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  #1  
Old 06-28-2014, 05:21 PM
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Jeepdawg Jeepdawg is offline
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GM TBI / Howell ported vacuum, Port A

I just cleaned up a vacuum hose mess from the PO. The PO had the ported vacuum (port A) on the throttle body going to the wrong ports on the TCO so the EGR valve never got a vacuum signal to operate.

But now the EGR valve is always open because I have 15 in of vacuum at port A, even at an idle.

This is enough to trigger both the canister purge and EGR valve.

Is this correct to have 15in on port A on a GM throttle body at idle? I always though that ported vacuum was 0 at idle.
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Old 06-28-2014, 11:42 PM
Bill USN-1 Bill USN-1 is offline
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Which port are you referring to?
Ports above the throttle plates are ported, those below are manifold.
Note the locations on the outside are opposite of those on the inside of the TBI.
You also need to verify the gasket and adapter as most adapters are open plenum and do not seal the passages for the ported passages.

But the bigger issue is the EGR should only be controlled by the ECM with EFI.
It is a solenoid that controls the manifold vacuum to the EGR based on specific settings and tables in the chip.
By connecting like a carb the ecm/O2 will see the change in O2 as a change in fuel mixture and try to adjust for it.
Which would make you use more fuel not less.
It only take the solenoid and 2 wires to connect properly.

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Last edited by Bill USN-1 : 06-28-2014 at 11:47 PM.
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  #3  
Old 06-29-2014, 09:33 AM
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Port A marked "ported vacuum" on your pic is the port Howell says to use.

Howell's instructions say connect port A to the CTO switch, from there the vacuum line tees off and goes to the EGR valve and the signal port on the vacuum canister.

The CTO switch is a thermal vacuum switch that prevents the EGR from operating until the engine warms up.

The problem is I have a lot of vacuum on port A even at idle.

Having an electric valve for the EGR is a great idea, but Howell does not give you an circuit to activate one.
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Old 06-29-2014, 12:20 PM
Bill USN-1 Bill USN-1 is offline
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As mentioned, you may want to check the adapter/gasket they supply to make sure the A port passages are sealed off.

Here is a pic of the passages. The inner most "A" passages have to be sealed or they will blend with the manifold vacuum.
Howell may have overlooked the obvious and just used generic instructions for the EGR.
Unfortunately I can't afford the money CA wants for a CARB sticker to certify my systems for CA use. But at least I provide the option to control the EGR just like GM designed it to work. I'm not sure how Howell is getting away with operating it that way. But CA CARB is more about money then actually helping emissions. To fail a vehicle with EFI on a visual instead of tailpipe emissions kind of says it all.



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Last edited by Bill USN-1 : 06-29-2014 at 12:46 PM.
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  #5  
Old 06-29-2014, 12:29 PM
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The links you posted come back as blank pages for me.

I didn't put the EFI system on, so I don't know if the sealing was done or not. But since I have so much vacuum at idle, my guess is it was not done.

How is the sealing done?
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  #6  
Old 06-29-2014, 12:49 PM
Bill USN-1 Bill USN-1 is offline
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fixed the pics and added more info.
You need to pull your throttle body and look at the adapter design and the gasket.
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  #7  
Old 06-29-2014, 12:51 PM
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This is great thanks for posting! I will go rip it apart and see what the PO did.
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Old 06-29-2014, 01:01 PM
Bill USN-1 Bill USN-1 is offline
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http://howellefi.com/pdfs/vacuum_schematic.pdf

http://www.howellefi.com/pdfs/jeep_kit.pdf

Their adapter looks like an open plenum style so I doubt the ports are sealed.

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  #9  
Old 06-29-2014, 01:12 PM
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Dumb question...what is the best way to seal off that passageway? JB weld was my first thought.
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Old 06-29-2014, 01:32 PM
Bill USN-1 Bill USN-1 is offline
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Best way is to use an adapter designed to allow the use of the ported ports.
I still have a couple of my original designed plates available if needed.
I went away from these due to higher machining cost and I run the factory GM EGR solenoid so no need for ported vacuum.
They are $80.
that's assuming you have the 2bbl manifold.
Which engine are you working on? You show 2 in your sig.


