I seem to have a vacuum leak between the port in the fender (under the hood on drivers side) and the vacuum reservoir. Has anyone had trouble with this line that runs through the body and down the frame? If so, how did you repair it?

 

The "port" in the fender is a reservoir with no line that runs through the fender or frame. Check vacum at "port". here are some helpful pics. Mystery vacuum line near ABS - S-10 Forum

 

Thanks for the reply. I'll take a closer look under the ABS and stuff when the weather gets a little warmer. I didn't realize the fender reservoir was removable.

A little background about the problem. With the vac line plugged in to the fender, the vent selector does not work at all. With the vac line capped off and not plugged in to the fender, the vent selector works normally except for when the engine is under a load (going up hill).

I feel like this vac leak is also contributing to power loss and poor gas mileage. I will let you know if correcting the vac line helps.

 

The reservoir is designed to compensate for then the vacuum at the engine is reduced which happens when the engine is under load. The reservoir has enough volume under vacuum that even with a small leak, there will be enough vacuum to move the actuators until greater vacuum can be supplied again by the engine.

An important part of the system that keeps the hoses under vacuum is the one-way vacuum valve. So if this has failed, then the system can have the symptoms you describe.

This leads to the final question, at what point in the system did you isolate the vacuum reservoir? This is important to help isolate the bad component; the valve, reservoir, or the valve. E.g. Did you cap off the vacuum reservoir hose at the reservoir end or did you cap off the nipple to which the reservoir line connects at the one-way vacuum valve?

Considering the age of our Blazers, I would suggest you consider replacing all of the under-hood vacuum hoses anyway. I replaced mine when they were getting old and rotting. For extra insurance, I used zip-ties as mini-hose clamps to secure them. In case you might find it useful, this is a thread I started to report on when I did replace all the hoses. https://blazerforum.com/forum/2nd-ge...replace-95425/

 

Thanks Christine. I was led to believe that the fender port/reservoir connected to the charcoal canister behind the rear wheel/frame. Is that now how it goes?

The check valve has been replaced with a new part and the direction of it is correct. The charcoal canister on the rear of the truck has been replaced new.

The vacuum line under the hood is capped at the check valve now. The port in the fender is open now.

 

Jagibsonmd,

The charcoal canister and the vacuum reservoir are not connected and serve different systems.

With the check-valve capped so that there is no connection to the vacuum reservoir, you will have no "reserve" vacuum to actuate your HVAC controls when the engine is unable to supply sufficient vacuum such as when it is under load due to going up a hill or accelerating. With no vacuum reservoir connected, I would expect you to have exactly the symptoms you describe.

From what you described either the vacuum reservoir has a leak and is incapable of holding vacuum or the hose between the check-valve to the reservoir was bad; cracked and leaking or overly loose at the nipples. A bad hose is very much more likely the problem than having a bad reservoir.

The way to test and possibly fix this is to install a new hose between the check-valve and reservoir. It might take a bit for the engine to "pump out" the vacuum reservoir so let it run a bit before deciding if the reservoir is bad. At least 5 minutes?

Being the type of person who likes to understand why something happened, I'd try to test the reservoir first to satisfy my curiosity.

The best way to test is to use a pump with a gauge on it such as a Mityvac. This will allow you to create a vacuum and then monitor the pressure change over several minutes. It should not change. If you don't have a vacuum pump, you could suck on the hose to the reservoir and plug the end of the hose with a (wet) fingertip and see if it stays under vacuum.

Because it looked hard to replace, when I thought my vacuum reservoir might have been bad, I considered getting one for a 1st Gen Blazer and installing it somewhere easier to get to. LOL

 

Wow. Thank you for the clarification on the canister and reservoir. That would lead me to believe that the reservoir is damaged and not holding vacuum. I had replaced lines with the proper sizes when first troubleshooting.

I had replaced the charcoal canister, purge, and vent solenoids prior to this problem when fixing an emmisions problem.

I had been given "bad" information about the vacuum lines thinking they all connected together somehow.

Thanks again. I will let you know how it goes.

 

This also explains why I could never find a diagram showing the connecting line between the canister and reservoir. Doh!!

 

Check out these links. They each have diagrams and pictures for you.

https://blazerforum.com/forum/steeri...uestion-75602/

https://blazerforum.com/forum/engine...ng-help-93443/

https://blazerforum.com/forum/2nd-ge...no-heat-14749/

 

Ok. So I replaced the hose going from the check valve to the reservoir with a new piece of 3/16 I.D. hose like you recommended. Looks like the hose I was using was the wrong size after all. The vent selector worked normal at idle. I was still losing vacuum under load though.

After looking through the links that you posted and reading some more about the issue, I discovered that the lines going to the 4wd Actuator mounted on the firewall were backwards!! After correcting this, all seems well.

I haven't had a chance to give it a thorough road test yet.

Thank you again for your help. I will follow up with this after driving for a while