Timing, cam lobes, washed rings? What was it?

1999 Volkswagen Passat GLS 2.8 Lts. was brought from a transmission shop (after repairing it) with severe misfires.

Here's the codes :

Next, I did a relative compression test along with intake and exhaust pulse waveforms

It's starting to look like bank 1 timing is off, so I use an In-cylinder pressure transducer to TRY to see something (even tough I'm not ANY good at it).

I,m not sure but I think I shouldn't have that much vacuum cranking, right?

I could only do the bank 1 In-cylinder pressure transducer,because when I tried to do it on a contributing cylinder, the car obviously would not start (4 cyl not contributing).
So here's cyl 1 running :

The customer declined to go further in the diagnosis, and I wish I could have open the timing covers and visually check timing marks to be 100% sure about my diagnosis.
Any feedback would be greatly appreciated.

Ok so looking at your scope captures it's pretty obvious you have a compression problem on those cylinders from bank 1.
I think it would be a good thing to add some more waveforms/variables in order to call this a jumped timing chain or belt. Did some research and found a couple videos you might wanna take a look at. 2 are from ScannerDanner's free channel and 1 is from Pico.
Let us know what you think or if you have any further questions.

Ok, I will watch and ask.

Thank you.

Dylan wrote: I think it would be a good thing to add some more waveforms/variables in order to call this a jumped timing chain or belt.

After watching the videos and reviewing my captures, I came to realize that spark is occurring at around 20 degrees before TDC.That's 9 or 10 degrees more advanced right?

And yet another clue, when we compare cam timing on a "known good" cranking cylinder vs a known bad one (cyl 1), they are night and day different.

But what I would really like to be able to plug in is the intake and exhaust pulses.

After watching the videos and reviewing my captures, I came to realize that spark is occurring at around 20 degrees before TDC.

Yes sir. Indeed, that's bad news.

And yet another clue, when we compare cam timing on a "known good" cranking cylinder vs a known bad one (cyl 1), they are night and day different.

Good idea. I was going to suggest that but you got there first. We can see that compression is lower on cylinder 1 and that there's a difference when the exhaust valve opens.

But what I would really like to be able to plug in is the intake and exhaust pulses.

I'll take a closer look when I'm on my laptop. But I agree it's quite interesting. We'll figure it out. If my colleagues read this they might also chime in.
Would like to thank you for the nice scope captures.

Indeed, nice captures! Thanks for taking the time and effort to compile your data and label everything so that we all know whats going on. You're getting a Karma bump from me for sure
To say that i'm a novice when it comes to in cylinder capture would be an OVERstatement. I've never employed this test in a diagnosis, and can glean very little from those capture. That's really why I was hesitant to add my opinion to this post, and still am...

Based on the intake pulses, the relative compression test and the firing order, coupled with the advanced spark timing on the effected cylinders, I think it's safe to say that bank one timing is off.

Keep up the good work man, impressive!

Love your captures, GeorG. Real shame the customer pulled the plug

Let me know if I'm wrong, but I'm seeing retarded exhaust AND intake timing on bank one. I can't do measurements on the images, of course, but it seems to be around 20-30 degrees.

Both cams being out of time makes sense on this design, since the timing belt only drives one cam per bank, and a chain is used to connect between cams. I've never done one of these belts, but it doesn't look like a walk in the park.

So, this came from a transmission shop originally? I'd be curious to know the history. Wondering if the timing was part of the original complaint, or someone at the trans shop spun the engine backwards (while working with the flexplate?) during the repair.

Tyler wrote: Let me know if I'm wrong, but I'm seeing retarded exhaust AND intake timing on bank one. I can't do measurements on the images, of course, but it seems to be around 20-30 degrees.

I'm thinking more like 50 degrees if the exhaust cam should open around 30 degrees BTDC, but I could be wrong, maybe someone with more knowledge than me could explain to us.

Tyler wrote: So, this came from a transmission shop originally? I'd be curious to know the history. Wondering if the timing was part of the original complaint, or someone at the trans shop spun the engine backwards (while working with the flexplate?) during the repair.

I think that's what the customer suspects that happen, and just needed a second opinion. :whistle:

If you care to send me the Pico captures, we can do some calculations and figure out exactly (more or less) how far off the exhaust timing is. I think you're right, though, it probably is more like 50 degrees.

Also, if we knew how many belt teeth were on a camshaft sprocket, we could use that to estimate how many teeth the belt has jumped. Not that it would have any real value at this point, but it might be a fun exercise.

I think that's what the customer suspects that happen, and just needed a second opinion. :whistle:

Understood.

Tyler wrote: If you care to send me the Pico captures, we can do some calculations and figure out exactly (more or less) how far off the exhaust timing is. I think you're right, though, it probably is more like 50 degrees.

Also, if we knew how many belt teeth were on a camshaft sprocket, we could use that to estimate how many teeth the belt has jumped. Not that it would have any real value at this point, but it might be a fun exercise.

Yes, I would like that.

I tryed to upload the psdata file but I don't see it.