Valve timing with wps

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Valve timing with wps

Post by pinpointdiag » Wed Oct 09, 2019 3:33 pm

Hi I have had a Vauxhall Zafira VXR Z20LEH brought to me with a misfire.
It has a misfire at idle. Lowish compression on all 4 cylinders. but it is a turbo.
A bit worse on cyl 4.
With wps it looks like the exhaust cam timing is advanced. Can any one confirm
What i thought. I was fairly confidant but now im not so sure.
The garage that brought it to me have now replaced the belt and tell me the timing
is correct. I told them to check the pully for broken woodruff key ect.
They recon all is good. But it still has this spike before TDC.
Vauxhall_Zafira_Petrol_20190928-0001 cyl 2.psdata
(4.59 MiB) Downloaded 19 times

Steve Smith
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Re: Valve timing with wps

Post by Steve Smith » Thu Oct 10, 2019 1:53 pm

Hello and thank you for the posts.
Could you confirm all cylinders replicate the cylinder 2 capture you have provided?

The peak compression of approx. 5 bar is quite normal given we are at idle speed with closed throttle
There are a number of concerns I can see with the waveform and these surround the non-symmetrical compression towers (The expansion stroke is stepped)

The expansion pocket differs considerably in pressure when compared to the intake pocket.
They are not always equal (expansion and intake pockets) with performance engines, however, the expansion pocket is typically deeper than the intake pocket at closed throttle (high performance engines)

The exhaust valve open event is in the ball park but appears to close early (advanced) at 320° ATDC compression
The intake valve appears to open at 344° ATDC compression (approx..) which would need qualifying against specification (this would give a huge overlap!)

The intake valve close event appears advanced at approx. 551° ATDC Compression but again needs qualifying against specification
IMAGE 1.png
Cyl 2

If we can obtain a good example from the waveform library or from anyone on the forum this will help clarify the observations above.

I hope this helps, take care.....Steve

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Re: Valve timing with wps

Post by pinpointdiag » Thu Oct 10, 2019 4:30 pm

Hi Steve thanks for taking a look.
Yes the other cylinders are the same. Ill post some other captures.
The car has bad misfire at idle and fault codes for random misfire and misfire cyl 4.
Cylinder 4 has the lowest compression of all. However If there was a valve timing error
and this was corrected there was in my opinion a chance that the improvement would be on
all 4 cylinders and although cyl4 may still be lower than the others, it might not matter.
The car apparently had the valve stem oil seals replaced and a new belt. 8 months ago.

The car is back with the repairing garage. They just asked me to do a quick check :D
as they have allready spent a lot of time and money.
I told them it appered to have timing issues. So any further involvment from me is probably for
my own learning.
My thoughts were that the exhaust valves were closing very early. on all 4 cylinders.
Where you put the first circle.
If marks all line up then checking for pully slip on a shaft was my next suggestion
But they are telling me they have checked all that now and found nothing wrong.
However they tell me the belt did not look new and it was loose, so they replaced it
and brought it back to me to to check again it was just the same.

So do you think i am correct ? Exhaust valve closes at 320 deg. Very early.
and inlet valve opens at 345 deg between that there is a period on the exhaust stroke when both
valves are closed causing a brief increase in pressure? So no valve overlap?

I could try and find the actual spec.
What could cause the stepping effect on the expansion stroke?
Vauxhall_Zafira_Petrol_20190930-0001 no turbo.psdata
(6.93 MiB) Downloaded 8 times
Vauxhall_Zafira_Petrol_In cyl 4 with misfire.psdata
(3.73 MiB) Downloaded 9 times

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Re: Valve timing with wps

Post by PicoKev » Thu Oct 10, 2019 5:37 pm

Try watching this TY Vid


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Re: Valve timing with wps

Post by kona » Fri Oct 11, 2019 7:51 pm

Most likely that the problem is in the valves. The belt is installed correctly.
Make a record of pressure in the intake manifold at idle.

Good luck.

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