Vacuum/Idle Issue - JeepForum.com
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post #1 of 18 Old 10-25-2021, 08:59 AM Thread Starter
Charleston82CJ7
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Vacuum/Idle Issue

I converted to power brakes and installed a new EGR this weekend.

I plumbed in the booster first (I tapped into the line for the PCV valve which comes off of the port circled in red). When I cranked the Jeep, the brake pedal was tight (never went soft like the booster was engaging) the brakes were really tight, the jeep idled like crap and ran really weird (low power and almost pulsing). I checked vacuum at that line and it was only at about 10in, but when I checked the vac from the port circled in blue (known manifold) is was around 20in. I figured there was an issue with the booster, so I unplugged the line from the booster and capped it. The Jeep still idled really badly, until I unplugged the capped line (video link below).

PCV line unplugged

I replumbed the booster to the vac port on the manifold by the fire wall, and tied the PCV line back to the red port, as it was originally tied in (by PO).

Before I cranked it again (stupid, I know, eliminate one problem before creating another), I also replaced the EGR valve ( I didn't know if the existing EGR was working or not, but it looked rough and I figured I might as well swap it out). I fired the Jeep up and initially it idled pretty good, but slowly dropped from 20in to less than 10, then close to zero in the matter of a few seconds.

I went through trial and error and finally found that if I disconnect the new EGR valve, it would idle great and I had over 20 in of vacuum.

- without EGR
- with EGR

Brake booster feels correct now, so I think it is good.

I am wondering about a few things:

1. Is the port circled in red (my PCV valve ties into this) signal or manifold vacuum? It looks like it is below the throttle plate, but makes no sense that it didn't have the same vac pressure as the manifold.

2. I am guessing the new EGR is bad out of the box? I am going to put the old one back in and see what happens (I know, delete the EGR, but the Jeep stinks without it.) I don't think the CTO is bad, unless both it (constantly open) and the old EGR (constantly closed)were bad, but if the CTO was bad, my vac advance would not work (it is plumbed from the CTO, per the FSM diagram), right?

Thoughts?

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post #2 of 18 Old 10-25-2021, 01:26 PM
pedal2themetai
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HI, No picture of anything circled in any color just your video's .. can't tell much with those.. do a google search on how to read a vacuum gauge.. the needle should be steady with it bouncing around when the EGR is plugged in there is a problem..

good luck
tim
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post #3 of 18 Old 10-25-2021, 01:46 PM Thread Starter
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Not sure why it didn't post...
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post #4 of 18 Old 10-25-2021, 08:50 PM
John Strenk
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The EGR should not open at idle. But if it is connected to manifold vacuum then it will open and mess up your idle.

The old one may of been stuck shut but you said it operated properly.

Also that port is labeled as "E" "emission". You PCV valve should be connected to the larger port on the back of the carb.

something like this 1982 vacuum diagram.:
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post #5 of 18 Old 10-26-2021, 06:19 AM Thread Starter
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Quote:
Originally Posted by John Strenk View Post
The EGR should not open at idle. But if it is connected to manifold vacuum then it will open and mess up your idle.

The old one may of been stuck shut but you said it operated properly.

Also that port is labeled as "E" "emission". You PCV valve should be connected to the larger port on the back of the carb.

something like this 1982 vacuum diagram.:
John,

This is how it is plumbed right now. The port with the purple line is the one with the red circle in the pic above. The yellow line is the non-circled port and the port circled in blue is the one from the manifold to the CTOs. I have a Weber knockoff (Solex 34) carb so the ports in the pic are the only ones I have to work with.

The EGR connects to vacuum through the CTO Valve. I was thinking the CTO might have gone bad, but that still makes no sense because the other EGR was working (at least I never had the bad exhaust fumes when it was hooked up).

Your other post on the PCV system leak ties in to my question as well.

https://www.jeepforum.com/forum/f8/h...-port-4445017/

What vacuum would you expect at idle between the manifold and the PCV valve?

