Deceleration Valve
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Car: '86 Camaro SC, '16 QX60
Engine: 2.8 V6 POWER, 3.5L V6 N/A
Transmission: T-5, CVT
Deceleration Valve
This question goes out to those with a 5 speed. I have this backfiring problem with my car. Every time I rev the engine up to 3000 or so rpm, and then shift, it backfires. Not sure what it is. I'm pretty sure it's not the MAF sensor or the intake from the filters to the throttle body. It could be the EGR, or maybe crossfire on the spark leads, or the timing chain, or the deceleration valve. Anyways, I was testing the deceleration valve, and according to the camaro shop manual, if you take the vacuum signal off and then put it back on, the rpms should drop and the valve should open for at least one second. One second is pretty hard to measure, but my guess, it was only 1/2 second that it stayed open. My question is, is there a definitive test to see if the deceleration valve is bad?
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If you have a 2.8L with a 5 speed, you probably have a deceleration valve. It's there for the same reason as the A.I.R. pump (for down shifting). It's that small black cylinder with two medium size hoses and a small hose coming out of it. It's mounted on a bracket coming off the alternator
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Actually the A.I.R. pump is for emissions control..... (Also referred to as the smog pump)
Are you referring to the check valve in the smog pump? It's a trick one way valve..if the valve is blown, it will allow air to move past it in the direction it's not designed to, and it will damage/destroy your smog (A.I.R.) pump... A physical way to test the valve...but it's kinda gross, and it has to be removed in order to do this...is to blow into it as hard as you can. You should only be able to blow through it one way.... (Obviously)
Are you referring to the check valve in the smog pump? It's a trick one way valve..if the valve is blown, it will allow air to move past it in the direction it's not designed to, and it will damage/destroy your smog (A.I.R.) pump... A physical way to test the valve...but it's kinda gross, and it has to be removed in order to do this...is to blow into it as hard as you can. You should only be able to blow through it one way.... (Obviously)
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Yes, the A.I.R. pump is for emissions, but the reason it's there is because of the down shifting that is done with the manual transmission.
But, no, I'm not talking about the check valve. I already had a good time with that part a couple of years ago. It was staying open and it burned the rubber hose that connects the check valve to the pipe from the pump. When I tried to take it off, the threads were screwed, so I had to pull out that whole three-pipe assembly.
Anyways, if you have a 5 speed (as I assume you do, since you replied to my post) you will see this valve mounted on a bracket coming off the alternator. It allows intake air to bypass the throttle valve when the throttle closes and creates a high vacuum. It's a small black cylinder about 1" in diameter and 2" long, you can't miss it. But since no one seems to know what I'm talking about, it doesn't look like anyone will be able to help me.
But, no, I'm not talking about the check valve. I already had a good time with that part a couple of years ago. It was staying open and it burned the rubber hose that connects the check valve to the pipe from the pump. When I tried to take it off, the threads were screwed, so I had to pull out that whole three-pipe assembly.
Anyways, if you have a 5 speed (as I assume you do, since you replied to my post) you will see this valve mounted on a bracket coming off the alternator. It allows intake air to bypass the throttle valve when the throttle closes and creates a high vacuum. It's a small black cylinder about 1" in diameter and 2" long, you can't miss it. But since no one seems to know what I'm talking about, it doesn't look like anyone will be able to help me.
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Car: 95 E-150 & 07 Kawasaki ZX-6R
Engine: A slow one & a fast one
Transmission: A bad one & a good one
Axle/Gears: A weak one & a chained one
I'd look, but....I HAD an automatic Camaro, and I don't have my Camaro anymore.... Here's the sig for ya.
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Car: 95 E-150 & 07 Kawasaki ZX-6R
Engine: A slow one & a fast one
Transmission: A bad one & a good one
Axle/Gears: A weak one & a chained one
You know it took me almost a full minute to spot why your engine bay looks so.....easy to access. No EGR! And that valve thing was definitely not on my car....and I dont recall seeing it on auto 2.8's or 3.1's, so it looks like it is exclusive to 5 speeds...
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Car: 1988 Chevy Camaro Hardtop
Engine: Turbocharged/Intercooled 3.1
Transmission: World Class T5 5 Speed
#1) PCV Actuation Valve (Don't know the exact name
)
#2) T Fitting for vacuum source
#3) IAC connection
#4) IAC
In a nutshell - you do know the pcv system, right?
Positive Crankcase Ventilation. if your engine were totally sealed, it would actually pop due to built up pressure from various things - air heating up inside the engine, oil vapors from heat, all sorts of things. Basically, prevents your engine from getting bloated![Wink](https://www.thirdgen.org/forums/images/smilies/wink.gif)
Ever seen a PCV valve? It's a one way check-ball valve. When pressure builds up enough, the ball comes up, and the pressure is released.
The vacuum valve helps that, since the RPMs stay up in a stick shift when you shift (air pressure in the plenum has to be pulled through still) and pressure spikes up. The vacuum valve senses the vacuum pull, and helps pull the crankcase vapors out.
