"Correct" Vac/Emissions/EGR Hose Routing and Rough Starts
08-08-2001, 09:00 AM
#1
Le Mans Master
Thread Starter
"Correct" Vac/Emissions/EGR Hose Routing and Rough Starts
Ever since I took the plunge and bought the 'correct' hoses and diagram kits for my '80 and installed according to the underhood emissions diagram, I've had nothing but poor starting and an inoperable choke. I finally decided to exorcise my L48's (mildly upgraded 
) demons and re-route a few to see what impact they would have. Vast improvement!!! Turns out, the devices, which I'll refer to as thermal sensors that are built into the front of my intake manifold (there are three of them) were the culprits. They are color-coded blue, tan and light purple. After I re-routed/bypassed them, the choke now engages and the car runs smoothly both with choke engaged (about 1600rpm) and with the choke disengaged (light blip on throttle, settles to 800rpm). What gives on those darn sensors? I can see that the car used to 'smooth out' once I hit a certain temp and that's why I focused on the 'thermal' (heat) sensors since they all were in-line with critical emissions/vac/egr systems. Should they have been 'behaving' in this way? I had recently replaced the 'purple' sensor that drives the EGR line since its top had come loose (suspected a leak there for sure). The blue sensor's top is also a tad loose. Would that be the cause for the rough running then smoothing out after warm-up or should I just NOT be using those darn sensors at all (ie. do they block the vac signal until warmed up or could they just be worn out? perhaps fresh ones will allow proper warmup and start?)? I transferred them from the OEM manifold and intake radiator hose neck back when I swapped in a fresh Performer manifold and intake rad. neck. Arghh!!! :mad
) demons and re-route a few to see what impact they would have. Vast improvement!!! Turns out, the devices, which I'll refer to as thermal sensors that are built into the front of my intake manifold (there are three of them) were the culprits. They are color-coded blue, tan and light purple. After I re-routed/bypassed them, the choke now engages and the car runs smoothly both with choke engaged (about 1600rpm) and with the choke disengaged (light blip on throttle, settles to 800rpm). What gives on those darn sensors? I can see that the car used to 'smooth out' once I hit a certain temp and that's why I focused on the 'thermal' (heat) sensors since they all were in-line with critical emissions/vac/egr systems. Should they have been 'behaving' in this way? I had recently replaced the 'purple' sensor that drives the EGR line since its top had come loose (suspected a leak there for sure). The blue sensor's top is also a tad loose. Would that be the cause for the rough running then smoothing out after warm-up or should I just NOT be using those darn sensors at all (ie. do they block the vac signal until warmed up or could they just be worn out? perhaps fresh ones will allow proper warmup and start?)? I transferred them from the OEM manifold and intake radiator hose neck back when I swapped in a fresh Performer manifold and intake rad. neck. Arghh!!! :mad
08-08-2001, 11:27 AM
#2
Le Mans Master
Re: "Correct" Vac/Emissions/EGR Hose Routing and Rough Starts (TedH)
I would replace them and try that, they are not terribly expensive and they do actually perform a function. Aprat from that if you are happy with the setup now , it passes inspection (tailpipe) and doesnt effect fuel economy then Id say stay with it.
08-09-2001, 01:06 AM
#3
Racer
Member Since: Nov 1999
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Re: "Correct" Vac/Emissions/EGR Hose Routing and Rough Starts (TedH)
I have replaced all of them on my 80 because they were all defective. FYI they are known as TVS - Thermal Vacuum Switches or Ported Vacuum Switches. If you remove them, you will see a temperature number stamped on the bottom. This is the temperature the switch opens at. The switches function are to: 1. Close the exhaust crossover when it's COLD outside. 2. Keep the EGR, vacuum timing advance and AIR pump from kicking in until the engine is warm. If you get replacements make sure you take the olds ones with you to the store. I've had guys at the parts stores give me the wrong size threads and/or temperature and/or connectors.
If the tops are loose at all, they are defective. They're about $5-10 each to replace. If you have a vacuum pump and hair drier you can test them.
The choke on an 80 is electronic and should have nothing to do with these switches or hoses.
I've got a couple of diagrams that show the correct routing/connections, do you need it?
The only problem I found on my engine was the vacuum advance was getting full vacuum from the port on the Q-Jet. I asked Lars and he thought it was connected wrong, but I confirmed with other members that I did indeed have it connected to the right place. Against Lars advice, I disassembled my Q-Jet and plugged the slot in the primary venturies below the blades with JB weld and drilled a small (3/32") above them, and it fixed my problems. I figured if I screwed up I could just buy another Q-Jet off ebay for $15.
If the tops are loose at all, they are defective. They're about $5-10 each to replace. If you have a vacuum pump and hair drier you can test them.
The choke on an 80 is electronic and should have nothing to do with these switches or hoses.
I've got a couple of diagrams that show the correct routing/connections, do you need it?
The only problem I found on my engine was the vacuum advance was getting full vacuum from the port on the Q-Jet. I asked Lars and he thought it was connected wrong, but I confirmed with other members that I did indeed have it connected to the right place. Against Lars advice, I disassembled my Q-Jet and plugged the slot in the primary venturies below the blades with JB weld and drilled a small (3/32") above them, and it fixed my problems. I figured if I screwed up I could just buy another Q-Jet off ebay for $15.
