VW CPKA In Cylinder Pressure?

I’d say no there is no exhaust back pressure but using getting some cursors on there would help as well. When you accelerate there will be a lot more back pressure of course but at idle there is normally 0-2 psi “ish” depending on the engine. I want to say anything or 5 is excessive as hell. If it was bad enough you would be looking at 10 plus psi around the 180 mark. I’m fairly new to pressure…

I too am far from an expert, but, 23+ psi of exhaust pressure seems a bit excessive, lol. The EVO seems awfully late as well.

Depends on engine load.

Erik, Which depends on engine load? EBP or EVO? The EVO looks to be happening about 17degrees After BDC. Thanks for replying. I'm always willing to learn.

Backpressure.

I downloaded his Pico capture and see 23 PSI. To me, that seems excessive regardless of load. Do you have reason to believe that would be acceptable?

Ill give you and Bill the benefit since I am new to this as well. It should be near zero by the book but as I have said I thought an engine was the same way but no clogged exhaust. This is backed up by the timing on this looking a bit retarded which tells me look for a tensioner extended but we would have correlation codes. Easy enough to look at MAP voltage at idle and snap since both should be…

Does the fuel pressure actual and desired stay the same all the time or does the pressure go too high at higher RPMs? Does the turbo create boost at all? The turbo will create some back pressure from the turbine. With the rich code, I would be looking for a boost leak causing the MAF to read too high and run rich. It has been a while since I took a waveform on a turbo car and I don't have…

I would look in scan data to see if rail pressure drops koeo. P0299 is loss of pressure. Check the turbo wastegate arm first and then the diverter valve. The fault codes might be different depending on what scan tool you are using…

Bill, The waveform definitely shows back pressure. The exhaust platue is maintained and even increases when snapped. That should not happen. Zoom in on the snap and you will see a sudden high pressure spike as soon as the exhaust valve opens. With no back pressure you won't get that spike at Evo on a snap accel.

Bob, with the back pressure increasing gradually, is it possible to tell how far down the pipe the restriction is?

I couldn't say. You might be able to make some assumptions but I don't know how accurate it would be without a bunch of research on various types of restrictions.

That is definitely a exhaust pressure issue if that is a snap throttle there should be virtually no pockets, however With the underboost code and the lack of flow from high back pressure already and The turbo not spooled , now compounding with the fact that a turbo is a restriction until its spoiled, So yes you have a back pressure issue. negative file trims is also key do a VE TEST.

Good Afternoon Bill, How have you been? I am happy to see that the WP S500 is serving you well. This waveform does not show an exhaust restriction. During the snap throttle, the exhaust plateau will be close to the same height or higher than the compression peaks. Also, this is a turbocharged engine. It is normal to see high exhaust pressure spikes close to where the exhaust valve closes…

Hi Bill, Not a subject matter expert… however, here is what I see. I did take a look at a few different points in the waveform (as Bernie Thompson tells us to do). I do see 15-22 psi during snap throttle. I looked at a few snap throttle from my own files (not VW) and I don't see that much backpressure. The complete exhaust ramp is to the right of the 180 degree mark which suggests the exhaust…

Loving the involved discussion. This is what learning is all about. Brandon Steckler’s book has some good case studies as well. A year or so ago I thought I had a Sequoia with excesssive back pressure but I was just looking too much in to the snap throttle which when lots of exhaust at high engine load goes through a small port or orifice of course back pressure will elevate and give you tunnel…

Bill your timing keeps retarding further from idle being approximately 31 deg from 180 EVO and bacpressure at almost 2 psi. At WOT and I took just a random part close to the highest backpressure of 23.69 psi….this gave me approximately 47 deg from 180 for EVO at 23 psi. The first at idle looks rounded to me indicating a sealing issue and then at WOT it is very sharp like a check mark, if that…

Valve timing measurements are not accurate under a snap throttle condition.

The EVO is past BDC even at idle.

Bill, I know you know what your doing this is just my thought process on what you posted information wise. I could be way off - We have a low power complaint on a speed density engine with negative fuel trims. Suggesting that the ecm is seeing more load than is actually there and gets worse with more rpm. - We have an underboost code, on a NA engine under snap/WO throttle the exhaust and…

Hundred percent agree for volume efficiency the pressure in the intake and the pressure within the turbine should match or are closely related. just like a NA engine, we want atmospheric pressure in the intake with throttle open and this allows a large volume of air to fill the cylinder and exit the engine having atmospheric pressure exhausting the engine possibly based on exhaust design a…

Joe, I think your thought process is good.

