TR6 TR6 Emissions

[bash]

I finally got to cleaning out the radiator last weekend and found that the anti-run-on valve has a broken connector (the vacuum line from the manifold - which explains the open connector on the manifold!). The car still runs without this connector, though (I haven't driven it yet, but it idles fine and it will rev, though I haven't pushed it). I can get a new anti-run on valve, but rather than spend the money, I wondered if anyone can tell me why the car idles okay with an open vacuum connection on the manifold?

If the broken valve is the start of the emissions removal, can anyone tell me exactly what needs to be removed, what should be left where it is, what should be plugged etc.

As ever, I would be grateful for any help and advice!

 

[Yellowdog]

I will take a stab . . . .

The anti-run-on valve is part of the crankcase emission control system.

When the engine is not running the gas vapors from the tank and carb float bowls as well as the oil vapors from the crankcase are stored in the carbon canister and associated tubing. When the engine is started the anti-run-on valve opens and allows these vapors/fumes to be sucked into the intake manifold to be burned during the combustion cycle. The vacuum line from the intake manifold to the anti-run-on valve has a very low negative pressure. Just enough to maintain the air flow from the valve cover through the carbon canister / valve on to the intake manifold. When the engine is shut off the anti-run-on valve closes sealing off the carbon canister again and allowing fresh air to be sucked into the manifold, thus preventing the unburned vapors from continuing the ignition process in a hot engine. This is not a true vacuum line like the one for the distributor.

The anti-run-on valve operation is tied into the oil pressure switch. Low/no oil pressure, the valve seals off the canister; high oil pressure the valve opens and allows for the unburned vapors and crancase emissions to be sucked into the engine.

So, the engine idles 'normally' because there really is no vacuum leak, the same amount of negative pressure is there no matter whether the line is attached to the anti-run-on valve or not. An issue may develop at higher rpm's under load.

If you want to remove these parts, you will need to find another way to vent the gas tank as it is a sealed unit and you will need to insure that you maintain a positive crankcase vent path so you do not develop other problems.

Hope this helps a little bit . . . .

 

[RomanH]

I have to disagree with Yellowdog. The anti-run on valve does not operate when the engine is turned on but rather when it is turned off. The oil pressure switch senses the loss of pressure and closes the contacts for 1 or 2 seconds which opens the bottom of the solenoid valve to atmosphere.
This allows air to be drawn in through the valve then the small hose and finally in the intake manifold.This creates a large depression (i.e. vacuum leak)in the intake manifold and squeltches the combustion process thus preventing run on.
Why your car runs fine with this fitting open I can not tell you. All I know is that my car would not run like that and I had to cap the manifold fitting until I could repair the ant-run on valve.
Yellowdog is right about the fuel tank venting and the positive crankcase venting. I would not remove the charcoal can since it is an easy (already there) and safe way to vent the gas tank. It also does not rob power. I had to rebuild this system because PO removed parts of it sealing the fuel system. The car could not be driven with the gas cap closed.
If you want to re-route the crankcase venting there are several interesting methods you can use. You can find them on-line by doing a search or let me know and I can direct you to a commercial site.

 

[Yellowdog]

Roman,

You post prompted a search in my stash of tech articles. I knew there was something else going on in there but could not recall exactly what it was.

Upon start-up a purge valve (more like a fitting) in the cannister opens due to the manifold vacuum, to allow the trapped vapors in the cannister to go through the manifold to the cylinders. This is what I was thinking of initially. This is what vents the fuel tank while the engine is running.

You are correct, the anti-run-on valve is closed during this time. And does open during shutdown. I was thinking about the valve having to open during operation in order to vent the fuel tank. Forgot about the purge line.

As for the engine running without the line to the manifold connected, I will only say that all of our engines will run at idle in this condition, but not at any speed, I mean don't even think about cracking the throttle. Just tried it. I did not get out the vacuum gauge but there was hardly any suction at idle. Magic I guess . . . .

 

[Guest]

Bash,
As far as emissions go, you will have to be careful on what you remove according to where you live. I know in the 64 parishes in Louisiana, only 3 have emissions checks, thank goodness I am not in one of these. The point being, if you start stripping emissions, can you pass the test in your area. The 74-76 TR6 have a fair amount of emission controls. To really strip the car of any of these you will probably have to change your intake manifold and possibly plug a few hole in other places. Getting the car to run properly afterwards can be a challenge. My 73 has zero remaining factory emission controls and actually emits less than what was permitted for that year (had it checked) because of aggressive tuning. What you DON'T want to do is start scavenging any gasses or fumes from your tank or valve cover with your intake manifold vacuum. This should be used only for your brake servo. I scavenge my valve cover with my triple carbs and vent the gas tank in a safe location beneath the car, through a replaceable charcoal filter (not the original canister). You might search out an early slanted intake (not the boxed ones on a 69), dump the air pump if you have one, and think of the engine as just a 6-cylinder tractor engine with no add-ons. Another trick to reduce the number of hoses under the bonnet is to go without the vacuum advance hoses and tune the car with centrifugal advance.

Bill

 

[bash]

Thanks for all the replies, guys. As I said, I haven't driven the car yet, so I don't know if the engine will run well under load, but it looks like I should be plugging that hole in the manifold - I knew I should do that, but couldn't figure out why it was running now! It sounds like removing the emissions stuff will be a much bigger pain than I originally thought when I bought the car, so I guess I will work on making it all work, rather than trying to work out what to remove.

Thanks again for the information