In the snap throttle video I notice that your vacuum is down to about 13 in.hg at idle.
which is low vacuum
The needle acts sort of correct on snap throttle.
But vacuum is low
I also notice your spoiler light is on.

In the next video your gauge is now (around 1:15- 1:30) in the green at around 19 in.hg

I notice a needle tick several times when holding steady RPM those are probably due to misfires.
Toward the end of the vid I see the needle tick and a light flash on the dash.
But I can't tell if it is a CEL or an oil light.
And the spoiler light is still on:D

You may have some restriction in you exhaust. that can cause low vacuum at idle.
Also causes needle to slowly drop at idle or steady RPM
It can cause misfires because the cylinder cannot fill with fuel/air mixture correctly.

what do your post cat O-2sensor signals look like at idle???
Can you graph them with Durametric for a few minutes and post them???
put all 4 O2 signals up on one graph if you can with RPM;)

It's the oil light. It comes on, but only sometimes when coming off the throttle such as coming to a stop light. Oil level is correct (just changed the oil last weekend, 8.5qt) and even has a brand new level/temp sender. Only happens when coming off the throttle though.

Other thing...watch the lights dim when coming off throttle.

Yes, spoiler light on this car stays on until the car moves a few feet and then goes off. Always been that way. My 03 doesn't do that.

I'll get the o2 stuff in the morning. Do you know which values they are?

clogged cat could be the issue. Going to see if I can make adapters this week to fit the pressure gauge/vac gauge. If I can will see what pressure is before & after the 1st cat that is part of the header. I would just loosen the bolts between the header & muffler but those are ones I can't get off unless I'm going to cut them off.

I get vacuum not building until the rpms increase, makes sense. What doesn't make sense to me is the vacuum dropping so much and so fast after though. It should hold or drop very very slowly right?

How about I hook up my Durametric to my 2000S in the morning and then I let you know which values to graph.
It's cocktail time here;);)

Jake Raby has a post somewhere that states there are different modes of failure of the AOS. One is the vacuuming of oil from the crankcase but there is also a mode that causes massive vacuum to the crankcase which can suck the shaft seals in and can cause oil starvation to the oil pump. With the oil pressure dropping low when coming off idle you might want to get a manometer and see what is happening there.

How is that possible? Not questioning your experience, but the math there doesnt add (or multiply) up lol.

Sent from my SM-G970U1 using Tapatalk

Sorry, i misread the post earlier, I thought it was 18 at idle I haven't gotten to watch any videos (everyone else asleep in the house) but the voltage and light dimming that youre describing is no bueno. Have you checked your alternator and battery? Im not sure how that would play in here but it's hard to tell with electronically controlled fuel injectors.

To measure the exhaust pressure, don't try to separate the joints. There are 18mm bung adapters to hook a pressure gauge to. The cheap way to do it would actually be just remove a sensor and leave them bung open - if that changes performance then you know you have a backpressure issue.

I didn't see if you responded earlier but what's the deal with your aos? Monty is right, the aos can actually kill your oil pressure if the failure is complete. All this could go together - bad aos, poor idle vacuum, intake flooded with oil, intake gasket degraded, fouled injectors causing lean running (? Maybe?), fouled spark plugs, clogged cats.

Sent from my SM-G970U1 using Tapatalk

AOS is good, it's actually new oem one. dont get any smoke on startup

off topic, but, I know what you are saying here, but.....his numbers are right. I thought the same about the multiplication you mentioned. Even our cars the math doesn't work cause these are 11.1 compression rate which means they should top out at 163.17. Not the case though. This isn't my video but one I found while going through the process today: https://www.youtube.com/watch?v=cznw9idwpkU & this: http://986forum.com/forums/boxster-general-discussions/35231-compression-test-results.html

in my own words....no clue how it's all calculated. Too much work to figure it out. :cheers:

I actually had this same thought about an hour ago. IF it doesn't throw any codes in the morning I am going to try and get it inspected. If that happens and it passes I will have some breathing room and can start to do things like this. Dont want an O2 code to come up if I can prevent it for the moment.

I was just thinkingore about your alternator...

A year ago the alternator on my wife's escalade went bad. The primary symptom was rough running at low rpm and then stall at idle. At higher rpms, everything was fine

It still doesn't explain the low vac at idle but just something (even more) to think about. Good luck with the emissions test!

Sent from my SM-G970U1 using Tapatalk

Well you can start with things like valve overlap.
Valve timing. air temp.
The simple math formula of multiplying atmospheric air pressure by CR assumes things like.
Intake valve wide open exactly at BDC and closed at exactly TDC with no exhaust valve overlap.
Piston cranking speed is another example. Watch the needle on the vacuum gauge in the video's in this thread.
As RPM increases vacuum increases. = increased cylinder fill.

