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Old 07-21-2009, 12:44 AM   #1
ArcticSteve
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Default Vapour Canister Purge Valve/how does it work

How do these things work? What is their function? They obviously receive an electrical instruction to open or close. The worse my idle became, the louder this thing "clacked".

Original thread with pics:

http://forums.rennlist.com/rennforum...ower-loss.html

So out of the vehicle it's open; you can blow straight thru it. Do I need this thing? It's connected directly to the lower side of the intake manifold.
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Old 07-21-2009, 01:04 AM   #2
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it is emissions related. This is speaking more generically, rather than specifically, but the concept should still apply. There is a charcoal cannister, nowadays mounted on gas tanks, that absorbs vapor as pressure in the tank builds. When you are driving, the CPS will cycle to feed teh engine some of the fuel vapor, emptying the cannister.
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Old 07-21-2009, 02:13 AM   #3
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Like King said, there is a charcoal canister. It is mounted in the drivers wheel well. There is a hose that goes back to the top of the tank, and the charcoal absorbs the fuel vapors as the car is parked.

Next up there is the pair of vacuum valves in by the brake booster, close to the fender. These control the flow based on the vacuum they receive.

On the back of the cylinder head there is a thing called a thermovalve. It is closed below I think 80C. It has two ports on it, one goes to the intake manifold for vacuum signal, the other goes to one of the valves by the brake booster. When the coolant temp hits 80C, the thermovalve opens internally, allowing the vacuum to reach the other valve. That opens that valve.

Once that happens, and the engine is running, then the vapors from the tank and charcoal canister can get sucked into the engine. There is a hose that goes into the JBoot so the vapors get sucked in preturbo.
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Old 07-21-2009, 05:02 PM   #4
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King and Edge, thanks for that.

I took a look and have found everything, but the thermo switch.

What I have located so far is the line coming from the tank coming into a T. From there continuing on to the cannister in the driver's fender. From that T there is a mechanical on way valve which is open to the intake manifold, but first travels thru this electrically controlled "vapour canister purge valve", which out of the vehicle tests open flow both directions. Then there is a very small line to the J boot which seems very restricted.

So I was thinking of blocking off the line from the intake manifold where this "clacking" vapour canister purge valve plugs into, blocking off the tiny line to the J Boot and letting the line from the tank vent to atmosphere ... until I can get my hands on another vapour canister purge valve to actually see if that's my problem.

Another pics of the electrically controlled vapour canister purge valve.
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Old 07-21-2009, 05:33 PM   #5
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Sounds good; but I personally would not vent the fuel vapor line in or near the engine compartment. Fumes are explosive, and there are many spark sources in the engine compartment.

I removed the emissions system completely and removed the vapor line back to the tank, and vented it to atmosphere (via an air filter) there.

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Old 07-21-2009, 05:54 PM   #6
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Thanks Gary for keeping me from getting lazy and I will disconnect at the tank. I reside in a no emission testing zone so I don't need this all this crap.
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Old 07-21-2009, 07:35 PM   #7
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http://www.clarks-garage.com/shop-manual/fuel-13.htm

Dont plug the charcoal canister line. I did that and I suspect that is the reason why my gas tank is sucked in and deformed (88' 944S with plastic tank) near the transmission. It seems that if there is no venting the biggest problem is that there will be vacuum in the tank after a long ride.
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Old 07-22-2009, 04:10 AM   #8
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Jonas, thank you for that diagram. I will not just plug the line.

UPDATE:

The saga continues despite bypassing the purge valve.

Thought I was golden earlier today. Drove 2 miles to my moms. Then left there and was bootin along great for another 2 miles and then blammo, same symptoms: almost total power loss, sputtering engine, then dies. Restarts immediately, but can only move car a few feet and dies.

However, during all this my charging voltage drops from a solid 13.5 volts to 12.5 volts. My gauge needles are jumping around. I turn on my parking lights that operate my fogs and I hear a crackling from the switch.

