Off Idle miss/bog

[jbojo]

The passenger side is manifold vacuum.

Is there a part number on that vac temp switch? The center port should be for the vac source and the top and bottom would be enabled by the coolant temp. I would like to research how that valve works and we can probably get all the emission stuff hooked up properly if we know what that valve was intended to do..

 

[naa10104]

The passenger side is manifold vacuum.

Is there a part number on that vac temp switch? The center port should be for the vac source and the top and bottom would be enabled by the coolant temp. I would like to research how that valve works and we can probably get all the emission stuff hooked up properly if we know what that valve was intended to do..

I will check and let you know ... I know that the bottom nipple on the sensor is plugged. Thanks

 

[jbojo]

The 4 port connections on the firewall are all connections used?

On your transmission does the vacuum modulator have 1 or 2 vacuum connections to it?

 

[naa10104]

The 4 port connections on the firewall are all connections used?

On your transmission does the vacuum modulator have 1 or 2 vacuum connections to it?

Hello,

All four firewall connections are utilized and two go to the C6 auto trans. Don't know if you saw it but if you go back to my earlier posts on this thread I have a complete breakdown of where all the vacuum hoses run. Interested in any guidance I can get on the proper placement of the vacuum lines. I have reviewed dozens of vacuum schematics and have yet to find one that is identical to my 351 C motor. Thanks

 

[jbojo]

I think I figured this out now and you are missing a 2 port vacuum switch. see attached pic.

 

[naa10104]

I think I figured this out now and you are missing a 2 port vacuum switch. see attached pic.

Hello,

I will be with the car tomorrow and get additional info. I will try to attach a photo of the switch/sensor to this post. I will tell you that the current sensor looks original and looks like it belongs to the car. The bottom nipple on the switch is capped and the middle and top have hoses. Thanks

 

[jbojo]

There are 2 vacuum switches, the 3 port one is connected to the pump and the 2 port one is attached to the heater hose. All 3 ports on that one switch should be used and its used to throttle either ported or manifold vacuum depending on the engine temp. As I said, you are missing parts on your emission system.

 

[naa10104]

There are 2 vacuum switches, the 3 port one is connected to the pump and the 2 port one is attached to the heater hose. All 3 ports on that one switch should be used and its used to throttle either ported or manifold vacuum depending on the engine temp. As I said, you are missing parts on your emission system.

THanks, I will take some detailed photo's and post them next time I am at the car. Hopefully I can get this figured out.

 

[Jeff73Mach1]

I am very impressed at how far you have come on this thread in getting this issue sorted out-kudos to all!

 

[naa10104]

View attachment 37708

There are 2 vacuum switches, the 3 port one is connected to the pump and the 2 port one is attached to the heater hose. All 3 ports on that one switch should be used and its used to throttle either ported or manifold vacuum depending on the engine temp. As I said, you are missing parts on your emission system.

THanks, I will take some detailed photo's and post them next time I am at the car. Hopefully I can get this figured out.

I went to the car today and looked it over carefully ... I will attach some photos, although don't know if they are going to be of much help. I will tell you that I could find no part numbers on the 3 port vacuum switch. It does look original to the car and is mounted into the water pump housing. Immediately in front of it is a one wire sensor,(assuming temp.) which is screwed into the block near a heater hose and immediately below the housing for the thermostat. I looked carefully for a second 2 port vacuum switch anywhere on the motor and there is not one to be found. I checked near all the heater hoses - none. I did not see any place where it looked like there was supposed to be one, no plugs etc. I don't believe my car ever had one.

Of interest I looked at a 71 Mustang with a 351 C 2v auto with AC ... my car is non AC. It did not have an EGR or the 4 port vacuum hook up on the firewall. It did have the 3 port vacuum switch basically in the same place as mine. It was hooked up as follows :

top port to ported vacuum on carb

middle port to manifold vacuum on intake forward of carb.( on my car this manifold port is capped.

bottom port to distributor,(single diaphram) like mine.

