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ClassicCamper
Samba Member
Joined: December 17, 2002
Posts: 679
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 Posted: Tue Aug 04, 2015 2:13 pm Post subject: Vacuum port on TB |
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Can someone help me out with where this vacuum port?
I'm not sure where it connects to. I originally thought it was to the transmission, but that goes on the plenum.
Thanks, -Ron |
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raygreenwood
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Joined: November 24, 2008
Posts: 21513
Location: Oklahoma City
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| Posted: Tue Aug 04, 2015 2:50 pm Post subject: |
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There are some differences in where that goes depending on a couple of things. I need to check a couple of diagrams.
From the vacuum diagram under the decel valve thread....which is vague......it tees with the line from the tranmission.....which also goes to the plenum nipple between the #1 and 2 runners.
The problem with that diagram as I mentioned is that not all autos had a decel valve....and not all autos that had a decel valve had an electric one.
In that case.....th3 manual decel valve always went to the funky three way rubber niple between the AAR and plenum.....and the throttle kicker.....I think...went to that nipple on the TB. Let me check. Ray |
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ClassicCamper
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Joined: December 17, 2002
Posts: 679
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| Posted: Wed Aug 05, 2015 10:19 am Post subject: |
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| Thanks for looking, Ray. There is no evidence on this engine that it ever had any type of decel valve. |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21513
Location: Oklahoma City
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| Posted: Wed Aug 05, 2015 11:40 am Post subject: |
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| ClassicCamper wrote: |
| Thanks for looking, Ray. There is no evidence on this engine that it ever had any type of decel valve. |
Ok....this is one of the strangeness items I have spoken about numerous times over the years.
With D-jet....You have three systems that do...virtually (somewhat) the same thing...final effect wise.
They are somewhat redundant. In some ways they work together, in some ways they work against each other and in some cases they can be substituted for each other.
1. Deceleration valve (found on both auto and manual trans in both vacuum and electrical operated but only vacuum operated on 4 speed)
2. TPS fuel shut off circuit (found on both auto and manual trans of certain years)...purely an emissions device
3. Vacuum retard
The deceleration valve function...many assume to just be an emissions device. Its actually a little more than that. High vacuum at high rpm....and closed throttle....is referred to as over-run.
Think about this interaction loop now....
A. High vacuum generated by high rpm (2500 and up) pulls the MPS to its leanest state..especially with the throttle closed
NOTE: if the model in question has fuel shut off on throttle closed position...this is not a worry. In that case you may not need a deceleration valve
B. Simultaneously....high rpm makes for high ignition advance #'s
C. Simultaneously...throttle closed...means vacuum retard at least pulls the vacuum advance out of the picture and its only centrifugal
NOTE:
On models without fuel shut-off on throttle closed position....the deceleration valve is important to make sure that mixture on overrun is not excessively lean for the ignition advance level
The vacuum throttle kicker (found on automatics only).....is primarily to allow a second or so for uncoupling of the torque converter to prevent the idle from dropping too low.....and....if a decel valve is adjusted just right....this will do the same thing.
On models that had a throttle kicker they connected heh kicker to the strange Tee on the AAR.
On vacuum decel models....which were "generally" not on autos....they connected the decel valve to that strange Tee...ad there was no throttle kicker which was automatic only.
There were models that used neither and automatic or a decel valve (manual with fuel injection...possibly with fuel cut-off...I would think....)....and had no strange tee at the AAR. It had a straight pipe seen in the diagram part #58
Also the diagram on the lower right shows a strange Tee going to the right side of plenum.
I find that the manual vacuum decel valve works very well and is easily adjusted.
And....I ALWAYS disconnect the fuel shut off function contact in the TPS by simply pushing the terminal back into the harness plug boot.
WHY DO I DO THIS?
I have found that not having fuel shut off....it makes for better/quicker throttle transition and allows much tighter adjustment of the acceleration enrichment circuit wiper in the TPS.....
and the fuel shut-off...makes the NEED for the throttle kicker more noticeable on an automatic.
Think about this......When the throttle snaps shut....the fuel is automatically and instantly....SHUT OFF....which means without fuel and the torque converter not yet decoupled...the engine will STRUGGLE to keep an idle speed.
The throttle kicker actually tries hard (by adjustment) not to kick the throttle far enough open to cause a super rich surge by disturbing the vacuum and the MPS (but it does not succeed at that because it holds the throttle too far open).....what its really doing is kicking the TPS into enrich mode on the forward forked switch contact...and out of fuel shut off.
If you disconnect fuel shut off and plumb in a vacuum decel valve...you can lose that throttle kicker with much better results.
Ray |
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