A helpful way to finding if you have a vacuum leak
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Champion
Joined: Feb 2010
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From: Greenfield, Wisconsin
A helpful way to finding if you have a vacuum leak
Hey guys,
Just want to let you all know a good way to find if you have a vacuum leak. I installed my TB with a new gasket the day I got it, and after my idle was always off even after resetting the computer. It would idle high in nuetral when the engine was hot or if it was revved, the idle wouldnt come down complelty. Thats the first sign of a vacuum leak, but when I tried using propane and brakleen around the engine bay trying to get the RPMs to change to pinpoint the leak, I had no luck. I replaced the IACV and TBS and still no luck. I tried tightening the bolts on the TB up a bit and the same problem still existed.
So, to be positive its a vacuum leak, a couple things I did were:
While in park/nuetral, step on the brake hard repeatedly as fast as you can. If your RPMs raise, its a vacuum leak. Now even with no vacuum leak, the RPMs will raise 20-50 RPM. The raise in RPM you want to look for is 100+.
The other thing I used to know I had a vacuum leak, and to know I corrected it after attempting to fix it was by looking at the fuel trim. Using your OBDII reader, you can see the fuel trim for Short Term 1 and 2 trims, and Long Term 1 and 2 trims. Normal values should be between +8 and -8. Anything more or less and chances are you have a vacuum leak. I was reading -11.7 on my LTFT when at a stop in drive so the engine was running lean. Now, after I fixed my vacuum leak the highest I ever see the LTFT is at -7.7 when coasting at about 40mph to a stop, and at a stop its at -4.7. Every once in a while it will spike to -10 or so for a second, but it is never consistent. The fuel trims are actually pretty neat to watch if youre interested in knowing how much fuel the injectors are dumping in.
Just wanted to let you guys know how you can find if you have a small vacuum leak that is almost undetectable. I had a whistle from the TB, but I always had a small whistle from the stock TB and still do after my vacuum leak was repaired so it was hard to tell if there was a vacuum leak. Feel free to add your way of finding a leak, or even fixing a pesky one.
I fixed my vacuum leak by removing the TB (after stripping a bolt and having to drill the head off), and I cleaned the back of it just to make sure there was nothing on the mounting surface. I removed the gasket, and took conventional motor oil and just rubbed a small amount on the gasket to lube it up. I also took a finger of oil and rubbed it on the back of the TB. The amount of oil used was minimal, I figured it was just a way to get an air tight seal being it was a new gasket. Motor oil seemed best because even if the small amount go in to the intake, it wont damage anything and it should be able to hold up to the heat unlike a household oil which may burn off. I remounted the TB with new 6mm bolts, and snugged them up but not too tight to avoid stripping one again. Now to verify that I fixed the leak, I drove it for 50 miles and allowed the ECU to relearn/tweak everything. I didnt want to reset the computer another time as I have dont it 10+ times in the past 300 miles. During the 50 miles of relearn, my idle was still a little sloppy and the fuel trim was lean. After the 50 miles though and a couple of cold restarts, my fuel trim looks good and the idle works great. Just thought I would share how I found my small vacuum leak as it could have been other things. Feel free to add your methods because it is hard finding trusted ways to verify if you have a vacuum leak, finding it and fixing it.
Just want to let you all know a good way to find if you have a vacuum leak. I installed my TB with a new gasket the day I got it, and after my idle was always off even after resetting the computer. It would idle high in nuetral when the engine was hot or if it was revved, the idle wouldnt come down complelty. Thats the first sign of a vacuum leak, but when I tried using propane and brakleen around the engine bay trying to get the RPMs to change to pinpoint the leak, I had no luck. I replaced the IACV and TBS and still no luck. I tried tightening the bolts on the TB up a bit and the same problem still existed.
So, to be positive its a vacuum leak, a couple things I did were:
While in park/nuetral, step on the brake hard repeatedly as fast as you can. If your RPMs raise, its a vacuum leak. Now even with no vacuum leak, the RPMs will raise 20-50 RPM. The raise in RPM you want to look for is 100+.
The other thing I used to know I had a vacuum leak, and to know I corrected it after attempting to fix it was by looking at the fuel trim. Using your OBDII reader, you can see the fuel trim for Short Term 1 and 2 trims, and Long Term 1 and 2 trims. Normal values should be between +8 and -8. Anything more or less and chances are you have a vacuum leak. I was reading -11.7 on my LTFT when at a stop in drive so the engine was running lean. Now, after I fixed my vacuum leak the highest I ever see the LTFT is at -7.7 when coasting at about 40mph to a stop, and at a stop its at -4.7. Every once in a while it will spike to -10 or so for a second, but it is never consistent. The fuel trims are actually pretty neat to watch if youre interested in knowing how much fuel the injectors are dumping in.
Just wanted to let you guys know how you can find if you have a small vacuum leak that is almost undetectable. I had a whistle from the TB, but I always had a small whistle from the stock TB and still do after my vacuum leak was repaired so it was hard to tell if there was a vacuum leak. Feel free to add your way of finding a leak, or even fixing a pesky one.
I fixed my vacuum leak by removing the TB (after stripping a bolt and having to drill the head off), and I cleaned the back of it just to make sure there was nothing on the mounting surface. I removed the gasket, and took conventional motor oil and just rubbed a small amount on the gasket to lube it up. I also took a finger of oil and rubbed it on the back of the TB. The amount of oil used was minimal, I figured it was just a way to get an air tight seal being it was a new gasket. Motor oil seemed best because even if the small amount go in to the intake, it wont damage anything and it should be able to hold up to the heat unlike a household oil which may burn off. I remounted the TB with new 6mm bolts, and snugged them up but not too tight to avoid stripping one again. Now to verify that I fixed the leak, I drove it for 50 miles and allowed the ECU to relearn/tweak everything. I didnt want to reset the computer another time as I have dont it 10+ times in the past 300 miles. During the 50 miles of relearn, my idle was still a little sloppy and the fuel trim was lean. After the 50 miles though and a couple of cold restarts, my fuel trim looks good and the idle works great. Just thought I would share how I found my small vacuum leak as it could have been other things. Feel free to add your methods because it is hard finding trusted ways to verify if you have a vacuum leak, finding it and fixing it.