Let me kow what you all think ... thanks

There are 2 vacuum switches, the 3 port one is connected to the pump and the 2 port one is attached to the heater hose. All 3 ports on that one switch should be used and its used to throttle either ported or manifold vacuum depending on the engine temp. As I said, you are missing parts on your emission system.

THanks, I will take some detailed photo's and post them next time I am at the car. Hopefully I can get this figured out.

I went to the car today and looked it over carefully ... I will attach some photos, although don't know if they are going to be of much help. I will tell you that I could find no part numbers on the 3 port vacuum switch. It does look original to the car and is mounted into the water pump housing. Immediately in front of it is a one wire sensor,(assuming temp.) which is screwed into the block near a heater hose and immediately below the housing for the thermostat. I looked carefully for a second 2 port vacuum switch anywhere on the motor and there is not one to be found. I checked near all the heater hoses - none. I did not see any place where it looked like there was supposed to be one, no plugs etc. I don't believe my car ever had one.

Of interest I looked at a 71 Mustang with a 351 C 2v auto with AC ... my car is non AC. It did not have an EGR or the 4 port vacuum hook up on the firewall. It did have the 3 port vacuum switch basically in the same place as mine. It was hooked up as follows :

top port to ported vacuum on carb

middle port to manifold vacuum on intake forward of carb.( on my car this manifold port is capped.

bottom port to distributor,(single diaphram) like mine.

Let me kow what you all think ... thanks

THanks, I will take some detailed photo's and post them next time I am at the car. Hopefully I can get this figured out.

I went to the car today and looked it over carefully ... I will attach some photos, although don't know if they are going to be of much help. I will tell you that I could find no part numbers on the 3 port vacuum switch. It does look original to the car and is mounted into the water pump housing. Immediately in front of it is a one wire sensor,(assuming temp.) which is screwed into the block near a heater hose and immediately below the housing for the thermostat. I looked carefully for a second 2 port vacuum switch anywhere on the motor and there is not one to be found. I checked near all the heater hoses - none. I did not see any place where it looked like there was supposed to be one, no plugs etc. I don't believe my car ever had one.

Of interest I looked at a 71 Mustang with a 351 C 2v auto with AC ... my car is non AC. It did not have an EGR or the 4 port vacuum hook up on the firewall. It did have the 3 port vacuum switch basically in the same place as mine. It was hooked up as follows :

top port to ported vacuum on carb

middle port to manifold vacuum on intake forward of carb.( on my car this manifold port is capped.

bottom port to distributor,(single diaphram) like mine.

Let me kow what you all think ... thanks

 

[jbojo]

OK, here is what I see"

top port to ported vacuum on carb This is correct

middle port to manifold vacuum on intake forward of carb.( on my car this manifold port is capped. This goes to distributor

bottom port to distributor,(single diaphram) like mine. This goes to Manifold vacuum.




The 2 port vacuum switch is a fitting that is connected to the heater hose and is used to control when the EGR is opened.

Is the vacuum modulator on the transmission a single or dual vacuum connection?

 

[barnett468]

Never assume the switches work . Check them with the engine cold and with it hot.

If you live near sea level and the engine has ever been rebuilt, it will still be lean when all the smog is operating correctly.

 

[naa10104]

OK, here is what I see"

top port to ported vacuum on carb This is correct

middle port to manifold vacuum on intake forward of carb.( on my car this manifold port is capped. This goes to distributor

bottom port to distributor,(single diaphram) like mine. This goes to Manifold vacuum.




The 2 port vacuum switch is a fitting that is connected to the heater hose and is used to control when the EGR is opened.

Is the vacuum modulator on the transmission a single or dual vacuum connection?

Hello,

Just to clarify the locations that you commented on in Red are from a 71 Mustang that I went to look at ... not my car. I checked all the heater hoses and my car has no 2 port vacuum switch. Do you have a photo of exactly where it would be and what it looks like ? The trans modulator is a dual and both are connected .... trans functions fine. Thanks again for all the input ... appreciate it.

Never assume the switches work . Check them with the engine cold and with it hot.

