just re read this thread and see that I missed a few posts.

You say your getting 8 in.hg of vacuum????
Is that with a standard vacuum gauge???
Car at idle??

When I did that test I capped #18 off where it goes into the T. Getting to the other hose isn't all that easy as it is under the intake

To catch up this mornings work.

Using the 03 as a test I disconnected the check valve at the intake and put the gauge in the hole. Got 14hg. Doing the exact same thing on the 00 I get 8hg. This is using the mity vac pump which has a gauge on it, that might not be all that accurate, but at least it does show how much of a difference there is at idle between the 2 doing the exact same results.

The 03 has ZERO issues and runs wonderful so I know that it is good to compare against.

In my mind I am thinking the most likely possible culprits are:
Intake gasket(s)
resonance tube
intermediate tube and/or o-ring
flapper change over

So if your only getting 8 in.hg at idle!!
Is the needle steady??? drifting??? ticking??
What action if any is there from the needle???

Also how many miles on the car.????

8 in.hg at idle says you have a major vacuum leak at the intake manifold.
big enough that you should be able to hear it and find it easily.
It can also indicate that you have late valve timing..
Or a combination of both.

I would do the vacuum test again with a standard vacuum gauge just to verify readings from the mini vac gauge.
If you still have low vacuum readings I would do a compression test to compare cyl. to cyl and bank to bank.
a compression test will help tell us if you have valve train issues.

You can get low vacuum readings from leaks, poor valve timing, poor valve seating, any kind of issue with the valve train, head gasket leaks, worn rings, all manner of things.

The action of the needle can tell you where the problem is.

ok, quick update then I have to go work on my TJ since it decided to have an injector got bad today.

Have a good gauge. I am getting 14hg at idle. reving the engine up does make it increase, but still not to 20-25. Haven't hooked it up to the 03 yet, but I system vacuum is still low on the 00.

Once I get done with the Jeep I am going to just replace the intake gaskets. I'm not 100% it is even contributing, but I have them and they have never been replaced so it cant hurt (in theory). I'll have access to a smoke machine next weekend and can get it tested then but I'll keep messing with it this week till that gets here.

I doubt I am having a HG issue, would see other indications of that. Other then the misfires the car runs great and drives great. Idle is just crap and I cant get it to pass emissions testing cause of it.

What was the action of the needle at idle???
When you get a chance test vacuum at a steady 3000 RPM and note gauge reading and needle action.
Also do a snap throttle test and note what needle falls and rises to.

I would also do a compression test on all cyl. that way we can compare one cyl to all others and compare bank 1 to bank 2.
Try to rule out valve train issues.

Finally getting time to get back to this.

Tomorrow I am going to do compression test.

In the mean time, this is what the plenum looks like with bank 1 intake removed. I have been meaning to replace the intake gaskets so just went ahead and pulled the intake tonight, will get it back in tomorrow morning.
http://986forum.com/forums/uploads02...1627183350.jpg

And bank 1 intake:

http://986forum.com/forums/uploads02...1627183385.jpg

In the second picture the top intake port (top of the picture) it looks like there is an indentation running from 1-7 o clock is that factory???? I can't see it very clearly.

Not sure what you mean. It wasn't that easy to get a picture that would show up with a flashlight & the camera flash and doing it by myself and the angle isn't all that great to show cyl #1

That's pretty grimy looking. Have you gone through a few aoses?

How did the gasket look when you go the runner off?

Sent from my SM-G970U1 using Tapatalk

Got the intake back in with new gaskets. Got vacuum up to 14hg on a cold engine. Didn't want it to get too warm so I moved on to the compression test.

1: 180
2: 182
3: 180
4: 179
5: 180
6: 182

This is with throttle fully open, cranking same amount on all and on a warmish engine.

All plugs are new Bosch plugs and look tan.

While watching durametric I get way more misfires on bank 1 then I do on 2 & 3.

Moving on to testing the coil to making sure it is firing. Need to get the gopro setup.

Would you know the factory spec. for compression in psi. for these engines.???
Looking at your data your psi is 25-30 psi higher than the fella on the (car dies) thread.
So I may have given him bad info when I told him compression looked good.

Ya know...was hoping you would know. lol.

Been searching & searching. 190-210 seems to be the ranges I have seen but also down to 150 range is out there too. What I always go for is to make sure they are all within 10% of each other unless the numbers are all just really low.

oh, and obviously mileage plays a role too. This car has only 109k on it.

Yes 10% as the greatest spread is the general rule of thumb.
He is down to 150 psi on the one bank but it is the good bank if I understand his post correctly.
So if that is true it should run ok at 150 psi
He is also within the 10% margin.

Yup. The difference between ours is that I get misfires on all of bank 1 & I get codes for misfires and my vacuum numbers are crap compared to his.

You also get a CEL and codes for your misfires correct???
(car dies) says no CEL and no codes, so something is not right with the DME/ECU not seeing misfires.

Also his vacuum numbers changed drastically from yesterday.
So he didn't test under the same conditions as the day before.
Or he did something radically different to cause reading differences to be that great.

I get misfire codes, his does not according to his first post.

I get P0300, P0301, P0302, P0303

Just had a better look at the plugs. Makes no sense. 1-3 look good/normal to me. #4 though looks almost new.

Yes....made sure I am working on the correct sides.
1-3 being passenger, 4-6 being driver.

http://986forum.com/forums/uploads02...1627249914.jpg

http://986forum.com/forums/uploads02...1627249922.jpg