I was wondering if the first issue I was having was because the brake booster was tied into the PCV line, and it couldn't generate the vacuum needed. The booster is working like it should now that it is plumbed directly to the manifold.
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post #6 of 18 Old 10-26-2021, 08:48 AM
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Verify there is no vacuum at idle on that yellow line. It could be the Weber throttle plate is not fully closed at idle and giving you some vacuum signal that's messing you up.

I never saw a heavy duty cooling CTO yet, I'll have to check up on that to see what it is doing. I think it's switching between the ported and manifold vacuum to the distributor.


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post #7 of 18 Old 10-26-2021, 12:46 PM Thread Starter
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I'll check it out when I get home and report back.
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post #8 of 18 Old 10-29-2021, 07:51 AM Thread Starter
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Ok John, I checked CTO vac at idle before and after warm. No vac before. When it hits temp, I have vac. If I press the EGR diaphragm, it sputters and dies.
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post #9 of 18 Old 10-29-2021, 08:52 AM
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Check the port on the carb and see if there is a vacuum on that port at idle.

What carb do you have? Don't know to much about a Solex 34 carb ( I thought they were a 1 bbl used on VW engines) and what ports are ported (No vacuum at idle) or manifold (vacuum all the time at idle.)

You need to find a vacuum port that has no vacuum at idle and vacuum when the throttle is opened up. Solex carbs had some strange setups with Air bypass valves and such.

If you can't find the right port, you will need to look at other options.
1. Learn how to setup the carb you have. I'm sure there is a ported vacuum source but your carb may not be adjusted properly. There is more than cranking the mixture and idle speed screws.
2. Get a better carb, Weber 38/38 would be simplest replacement for what you have. Maybe someone who has converted to FI might have one laying around.
3. Run without the EGR


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post #10 of 18 Old 10-29-2021, 09:28 AM Thread Starter
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Funny thing is I have the Weber 38 on the way. The Solex runs pretty good (I’ve had the Jeep for almost a year and no huge issues) but I can’t find any info on adjusting it, and I hear the 38 will wake the 258 up.

I put a vac gauge on the port and it has about 8 inches at idle and goes to 20 with the throttle open.

If I understand you correctly, there should be no vac to the EGR at idle, even if the CTO is open. Then when I hit the throttle, there should be vac on the line, correct?
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post #11 of 18 Old 10-29-2021, 10:25 AM
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[QUOTE=Charleston82CJ7;41381849.....

If I understand you correctly, there should be no vac to the EGR at idle, even if the CTO is open. Then when I hit the throttle, there should be vac on the line, correct?[/QUOTE]

Exactly !!!

Some Solex carbs have an Air Bypass screw that lets you close the throttle all the way but allows air to come in Bypassing the throttle plate so you can adjust the idle speed.
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post #12 of 18 Old 10-29-2021, 11:00 AM Thread Starter
Charleston82CJ7
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Thanks for the help. I am just going to run with the lines plugged and the EGR capped until the Weber gets here.

Side note , how much vacuum would you expect the port for the PCV system to pull? Full manifold?
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post #13 of 18 Old 10-30-2021, 07:29 AM
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Quote:
Originally Posted by Charleston82CJ7 View Post
Side note , how much vacuum would you expect the port for the PCV system to pull? Full manifold?

15-20" is the normal range. It varies with elevation. 18" is good vacuum under normal circumstances.

Matt


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post #14 of 18 Old 10-30-2021, 01:57 PM
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Nice to hear your Solex can even adjust anything. Had one on mine too when purchased, and none of the screws did anything at all, but it did run decent enough to get around and able to drive it. Last weekend went to a MC 2100, but issues with vac leak on lower gaskets, has me sitting until I can get back to it.

Looking at your pics and see the Manifold vac port is same as mine. Found this adapter on Amazon I added to give me a better setup on vac lines. Sharing in case it would help

Midland 38-874 Brass Inverted Flare Male Swivel, 90 Degree Elbow, 3/8" Hose ID x 3/8" Tube OD
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post #15 of 18 Old 11-01-2021, 03:43 PM Thread Starter
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This might be part of my problem. That’s my choke…fully open…and fully closed…
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