Hurray !! Hurray
someone reads this stuff.
Have to go after these points one at a time.....
First I cannot blame Dave Meekoff,,,, I am the author of the article...I
fixed that ;>)
Both of the PORTED VACUUM references I thought were from the same source,
so I will have to go after that and find the first reference.
The back fitting on the Holley the Howell says DO NOT USE THIS PORT it is
shared with the IDLE AIR CONTROL. Jerry got it from Troy, and I got it
from Tom at Howell who went off and said he read it from a piece of Holley
literature. I would sure like to see something current from Holley to set
this straight. I have looked on there web site and there is noting there.....
more later. We will get to the bottom of these....... I love it.
gene
>Dave Meekoff has done an excellent job of describing the installation of a
>Howell Throttle Body Fuel Injection system and there is a posting of this on
>Gene Fisher's web site http://www.california.com/~eagle/
>
>I feel, though, that there is an error in the discussion of PORTED VACUUM.
>The last sentence says "At wide-open throttle (WOT) and high RPM, the port
>vacuum signal is strongest."
>
>However, if you use the link in the article and read the VACUUM TESTING IN
>THE 90'S article it lists Manifold, Ported, and Venturi and for the PORTED
>VACUUM the last sentence says: "Since ported vacuum is actually manifold
>vacuum applied to a different passage it will also be near zero when wide
>open throttle. This is in direct contrast to the statement in the article.
>
>I have had the Holley TBI system installed for several years and installed
it
>as shown in Holley's instructions. I still have the original Holley
>instructions. They show the vacuum hookups differently from that in the
>Meekoff article. Mine has been hooked up for several years and is running
>well.
>
>Holley shows the left front port going to the center port of the TVS
(Thermal
>Valve Switch, which I'll discuss later). The large center top one goes to
>the PCV. The center bottom goes to the vapor recover canister. The right
>one is shown as going to an EGR valve (which our 455 GMC engine does not
>have, so I plugged this port.
>
>Holley shows the single rear fitting as direct "Manifold Vacuum." Since my
>455 had vacuum fittings in the manifold at both the front and rear, I just
>plugged this port of the Holley TBI.
>
>The TVS valve is a water temperature actuated valve that is designed to
>prevent overheating during idle or low speed operations. Our Maintenance
>Manual says: "The retarded spark setting of the distributor that GMC built
in
>for effective emission control makes engines run hotter during idle and low
>speed conditions. To protect against overheating, the engine is equipped
>with a TVS. This switch and valve assembly is mounted in the engine cooling
>jacket near the right front of the engine and is connected into the vacuum
>advance system.
>
>When the engine is cool the TVS valve directs crab vacuum to the distributor
>vacuum advance to retard the timing. When the engine reaches 224-230 deg.
F.
>the valve opens to direct manifold vacuum to the distributor vacuum
advance.
>This advances the spark timing slightly and speeds up the engine. The
result
>is less heat rejected to the coolant together with higher fan speeds for
>better cooling action."
>
>The TVS has three vacuum ports. The top marked D goes to the distributor.
>The center marked C goes to the carburetor ported vacuum (left front of
>Holley TBI). The lower port marked MT goes to the intake manifold elbow (on
>my 455 it goes to a "Tee" and from there to the front manifold fitting and
to
>the transmission).
>
>If anyone has eliminated the TVS then the vacuum line from the distributor
>should go directly to the engine manifold (or the back fitting on the
Holley)
>and not to the lower front connection on the Holley TBI. I doubt that you'd
>get enough vacuum from that fitting to properly operate the distributor
>advance. Since Holley's manual says that is for the vapor canister it would
>be a low vacuum source. It is probably Venturi vacuum which get to about 3"
>HG at its highest.
>
>In the article you indicate that Howell's instructions have an error and
that
>"Troy" told you how to hook it up. I suspect that Troy made a mistake and
>that the Holley instructions are correct. The bottom front one definitely
>goes to the canister and one of the outside ones go to the TVS. If the TVS
>is eliminated then that port should be plugged. The Holley model that I
have
>doesn't have a MAP to control the system. I would guess that the MAP should
>be connected to the other outer port on the front of the TBI (the one that I
>plugged).
>
>The other vacuum lines are: My vacuum canister (little black tank under the
>front driver's side access door) also goes to the front manifold vacuum
port,
>not to the TBI. The brake booster goes to the rear manifold fitting and the
>cruise control and air cleaner temperature vacuum motor also go to the rear
>manifold vacuum fitting.
>
>Dave, you might want to get out a vacuum gauge and check the various
fittings
>on the TBI to see if they don't conform to the Holley instructions. The
>distributor must have a direct lead to the manifold and not to the throttle
>body except for when the engine is cold if you are using the TVS.
>
>Just before sending this, I decided to telephone Holley at 1-800-225-0908
and
>a technician told me that the center bottom one definitely goes to the
>canister and that it would not have enough vacuum to properly operate the
>distributor advance. We went over all the connections and he agreed with
the
>information that I have posted above.
>
>He indicated that the TBI part with the injectors had not changed. One
thing
>I neglected to ask the technician was if the information was still valid for
>a MAP controlled system. Mine is an analog two barrel system, Model 502-1.
>But since I was told that the TBI part was not changed the connections
should
>be the same.
>
>Emery Stora
>77 Kingsley
>Santa Fe, NM
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
someone reads this stuff.