So the simple math formula of multiplying atmospheric air pressure by CR will not work to give you cranking PSI.
Look up any engine specs. you can find that show CR and cranking compression PSI
That simple math formula will not give you stated cranking PSI

As for leak down tests being more helpful than compression tests:
A leak down test is a "static test" of the cylinders ability to seal. (hold pressure)

A compression test is more of an operational test of volumetric efficiency (cylinder air filling ability) which is directly related to vacuum
and the ability to "build pressure"
Very closely related but you can get a little different info from each test.
So it depends on what info your after on how helpful a given test method is.

STL-986

When you get time graph your O2 sensor "voltage signals" for all 4 O2 sensors at idle.
and RPM. Then post the graph so I can have a look see.:)

They are in actual values under the engine module.
Before you do the graphing go in and click on each O2 sensor "voltage signal" with key on but engine off.
That should show you the "BIAS" voltage on the signal wire.
It should be 0.45V That will test the signal wiring between the DME/ECU and the O2sensor.
Then click on the O2 sensor heater signal again with key on but engine off. This will test the wiring and voltage to the O2 sensor heater circuit. I think the spec. is 4.5V or close to that.

Then get the car up to operating temp. and graph the 4 O2 sensor voltage signals and the RPM.
Just let it idle during the graphing;)

Here you go. Couple charts from a cold engine:

http://986forum.com/forums/uploads02/o2_11627310296.jpg

http://986forum.com/forums/uploads02/o2_21627310306.jpg

Without rpm - Easier to see just the voltages
http://986forum.com/forums/uploads02...1627310316.jpg

And a few more:
http://986forum.com/forums/uploads02...1627310808.jpg

http://986forum.com/forums/uploads02...1627310823.jpg

http://986forum.com/forums/uploads02...1627310839.jpg

Everything looks good to me with one possible exception.

In the third chart the post cat O2 sensor (green line) should be more like the yellow line.
More steady and above .450mv around .650-.750mv
"BUT" you did the test with a cold engine. The dips could also be from misfires or rise and fall of RPM.
So it could be fine.

When you get time you could test that post cat O2 sensor on bank 2 again as a follow up check or proof.
Do it after a good drive and at idle. you want a graph line more like the other post cat O2 sensor (yellow line)

You may also want to think about the alternator situation you brought up.
I had not thought about that.
Could very well be a factor in the misfire situation.

The alternator thing is just something that has stuck in my mind. It does make some sense. Electrical issues can be so weird at times, especially with noise. But it's also like trying to find a bad ground. Such a rabbit hole you could go down and still come to no conclusion.

I am going to pull bank 1 front o2 to see if it runs any better to see if cat is an issue.

It's back to running as bad as it did before. The only thing I have done is just let it run. Didn't touch anything else.

Video from this morning. Car warmed up. Not sure how the audio will be from the gopro. I'm not even sitting in the car when I did this.

It is back to do exactly the same thing as before. Constant misfire on cyl 1-3 but I haven't touched a single thing since last evening when it was doing so much better & idling higher.

Cat test up next as soon as it cools enough some for me to get under it.

At the least you could have the alternator tested.
Either remove it and take it in.
Or find a shop that will test it on the car.
Or find all the specs. and test it yourself with a mutimeter

Interesting.
May be time to disconnect and block off the SAI which I think is just one vacuum hose connected to the intake plenum. easy to get to.
Also disconnect the EVAP system more of a PITA.
Just to see if doing that changes anything???

couple of question????
Have you recalibrated your E-gas pedal lately????
Also have you checked for exhaust leaks???

Exhaust leaks is where a smoke machine could be handy.
plug the tail pipes and the intake.
Insert the smoke into the tailpipe

Always suspected an exhaust leak. I'll get a picture later on to show you why.

did the e-pedal this morning after clearing the misfire codes

So, let's talk about exhaust & O2 sensors. Are there 4 or 6 on a 2000? I thought there were just 2, at the cat on the header. These are the 2 (red) that I have replaced. Is the 3rd (blue) really there and if so, what is it's purpose? Looks like it is on the secondary cat. And if there are 3, how come only 2 show up in any tester?
http://986forum.com/forums/uploads02...1627330116.jpg

Assuming for a moment there is clogged cat. Would it most likely be the one at the header or the secondary cat? Waiting for pb blaster to soak in to get the front o2 removed on the header so my mind is just starting to think 10 steps further down the list.

There should be 4 on stock dual exhaust systems.
1 O2sensor before each precat:
In simple terms they see unused oxygen from the combustion cycle which creates a small voltage.. The DME/ECU uses that voltage signal to adjust fuel trims.

Then you have 1 O2 sensor each side that are post cat.
They are for reading oxygen after the catalytic process. The DME/ECU compares the Pre and Post cat signals to see if the Cats are operating correctly.