Eventually I got it home the 4 miles in two attempts about equal in distance. Starts off strong and then dies. Got home and since I was very close to the R mark on the gas gauge I added about 4 gallons of gas. Started it up and it was idling fine, Charging voltage was back to 13.5V. Took it out for a 10 miles rip and just perfect.

New Theory:

Fuel Pressure Regulator. According to Clarks if this device screws up it can result in the injectors drawing excessive amounts of current shuting the motor down, etc. This might explain why my vapour switch started clacking because it was robbed of current.

So now my first move is to buy and permanently install a Fuel Pressure Gauge at the end of the fuel rail.

Suggestions welcome.
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Old 07-22-2009, 07:24 AM   #9
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I would wiggle the reference sensor wires and test the TPS first. You could also check battery cables if they are correctly connected.
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Old 07-22-2009, 03:58 PM   #10
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Swaped battery already. Checked reference sensor because I had the bell housing off a few months ago. Test TPS .... I will read up on that. Thanks.
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Old 07-22-2009, 05:40 PM   #11
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If the battery and ground connections are fine, then this sounds more like an issue with your alternator to me. You could take off the serpentine belt and drive around for a bit to see if that solves your problem.
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Old 07-23-2009, 05:13 AM   #12
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Alternator is on the suspect list.

Today, knew it was too good to be true. Went for a 20 minute country ride. Stopped for gas. Restart and then another mile to a mall. All good. Was back out in 20 minutes. Started up and knew instantly I was back to the troubles. Got it around to the back away from ppl and it died. Hardly idling no power. Charging volts averaging 12.5., but very erratic. Normal is 13.5 plus steady. Sat around for 20 minutes. Restarted and made it another mile. Called flatbed and went home.

Two hours later at home it starts and idles perfectly, full power, 13.6 volts steady. I park it in the garage. Have ordered a Fuel Pressure Gauge, but won't get it until week Saturday. May order a new FP regulator anyways. Original car has 210k miles so if it's original it's well used. The alternator is well used too. They don't last forever.

Keep you posted, but it will be a week or so.
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Old 07-23-2009, 11:48 PM   #13
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Symptoms in your other thread seem to me to be a little too screwy for this to FPR failure alone. Any other signs of bad FPR - groaning fuel pump, longer hot starts...I guess you'll be measuring fuel pressure and leakdown soon so we'll know about the FPR

If this were my gremlin, I'd be looking at AFM and alternator after the FPR question's answered.

And if it were me I'd make sure my crank bolt is tight - bizarre things happened when mine came loose. But that might be my own personal paranoia.

Good luck.
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Old 07-24-2009, 03:46 AM   #14
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Symptoms in your other thread seem to me to be a little too screwy for this to FPR failure alone. Any other signs of bad FPR - groaning fuel pump, longer hot starts...I guess you'll be measuring fuel pressure and leakdown soon so we'll know about the FPR

According to Clarks my symptoms are right in line with what I am experiencing regarding a failed FPR. Here is what they say about possible electrical interactions:

One of the most common failure modes for the FPR is to fail closed to the point that fuel rail pressure is extremely high. The high differential pressure across the injectors causes them to draw excessive current

That may explain the erratic drop in voltage and why the purge valve starts to sound off (it's actually vibrating). As soon as the car sits for an hour it's back to normal.

A failed FPR would be sweet. I'm going to install a guage permanently. It's coming in a week. The FPR should be here by Saturday.
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Old 07-24-2009, 08:57 AM   #15
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Quote:
Originally Posted by Gary Gaukler View Post
Sounds good; but I personally would not vent the fuel vapor line in or near the engine compartment. Fumes are explosive, and there are many spark sources in the engine compartment.

I removed the emissions system completely and removed the vapor line back to the tank, and vented it to atmosphere (via an air filter) there.

Gary
It isn't vented in the engine compartment, it is vented into the engine and burned. There is no safety issue with the purge system that isn't completely dwarfed by the rest of the fuel delivery system.
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Old 07-24-2009, 08:57 AM
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