Pointing out the obvious: A simple way to find minor vacuum leaks
#1
Eats, Sleeps, Dreams Rotary
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Pointing out the obvious: A simple way to find minor vacuum leaks
So my car was acting a little wonky for the last few weeks ever since I replaced a few vacuum hoses and fuel hoses (which involved taking the UIM off), and I suspected vacuum leaks, but I couldn't seem to find any.
Well, in case you don't happen to have a mechanics stethoscope (IMO enough hissing sounds already come from my engine, so trying this method seems futile anyway) or a can of carb cleaner (or starter fluid), or a fog machine used to find vacuum leaks, there are two simple tips I have for finding minor vacuum leaks (don't expect to find any of the horrifically, devious, hard to find ones that aren't caused by typical causes).
First off, try pinching all the small vacuum hoses you can get to... doing so will isolate at least part of the hose from the engine. If you pinch a hose and the engine idle goes down, this indicates a vacuum leak. Try other hoses on the same vacuum line (not nessicarily the same hose, but other hoses down the same metal line for example). Replace any hoses that cause the idle to go down to eliminate them from the problem. Pinching a hose may also cause an otherwise unnoticable hissing sound to go away, or a change in the sound that the intake makes (if you've got a modified intake at least).
Second, if replacing any hose that causes a drop (or change) in idle does not fix the apparent vacuum leak (there are two sure signs of vacuum leaks: one, unplugging the BAC or jumpering the initial set connector does not lower the idle, two, the idle will not change much or at all when you adjust it, even to it's limits, three, a low, pulsating idle... it may pulsate a little or it may pulsate a lot. Yes, I know that makes three, but that usually goes together with the first two signs), and pinching these hoses still causes a change in the idle, then it's likely that shutting off that hose just happens to make another vacuum leak stronger, so you'll need to try the next technique to find the leak.
Finally, feel every hose you can see, especially those that come in large clusters of 5 or so. If you work on the intake system, there's a fairly large change that you may forget to plug one back in, especially one that's hard to see.) This should be very obvious, but it's quite easy to tell if one side of a hose is disconnected by tugging gently on it (tugging a bit on each side of a hose will also tell you if it's lose and needs to be replaced), or simply pushing it around with your fingers, and having it move instead of staying put like it should.
Here's hoping my annoying popping sound has gone away... but there's still a possibility that I have a few minor leaks since the idle still responds to the brake pedal (increasing the vacuum pressure makes leaks more apparent, although the idle changing because of the brake booster is normal to a certain extent, because of the massive vacuum it pulls).
If these methods fail, you will probably have to rely on the use of some sort of flammable liquid, or a more advanced fogger technique.
Well, in case you don't happen to have a mechanics stethoscope (IMO enough hissing sounds already come from my engine, so trying this method seems futile anyway) or a can of carb cleaner (or starter fluid), or a fog machine used to find vacuum leaks, there are two simple tips I have for finding minor vacuum leaks (don't expect to find any of the horrifically, devious, hard to find ones that aren't caused by typical causes).
First off, try pinching all the small vacuum hoses you can get to... doing so will isolate at least part of the hose from the engine. If you pinch a hose and the engine idle goes down, this indicates a vacuum leak. Try other hoses on the same vacuum line (not nessicarily the same hose, but other hoses down the same metal line for example). Replace any hoses that cause the idle to go down to eliminate them from the problem. Pinching a hose may also cause an otherwise unnoticable hissing sound to go away, or a change in the sound that the intake makes (if you've got a modified intake at least).
Second, if replacing any hose that causes a drop (or change) in idle does not fix the apparent vacuum leak (there are two sure signs of vacuum leaks: one, unplugging the BAC or jumpering the initial set connector does not lower the idle, two, the idle will not change much or at all when you adjust it, even to it's limits, three, a low, pulsating idle... it may pulsate a little or it may pulsate a lot. Yes, I know that makes three, but that usually goes together with the first two signs), and pinching these hoses still causes a change in the idle, then it's likely that shutting off that hose just happens to make another vacuum leak stronger, so you'll need to try the next technique to find the leak.
Finally, feel every hose you can see, especially those that come in large clusters of 5 or so. If you work on the intake system, there's a fairly large change that you may forget to plug one back in, especially one that's hard to see.) This should be very obvious, but it's quite easy to tell if one side of a hose is disconnected by tugging gently on it (tugging a bit on each side of a hose will also tell you if it's lose and needs to be replaced), or simply pushing it around with your fingers, and having it move instead of staying put like it should.
Here's hoping my annoying popping sound has gone away... but there's still a possibility that I have a few minor leaks since the idle still responds to the brake pedal (increasing the vacuum pressure makes leaks more apparent, although the idle changing because of the brake booster is normal to a certain extent, because of the massive vacuum it pulls).
