I have a 92 Bronco 351.
I just did a tune up and my check engine light came on for the first time.
I noticed a vaccum line disconnected from the coffee can looking vaccum canister on passanger side fender well.

Can anyone tell me what this is, how it works and if it could make my check engine light come on?

Thanks

lwilli2

 

I never figured it out for sure, but I always assumed it was a vacume resivoir. If the line going to engine is breathing fresh air, it is sucking unmetered air and your not getting enough fuel in.

 

there is two 'canister type things' on the wheel well. the front one is the filter for the AIR injection system and is connected to the pump below the alternator via a 1" (ish) dia rubber hose.

The rearward one is the resovouir for the EGR system and if dicconected is likely to cause the Check Light to come on as the ECU won't see the EGR valve open when it requests it.

There are two hoses connected to it - on is certainly red and I forget about the other - have a look at the sticker on the underside of the hood above the heater system and there should be a diagram of how its connected up. On my 92 302 a line comes from the vacuum tree on the top of the plenum, runs around the back of the plenum and splits in two, one runs to this canister. I think the canister has a non-return valve in it so you have to connect it the right way around but as long as the rubber connector on the end of the hoses is intact it should be obvious.

One caution to bare in mind is after a while these vacuum hoses become very brittle with the heat and will snap like dry spagetti. They're prone to leaks and become very delicate so be careful when you're working with them. A hand held vacuum pump/ gauge is very handy for checking each one.

 

there is also another one that looks to be associated with the cruise control under the air cleaner. I think both the lines going ot the canister on the passenger side are red. Don't remember for certain though, but if they are cracked or broken, replace them. Umetered air will certainly make your truck run aweful. It will cause the engine ot race and when shifted the tranmission will slam into gear. So be careful of the vacuum leaks.