I need to replace all the vacume lines on my sons blazer. There all rotting and im getting a P0420 code and before i can diagnose it properly I need to change the hoses to make sure they are not the source of the problem.

My question is about the 2 lines running down to the transfer case. The lines follow the dipstick tube. One is the source from the intake manifold on the drivers side of the vehicle at the firewall. Starts at transfer case up along side the dipstick tube for trans. Goes over to a t. 1 side of t goes down to hard plastic line? I believe to heater controls the other up to a check valve t the left side with the check on it connects to the manifold vacume the right side to the vacume ball on the hood. I s this the correct connection for this line? Is the plastic line going town for the heater controls? Its loction is just below the main electrical connection drivers side firewall.

The second line starts at the transfer case up the side of the dipstick tube and connects to a T 1 side goes to a larger side tube maybe 3/8" and to a electrical connection at the end. Im not sure what this is for. The other side of the T goes to below the battery tray. I believe this is for the 4 fwd switching? Not sure have yet to remove the tray.

Does this all sound correct? There is 1 more tube from transfer case that comes up along side the dipstick tube which is a vent.

All connections at the transfer case are to a molded fitting so as long as there marked or done 1 at a time I have no fear of getting them wrong.
They will just be a pain to run. I plan on using fuel lne the same size instead it should last longer and no fear of pinching or crimping.

I have a AllData acount but it doesnt show these lines and the diagram it does have can not be read.

Help in this matter would be appreciated.

I know there is one other vaccum line that runs from the evap solenoid down to the canister by the gas tank but I havent got to that yet. I know the other line will not effect my P0420 code but I need to replace all of them.

 

Sounds correct to me. The line that just has a plastic fitting on the end is the vent for the t-case which also includes venting of the line to the actuator under the battery.

I'm not sure if you have seen the OBD2 code section, but here is more information about the code you posted:
P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

 

I would caution about running fuel line instead of vacuum line. Some of the vacuum line is an oddball size (as in 64ths") and don't know if you can get fuel line in those sizes. I stepped up my vacuum lines on my 84 Jimmy and just that little bit extra put more delay in the response time before the 4 wheel drive synced in filling up that little extra vacuum line. The difference was really noticeable. Just passing this on. I redid the job with the right stuff and it was like night and day.

 

That would be true for any line between a vacuum actuated device and the switch that sends vacuum to it. Any other line will actually increase the reserve of the vacuum system.

 

swartlkk Gimpy Blazer

Thanks for the replys. The device on the larger hose that is T off of the hose from the transfer case with the other end going under the battery is what I was questioning. I see the little plastic vent on the hose tied to the dipstick tube. THe device im questioning has a green electrical connector on it. The vacume line that runs from the transfer case to the actuator under battery is lets say 3/16" the T is 3/16" on the through side with a3/8" barb on the branch of the T with a hose on it about 12" long with this electrical device connected to the end. When I removed the hose with engine off it lost all its vaccum. Does it just monitor vacum. It doesnt have a hose on the other side so im not sure how it could control anything.?? Gimpy Blazer do you know what the actual size of the vaccum line is? I measured it at 3/16" and thats what size the fuel line is. I had my son pick it up at Autozone and thats what they gave him. I was also worried at first but as long as the inside sdimension was the same it should be fine. How do I find out the actual size of the vaccum hose? With a tape they measure the same. I know it will be a bear to install these. I would like to use this hose if possible because its thicker and there is so much heat and different fluids that could get on it. Any help would be great. THanks to both of you.

By the way I must have gave you the wrong code. It had something to do with the evap. Everyone tries a gas cap first to see if that works. Its a very small leak. It could be a week sometimes or a couple of day but it will return and ill let you know. The code was not P0420 it was P0442 sorry. Great job on the obd II section. That will help alot of people.

 

I thought that the code did not sound correct. Have a read through these two codes:
P0440 - Evaporative Emission Control System
P0442 - Evaporative Emission Control System Leak Detected (small leak)
P0440 is a general code which may give you insight into other things to check. You can also search for either of these codes to see what others have had to do (provided they responded with their fix).