If these methods fail, you will probably have to rely on the use of some sort of flammable liquid, or a more advanced fogger technique.
#2
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If you have a compressor, this is the quickest way to find vac leaks:
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/water-sensors-water-pump-diff-models-583211/ (posts #11 & #16)
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/water-sensors-water-pump-diff-models-583211/ (posts #11 & #16)
#3
Eats, Sleeps, Dreams Rotary
Thread Starter
That's a very good way to do it, but my way is free
Also, if you happen to have a vacuum gauge, you can tell if the car is running well or not by looking at the vacuum at idle. It should be 15-20 or so PSI, and ideally it shouldn't drop when you give it any throttle (I think?), and it should also be steady at idle, if there's no leaks.
Also, if you happen to have a vacuum gauge, you can tell if the car is running well or not by looking at the vacuum at idle. It should be 15-20 or so PSI, and ideally it shouldn't drop when you give it any throttle (I think?), and it should also be steady at idle, if there's no leaks.
#6
Eats, Sleeps, Dreams Rotary
Thread Starter
Right, it's inches of mercury... and according to my gauge the normal range is something like 16-23.
I would try it out but the crappy plastic T it came with broke so I need to go get a metal one.
I'm thinking I might have one of the demonic vacuum leaks that doesn't come from a rubber hose being loose... sure hope it isn't the lower manifold or something.
Also, to make matters work, I apparently have an exhaust leak since there are fumes in my engine bay now.
I would try it out but the crappy plastic T it came with broke so I need to go get a metal one.
I'm thinking I might have one of the demonic vacuum leaks that doesn't come from a rubber hose being loose... sure hope it isn't the lower manifold or something.
Also, to make matters work, I apparently have an exhaust leak since there are fumes in my engine bay now.
Last edited by Valkyrie; 10-24-06 at 06:12 PM.
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#9
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im using an After market gauge plumbed into one of the nipples for the oil bleed injectors
Im sure it was sitting around -20 ( on my PSI gauge ) before i blew it up
Im sure it was sitting around -20 ( on my PSI gauge ) before i blew it up
#10
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Originally Posted by Valkyrie
That's a very good way to do it, but my way is free
...and ideally it shouldn't drop when you give it any throttle (I think?)...
...and it should also be steady at idle, if there's no leaks.
Originally Posted by NZ_87_TURBO
im using an After market gauge plumbed into one of the nipples for the oil bleed injectors
Im sure it was sitting around -20 ( on my PSI gauge ) before i blew it up
#11
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hmmmmm
well. that would explain alot.
I hooked them up as per the emission diagram. ( im talking bout the lines that go from the TB into the LIM. Ive ( S5 manifolds ) got the top nipple hooked up to the primary air bleed, the middle ( large ) hooked up to my oil injector 4 way splitter thingy and the bottom one hooked up to my secondary air bleed nipple facing the firewall with a vac hose going in between the one on the other side to the front secondary air bleed nipple.
The nipple in the middle, slightly lower is hooked up to my FPR
if this isnt how its supposed to be then im stumped. and it is reading vac, approx 5-7 inHg
what have i done wrong?
The oil nozzles are fed air from in from of the throttle, so there can be no vacuum read there, only boost. If you saw vacuum then the oil nozzle air bleed line must be hooked up wrong, and they won't be working very well...
I hooked them up as per the emission diagram. ( im talking bout the lines that go from the TB into the LIM. Ive ( S5 manifolds ) got the top nipple hooked up to the primary air bleed, the middle ( large ) hooked up to my oil injector 4 way splitter thingy and the bottom one hooked up to my secondary air bleed nipple facing the firewall with a vac hose going in between the one on the other side to the front secondary air bleed nipple.
The nipple in the middle, slightly lower is hooked up to my FPR
if this isnt how its supposed to be then im stumped. and it is reading vac, approx 5-7 inHg
what have i done wrong?
#12
Eats, Sleeps, Dreams Rotary
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If you use a compressor that's too big, you'll end up making a lot more problems... I have a cheapo 12v-powered one that came with a highway safety kit, though...
Also, what do you need to hook up an end cap like that to a compressor? They didn't have any fittings like that when I went to hardware store to look for parts to make one of those a few months ago.
I wanted something that would hook up like a tire's stem valve, but they didn't have anything like that. Do they make hardware like that?
Also, what do you need to hook up an end cap like that to a compressor? They didn't have any fittings like that when I went to hardware store to look for parts to make one of those a few months ago.
I wanted something that would hook up like a tire's stem valve, but they didn't have anything like that. Do they make hardware like that?
