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Unread 09-01-2014, 01:30 PM   #1
snowplowdog
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No vacuum at idle

I picked up a vacuum tester so I can diagnose the problems I'm having in my 90 YJ. The only line other than the one for the pcv/brake booster is in the carb so that's where I hooked up. I get no reading whatsoever at idle and it jumps up as soon as you hit the throttle. Shouldn't there be a port coming out of the intake manifold somewhere. I've looked but I cant find anything anywhere. Some days id really like to shoot the PO of this jeep.

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Unread 09-01-2014, 02:02 PM   #2
Mike Romain
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Quote:
Originally Posted by snowplowdog View Post
I picked up a vacuum tester so I can diagnose the problems I'm having in my 90 YJ. The only line other than the one for the pcv/brake booster is in the carb so that's where I hooked up. I get no reading whatsoever at idle and it jumps up as soon as you hit the throttle. Shouldn't there be a port coming out of the intake manifold somewhere. I've looked but I cant find anything anywhere. Some days id really like to shoot the PO of this jeep.
The line off the back corner of the stock carb that goes to the air filter is a manifold vacuum.
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Unread 09-01-2014, 02:32 PM   #3
snowplowdog
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Quote:
Originally Posted by Mike Romain View Post
The line off the back corner of the stock carb that goes to the air filter is a manifold vacuum.
Sorry, forgot to mention its not a stock carb....PO replaced it with a holley
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Unread 09-01-2014, 03:14 PM   #4
dancytron
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There is a big port on the manifold behind the carb that goes with the decel valve. There is also another one that goes to the heater controls.

http://home.sprynet.com/~dale02/decel.htm
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Unread 09-01-2014, 03:24 PM   #5
snowplowdog
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Originally Posted by dancytron View Post
There is a big port on the manifold behind the carb that goes with the decel valve. There is also another one that goes to the heater controls.

http://home.sprynet.com/~dale02/decel.htm
Mine doesn't have any of that. The PO ripped out all of the vacuum lines and everything that he thought wasn't needed when he installed the new carb. It looks as though I'll have some "plumbing" to do in order to get this thing right.
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Unread 09-01-2014, 03:55 PM   #6
dancytron
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The port should still be there through. It would be under where the decel valve used to be.

Unless he actually sawed it off and welded it shut.
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Unread 09-01-2014, 03:59 PM   #7
Old4X
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The line to the brake booster is a vac line, or did the PO remove the brakes also?
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Unread 09-01-2014, 04:05 PM   #8
snowplowdog
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Quote:
Originally Posted by dancytron View Post
The port should still be there through. It would be under where the decel valve used to be.

Unless he actually sawed it off and welded it shut.
Looks as though he plugged it. I asked him if he had any parts left from when he did the carb swap and he gave me a bunch of stuff, including the original intake manifold. Apparently they broke it while bolting the new carb on so they had to replace it with a new one.

I'm thinking this is the little guy I'll need to install in the manifold...

vacuum.jpg
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Unread 09-01-2014, 04:10 PM   #9
dancytron
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Quote:
Originally Posted by snowplowdog View Post
Looks as though he plugged it. I asked him if he had any parts left from when he did the carb swap and he gave me a bunch of stuff, including the original intake manifold. Apparently they broke it while bolting the new carb on so they had to replace it with a new one.

I'm thinking this is the little guy I'll need to install in the manifold...

Attachment 1579386
That is the CTO valve. It is a temperature triggered valve that operates the EGR valve and the Vapor Canister.

edit: So the intake manifold may not be stock either. Could be off a 4.0 or something after market. Can't help you much then.
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Unread 09-01-2014, 04:24 PM   #10
snowplowdog
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Quote:
Originally Posted by dancytron View Post
That is the CTO valve. It is a temperature triggered valve that operates the EGR valve and the Vapor Canister.

edit: So the intake manifold may not be stock either. Could be off a 4.0 or something after market. Can't help you much then.
He said they ordered an OEM manifold, but that doesn't mean anything.
I'll have to look under there again, maybe I'm missing something.
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Unread 09-01-2014, 07:51 PM   #11
bpounds
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It is normal to have no vacuum on a ported source at idle. Because the carb throttle plates are closed.

The nipple manifold vacuum that is used for your brake booster should have a smaller side nipple that is a good source of manifold vacuum. It is right above the EGR valve. You can see it below my throttle body in this pic.

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Unread 09-02-2014, 06:04 AM   #12
Mike Romain
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Quote:
Originally Posted by snowplowdog View Post

Mine doesn't have any of that. The PO ripped out all of the vacuum lines and everything that he thought wasn't needed when he installed the new carb. It looks as though I'll have some "plumbing" to do in order to get this thing right.
There is a line off the back corner of the intake for the heater controls under the dash. That one should still be there. Also one going to the front axle disconnect.
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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 09-02-2014, 10:39 AM   #13
snowplowdog
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Quote:
Originally Posted by Mike Romain View Post
There is a line off the back corner of the intake for the heater controls under the dash. That one should still be there. Also one going to the front axle disconnect.
I'll be looking tonight after work.
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Unread 09-02-2014, 07:07 PM   #14
snowplowdog
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Here are some pictures of the 2 vacuum lines that are on my jeep.

carb1.jpg

carb2.jpg

The large on that comes off the back of the carb is for the PCV valve & brake booster. The small one tees off for the vacuum advance and front axle disconnect. There are threaded plugs all over the manifold, can one of these be used for a vacuum port?
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Unread 09-02-2014, 09:11 PM   #15
Drednot
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Yes, one of the ones on top to the rear of the carb. They should all be manifold vacuum.
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