Have to go after these points one at a time.....
First I cannot blame Dave Meekoff,,,, I am the author of the article...I
fixed that ;>)
Both of the PORTED VACUUM references I thought were from the same source,
so I will have to go after that and find the first reference.
The back fitting on the Holley the Howell says DO NOT USE THIS PORT it is
shared with the IDLE AIR CONTROL. Jerry got it from Troy, and I got it
from Tom at Howell who went off and said he read it from a piece of Holley
literature. I would sure like to see something current from Holley to set
this straight. I have looked on there web site and there is noting there.....
more later. We will get to the bottom of these....... I love it.
gene
>Dave Meekoff has done an excellent job of describing the installation of a
>Howell Throttle Body Fuel Injection system and there is a posting of this on
>Gene Fisher's web site http://www.california.com/~eagle/
>
>I feel, though, that there is an error in the discussion of PORTED VACUUM.
>The last sentence says "At wide-open throttle (WOT) and high RPM, the port
>vacuum signal is strongest."
>
>However, if you use the link in the article and read the VACUUM TESTING IN
>THE 90'S article it lists Manifold, Ported, and Venturi and for the PORTED
>VACUUM the last sentence says: "Since ported vacuum is actually manifold
>vacuum applied to a different passage it will also be near zero when wide
>open throttle. This is in direct contrast to the statement in the article.
>
>I have had the Holley TBI system installed for several years and installed
it
>as shown in Holley's instructions. I still have the original Holley
>instructions. They show the vacuum hookups differently from that in the
>Meekoff article. Mine has been hooked up for several years and is running
>well.
>
>Holley shows the left front port going to the center port of the TVS
(Thermal
>Valve Switch, which I'll discuss later). The large center top one goes to
>the PCV. The center bottom goes to the vapor recover canister. The right
>one is shown as going to an EGR valve (which our 455 GMC engine does not
>have, so I plugged this port.
>
>Holley shows the single rear fitting as direct "Manifold Vacuum." Since my
>455 had vacuum fittings in the manifold at both the front and rear, I just
>plugged this port of the Holley TBI.
>
>The TVS valve is a water temperature actuated valve that is designed to
>prevent overheating during idle or low speed operations. Our Maintenance
>Manual says: "The retarded spark setting of the distributor that GMC built
in
>for effective emission control makes engines run hotter during idle and low
>speed conditions. To protect against overheating, the engine is equipped
>with a TVS. This switch and valve assembly is mounted in the engine cooling
>jacket near the right front of the engine and is connected into the vacuum
>advance system.
>
>When the engine is cool the TVS valve directs crab vacuum to the distributor
>vacuum advance to retard the timing. When the engine reaches 224-230 deg.
F.
>the valve opens to direct manifold vacuum to the distributor vacuum
advance.
>This advances the spark timing slightly and speeds up the engine. The
result
>is less heat rejected to the coolant together with higher fan speeds for
>better cooling action."
>
>The TVS has three vacuum ports. The top marked D goes to the distributor.
>The center marked C goes to the carburetor ported vacuum (left front of
>Holley TBI). The lower port marked MT goes to the intake manifold elbow (on
>my 455 it goes to a "Tee" and from there to the front manifold fitting and
to
>the transmission).
>
>If anyone has eliminated the TVS then the vacuum line from the distributor
>should go directly to the engine manifold (or the back fitting on the
Holley)
>and not to the lower front connection on the Holley TBI. I doubt that you'd
>get enough vacuum from that fitting to properly operate the distributor
>advance. Since Holley's manual says that is for the vapor canister it would
>be a low vacuum source. It is probably Venturi vacuum which get to about 3"
>HG at its highest.
>
>In the article you indicate that Howell's instructions have an error and
that
>"Troy" told you how to hook it up. I suspect that Troy made a mistake and
>that the Holley instructions are correct. The bottom front one definitely
>goes to the canister and one of the outside ones go to the TVS. If the TVS
>is eliminated then that port should be plugged. The Holley model that I
have
>doesn't have a MAP to control the system. I would guess that the MAP should
>be connected to the other outer port on the front of the TBI (the one that I
>plugged).
>
>The other vacuum lines are: My vacuum canister (little black tank under the
>front driver's side access door) also goes to the front manifold vacuum
port,
>not to the TBI. The brake booster goes to the rear manifold fitting and the
>cruise control and air cleaner temperature vacuum motor also go to the rear
>manifold vacuum fitting.
>
>Dave, you might want to get out a vacuum gauge and check the various
fittings
>on the TBI to see if they don't conform to the Holley instructions. The
>distributor must have a direct lead to the manifold and not to the throttle
>body except for when the engine is cold if you are using the TVS.
>
>Just before sending this, I decided to telephone Holley at 1-800-225-0908
and
>a technician told me that the center bottom one definitely goes to the
>canister and that it would not have enough vacuum to properly operate the
>distributor advance. We went over all the connections and he agreed with
the
>information that I have posted above.
>
>He indicated that the TBI part with the injectors had not changed. One
thing
>I neglected to ask the technician was if the information was still valid for
>a MAP controlled system. Mine is an analog two barrel system, Model 502-1.
>But since I was told that the TBI part was not changed the connections
should
>be the same.
>
>Emery Stora
>77 Kingsley
>Santa Fe, NM
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