As far as your vacuum line questions, the vacuum system for the HVAC, 4wd, etc is separate from the EVAP system. I had typed out all of this in a previous reply only to read back through your first post and delete it because of the code...

About the lines though... Can you take a picture of the lines you are questioning? I can not visualize what the electrical device might be on the other side of the check valve... Any vacuum monitoring devices should be on the engine side of the check valve to read true manifold vacuum level, not the vacuum reserve of the system as maintained by the vacuum reservoir.

 

Swartlkk is right about the size of the line. The one you want to be concerned about is the one from the switch to the actuator (goes under the battery). It's been a while since I did mine (soon to do it again though) but I was like a 64th" off thinking it wouldn't matter. It did. I would (and will again) take a sample of hose and make a fresh cut in it (where it's not distorted) and you'll get the true ID. If the one you took off was 3/16" then go for it. Really, don't want to alarm you and the system will work just fine if it's too big. It just seemed to take forever with the larger hose. I know GM had some color coding on the vacuum lines such as Blk with a Tan or Gray hashed stripe. My book just shows them to be solid Blk on the t-case schematic. I think you'l be fine. I'll go out and crawl under my truck and if I find anything different I'll post again.

Chevy Nova I went out to my (94) and looked at the vacuum hoses. The hose to the actuator is definately different. The hose that runs to the vacuum tank is a normal 3/16" hose but the hose that runs to the "T" by the actuator is smaller (although not by much) and is marked as "5/32 GM 0093" from what I could make out and is repeated all along it as far as I could tell (about 3 ft). The 0093 is probably 1st quarter of 1993. The 5/32 is the size. Hey it's up to you. My hoses are still in pretty good shape but at least I know what to get for my 84 Jimmy.
I also saw the hose with the electrical connector on it. Pretty good size, right? I think it's got something to do with a vacuum release (dump valve) to increase response time being where it is but **** old me now has to find out for sure. Mine is a green connector with one white and one orange (looks like) wire coming out of it. Skimmed through the W/D manual real quick but couldn't find anything for sure. I WAS going to watch the baseball game tonight but now have other plans. Hope this helps. My transfer case isa Model 233 electronic shift. Probably the same as you're working on. I couldn't find even the hose in the Service Manual. I'll find out and let you know even if I have to do it the hard way.

 

Hey thanks A lot both of you for your help. It sure makes it a lot easier to repair something when someone has done it before you and knows what your talking about.

Gimpy blazer
How far does that smaller hose run just to the T that has what you believe to be a vacuum dump? Does it then run 3/16" from there? Mine have no writing on them maybe they were replaced before I bought it used. It was a one owner and the only problem I could find from his service records was an ignition switch and cylinder. I have just finished my second one. I bought Delco both times. Please let me know if you find out anymore info on what that device is I will look in Alldata and see if it mentions it anywhere. I appreciate you making me aware of the possibility of a problem. I don't want to have to do it twice. Is there an easy way to fish them again? I wish I had done it when I replaced the engine. Thanks

 

I just reached down by the big hose with the electrical plug and there the 5/32" line ended at the T fitting. I traced it back to the firewall and am afraid it runs to the t-case upper switch. Sorry. I didn't crawl underneath. Dinner was coming soon and didn't want to get into that (if you know what I mean). I see about it tomorrow morning and try to post something. I just know what I read and it's pretty plain that it's that way for a reason. I'll keep you posted.
As for an easy way to replace them you could heat about 3" of shrink tubing on each end and then just (carefully) pull the old out and the new should just slide into place. I'd use some silicone spray on it to help it along. We used to replace airplane cables that way if they were flexible and then install the end on it in the plane. Worked it through all the tight spots and pulleys too. Worked like a champ. Bosses thought we were heroes.

 

Gimpy blazer
I know that one is on of the three that end at the transfer case. It is connected to the molded plug. THe second is the vent tube which is exposed at the top of the trans dipstick tube. The third is the one that eventually connects to the manifold Vacuum source. So the line is 5/32" ? That means the other are too. Yours must be original if it is still marked or did you buy from the dealer? Your idea would probably work if I use the same size hose. Ill cut off a short piece and measure. Thanks for your help I'll keep you informed.