Individual cylinder valve timing errors

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Re: Individual cylinder valve timing errors

Postby Fat Freddy » Thu Jul 06, 2017 2:48 pm

jamesdillon wrote:Here's an image from our Oscilloscope Masterclass training course showing valve clearance and valve timing relationship as mentioned above..


I was thinking of the nose/peak of the cam being worn only. But in the real world that's pretty unlikely.
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Re: Individual cylinder valve timing errors

Postby Fat Freddy » Fri Jul 07, 2017 2:29 am

This is one of my favorite wave-forms (Diesel light vehicle). One of the reasons' is because it shows a major pitfall of carrying out a traditional comp test. This would pass. Yet in reality it's a big 'F' for fail. Anyway.

But in this example (Cranking) there is no rise in compression from an worn inlet cam lobe (that is the fault - Magenta) as suggested. Looking at I am surprised how much the pressure during the latter half of the intake and compression stroke follow each other between the two cylinders. The second compression towers are timed using the crank.

Worn cam.jpg


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Re: Individual cylinder valve timing errors

Postby Fat Freddy » Fri Jul 07, 2017 3:08 am

The same two cylinders now idling - badly.

The most immediate things that are noticeable is the increase in pressure in cylinder one and the loss in cylinder two. I believe this to be attributed to reduced leak down time and reduced filing time.

Fixed with a new cam and other worn valve components related to the worn cam.

Running comp.jpg


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FF
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Re: Individual cylinder valve timing errors

Postby Fat Freddy » Mon Sep 04, 2017 2:13 pm

Since this came through as a newsletter it gave me the chance to re look at the findings.

First, I would like to explain why I am beating this drum hard. When I first started scoping, I used to take every piece written by proclaimed guru's and the mentors as gospel. Only years later finding out what was told wasn't quite the full story. For example, I spent many hours trying to figure out how the experts located the valve overlap notch on exhaust waveforms. I still can’t figure it out. Today I would like to stop other up and coming picologists from falling into that time-wasting trap. So, this is only my observations and interpretation of this excellent voyage into valve timing error. I hopefully have presented it with evidence to back up my theory. But most important of all is the up and coming can come to their own logical, evidence based conclusion.

I would also point out that I’m basing my ideas on what Steve has presented, as is. Blocked breather hose and manifold etc. Not how it may be in the real world as JD has pointed out. Although it would have been interesting to see the difference in ‘real world’ compression and compared it way Steve has done it, which is to enable us to see the valve events better. I think it is quite important to analyse the waveforms as is, as it keeps a good grounding with cause and effect.

I still feel the interpretation of cylinder 2 waveform is very bad. The article claims, in effect, a shorter valve duration and lower lift is more effective at filling an unfilled cylinder than a standard valve lift and duration. The cylinder was still filling when the valve shut early as it has on all the cylinders. How can that contribute to a higher peak cylinder pressure?
The article also has no explanation as to why, immediately, after the inlet valve opens the cylinder pressure rises to a value higher than any of the other cylinder on the inlet stroke or why there is so much turbulence at that point. This, I believe, is the real reason behind the high compression on cylinder two.

And the theory
"I originally thought that the compressions may have been uneven before my adjustments as I did not check, but one of the delegates highlighted how the compression stroke has increased due to the early closure of the inlet valve!
He went onto discuss how this was a technique they used during the winter months with fixed duty diesel engines where the compression is raised to assist with cold starting. (Brilliant) I guess this is fine for fixed duty engine and for this engine during cranking but may introduce combustion anomalies at higher engine rpm and load."


"Brilliant", I can't agree with that.