Hi Bill, I posted some known-good in-cylinder data files ( startup, snap throttle) here from a 2016 CZTA Turbo engine that might be helpful; diag​.​net/msg/m595ndh642…

Bill, Here is a little more detail on what I see. I can't open your file on the computer i'm using so I will just markup the image you posted. Here's a car with no back pressure. The Blue channel is vacuum. Vacuum is what makes the exhaust ramp so as soon as you start to snap open the throttle, the vacuum goes away and so should the ramp. If you look at the first 3 compression events after the…

He’s correct everything shifts during the snap and valve events are inaccurate I would add that there will be some back pressure though considering the turbo. Until it spools it remains a restriction however the restriction is seen as where the exhaust Plato will ramp up towards the end of its duration. But this event is continuously elevated the entire time. I early on in analyis found this…

Right. The important place to look is at EVO on the first several compression events. In those first few moments when the throttle is stabbed open but before the engine rpm has a chance to spool up, the intake will be at atmospheric and so should the exhaust, which is why the ramp goes away. Once the rpm really spools up there will be some back pressure especially with a turbo inline. It's those…

always Good to get more insight on analysis im grateful

After reading all of the , so far, replies; the part that stands out to me is that the intake pressure does not go up. It appears to stay in a slight vacuum. The exhaust pressure goes up,(that is normal for a turbo engine) so the turbo should be spinning and increase the intake pressure. But no increase in intake pressure is seen. So is the turbo not spinning due to pressure behind it(ie:exhaust…

I was looking at that too. The snap is pretty brief however. About 0.6 seconds. I don't have a feel for how quickly that turbo should spin up. I'd sure like to see an in-cylinder waveform with 2-3 seconds at a constant ~2K rpm. I still think there's a restriction but I've no experience with in-cylinder on these small turbo engines.

Hi Bill, I have a few observations on your 1.8L performance issue. I don’t think it is good practice to check for an exhaust restriction by performing a WOT (pedal) snap test in Park or Neutral. Your 1.8L peaked at about 24 psi during the snap. I agree that this number seems to be too high. If you look at Scott Brown’s 1.4L example, that engine peaked at about 32 psi. He stated his engine was…

John, thanks for adding to the discussion. You of course make some very good points. I wanted to add a couple captures from Scott's known good to help clarify what I am looking at (or where I'm looking) to get an indication of backpressure. I think where you're looking in the waveform makes a big difference and we can get fooled if looking in the wrong place. Scott's capture is a know good and…

Great analysis, Bob, it totally makes a difference where to look.

Hi Bob, I agree with your analysis. I zoomed in on Bill's 1.8L and Scott's 1.4L. See attached. One can see a noticeable difference. My concern is that if one is not careful, it can be easy to misinterpret the pressure rise. You did a nice job making your point. I saw Bill's new saves with and without the converter. There is a big difference.

Thank you John. Most of what I know about this stuff I have learned from legends such as yourself. I am very grateful for the knowledge.

Bob, Thanks for the kind words. I am pretty sure I am not a legend but thank you.

John, thank you very much for sharing your observations and thoughts with me! I tried to get another capture today while doing a brake torque but the vehicle will not cooperate. I can only get … RPM out of it doing a brake torque. it just wont let me.… I do also see what you mean about the EVO now that you have pointed it out. I rechecked my data blocks today with vehicle running at a…

Hi Bill, Your brake torque file was good in that peak cylinder pressure hit about 250 psi. The engine is moving enough air to stress the exhaust when checking for a restriction. It seems that these 1.8L engines have issues with exhaust cam position more so than with intake cam position. I have seen the exhaust cams move significantly without affecting intake cam position. This may be due to…

John, the fuel trim reading/scan data screen shot was with convertor attached everything was hooked up as normal… The fault codes were cleared and the vehicle was started and let idle in the bay for about 10 minutes. (It does idle smoothly) Do you have a better test that i should be doing to prove the possible exhaust cam issue? I know you wouldn't be pulling the cover…. Did you feel the brake…

Bill, Not John obviously, but at this point with the in cylinder showing what it does in regards to exhaust timing not being what would be called conventional, no published valve timing specs (that I can find) and no known good,, especially with a cam that is non variable. And no vct or cam sensor to worry about or check I think you might you have gone as far as you can go with the scope. Not…

I’ll download this soon enough. I just started with VW so looking at their stuff is already a challenge coming from Toyota. It’s good to see a few folks not be scared to test the euros. I’ve enjoyed it regardless of speculating, being correct to being wrong. Helps us all. Thanks.