It has nothing to do with the AIR system. the AIR system's ONLY purpose is to inject extra oxygen after the exhaust comes out of the head, to help light the cat quicker for emissions. That's why I removed my AIR system after I removed the cat.
TomP, you want to back me up on some of this?
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#2) T Fitting for vacuum source
#3) IAC connection
#4) IAC
In a nutshell - you do know the pcv system, right?
Positive Crankcase Ventilation. if your engine were totally sealed, it would actually pop due to built up pressure from various things - air heating up inside the engine, oil vapors from heat, all sorts of things. Basically, prevents your engine from getting bloated
![Wink](https://www.thirdgen.org/forums/images/smilies/wink.gif)
Ever seen a PCV valve? It's a one way check-ball valve. When pressure builds up enough, the ball comes up, and the pressure is released.
The vacuum valve helps that, since the RPMs stay up in a stick shift when you shift (air pressure in the plenum has to be pulled through still) and pressure spikes up. The vacuum valve senses the vacuum pull, and helps pull the crankcase vapors out.
It has nothing to do with the AIR system. the AIR system's ONLY purpose is to inject extra oxygen after the exhaust comes out of the head, to help light the cat quicker for emissions. That's why I removed my AIR system after I removed the cat.
TomP, you want to back me up on some of this?
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Car: 1988 Chevy Camaro Hardtop
Engine: Turbocharged/Intercooled 3.1
Transmission: World Class T5 5 Speed
Originally posted by Nixon1
You know it took me almost a full minute to spot why your engine bay looks so.....easy to access. No EGR! And that valve thing was definitely not on my car....and I dont recall seeing it on auto 2.8's or 3.1's, so it looks like it is exclusive to 5 speeds...
You know it took me almost a full minute to spot why your engine bay looks so.....easy to access. No EGR! And that valve thing was definitely not on my car....and I dont recall seeing it on auto 2.8's or 3.1's, so it looks like it is exclusive to 5 speeds...
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Car: 95 E-150 & 07 Kawasaki ZX-6R
Engine: A slow one & a fast one
Transmission: A bad one & a good one
Axle/Gears: A weak one & a chained one
Shows what I know about 5 speeds huh? NOTHING!!
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Car: 1988 Chevy Camaro Hardtop
Engine: Turbocharged/Intercooled 3.1
Transmission: World Class T5 5 Speed
Which is EXACTLY why you need a 5 speed in that 'stang!!!
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Car: 95 E-150 & 07 Kawasaki ZX-6R
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Transmission: A bad one & a good one
Axle/Gears: A weak one & a chained one
5 speeds are slow. (Compared to race automatics, that is. Speaking of....check out www.lentechautomatics.com, look at the Street Terminator transmission. Ohhh yeah, give me like 3 or 4 months and that baby is MINE!)
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Are you referring to the check valve in the smog pump?
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Doward circled it in the first picture he attached. That's the deceleration valve. And as I said before, it's on the 5 speed, because when you downshift the throttle valve is closed and the vacuum in the intake is too high, so the deceleration valve allows air to bypass the throttle valve to decrease the vacuum.
But whatever the function, the fact remains that it can cause backfire if it's not operating properly. My question was, what is a definitive test to see if it's operating properly? I'm going to replace the valve anyways, I can get it for $13CAD. I just want to know out of curiosity. BTW, for anyone looking for this valve, no one makes them anymore, but there is a warehouse in the US that has stock, so you can get it through Chev.
But whatever the function, the fact remains that it can cause backfire if it's not operating properly. My question was, what is a definitive test to see if it's operating properly? I'm going to replace the valve anyways, I can get it for $13CAD. I just want to know out of curiosity. BTW, for anyone looking for this valve, no one makes them anymore, but there is a warehouse in the US that has stock, so you can get it through Chev.
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Actually, no, it doesn't decrease the vacuum - it actually uses that vacuum spike to help excavate the crankcase of all pressure.
Sorry, I don't know who told you it can cause a backfire -- but they are wrong. All it does, is help the PCV system. Trust me - I took it off, and plugged the pcv system to find out what it did when I was removing the smog crap. I decided the PCV system and teh Evaporative Gas Canister were two items I'd keep, as the PCV system is important.
Check your wires, plugs, and FIRING ORDER. #1 cylinder is the front PASSENGER side (I set my plugs according to #1 being the drivers side - it had your problem, as well)
Check your timing. Check your cat. Those can cause backfiring.
Where exactly are you hearing the backfire?
Sorry, I don't know who told you it can cause a backfire -- but they are wrong. All it does, is help the PCV system. Trust me - I took it off, and plugged the pcv system to find out what it did when I was removing the smog crap. I decided the PCV system and teh Evaporative Gas Canister were two items I'd keep, as the PCV system is important.
Check your wires, plugs, and FIRING ORDER. #1 cylinder is the front PASSENGER side (I set my plugs according to #1 being the drivers side - it had your problem, as well)
Check your timing. Check your cat. Those can cause backfiring.
