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Unread 12-30-2009, 11:24 AM   #1
CJ7_Jim
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PCV valve vacuum...how much is too much

I'm running a Howell TBI unit and it says to hook the PCV up to manifold vacuum.
At idle I'm getting a ton of suction.
I didn't think you should get suction at idle???
I also have a problem with not being able to get my idle down to 750 rpm.
No matter what I do it goes up to around 1,000 rpm as soon as it goes to closed loop.
I did check the programming and it's set for 700 rpm.
If I take the PCV out and plug it, the idle goes down.
So...it's acting like a vacuum leak.

Should I need to restrict my vacuum line down???

Jim

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Unread 12-30-2009, 11:33 AM   #2
Mike Romain
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Sounds like a bad PCV valve. They have a ball bearing in them so they shut off at high vacuum like when at idle. The Jeep one is also supposed to have the canister's (gas tank vent) flow into it when at speed to suck right.
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Unread 12-30-2009, 12:08 PM   #3
CJ7_Jim
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Thanks Mike!!!
Unfortunately I think my charcoal canister in bad.
Since the PCV valve is new, I started checking the other end...when I pinch the purge line that the PCV is plugged into, the idle drops

Guess I need to start looking for a new one.
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85 CJ-7, 258 I6, 35's, 4" BDS suspension lift, 1" body lift to clear tires, swaybar disconnects, Currie tie rod and steering rod, Rusty's BEEFY steering gear mount, Steering brace, Superior one piece axles, Detroit locker rear and Detroit TT up front, T5 Tranny, Dana 30, AMC 20, Dana 300 TC,TR upgrade, TJ flares, and Howell TBI.
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Unread 12-30-2009, 12:17 PM   #4
Mike Romain
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Quote:
Originally Posted by CJ7_Jim View Post
Thanks Mike!!!
Unfortunately I think my charcoal canister in bad.
Since the PCV valve is new, I started checking the other end...when I pinch the purge line that the PCV is plugged into, the idle drops

Guess I need to start looking for a new one.
Unless the plumbing is wrong so it is turned on at idle? It is supposed to get a ported signal via the CTO valve so it only turns on at speed when warmed up. I would pinch the small signal line closed to see if it shuts off first. If it still purges at idle, then check this link for part numbers. http://www.jeepforum.com/forum/f8/cj...ml#post5732729
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 12-30-2009, 01:16 PM   #5
CJ7_Jim
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Quote:
Originally Posted by Mike Romain View Post
Unless the plumbing is wrong so it is turned on at idle? It is supposed to get a ported signal via the CTO valve so it only turns on at speed when warmed up. I would pinch the small signal line closed to see if it shuts off first. If it still purges at idle, then check this link for part numbers. http://www.jeepforum.com/forum/f8/cj...ml#post5732729
It must be getting the signal from the CTO.
Everything is fine until it warms up.
Once it heats up the idle goes up.
I checked the signal hose and nothing happens when I pinch it.
It does drop rpm's when I pinch the purge hose though.
Does this sound like a bad canister
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Unread 12-30-2009, 01:21 PM   #6
Mike Romain
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Unfortunately yes. One last test would be to unplug the little signal line so then you are real sure it isn't turned on by mistake.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
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Unread 12-30-2009, 03:49 PM   #7
Curly5759
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The PCV is supposed to get full manifold vacuum. The check ball is designed to close when an intake backfire occurs to prevent flames from igniting any fumes in the crankcase.

curly
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Unread 12-31-2009, 06:30 AM   #8
Mike Romain
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Originally Posted by Curly5759 View Post
The PCV is supposed to get full manifold vacuum. The check ball is designed to close when an intake backfire occurs to prevent flames from igniting any fumes in the crankcase.

curly
PCV valve - Wikipedia, the free encyclopedia

It also cuts the flow almost off at high vacuum so that line he was seeing collapse sounded like a weak line on a properly working canister at first. Now I am not sure. If the canister is venting at idle, then the air filter on it must be plugged and it must have a bad shut off valve to cause that collapse.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 12-31-2009, 07:26 AM   #9
John Strenk
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The PCV valve should be closed at high vacuum like at idle. However is you have a vacuum leak, then your vacuum level will drop opening the PCV valve creating a bigger leak. It is also closed at low or now vacuum also.
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Unread 12-31-2009, 10:35 AM   #10
CJ7_Jim
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Quote:
Originally Posted by John Strenk View Post
The PCV valve should be closed at high vacuum like at idle. However is you have a vacuum leak, then your vacuum level will drop opening the PCV valve creating a bigger leak. It is also closed at low or now vacuum also.
With the Howell unit, you end up with very limited vacuum hoses.
I replaced all of them when I installed the tbi a few months back.
I don't think I have any other vacuum leaks anywhere.
I've checked countless times with carb cleaner, spraying it everywhere.
The canister must be bad....and I did change the filter just in case.
When the engine heats up the idle goes up.
If I pinch the purge ling at the canister the idle drops.
I'm thinking the diaphram in the canister may be cracked.
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Unread 12-31-2009, 10:39 AM   #11
Mike Romain
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Quote:
Originally Posted by CJ7_Jim View Post
If I pinch the purge ling at the canister the idle drops.
I'm thinking the diaphram in the canister may be cracked.
That is the test for a torn diaphragm. The only other test I can think of is to unplug the line from the CTO to the canister so it for sure can't be turned on. If it still acts the same, then you have it for sure.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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