Another Snap Throttle with the pipe disconnected would be helpful. You could also back it up with a pressure gage in place of the front O2 sensor.

Bob, thank you so much all the thought and time you have put into this investigation! I have provided a snap throttle waveform with the convertor disconnected for you. This is really interesting to me and helping me to better understand theses wave forms. I can see exactly what you are talking about in this waveform with the convertor disconnected, just as the throttle is depressed the valve…

Thanks for getting that waveform Bill. It's nice to see the difference between cat connected and disconnected under the same snap condition. It sure looks to me that you have confirmed a restriction. I've seen cases where a cat was replaced and it still had low power because the intermediate pipe or muffler was clogged with the remnants of the old cat. It might make sense to reconnect the cat…

There's something that bothers me in your disconnected cat trace. I'm at a loss to explain the little rise in pressure just past TDC exhaust. Anyone have an explanation?

That little rise is caused by the turbo. Check out the waveform in the post of Scott Brown's above. Or click this link diag​.​net/msg/m595ndh642… if that's easier.

In Scott's video, that hump occurred BEFORE TDC. On the waveform I commented on, it's AFTER TDC. Scott's explanation was that the exhaust valve closed while the piston was still rising. In our case here, the piston has already started falling so a valve close wouldn't cause a rise in pressure. Also, I didn't hear Scott mention it had anything to do with the turbo. Maybe I missed that.

Somewhere at some time I am sure I saw a video about this bump at the end of the exhaust stroke. I'm thinking it was Super Mario Diagnostics but I'm not sure and I haven't been able to locate it. I'm sure it only happened on turbocharged engines, something about the added resistance of the turbo creating extra back pressure in the exhaust. You don't see it with a pressure test in the O2 sensor…

Just recently watched this one. John refers to the bump at the end of the exhaust stroke around the 32 minute mark of the video youtu​.​be/v080RWORP3A

That's a great video. Thank for the link. You are correct that the image around 32:52 looks very much like our VW engine here, but, John never addresses the post TDC bump. He does address the pre-TDC bump as being VVT for the exhaust with an early valve close. I'm still left wondering about the post TDC bump however.

James i see what you mean the bump appears slightly past TDC? I do notice this pressure rise in Scott Browns known good but it appears to be declining after TDC. I also took some pressure readings from a CCT (a different VW 4 cyl. turbo engine) yesterday and see that same bump/pressure rise but again its declining at just after TDC. Your point is noted but i can not explain, perhaps someone else…

I have one idea, but, you won't like it. Head gasket leak (or other cylinder-to-cylinder leak) from and adjacent cylinder. Is this either cylinder 2 or 3?

Does it drive well enough to monitor intake air temp to see if it rises? Confirming a restriction?

Is the high pressure pump driven off the exhaust cam?

Bill, just wondering if you say my post asking about which cylinder you did this in-cylinder pressure test on?

James - the captures are from Cyl #2 but i have looked at cyl#1 and #2 they appeared similar

Can you post a Cylinder 1 trace?

James under what conditions are you looking for specifically? I will try and get you one

I'm not picky. Just any running condition. Idle is fine. Cat on or off is fine. Duplicating your first post's capture is fine. Thanks

Any ETA?

Hey, if it's not too much trouble, try to add a ckp sensor to the trace as well ;-)

James I have not forgot you or the vehicle… I got one man down at the shop, been super busy, and this is a car lot owned vehicle so it had to go to the back burner for a bit. Ill follow up soon as possible

Thanks, I feared you had moved on to something else. Sorry to hear you are down a tech. No hurry.

Awesome Bill. So your initial in-cylinder Waveform absolutely showed a restriction and now you have visual proof to go with it.

Thanks again Bob for all your time and help analyzing the files! You made some great observations on this one!!