So randomly messing around at my grandfathers house, I stumbled onto a vacuum gauge. Ok sweet! so i hooked it up and i got these results from it. Its accurate still despite being from the 40s


Hanging around 14 to 15 by the way it moved a little back and forth.



Hooked up to the intake port. Also tried it on the brake booster with same results.

These normal results? I have no clue and couldnt really find anything on factory vacuum readings for a 4.0.

 

Mine isn't from the 40's but is 40years old (at the least) and looks just like that.

Here's how to use one:
http://www.autospeed.com/cms/article...nostics&A=2393

 

hmm interesting i didnt go this in depth with it. Ill borrow it and do some more extensive testing to see exactly what it does

 

When I check vacuum on my XJs (98 and 99), my gauge reads right at 15 inches Hg. Seems normal to me. You can definitely use a vacuum gauge to diagnose engine problems.

 

this is a new step in my search for issues and maybe add more fire to my sadness on what else i have to fix or new found issue im about to stumble across

 

I feel your pain..... I've learned with these older Jeeps that you just have to come to terms with the fact that sh** of one kind or another is almost always in need of attention.
If we didn't make peace with that fact, we'd all probably turn around and just sell them. lol. Lord knows I've thought about it, but for some reason, can't bring myself to let go of my XJ even though she's pissed me off pretty good a few times.

 

Agree 100%. However, you can always look at it this way, if you have to GO LOOKING for problems, that's a pretty good place to be in. I still have both a major and a minor list of fixes that are very clearly telling me they are needed.

 

so is this normal vacuum pressure then? on a 210k mile engine in a 99?

 

Yup.

Read this: https://www.motor.com/magazine-summa...-vacuum-gauge/

 

Nice. That's the best summary I've read all in one place. Bookmark worthy!

 

A rooky question.

I got for free this vacuum gauge.
Where to plug it to test vaccuum ?
I just have a few plugs in the box.

I want to know If the system is leaky, if the computer gets the right data. Etc.


thanks

 

That's a fuel pressure gauge......

A vacuum gauge is used on an engine for diagnosing internal issues, not checking for vacuum leaks BTW.

https://www.motor.com/magazine-summa...-vacuum-gauge/

 

Needless to say I feel stupid

Here is the right pict and I found a documentation.
The gauge seems to be a vacuum and fuel pressure.

 

That makes more sense. Don't try to use it to test fuel pressure on a fuel injected engine. It only goes to 14-psi, and fuel injected will be about 3x that.

 

Ok. thanks