Valve timing with wps

Ask for and share advice on using the PicoScope kit to fix vehicles here.
Post Reply
Posts: 5
Joined: Wed Jun 17, 2015 1:25 pm

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 114 times

Steve Smith
Pico Staff Member
Pico Staff Member
Posts: 818
Joined: Sun Aug 25, 2013 7:22 am

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

Posts: 5
Joined: Wed Jun 17, 2015 1:25 pm

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 86 times
Vauxhall_Zafira_Petrol_In cyl 4 with misfire.psdata
(3.73 MiB) Downloaded 79 times

User avatar
Posts: 154
Joined: Thu Apr 05, 2012 9:16 am

Re: Valve timing with wps

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

Try watching this TY Vid


Posts: 48
Joined: Thu Feb 22, 2018 8:14 pm

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.

Posts: 5
Joined: Wed Jun 17, 2015 1:25 pm

Re: Valve timing with wps

Post by pinpointdiag » Thu Oct 24, 2019 2:26 pm

Hi this vehicle the zafira is coming back in tomorrow for further testing.
However it will be back to the original garage that asked me to look at it
So unfortunately out of my hands. I have to hope they are going to inspect it carefully.
Based on what I had captured before I had told them the valve timing events
were incorrect. They tell me however that the belt was loose but the marks
All line up.

Looking again at the exhaust closing time. 320 deg after TDC compression is this way to early ?
And a correct point for the exhaust closing should be 350 - 380 deg after TDC compression. (5-20 deg after tdc) from what I have read. And is usually hard to see ?
However the exhaust valve opening is late at 155 deg after tdc rather than between 130 - 150 deg after tdc compression. Is that correct ?

Could this then be due to insufficient valve lift ? and if so what could cause all 4 cylinders to have the same fault.

I see the other indicators of a fault. Like the stepping effect on the compression tower.
And the shallow exhaust pocket. And id like to know exactly what could cause these effects.
I cant find any mention of the stepping effect any whare on the net.

Yesterday I was looking at a VW with the 1.4 tsi twin air engine that had the same advanced exhaust
Pressure increase. But the exhaust open event was also advanced.
The compression tower has the same stepping effect and there was hardly any sign of the exhaust pocket.
It was fairly easy with a dti to set this engine to TDC and look at the cam locking pin holes and it was very clear the inlet cam was correct and the exhaust cam was advanced.
These are well known for timing chains skipping teeth.

Thanks to all for your previous input any further help will be received with great interest.
As I’m keen to be able to use this tool with confidence.

Regards Alan.
Last edited by pinpointdiag on Thu Oct 24, 2019 7:29 pm, edited 2 times in total.

Posts: 5
Joined: Wed Jun 17, 2015 1:25 pm

Re: Valve timing with wps

Post by pinpointdiag » Thu Oct 24, 2019 2:44 pm

Out of interest. Here is the VW Jetta 2008 1.4 tsi. Exhaust cam advanced confirmed.
Volkswagen_Jetta_Petrol_20191017-0001 cyl3.psdata
with ignition pulse and FRPS
(5.52 MiB) Downloaded 85 times
Volkswagen_Jetta_Petrol_20191017-0003 no ign.psdata
(4.36 MiB) Downloaded 96 times

Steve J
Posts: 9
Joined: Fri Aug 17, 2018 9:19 pm

Re: Valve timing with wps

Post by Steve J » Sun Nov 17, 2019 4:38 pm

Did you hear back about that Zafira?

Post Reply