Vacuum leak
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Vacuum leak I'm about ready to burn my car to the ground. So any help is really appreciated. I have a turbo 99 camaro on an ms3pro. I blew it up a few years back and I have really taken my time putting it together and changing things. About a year ago now I tried pretty hard to get the car at the track again. So after a good thrash I had it running, but running rough like it had a big cam. I pull it out of the garage and the brake pedal is hard as a rock. So my gut reaction is vacuum leak. Well since then I have pulled everything off the of the top of the motor and checked everything I can think of. I've used ether around every place that could possibly leak into the intake manifold and found nothing. I have checked every single thing i can think of. I have no idea how a vacuum leak can stump me so bad. Is it possible there is something more going on? I haven't tried new plugs or anything like that to see. But in my mind the only way the car can idle like it is and still have a rock hard pedal is if it's a vacuum leak. Can anyone help me out? Is there something simple I have overlooked or am over thinking? Thanks.
Last edited by moisbest42; Sep 9, 2024 at 07:41 PM.
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I've eliminated the booster as the cause. I've pulled the vacuum line to it and plugged it, still the same. Afr is in the 17's at idle. Cam was installed straight up. I know that seems super lean but as soon as you touch the throttle it goes to 13's or 12's. That being said, there's another symptom I forgot to mention, and that is a soon as you whack the throttle it stumbles almost to the point of dying, but if you roll into it slow it'll stumble a little then revs fine.
Last edited by moisbest42; Sep 10, 2024 at 03:58 AM.
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Had this problem a year or so ago and ended up being a broken valve spring that made zero noise and didn't affect the idle either.
Give those springs a look, start carefully spraying brake cleaner around the intake, if the idles jumps, you have a leak.
Give those springs a look, start carefully spraying brake cleaner around the intake, if the idles jumps, you have a leak.
I started installing a manual brake kit thinking it was bad and found the broken valve spring after removing the valve cover to get the booster out.
You may have a crack in the intake if using a factory plastic intake or maybe broke a nipple off the back during the swap.
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What is the idle vacuum? And what rpm ? Is the idle speed normal or high? Is the combo and tune the same, does it need a retune? Injectors sat for years ? What fuel ? Did they get gummed up from E85? A lot of questions I know but all possibilities
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No idea we've the actual in/hg is at idle. Idle speed is about 975. The combo is the exact same and doesn't need a re-tune. I sent the injectors back to id to be cleaned and checked and they're fine. Fuel is e85, and it's fresh.
Just thinking out loud here.
If it is a vacuum leak, then it'd have to be after the TB and the IAC valve, so I'd start unplugging and capping all vacuum sources one at a time and looking for a change.
If you get all the way down to the intake only and it still has an issue then maybe your intake got damaged somehow.
The leak could be on the bottom side of the flange of the intake as well.
Check throttle body gasket/o-ring.
Did you use sealant on the rocker bolts?
Some of them go into the intake runner and require loc-tite green iirc.
My Holley 105mm TB actually has an air bleed screw that was open when I was tuning mine that gave me grief.
If it is a vacuum leak, then it'd have to be after the TB and the IAC valve, so I'd start unplugging and capping all vacuum sources one at a time and looking for a change.
If you get all the way down to the intake only and it still has an issue then maybe your intake got damaged somehow.
The leak could be on the bottom side of the flange of the intake as well.
Check throttle body gasket/o-ring.
Did you use sealant on the rocker bolts?
Some of them go into the intake runner and require loc-tite green iirc.
My Holley 105mm TB actually has an air bleed screw that was open when I was tuning mine that gave me grief.
What ECU?
So start here.
So start here.
- I would start with a set of fresh plugs, what are you gapping them at and what coils are you running? Can you hear a misfire at all?
- Spray some fluid around potential vaccum leak culprits. If it idles up or stumbles it's a leak. I think some folks spray WD40 but I'm sure one of you guys can suggest a fluid.
- I would scan the car with HPT or with your Holley, and start looking at things. First thing is target idle RPM. If it's 950 and the car is idling at 1100, something is off.
- Then look at fuel trims. A stumble could be a fuel issue (tune, part is not working right). double digit trims are generally a sign of something, tune is off for example. If you are using HPT, a 25% trim value is the max the ECU can compensate, so if you have something like that, the actual trim might be even higher like 30%.
- I would check for boost leaks. Check the couplers, check the welds.
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You've covered everything I could think of so far , still have MAF ? any leak between MAF and TB will result in unmetered air and a lean condition. Any chance of a change in fuel pressure? Does it not go closed loop and add fuel ? Any changes to pcv / catch can set up that may result in more unmetered air ?
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I've pulled the intake off more than one time, Monday being the most recent. There's no damage to it or the heads at all. I pulled the tb of to check the o-ring and it's in good shape too. I went so far as to pull the iac and tps and they are fine too, with no damage to their o-rings. I'm pretty sure that my tfs heads have blind bolt holes for the rocker bolts, I've ran them for years having pulled bolts and rockers several times with no problems. What I am about to do for the third time is replace all of the vacuum line connections. I use a push lock type vacuum hose and fittings. Maybe there are multiple bad ones in a row that I have used.
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I'm not 100% on my plug gap, I believe it to be .035. I'm running heat sink coils. There is no misfire that I can detect. I've double checked all my plug wires to make sure none were burnt. I also checked each runner of the exhaust manifolds to make sure they're pretty close on temperature. They all are about 100 degrees of each other. I've checked with ether around the intake very thoroughly and get no noticeable change in idle. My car is on an ms3 pro,I believe the target idle and actual idle are very close, which is odd to me because I would expect the idle to be higher than normal, like you said. I will look at the fuel trims when I can tomorrow.
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There is no maf. Fuel pressure is solid, I verified that yesterday. No changes in any of the catch can setup, but the way mine is laid out that wouldn't be a possible place to get an air into the combustion chamber anyway.