If you live near sea level and the engine has ever been rebuilt, it will still be lean when all the smog is operating correctly.

You bring up a some interesting questions ...I live near the east coast of MD/VA. The engine has been rebuilt ... I know that the motor and heads were gone through. The heads were sent to a speed/machine shop where all the basics were done, possibly some porting or other performance tweaks, but I have no way of knowing exactly what was done. Don't believe anything in the motor was changed, sounds like a stock cam. Original Motorcraft 2100 2v that was just rebuilt.

I have not actually checked the 3 port vacuum switch, but may do that in the future. As the vacuum lines are currently installed ... the motor seems to be running correctly. The off idle miss is gone since I made the recommended change and run the EGR off of "ported" vacuum off of the carb. Some have said that the EGR should be controlled by the 3 port vacuum switch as it sends "ported" or "manifold" vacuum to the EGR depending on engine temp. I get that but of interest ... when I had the EGR connected in that fashion it had the miss whether the engine was warm or cold. I know the 3 port vacuum switch could be bad, but if I replace it and it sends "manifold" vacuum to the EGR when needed I will have the same problem all over again. Switching it to "ported" straight from the carb really seems to have corrected the issue. As I said before I have spent many hours trying to locate a straight forward diagram for vacuum hook ups for my vehicle. You would think that since my car is such a basic set up found on may Mustangs of that time there would be one .... if there is I can't find it. As always any input is appreciated !!!!!

 

[jbojo]

"Just to clarify the locations that you commented on in Red are from a 71 Mustang that I went to look at ... not my car. I checked all the heater hoses and my car has no 2 port vacuum switch. Do you have a photo of exactly where it would be and what it looks like ? The trans modulator is a dual and both are connected .... trans functions fine. Thanks again for all the input ... appreciate it."

The best photo is the one that I had posted earlier. I circled the part.

That 2 port vacuum switch goes to the side connector on the transmission and sends ported vacuum to that modulator. The center connection on the tranny receives manifold vacuum. That is the purpose of the 4 port connector on the firewall. Vacuum source in one and vacuum out to the tranny modulator.

"Switching it to "ported" straight from the carb really seems to have corrected the issue."

The ported vacuum source from the carb is tee'd and goes to the 2 port vacuum switch that sends ported vacuum to the transmission and to the top port of the 3 port vacuum switch. The 3 port valve (PVS Valve) goes to the distributor so the bog would still be fixed.

EDIT: Here is a description of these valves operation. We can probably modify the system to work with out the 2 port switch, I would need to think about it some.

 

[naa10104]

"Just to clarify the locations that you commented on in Red are from a 71 Mustang that I went to look at ... not my car. I checked all the heater hoses and my car has no 2 port vacuum switch. Do you have a photo of exactly where it would be and what it looks like ? The trans modulator is a dual and both are connected .... trans functions fine. Thanks again for all the input ... appreciate it."

The best photo is the one that I had posted earlier. I circled the part.

That 2 port vacuum switch goes to the side connector on the transmission and sends ported vacuum to that modulator. The center connection on the tranny receives manifold vacuum. That is the purpose of the 4 port connector on the firewall. Vacuum source in one and vacuum out to the tranny modulator.

"Switching it to "ported" straight from the carb really seems to have corrected the issue."

The ported vacuum source from the carb is tee'd and goes to the 2 port vacuum switch that sends ported vacuum to the transmission and to the top port of the 3 port vacuum switch. The 3 port valve (PVS Valve) goes to the distributor so the bog would still be fixed.

EDIT: Here is a description of these valves operation. We can probably modify the system to work with out the 2 port switch, I would need to think about it some.

Hello,

Want to make sure I understand you ... is there a way to keep my current set up with the 3 port vacuum switch but utilize all three ports,(bottom is currently capped), and somehow tie it in with the distributor and ported vacuum on the carb ? Thanks

 

[jbojo]

"Just to clarify the locations that you commented on in Red are from a 71 Mustang that I went to look at ... not my car. I checked all the heater hoses and my car has no 2 port vacuum switch. Do you have a photo of exactly where it would be and what it looks like ? The trans modulator is a dual and both are connected .... trans functions fine. Thanks again for all the input ... appreciate it."

