fuel vapors

[my85c10]

I have taken all emissions off my 85 C10 during the 350 swap. I'm sick of the gas fumes after parking in the garage. Can I just get a new canister and run the vent lines to it? Or, is there a better approach?

[Blue Bowtie]

If you install the fuel tank vent line you'll also need to install the purge control Without purging the canister, it will soon become saturated and useless, and the fuel vapors will be all over the parking space again.

[my85c10]

Thanks for the info. Since I have you here and I'm too lazy to look it up myself, what does the purge control consist of?

[Blue Bowtie]

On the '85 trucks there should have been an E4ME carburetor, and no TBI system That being the case, the system would have:

1. A tank pressure control valve and a purge control valve (both usually part of the EVAP canister arrangement or attached within inches of the canister);
2. 
   A TVS (Temperature/Vacuum Switch) mounted to the intake coolant crossover passage or thermostat housing;
3. And two timed ports on the carburetor. The typical 1985 E4ME carburetor installation would use the 'H' port to operate the purge conrtol valve and draw canister vapors through the 'T' port.

This diagram may help clarify the connections:

[my85c10]

The V6 is now a 350 with a 600 cfm Holley. What would be the bare requirements to add back to the block in order to cancle the fumes?

[Blue Bowtie]

Presuming that this is a typical Holley (like a 4150-4160) you can use a "T" on the timed vacuum port on the Holley (BLUE arrow). This is the same line used for distributor vacuum advance, and can also act as the purge control valve signal. Route the hose through a factory TVS to the purge control valve pilot.

Connect the purge vapor line via a "T" to the PCV line OR use the EGR line on the right side of the carb (RED arrow).



This will allow vapors to be purged to the intake whenever the engine is warm and above closed throttle. Obviously, WOT will drop vacuum at the timed port (just as it should for the distributor vacuum advance) so there will be no purge flow under heavier loads - Just as it should be.

[my85c10]

Thankyou very much, you are very informative.

[silicon212]

I like the arrows with the eyes.

[my85c10]

Factory TVS.................Is that the thermal vacuum switch?
OK, I think I got it. Install a new canister. "T" off the timed port from the holley, go through the TVS, into the canister. Come out of the canister and dump it back into the manifold via the egr port, correct?
Also, I have a three port fuel pump. The only hoses being used are the input from the tank and the output to the carb. Everything else has been capped. I know I need to run the vent line back to tank. There's another hose coming from the pump that is capped and is prone to leaking liquid fuel. Where dose that hook up to?

[Blue Bowtie]

Yes, TVS = Temperature (or Thermal) Vacuum Switch.

Use the timed line from the Holley, through the TVS, to the PURGE control valve for the canister.

The third line at the fuel pump is a fuel return line. Although a three-port mechanical fuel pump will WK with only two lines, the pump is designed to pump a continuous volume of fuel (much like an electric pump) and return the excess to the tank through this third line. The intent was to keep more fuel moving through the supply line so it did not linger in the line when the engine was using very little fuel. The fuel moving more constantly would stay cooler, and thisz system would nearly eliminate the possibility of vapor lock. Unlike some people believe, it has nothing to do with emissions other than the side benefit of keeping the fuel a bit cooler and keeping vapor pressure more constant.

You might be able to use this line - Maybe. Most systems used a dip tube to return fuel closer to the bottom of the tank, and that would not work well as a vapor line as far as the evap canistwer is concerned. They looked something like this:



If the truck originally had an evap canister, there should have been a vapor line for the canister somewhere at the tank.

[my85c10]

I did leave the TVS in the intake on the motor swap. It has four ports that are not marked. Can I attach the vacuum any way I want or are there in's and out's?

[Blue Bowtie]

There is usually one source or supply connection, one load or device connection, and one vent connection. Your 4-port TVS may have two device connections which open at different temperatures, or it may simply be a dual TVS stacked (for use with two different systems, such as EVAP purge and EGR). About the only way to verify is to connect vacuum to each port and see how it reacts, or find a diagram detailing the TVS you currently have installed.

[Blue Bowtie]

This should be the vacuum routing diagram specifically for your truck:

http://www.autozone.com/servlet/UiBr...3d80114c4a.jsp

You can probably find useful information about the system here:

http://www.autozone.com/servlet/UiBr...3d801150f0.jsp

[my85c10]

I got a new canister from LMC, used the existing TVS and began to try to figure out the routing. The canister had five ports on it. The single port was fuel tank in so that was easy. The other two ports had a large hole and a small hole each. One was labeled main vacuum in and the other carb bowl. I used a T fiting at my distributor line and went into the TVS using both lower ports on the TVS and out the top two ports to the canister. I used another T at the canister for the purge lines back to the pcv line. Adjusted the carb mixture and it fired right up. No more fumes. Thanks for the help! I'll probably be back soon as I need to redo the suspension soon.

[72elco]

Originally Posted by Blue Bowtie

Presuming that this is a typical Holley (like a 4150-4160) you can use a "T" on the timed vacuum port on the Holley (BLUE arrow). This is the same line used for distributor vacuum advance, and can also act as the purge control valve signal. Route the hose through a factory TVS to the purge control valve pilot.

Connect the purge vapor line via a "T" to the PCV line OR use the EGR line on the right side of the carb (RED arrow).



This will allow vapors to be purged to the intake whenever the engine is warm and above closed throttle. Obviously, WOT will drop vacuum at the timed port (just as it should for the distributor vacuum advance) so there will be no purge flow under heavier loads - Just as it should be.

Hi, a am a newbee here. I am having the same problem with fumes underhood. I am trying to figure out this picture here. I have read the details where to connect the vapor line on the timed vacuumed port using the tvs with the T fitting for the purge lines. My question is, where do you connect the distributor vacuum advance line after disconnected from the timed port? I have a Holley 4150 and my the cannister have only three ports. Secondly I have no pcv anywhere on the engine. How do I fix this problem with no fumes? Your help will be greatly appreciated to know how to remedy this problem.