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?

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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

They look about right considering random misfires on bank one.
Shows that they are firing most times.

I was just looking at the fuel trim data you posted in post #2 I saw something odd.
If I am reading it correctly RKAT is the idle range.
FRA is upper idle to mid range RPM..
Data is showing around 700 RPM
So looking at fuel trim I would expect to see positive fuel trim (RKAT idle range) for the bank with the misfires.
But you have a negative fuel trim for bank 1
and a very strong positive fuel trim for bank 2
Bank 2 trim should be very near 1 for trim it is at 3.42
Is there any possibility that the bank1 and bank2 pre cat O2sensor wires are crossed???

With this car, anything is possible, but that would require flipping the entire engine harness I think. The wires are only so long. dont see how I could even connect the front to rear, rear to front let alone bank 1 to bank 2.

Ok thought I would ask:D
your fuel trim data on bank 2 is what I would expect to see for bank 1.
When you have all three cylinders on the same bank misfiring your O2 sensor is going to see the unused oxygen from the misfires. not the unburned fuel.
So the DME/ECU will see that as a lean condition and add fuel.
But your car is taking away fuel at idle on bank 1
At the same time it is adding lots of fuel to bank 2
Which has no misfires.
Very odd.

your misfires are mostly at idle correct?????

well, take a look at this. Got it all back together. all this time I had been focusing on bank 1. After pulling coils/plugs for the compression test I went ahead and put the new coils & plugs in for bank 2. After seeing what plug #4 looked like had me scratching my head.

Still not seeing the vacuum I should but for the past 20 minutes this is what it has looked like

http://986forum.com/forums/uploads02...1627254613.jpg

Idle is too high, saw it shoot to 1012rpm, but....no misfires at idle. Car is up to temp too

For compression my understanding is multiply atmospheric pressure x compression ratio, so for our cars it should be on the 160 range. But, conditions vary as does equipment precision, so I always look for consistency rather than raw numbers. This is one reason why leakdown tests can be more helpful. Either way though your numbers look great.

Now that everything is back together you have strong vacuum and your fuel trims are spot on. Looks like you fixed it!

With the idle, it takes a few minutes after a big change for it to level out. Was your ac on though? Idle without ac should be around 650 but idle with ac on is much higher, closer to 1k.

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That's just it, dont have strong vacuum at idle. I have great vacuum when the rpms are high, but think I absolutely have a vac. leak.

I can get vacuum up to 20hg around 3k rpm, let off the throttle and watch to drop slowly. Seems to drop faster when all the fans kick in.

Misfires did come back after an hour. They reset themselves to 0 and then when the front fan kicks it they start to climb up again. They are not happening anywhere near like they were before though.

Didn't grab a chart, but I started to graph voltage the last time and noticed that it is around 13.5 and then when the engine fan kicks in it goes to down to 13.2 for a bit, then when they front cooling fans kick in it goes down to 12.8 but does start to climb back up to around 13.4.

I'm just rambling, but the past 2 years I have been working on this issue I found 1 person who was having similar misfires and what fixed it was a new alternator. Electrical issues can cause some weird things to happen but I have kept it in my mind since seeing it

AC was off

Here is the video:
https://youtu.be/XqlX4KJZ24U

that formula for compression does not work:eek:
My 1969 Jaguar E-type XK engine has a 9:1 CR factory spec.for compression is 175 PSI
My 1960 Austin healey BT7 engine has 9:1 CR factory spec. for compression is also 175 PSI;)

Ok now we are talking fuel trims look like they the should.
You have excellent compression.
Is this car a tip trans. Automatic transmission??? what ever they are called???
Idle RPM is usually higher then a standard trans.
Do you know the idle spec???
I am going to view you video a few more times then get back to you on vacuum testing.

Yes its a tiptronic. Had to get the wife something she would drive

Do you know the idle RPM spec???
or how far from spec. it idles at??

Looks like it's the same as Mt cars. 750 +/- 40

STI-986

From what I see in your video you "DO NOT" have a vacuum leak:D
The test for a vacuum leak is like this.
Get the car fully warmed up.
Get idle as close to spec as possible.
Hook the vacuum gauge up.
Let the car idle for 3-5 minutes and observe gauge reading and needle action.
At idle your in the green zone on your gauge. and the needle is very steady.
That is good:D:D:D

Now bring RPM up to 2000 RPM the needle should rise a little and stay steady.
that is what your gauge is doing at 3000 RPM.
If you had a vacuum leak the needle would fall when you held RPM at a higher level.;););)

Do the vac test again. get the car at operating temp.
Do the above test.
Do it closer to 2000 RPM

Then let the engine idle again for a minute or two.
Then do a "snap throttle test"
Go from idle to floored to off throttle very quickly.
Needle should drop to near 0 then rebound above idle reading very quickly.
then it should settle back to idle reading.

Your going to have a little lower vacuum reading at idle then your expecting.
Your reading very very close to my 2000S
The reason is that you have things like vacuum canisters on both your SAI and your EVAP systems along with all the valves and hoses.
If they were blocked off you would probably gain 2 in.hg

Another thing that is going to affect vacuum is the Vario Cam system.
Cam timing changes at around 1500RPM so as you increase RPM the vacuum gauge readings may not be what you expect.:):):)

Watch it again, you can see it decreasing while it is idling. The 1st 25 seconds are so you can see it drop, this was at idle.

Did the snap test a couple times, never goes to 0. At the end of the video is it coming down after being held around 3k rpm and you can see it decrease.

With all that said, it is WAY better then it has ever been.

I'm letting it cool down. In the past when it would misfire like crazy turning the car off for a while and then starting it back up again would turn the MIL on. Want to see if that happens again.

My biggest thing I want to solve for now is to get it to just pass emission testing. At worse I want it to get to a point where all 5 of the tests pass even if it does throw misfire codes cause I have a waiver that will get approved if that happens.

At 1:24 is when it goes back to idle and you can see it dropping.
at 1:40 the cooling fans start to kick in and it drops even more but hard to tell.

I'll do another video in a bit. want to get things setup with the gauge by the cluster. Want to see if you can spot another issue that happens had really has me stumped (but I think it is all related)

Yes watching RPM and the needle is very important.
Hard to relate everything about using that simple little vacuum gauge via the internet:D

I turned the sound on so I could hear the engine. That little drop in vacuum when the fans kick in is due to a little drop in RPM.
That slow drop at idle looks like you could have some restriction in your exhaust.
Cats may be partially plugged which could lead to random misfires.:eek::eek::eek:

When you do your next vacuum test bring the RPM to 2000 and hold it as steady as you can for 2-3 minutes watch the needle. if it drops slowly you have some restriction in the exhaust.;)

I am doing horrible with holding this one at 2k. My feet just can't get the feel for it.

Have 2 videos uploading right now

Here is the 1st one with the snap throttle.

https://youtu.be/IFBKNcp69X4

Here is the next one.

https://youtu.be/s5ZbH4Y-GD0

Really start watching around the 2:15 mark and let me know what else you notice besides the rpm & vac gauge.

Keep in mind...I dont know what "normal" is or how the vacuum should be. With all the reading & video watching this weekend it just doesn't feel right that it should decrease like it does after going back to idle and I really dont want to tear my 03 apart comparing it against right now since it drives perfectly. :D