I have a 91 F150 300-6 and I do not have a evap canister purge valve, just a straight connection to the throttle body.
Do I need a purge valve at all? Or can I block off the line completly? Maybe a cause of my hesation I get sometimes when I step on the gas from a red light...
Is it possible that it never came with one?
Or more likely someone took it off for who knows what reason.

 

I don't think that the canister purge valve would cause a hesitation. It could be possible that it never came with one...my truck does not have one, although I have a 302. If you check the computer for codes, it should set a code if it is supposed the have the purge valve and one is not present. If you don't have any codes, don't worry about it.

 

My information says you should have a canister purge valve with a 91 F150 300-6.
It should cause surging if it is missing at idle, as it will cause an extra rich mix.
That is why the canister purge valve only opens on a warm engine at mid throttle.
I guess it could cause hesitation early in the engine operation each day.

 

So would it be a good idea to disconnect the line would this hurt anything?

 

This line removes the gas vapors that were trapped by the canister from the fuel tank.

The fuel tank(s) fuel (gas) cap is a one way check valve letting air in but not out.
If the fuel expands there is a one way check valve in the top of the tank(s) to let the pressure out. Then from the check valve the gas fumes goes through hoses to the canister to be collected there until the engine is warm and the throttle is at mid range. This is when the purge valve lets the gas fumes into the engine to be burnt.

If you plug this line you have to find an old stile venting gas cap and you should not park the truck inside any building ever again. Not to mention that this is one of your main emission systems.

 

Just be sure to block the port off after the disconnect otherwise you will go to high idle with a vacuum leak. You should still have the connector to plug a purge valve in to if you wanted to replace it, if you disconnect the worse is that you may have a gas smell from the truck because the purge cannister has no way to hold the evap from the tank.

 

I checked my ecm, I found no purge valve codes.
I wonder if the ecm knows if it is there or not?

 

If there's not a code for it being missing, I'd leave it alone.

 

subford,

I know a really old thread.

My 87 F150 4.9 does not have the purge solenoid on it. What is different between the trucks with the purge solenoid and not having the solenoid.
I am having a surging idle when first started and then it clears up and runs fine.

Is the truck calibrated to have the vacuum leak 100% of the time? As that is what is happening on the trucks without the purge solenoid a constant vacuum leak.