"I guess this is fine for fixed duty engine and for this engine during cranking but may introduce combustion anomalies at higher engine rpm and load." Which we know, it does. Miss-fire starts at high RPM because of poor volumetric efficiency the ecu can then shut that cylinder down. Generally we see the engine light flash at high RPM and feel a miss as we slow down.
The theory I have put forward (That the leaking exhaust valve in the previous events of cylinder 4 contributed to inlet manifold pressure) is further supported by cylinder 3 waveform which is of an early closing exhaust valve.
In that waveform (cylinder 3) we can see the exhaust valve closed early and we can see there was residual pressure in the cylinder at TDC of the exhaust stroke. That residual pressure did not simply disappear. It equalised into the inlet manifold raising the inlet manifold pressure. This resulted in a more efficiently filled cylinder during the following intake stroke.
What’s particularly worth noting is Cylinder 4 has the highest cylinder pressure during the intake stroke because the cylinder and intake manifold are being filled from both the throttle body and the open exhaust valve. Followed by cylinder 2 then 3. Both 2 and 3 then go on to produce higher than normal peak compression cylinder pressure. The 'normal' cylinder has the lowest cylinder pressure during the intake stroke. Cylinder two is higher because of the residual higher than normal inlet manifold pressure from the leaking exhaust valve from cylinder 4. And 3 is higher because the cylinder was not fully ‘emptied’ during the exhaust stroke. This is supportive to the accuracy of the WPS 500.

This brings up another point that the high cylinder pressure of cylinder two is caused by cyl 4. When the inlet valve of cylinder 4 closes we can see cylinder pressure of 4 was way higher than cylinder one, the normal/good cylinder. It goes without saying that the inlet manifold pressure was higher also. A higher amount of air waiting to fill cylinder two almost immediately as cylinder 4’s inlet valve closed.

The representation of cylinder 4 must be taken with a pinch of salt. And demonstrates why having a clock, such as the crank angle sensor, is required if you not fortunate to own 4 WPS sensors to carry out a test like this. The waveform is right aligned biased by about 43*. At TDC the pressure is approx. 0 psi. Peak cylinder pressure did not actually occur at TDC. As the long increase in pressure is because the rising piston is trying to increase the pressure while the exhaust valve is reducing it. While during the down stoke both are swiftly reducing the pressure. But prior to TDC the rising piston speed is relatively low and there will be a point that the exhaust valve is lowering the pressure faster than the piston can compress the gas as it approaches 0 M/sec. As shown in the actual file. Note actual TDC compared to how it would be expected at peak compression. Although this assumes max pressure of cylinder one is at TDC.


This may seem like I have picked on Steve’s work. Which I guess I have but it’s only because I find it worth the time to try and glean as much information from his journey as I find a lot of his work interesting. But it is up to the individual reader to draw their own conclusions from the evidence provided and base their findings on this evidence. After all this is my opinion and may be completely off field but I would love to hear the conclusions of other picologists.

FF

NOTE. I am unable to load up the accompanying images because of this never ending capture problem that persists. But I will continue trying to post them.
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Re: Individual cylinder valve timing errors

Postby victor2k » Tue Sep 05, 2017 6:06 pm

Hello,
Today I made a capture from a 2006 Toyota Avensis /1ZZFE engine with misfire at cylinder 1.
The ignition coil and spark plugs was replaced,on petrol or LPG the misfire is recorded at cylinder 1.Also the total (short and long )fuel trim is at 6-10% ...
The compression is good:11,12,12,12.
The measure valves clearance was good on intake(0.2 mm ),but on the exhaust it was:0.03mm!,0.2mm,0.2mm,0.25mm,0.25mm,0.25mm,0.2mm,0.25mm.
Someone can help me to understand why the recorded pressure at cyl 1 and 2 don't show this?
Regards.
Attachments
Cyl 1 vs Cyl 2 pressure.png
20170905_162332.jpg
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Re: Individual cylinder valve timing errors

Postby Steve Smith » Wed Sep 06, 2017 10:57 am

Hello and thank you for the continued posts on this one and sorry FF I should have replied sooner.

First of all you should beat your drum as loud and as long as possible because it is only by being challenged we learn and develop.

I have been re-educated by this forum time and time again with things I believed were set in stone only to find the scope and its users reveal something completely different.

Hind sight is a wonderful thing and I wish I had included a 5th WPS within the intake manifold during these tests as the pressure differential values during the transition from exhaust to inlet would have been invaluable.

Having said that, before flying to Holland to present this study, we rehearsed with a vehicle using the identical PSA “TU” engine. On this occasion I did sacrifice channel A (Cylinder 1) for the vehicle MAP sensor as I knew there would be “value” in the waveform. I could kick myself though as with the “TU” engine rehearsal, I did not add the additional restriction to the intake like in Holland.