Where exactly are you hearing the backfire?
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Sorry, that was a misquote. I'm pretty sure it does decrease the vacuum, but what it's actually meant for is to lean the a/f mixture when the throttle closes and the manifold is at high vacuum.
This translates to YES it can cause backfire. Trust me. I have the definitive source, just short of the people who designed the car.
An as for where the backfire is coming from. Who knows! Too hard to tell.
This translates to YES it can cause backfire. Trust me. I have the definitive source, just short of the people who designed the car.
An as for where the backfire is coming from. Who knows! Too hard to tell.
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Think about that for just a second...
Computer is feeding enough fuel for 3k rpms at full tps voltage (batch fire here) so a bit of the fuel is pooled behind the valve when you let off the throttle.
That gas gets sucked in, with a LOT less air - quick rich condition. The computer has compensated by now so all is well again.
If what you say were to be correct, then it would lean out the a/f ratio whenever you were cruising the highway (little throttle, high vacuum). Why doesn't it? The O2 sensor will tell teh computer to add fuel if more air is introduced (as you are saying with the p/t - hi vac scenario)
You don't have to believe me. Screw what the book says - follow the pipe yourself. Pull off teh pipe, plug it up (don't need a vacuum leak) and go for a spin - see if the backfire leaves.
I'm 99% sure your backfire is being caused by too much fuel not being burned in the cylinder - check your spark.
Computer is feeding enough fuel for 3k rpms at full tps voltage (batch fire here) so a bit of the fuel is pooled behind the valve when you let off the throttle.
That gas gets sucked in, with a LOT less air - quick rich condition. The computer has compensated by now so all is well again.
If what you say were to be correct, then it would lean out the a/f ratio whenever you were cruising the highway (little throttle, high vacuum). Why doesn't it? The O2 sensor will tell teh computer to add fuel if more air is introduced (as you are saying with the p/t - hi vac scenario)
You don't have to believe me. Screw what the book says - follow the pipe yourself. Pull off teh pipe, plug it up (don't need a vacuum leak) and go for a spin - see if the backfire leaves.
I'm 99% sure your backfire is being caused by too much fuel not being burned in the cylinder - check your spark.
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First off Doward, I respect your opinion. Don't think I'm getting pissed off at you or anything. This is just a friendly conversation, not an argument.
Secondly, WHATEVER! Who cares what that thing does. I just want to know how to check to see if it's operating properly no matter what the function of the thing is (besides replacing it).
Secondly, WHATEVER! Who cares what that thing does. I just want to know how to check to see if it's operating properly no matter what the function of the thing is (besides replacing it).
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Car: 1988 Chevy Camaro Hardtop
Engine: Turbocharged/Intercooled 3.1
Transmission: World Class T5 5 Speed
Originally posted by camaro_junkie
First off Doward, I respect your opinion. Don't think I'm getting pissed off at you or anything. This is just a friendly conversation, not an argument.
Secondly, WHATEVER! Who cares what that thing does. I just want to know how to check to see if it's operating properly no matter what the function of the thing is (besides replacing it).
First off Doward, I respect your opinion. Don't think I'm getting pissed off at you or anything. This is just a friendly conversation, not an argument.
Secondly, WHATEVER! Who cares what that thing does. I just want to know how to check to see if it's operating properly no matter what the function of the thing is (besides replacing it).
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If when vacuum is applied, it opens, then it's working - you said it yourself. It's just a vacuum activated valve, to the best of my knowledge,
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Originally posted by camaro_junkie
Look a little to the left BackInBlackGP.
Look a little to the left BackInBlackGP.
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Doward: I'm assuming it works on a spring, so even if it opens, it may not stay open long enough to do whatever it's supposed to do.
BackInBlackGP: I just meant that we're not talking about the smog pump check valve at all.
BackInBlackGP: I just meant that we're not talking about the smog pump check valve at all.
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If the spring were weak/broken, it wouldn't close again against the vacuum (even idle vacuum which should be around 18-20in).
Since it does open, and it does close... it's working fine
Since it does open, and it does close... it's working fine
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The spring can get fatigued though. That's why you need a different test to see if it's working.
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I just want to know how to check to see if it's operating properly
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Suck on the actuator port
, and see if air is allowed to flow through the valve passage.
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Last edited by BackInBlackGP; 05-28-2003 at 12:00 AM.
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Originally posted by camaro_junkie
BackInBlackGP: I just meant that we're not talking about the smog pump check valve at all.
BackInBlackGP: I just meant that we're not talking about the smog pump check valve at all.
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That test will determine if it is working at all, but not if it is working properly, for instance if the spring/diaphragm is weakened.
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It's $13. If it's worrying you that much, just replace it.
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We should just have a conference call.
Yeah, I will just replace it anyways, but what can I say... I just have to know.
Yeah, I will just replace it anyways, but what can I say... I just have to know.
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