08-09-2001, 08:53 AM
#4
Le Mans Master
Thread Starter
Re: "Correct" Vac/Emissions/EGR Hose Routing and Rough Starts (Gerry)
I think the switches were so defective they were 'overpowering' the choke due to the leaks around the bases of the loose switches. I've replaced the plumb/purple switch via Dr Rebuild. I'll look into the blue and tan/brown switches now that I know they can be the cause. That may also be the reason my replacement EGR valve never wanted to work right (vac leaks around the switches). I had tried replacing the EGR two years ago after realizing that someone had cleverly welded the underside of the EGR closed (it still passed emissions). I have since added a 3-way cat converter to address the NOx emissions that I recall the EGR is meant to manage. This car WILL be better than the day it was manufactured SOMEDAY... :smash: :D
09-17-2020, 03:14 PM
#5
Intermediate
I have replaced all of them on my 80 because they were all defective. FYI they are known as TVS - Thermal Vacuum Switches or Ported Vacuum Switches. If you remove them, you will see a temperature number stamped on the bottom. This is the temperature the switch opens at. The switches function are to: 1. Close the exhaust crossover when it's COLD outside. 2. Keep the EGR, vacuum timing advance and AIR pump from kicking in until the engine is warm. If you get replacements make sure you take the olds ones with you to the store. I've had guys at the parts stores give me the wrong size threads and/or temperature and/or connectors.
If the tops are loose at all, they are defective. They're about $5-10 each to replace. If you have a vacuum pump and hair drier you can test them.
The choke on an 80 is electronic and should have nothing to do with these switches or hoses.
I've got a couple of diagrams that show the correct routing/connections, do you need it?
The only problem I found on my engine was the vacuum advance was getting full vacuum from the port on the Q-Jet. I asked Lars and he thought it was connected wrong, but I confirmed with other members that I did indeed have it connected to the right place. Against Lars advice, I disassembled my Q-Jet and plugged the slot in the primary venturies below the blades with JB weld and drilled a small (3/32") above them, and it fixed my problems. I figured if I screwed up I could just buy another Q-Jet off ebay for $15.
If the tops are loose at all, they are defective. They're about $5-10 each to replace. If you have a vacuum pump and hair drier you can test them.
The choke on an 80 is electronic and should have nothing to do with these switches or hoses.
I've got a couple of diagrams that show the correct routing/connections, do you need it?
The only problem I found on my engine was the vacuum advance was getting full vacuum from the port on the Q-Jet. I asked Lars and he thought it was connected wrong, but I confirmed with other members that I did indeed have it connected to the right place. Against Lars advice, I disassembled my Q-Jet and plugged the slot in the primary venturies below the blades with JB weld and drilled a small (3/32") above them, and it fixed my problems. I figured if I screwed up I could just buy another Q-Jet off ebay for $15.
Last edited by Dee69911; 12-14-2020 at 01:19 PM.
09-17-2020, 03:56 PM
#6
Melting Slicks
Member Since: May 2015
Location: Cape Girardeau Missouri
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Is the aluminum emission system sticker still there? It's near the power brake booster. If so it shows the emission vacuum hose layout; Granted it's in graphic form but it's easy to follow.
I believe that the '80 L-82 uses three TVS switches. One is for EFE (early fuel evaporation), one for EGR (exhaust gas recirculation) and the third for "spark".
The "sprark" one isn't present in my '79 L82 so I'm not sure what it really does but I suspect it modifies vacuum advance with engine coolant temperature.
it's important to get the exact right TRVs switches for your engine as not only do they have different temperature operation points but I believe that opening and closing rates vary as well. In other words some or all will modulate (vary) vacuum within a certain temperature range. That ability to modulate is inherent with both vacuum and compressed air control systems and explains why they found great use in automotive and other control systems as before digital electronics it was it was difficult/expensive/unreliable to produce similar control systems using other methods. While greatly reduced vacuum control systems still exist on most? all? new vehicle engines as there's no simpler, effective or more reliable method to use.
I recall reading that the purely mechanical computers used in the main gun fire control system in the Iowa class US battleships was so exceptionally engineered that it actually outperformed digital computers were retained through various refittings and upgrades and would still be used should the ships be put back in service. Look them up for some very interesting reading.
I believe that the '80 L-82 uses three TVS switches. One is for EFE (early fuel evaporation), one for EGR (exhaust gas recirculation) and the third for "spark".
The "sprark" one isn't present in my '79 L82 so I'm not sure what it really does but I suspect it modifies vacuum advance with engine coolant temperature.
it's important to get the exact right TRVs switches for your engine as not only do they have different temperature operation points but I believe that opening and closing rates vary as well. In other words some or all will modulate (vary) vacuum within a certain temperature range. That ability to modulate is inherent with both vacuum and compressed air control systems and explains why they found great use in automotive and other control systems as before digital electronics it was it was difficult/expensive/unreliable to produce similar control systems using other methods. While greatly reduced vacuum control systems still exist on most? all? new vehicle engines as there's no simpler, effective or more reliable method to use.
I recall reading that the purely mechanical computers used in the main gun fire control system in the Iowa class US battleships was so exceptionally engineered that it actually outperformed digital computers were retained through various refittings and upgrades and would still be used should the ships be put back in service. Look them up for some very interesting reading.
