Vacuum Leak Diagnosis

[Mercury]

I have what I suspect is a vacuum leak. Yesterday my vents were working normally, I rolled the windows down for about twenty minutes, then when I tried my cruise control it didn't work and when I turned my AC back on it was defrost only.

I looked up a diagram for the 4.0 vacuum lines, sprayed throttle body cleaner all along them, there was no change in engine idle. I'm not really sure what to do at this point other than throwing parts at the issue. Luckily it's not terribly hot but I have 5 hours of driving tomorrow with my 10-year-old and I'd like her not to fry if I can avoid it, as well as be able to cruise since most of the drive is interstate.

Does anyone have any advice?

 

[Mercury]

Cancel, tracked the sucker down, finally. Didn't respond at all to being sprayed with TBC, but it's fixed now.

 

[GregBelleville]

Cancel, tracked the sucker down, finally. Didn't respond at all to being sprayed with TBC, but it's fixed now.

How'd you find the leak and where was it located out of curiosity? I was suspicious of a vacuum leak on mine as well but wasn't able to find it using TB cleaner either.

 

[Mercury]

How'd you find the leak and where was it located out of curiosity? I was suspicious of a vacuum leak on mine as well but wasn't able to find it using TB cleaner either.

I started following all of the hoses from the intake manifold looking for breaks instead of using the diagram. Turns out there's a hose that wasn't on the diagram, goes all of the way to the driver's side edge of the engine bay, and the hose had separated (looks to be a previous repair). Nothing fancy, I was just too focused on using the diagram and expecting the TB cleaner to make something happen.

Once I found it I confirmed it was vacuum by putting my finger over the end, and out of curiosity I sprayed TB cleaner at the end. Didn't change the idle a single bit, so I'll no longer be relying on that for a diagnosis.

 

[JEEPCJTJ]

I'm glad you found your leak. I don't know what is used in TB cleaner but I do know what is in a can of starting fluid. I'll also suggest not huffing the starting fluid while near a running engine. You won't realize what the spinning fan did to your fingers until you wake up and even then you still may not be able to find all of them.

 

[Mercury]

I'm glad you found your leak. I don't know what is used in TB cleaner but I do know what is in a can of starting fluid. I'll also suggest not huffing the starting fluid while near a running engine. You won't realize what the spinning fan did to your fingers until you wake up and even then you still may not be able to find all of them.

View attachment 444297

Ahahahahahahahahhaha.


Oddly enough, the vacuum went down for about 20 seconds while I was driving, vents went from front to defrost, then it came back and it didn't happen again in a 5-hour session of driving. No idea.

 

[ChasUGC]

Yeah, I would check the hoses one at a time. Once you fix one leak, any other leaks will be magnified. So, it sounds like you may have other leaks. I would avoid spraying any solvents into the vacuum system. Solvents and rubber don't mix well. Solvents tend to ruin rubber.

 

[Mercury]

Yeah, I would check the hoses one at a time. Once you fix one leak, any other leaks will be magnified. So, it sounds like you may have other leaks. I would avoid spraying any solvents into the vacuum system. Solvents and rubber don't mix well. Solvents tend to ruin rubber.

Interesting, hadn't thought of that. I'll make it a point to rinse or wipe them off, then.

At this point I'm looking at vacuum hose/connector kits on Amazon, may as well just replace all of it, though I'd like whatever is causing the problem so I can tape it up for the next few days.

 

[jdh2ocrzy]

I know this is a couple month old thread, but... I was searching for information leading to discontinued vacuum connector fitting and I though I'd add this information for helping others. I use silicone lubricant spray when testing plastic/rubber vacuum hose leaks. It shouldn't harm those materials.