The MAP sensor waveform below most certainly indicates a greater pressure differential during the intake stroke of cylinder 2 (I am sure this would have been greater still if I had the added intake restriction)

TU PREP.jpg
PREP TU


I agree with you FF; In effect, during the reduced intake duration of Cylinder 2, the greater pressure differential between Cylinder 2 and the intake manifold (due to Cylinder 4 behaviour) results in superior “charging” of Cylinder 2 during the intake.

With that said, I believe we have a combination of factors that contribute to the increased peak compression of cylinder 2.

1. Superior air charging of the cylinder due to the increased pressure differential between Cylinder 2 and intake manifold
2. An increased compression stroke due to the early closure of the intake valve
3. Crankshaft speed/Piston velocity variation

Point 3 above sprang to mind after re-reading all the posts, in particular the Piston Travel and Velocity chart.

Given Cylinder 4 has very little compression in which to reduce crankshaft speed, this must have a momentary favourable effect on Cylinder 2 intake stroke that once again will promote superior air charging.

It’s all food for thought and makes for great discussion. Thank you again FF for not letting this one go as without challenge all this would be easy and “nothing is easy”

Returning to the image above:

The black oval marker in the waveform highlights the effects of neighbouring cylinders on the intake manifold pressure. Here we can see the effects of the early closure of the exhaust valve on Cylinder 3 followed by the release of this residual pressure into the intake manifold when the intake valve opens. (Notice the abrupt increase in manifold pressure at this precise moment)

As we have eluded to throughout these posts “We also have to be mindful of the effects of neighbouring cylinders upon the cylinder we are measuring.”

I will ask Mike to add a link back to this forum post in the website article as the additional information included is priceless.

Take care……Steve
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Re: Individual cylinder valve timing errors

Postby Steve Smith » Wed Sep 06, 2017 11:21 am

Hello Victor and thank you for your post.

Could you post the psdata file for this capture?

Could you clarify the engine speed and temperature when this image was captured?

I know these engines particularly well and their vulnerability when running on LPG

The exhaust valve seats deplete rapidly and command a valve clearance check every 10,000 miles if using LPG

When not using LPG the valve clearances never need adjustment (assuming good service history)

Take care......Steve
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Re: Individual cylinder valve timing errors

Postby victor2k » Wed Sep 06, 2017 3:25 pm

Steve Smith wrote:
Could you post the psdata file for this capture?

Could you clarify the engine speed and temperature when this image was captured?

I know these engines particularly well and their vulnerability when running on LPG

The exhaust valve seats deplete rapidly and command a valve clearance check every 10,000 miles if using LPG

When not using LPG the valve clearances never need adjustment (assuming good service history)

Take care......Steve

Hello,
The engine was hot when I recorded psdata(85*C) at 235 rpm,the valve clearance was checked at cold engine(25*C).
Psdata was attached.
Thank you
Attachments
Toyota_Avensis_2006_Petrol_20170905-0001.psdata
(2.91 MiB) Downloaded 21 times
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Re: Individual cylinder valve timing errors

Postby Steve Smith » Thu Sep 07, 2017 10:25 am

Hello Victor and thank you for the feedback.

Knowing the temperature here was vital as the engine would most probably perform well when cold until expansion decreased the valve clearance further.

Looking at the reference waveform of cylinder 1 (black) against cylinder 2 waveform (Red) there is a clue in the expansion pocket. (See Image below)

VICTOR IMAGE.jpg
Zoom Expansion Pocket


Given we know the exhaust valve to be weeping slightly due to insufficient valve clearance, the expansion pocket decay towards atmospheric pressure occurs much sooner with cylinder 1 (approx. 124.8 degrees after TDC)

Cylinder 2 decay is far more pronounced and "definite" at approx. 141.3 degrees which can attribute to the commencement of exhaust valve opening.

What would help define this expansion pocket (and peak compression) would be to run the engine when hot at idle speed and capture the waveform again if you have not already rectified the concern.

Either way victor, great work and thank you for the post
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