#13
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you basically need to find a fitting that can go into you compressor and go from there. im assuming it is one of those compressors with a fitting to pump up a tire? unless you can unscrew that or you cut up an old bike tube i dont think you can use that compressor
#14
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Originally Posted by NZ_87_TURBO
Ive ( S5 manifolds ) got the top nipple hooked up to the primary air bleed, the middle ( large ) hooked up to my oil injector 4 way splitter thingy and the bottom one hooked up to my secondary air bleed nipple facing the firewall with a vac hose going in between the one on the other side to the front secondary air bleed nipple.
if this isnt how its supposed to be then im stumped. and it is reading vac, approx 5-7 inHg
Originally Posted by Valkyrie
If you use a compressor that's too big, you'll end up making a lot more problems...
I have a cheapo 12v-powered one that came with a highway safety kit, though...
Also, what do you need to hook up an end cap like that to a compressor? They didn't have any fittings like that when I went to hardware store to look for parts to make one of those a few months ago.
I wanted something that would hook up like a tire's stem valve, but they didn't have anything like that. Do they make hardware like that?
#15
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It's *way* too loud to hear hissing sounds...
I guess I'll just go home and use my dad's compressor... makes finding the proper fittings easier anyway.
I'm not sure if the pressure regulator works worth a crap on it though...
I guess I'll just go home and use my dad's compressor... makes finding the proper fittings easier anyway.
I'm not sure if the pressure regulator works worth a crap on it though...
#17
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haha, i swaped my boost gauge over to my BOV nipple and got a solid 20 inHg. Stoaked. my vavum issues are sorted. now i think my TPS is fucked. wasnt getting any reading when i opened the throttle right up. better get a new one aye
#18
Red Pill Dealer
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NZ. Am I correct that you pressurize the intake system to find leaks with the engine running?
#20
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Originally Posted by TonyD89
NZ. Am I correct that you pressurize the intake system to find leaks with the engine running?
You'd never find the leak that way anyway, not to mention the engine wouldn't run (not enough air).
#21
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Originally Posted by Valkyrie
Um, no.
You'd never find the leak that way anyway, not to mention the engine wouldn't run (not enough air).
You'd never find the leak that way anyway, not to mention the engine wouldn't run (not enough air).
Or are you just checking up to the TB?
#22
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Originally Posted by staticguitar313
how much PSI it too much for N/A??
Originally Posted by TonyD89
I guess ya have to rotate the engine to find a spot that doesn't have an intake/exaust overlap.
Possible in a bridge port motor?
Or are you just checking up to the TB?
Last edited by NZConvertible; 10-27-06 at 03:32 AM.
#23
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So I take it I need a male 1/4th inch (ish) coupling plug (that will hook up to the compressor hose), a female 1/4th inch (ish) ball valve, and a 1/4th inch male threaded peice adapter with a suitable bolt in order to bolt the item on to whatever cap is suitable?
IIRC the OD of the FC's AFM is 2.5 inches, but I'm not sure who carries 2.5" OD or 2.5" ID end caps (besides special ordering it or something).
If it's going to be slipped OVER the AFM it needs to be flexible, and if it's going to go into the intake hose with the AFM off, it needs to be hard.
I don't have any silicone couplers and I'd rather avoid having to order to many things off the internet...as a matter of simplicity.
(actually come to think of it, they AFM's sides aren't the same diameters, are they? The filter side is about 2.5 inches (I think), but the engine side might be upwards of 3?)
IIRC the OD of the FC's AFM is 2.5 inches, but I'm not sure who carries 2.5" OD or 2.5" ID end caps (besides special ordering it or something).
If it's going to be slipped OVER the AFM it needs to be flexible, and if it's going to go into the intake hose with the AFM off, it needs to be hard.
I don't have any silicone couplers and I'd rather avoid having to order to many things off the internet...as a matter of simplicity.
(actually come to think of it, they AFM's sides aren't the same diameters, are they? The filter side is about 2.5 inches (I think), but the engine side might be upwards of 3?)
#24
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My tester replaces the TID, but the S5's 2.5" AFM inlet is a convenient place to connect. I'd buy a cheap 2.5" coupler (and clamps) from an autoparts store, take it to a plumbing store and find a PVC end cap that fits inside it. If you can't find one that fits well you might need to mix and match reducers and short lengths of pipe. PVC pipe sizing is a bit wierd and the walls are quite thick, so don't get hung up on the nominal sizes (my "50mm" end cap has an OD of 70mm). Use you imagination. Remember it has to seal perfectly. A leak tester that leaks is useless...
For the brass bits, go to an engineering supply store with the PVC bits and tell them exactly what you're going to do. They should be able to give you the bits you need.
Why do you have to order anything off the internet? Just go to a shop.
For the brass bits, go to an engineering supply store with the PVC bits and tell them exactly what you're going to do. They should be able to give you the bits you need.
Why do you have to order anything off the internet? Just go to a shop.
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