The best photo is the one that I had posted earlier. I circled the part.

That 2 port vacuum switch goes to the side connector on the transmission and sends ported vacuum to that modulator. The center connection on the tranny receives manifold vacuum. That is the purpose of the 4 port connector on the firewall. Vacuum source in one and vacuum out to the tranny modulator.

"Switching it to "ported" straight from the carb really seems to have corrected the issue."

The ported vacuum source from the carb is tee'd and goes to the 2 port vacuum switch that sends ported vacuum to the transmission and to the top port of the 3 port vacuum switch. The 3 port valve (PVS Valve) goes to the distributor so the bog would still be fixed.

EDIT: Here is a description of these valves operation. We can probably modify the system to work with out the 2 port switch, I would need to think about it some.

Hello,

Want to make sure I understand you ... is there a way to keep my current set up with the 3 port vacuum switch but utilize all three ports,(bottom is currently capped), and somehow tie it in with the distributor and ported vacuum on the carb ? Thanks

yeah I believe so, working on it. It would work as designed if you used the 2 port switch though. Are you trying to keep this all original?

 

[naa10104]

"Just to clarify the locations that you commented on in Red are from a 71 Mustang that I went to look at ... not my car. I checked all the heater hoses and my car has no 2 port vacuum switch. Do you have a photo of exactly where it would be and what it looks like ? The trans modulator is a dual and both are connected .... trans functions fine. Thanks again for all the input ... appreciate it."

The best photo is the one that I had posted earlier. I circled the part.

That 2 port vacuum switch goes to the side connector on the transmission and sends ported vacuum to that modulator. The center connection on the tranny receives manifold vacuum. That is the purpose of the 4 port connector on the firewall. Vacuum source in one and vacuum out to the tranny modulator.

"Switching it to "ported" straight from the carb really seems to have corrected the issue."

The ported vacuum source from the carb is tee'd and goes to the 2 port vacuum switch that sends ported vacuum to the transmission and to the top port of the 3 port vacuum switch. The 3 port valve (PVS Valve) goes to the distributor so the bog would still be fixed.

EDIT: Here is a description of these valves operation. We can probably modify the system to work with out the 2 port switch, I would need to think about it some.

Hello,

Want to make sure I understand you ... is there a way to keep my current set up with the 3 port vacuum switch but utilize all three ports,(bottom is currently capped), and somehow tie it in with the distributor and ported vacuum on the carb ? Thanks

yeah I believe so, working on it. It would work as designed if you used the 2 port switch though. Are you trying to keep this all original?

Hi, it does not have to be original. This is just a driver it's not a concourse level car. It does appear that it came with the three port switch so if I can make that work that is probably the way I would want to go. But if the two port switch would work then that would be an option. If you need an updated diagram of how the vacuum is running now, let me know but I think it is in this thread somewhere. Thx again

 

[jbojo]

One more question, the vacuum tree on the manifold behind your carb, how many small ports does it have?

 

[barnett468]

If it doesn't have to be original, why are you going thru all this effort to connect the EGR.

You can buy replacement switches from any auto parts store.

If your carb is original, you definitely need to go up at least 1 size on the main jet . You can "guestimate" the correct jetting by test driving AND looking at the spark plugs, unfortunately, since you have beevn running on those plugs for a while with the EGR causing probs . They are not an accurate source for judging jetting.

You can remove the front plug from each bank and post a photo of the end.

Post the part number.

Tell us what your actual water temp is.

The timing curve on those cars is horrible because they had to be timed to meet emissions requirements . You can increase power and mileage and reduce engine temps by changing the timing curve.

 

[Don C]

Unless you are required to have the EGR and/or switches functional I would simplify it as much as possible. Disconnect and plug/cap everything and see if you can get it running better. You may have to change jets or re-clock your distributor. After you get it running better then connect your vacuum advance directly to manifold vacuum and see how it runs. Then try it connected to ported vacuum.