Driving it off the cliff

[Stl-986]

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

[Stl-986]

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?


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.

[blue62]

Originally Posted by Stl-986

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?


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
If one is

[Stl-986]

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.

[Stl-986]

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.



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.

[blue62]

Originally Posted by Stl-986

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.



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

[Stl-986]

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

[blue62]

Originally Posted by Stl-986

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.

[Stl-986]

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.

[blue62]

Originally Posted by Stl-986

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.

[Stl-986]

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.

[blue62]

Originally Posted by Stl-986

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.

[Stl-986]

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?

[blue62]

Originally Posted by Stl-986

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?

You have a Pico???
HELL YES
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

[Stl-986]

Have a 2204a so only 2 channels.

[Stl-986]

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

[Stl-986]

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

[blue62]

Originally Posted by Stl-986

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

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.

[Stl-986]

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

[blue62]

Originally Posted by Stl-986

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.