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  #11  
Old 06-29-2014, 01:50 PM
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It's on the '87 wag, so a 360 that used to have the motorcraft 2150 living on it.

*EDIT*

Interesting, I have a whole 'nother thread about trying to find out how the CTO switch is connected. The Howell Jeep V8 install directions are totally silent, but the Howell 6 cyl links you posted above show them. That's great! Now I know.
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  #12  
Old 06-29-2014, 03:00 PM
Bill USN-1 Bill USN-1 is offline
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Yep, it shows how to connect them but it's still technically wrong.
The GM EFI system would not know when the EGR was being turned on.
It is the same as a canister purge. It should also be controlled by the ECM so it knows when the fuel vapors are present.
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  #13  
Old 06-29-2014, 07:42 PM
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Well, I found that the problem was the minimum idle screw was screwed too far in which was preventing the throttle plates from closing enough to cover the ported vacuum holes in the venturi.

By backing off the min idle screw I can get the vacuum down to 0 in, but the idle is too low there. At 1-2" of ported vacuum I can get an idle of 830 rpm in N.

But now I have a new issue. The idle surges a bit in N but is steady in D. It seems to steady out a bit putting a load on the engine.

I hear what you are saying about how the canister purge and EGR should be connected to the ECU. On my '74 maybe I will do a junkyard EFI and set it up right. But for now I am in CA and I either use Howell's kit, or go back to the 2150, and the 2150 isn't an option. I have to make this setup work so I can pass smog.
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Old 06-29-2014, 10:18 PM
Bill USN-1 Bill USN-1 is offline
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No problem on the Howell setup.
I was just explaining how they are meant to work.
Lots of guys other than you will read this in the future so it's good for them to know when they do theirs.

I recommend you perform the Initial setup procedures listed here.
ISPs
Obviously your timing is not controlled by the computer so you can skip that.

The Min idle screw has nothing to do with the idle, that is controlled by the IAC. That's it's sole job, maintain a correct idle. The min idle is just that, the min idle speed you want your engine to run at. So normally about 100rpm less then the preset idle speed in the chip or about 550-600.

And the last setting to do is the TPS.
It has to be below 1.2% but best to set it per the instructions at .54v or .2% if using winaldl.
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Old 06-29-2014, 11:46 PM
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I checked my adapter after reading this post and I noticed that the Holley 17-4 adapter that I have dose not cover the ported vacuum passages. If I have the correct understanding; you are saying if you do not plan on running a EGR or something that needs ported vacuum it dose not matter if the adapter plate dose not seal off the ported vacuum passages? Can the ported vacuum port be used as a regular vacuum port then?
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  #16  
Old 06-30-2014, 12:05 AM
Bill USN-1 Bill USN-1 is offline
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You should test your vacuum on each port you have avail to verify if it will work for you.
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Old 06-30-2014, 11:50 AM
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Well the good news is I passed the CA 2 speed test this morning. The tech did not do the ASM treadmill test which was a surprise.

The bad news is my idle results were worse with a brand new cat than they were with my old cat. There is something wrong with my idle since I replumbed my hoses. It's a little lumpy and the test results were just OK.

Results:

Idle test, 951 RPM (out of gear in N)
CO2%; meas=13.9
O2%; meas=0.7
HC (PPM); max=150, meas=125 PASS
CO%; max=1.2, meas=0.10 PASS

2500 RPM test
CO2%; meas=14.4
O2%; meas=0.0
HC (PPM); max=180, meas=22 PASS
CO%; max=1.2, meas=0.13 PASS

I did not have time to go through the setup yet as I needed to get my smog certificate for a DMV appt this afternoon. Wednesday I will have time to take a look and see if I can't settle out my idle. I want my cat to last and not wear it out with the high HC levels at idle.
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  #18  
Old 06-30-2014, 01:21 PM
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HC at idle can be lowered by lowering the idle and lowering the timing at idle.
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  #19  
Old 06-30-2014, 01:27 PM
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By lowering the timing do you mean retarding it?
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  #20  
Old 06-30-2014, 11:31 PM
Bill USN-1 Bill USN-1 is offline
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yes
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