.

Red04GT · Apr 20, 2009

the98stang said:
It's pulling in air somewhere from a vacuum leak. Use a butane torch to find the leak (butane will cause a rise in RPM once the leak it found). Check all vacuum hoses, especially the ones you removed for the swap.

i do not suggest using a TORCH to check for vacuum leaks. Plastic intake......propane is an option but the safest way is to check the car is with a smoke machine. but i know most people dont have access to one.

jivepepper · Apr 21, 2009

There's a vacuum leak some where.

SFC.Kill · Apr 21, 2009

You don't light the touch, just turn the propane on. Wherever the vacuum leak is it will suck in the propane increasing the idle. I hope you were only kidding.

squeak93 · Apr 21, 2009

+1 on the major vac leak. Souds like with your coolant leak and vac leak, your for sure going to be pulling the lower intake.

justinschmidt1 · Apr 21, 2009

Im pretty sure my car is usually pulling about 20 hg vacuum at idle

Skud · Apr 21, 2009

I pull 15" and that's with MPH blower cams..

I think 20+ is normal for stock cammed cars.

Riley

smasher41 · Apr 21, 2009

yeah, im about 20 also with full PI swap... somthing is wrong, very wrong.

Winters98GT · Apr 21, 2009

bhuff30 said:
Yup, definately a vacuum leak somewhere. Even 12" Hg seems a bit low. Another trick is to use starter fluid and spray in various places you suspect. If the idle speed increases, you found the leak.

I agree, but always be careful. I've used it to find a leak on a fuel injector, but stood back knowing it's flammable.

SFC.Kill · Apr 22, 2009

I found 3 leaks, a intake manifold bolt was even tighten, back in the right corner there is about a 3/8 inch rubber vacuum hose that goes from the back of the plenum, to some sort of black round valve, that hose is falling apart in my hands. Found coolant leak at back of thermostat housing.

squeak93 · Apr 22, 2009

Did ur vac get any better?

Red04GT · Apr 24, 2009

SFC.Kill said:
You don't light the touch, just turn the propane on. Wherever the vacuum leak is it will suck in the propane increasing the idle. I hope you were only kidding.

yes i was kidding. but it does sound funny when someone says torch and vacuum leaks. i just like using a smoke machine.

SFC.Kill · Apr 25, 2009

Yeah it was the vacuum line going thru the firewall up to my gauge, the rubber grommet came loose so the plastic line had the leak.

Vacuum drop after PI Swap

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