So you have 4 O2 sensors total

No way of telling which cat could be restricted:eek::eek:
If one is:eek::eek::eek:

still cant get the front sensor off, it is being a royal pain.

Ironicall, I can get all the header bolts off without any issue and those are the ones that usually snap.

Got the rear o2 sensor out. Made a difference. Still saw some misfires, but in the single digits and they didn't rise like they were doing before and after some time they reset themselves back to 0. Just this test tells me it could be the rear that is clogged.

It does make it easier to do a video though with sound to listen to the idle.

The biggest issue with this car is that it is so damn random. Like yesterday. Ran good last night and then this morning misfires like crazy.

well, can't get the sensor out, but there is a small bolt right below #2 cylinder that was happy to come out. Not sure if that hole is for all cylinders or just #2, but here is a new chart. Also rear O2 re-installed.

http://986forum.com/forums/uploads02...1627336068.jpg

I guess the next thing would be to have both plugs where I can remove 1, graph it, then reinstall, then remove the other & graph it, then re-install. I didn't graph it when I had the rear installed cause I was still seeing some misfires but not like in the picture above.

If you have an O2 sensor out or a cat off.
Try another Vacuum test.
See if it is the same as yesterday when the idle reading was dropping.
See what happens when you hold RPM at 2000. Or 3000 if you can't hold 2000
Look far any changes from the other times you vacuum tested.

Recording readings and action of the needle each time you test could be handy while your trying to fix this issue. Could show improvements and help point a direction;)

Here is another video to watch. this is with the front plug installed & rear o2 removed. Watch what happens with the misfire numbers. did a video cause the normal graph is just a moment in time and doesn't capture what happens.

https://youtu.be/o3K6dzE9IiQ

So that is bank 1 that has the increasing misfires right after you hold around 1700 RPM
Correct???????

What bank =side is the O2 sensor removed from???????

You need to get the front O2 sensors out.

everything is bank 1, pass side.

On the header is a small bolt it is right in the tube for cyl 2 before the 02 sensor, that is what I removed. Tried 2 different o2 sensor tools and that thing isn't budging right now. It's going to need some heat cycles to break it free.

Not only do the misfires increase, they reset themselves to 0, and never throws a code.

They are all or mostly on cyl 1 not random across the bank.
So what's going on with cyl 1 ??? also after holding higher RPM
Is it heat related???? we know that cyl 1 coil and plug is ok at idle.
try switching the with cyl 2 and see what happens if you do the same thing you just did.

I have done that before and it's the same results.

yes, it does seem like it is heat related.

My gut tells me there is a single thing that is causing all of these things to happen, but, each individual item could be caused by multiple things too. I just can't seem to narrow down what the 1 or 2 things are that is causing this.

It could be a couple things and when combined are causing misfires, low vacuum, oil light coming on when coming to a stop, hard downshift from 3rd to 2nd. It's just the only thing I can think of that could cause all of these things is an air leak or an AOS but I dont have any other symptoms of a bad AOS or a bad cat. it misfires at idle and around 2800. The misfires are a symptom of the issue, dont think they are the cause of the issue.

So limited mostly to cyl 1 no matter what coil or plug used.
If you could hook a Digital multi meter into the wiring for cyl 1 make it misfire and see if the signal from the DME/ECU is at fault.
Or use a spark test thing that goes between the plug and the coil.
Try to eliminate the DME/ECU and wiring as an issue. (electrical).
That would eliminate the Alternator as well if the issue is not electrical.

I have a picoscope. think hooking that up to the wiring at the coil or the dme is better?
Is this the right one to connect to?

http://986forum.com/forums/uploads02...1627348289.jpg

You have a Pico???
HELL YES :D:D
Hook up at the coil that will let you see the signal from the DME via the wiring to the coil.
Do you have enough channels to hook up to more that one coil at a time???
That way you check signal and compare the signal to a good firing cyl all at the same time.
Two birds with one Pico:):)
If cyl 1 shows fault you can work your way backwards to the DME

Have a 2204a so only 2 channels.

taking the lazy way right now. have channel a on coil 1 & b on coil 4 at the dme, connector 5. backpin on them. The settings are most likely not correct, but

http://986forum.com/forums/uploads02...1627352095.jpg

I so need a different diag tool that will do durametric & pico all in one. Not easy to capture the screen immediately after a misfire before the pico buffer goes away

http://986forum.com/forums/uploads02...1627352563.jpg

So If I am correct blue is A=Cyl 1
The long tails on the blue dropping to what looks like negative voltage are misfires????
If that is correct now I would hook up at the DME if you don't see the misfires then you have a wiring issue.

Correct. Blue = A = Cyl 1
Red = B = Cyl 4

I have it hooked up at the DME

Channel B also has the negative spikes and there are NO misfires on that cylinder

So those are not misfires??
Then I would hook up at the coil and see what happens.