Chevrolet Kalos 1.4 16v 2005 - Misfire after 3 mins of running - Fixed #
Posted by James Eardley on December 9, 2012, 9:38 pm
Year of Manufacture *: 2005
Engine Size and Code *: 1.4 16v
( Optional ) Scanner Used: Autel
( Optional) Fault Codes: NONE
This car came to me from another garage saying the vehicle started to mis-fire after you revved it a couple of times.
It had been to a different garage prior to this that changed and swapped some parts.
The last garage to have it before I got it, changed the spark plugs, coil pack and swapped the injectors from cylinder to cylinder.
The car sounded fine when I first started it but sure enough before long the engine became unstable and lumpy.
When I listened to the vehicle I got suspicious straight away because the mis-fire didn't seem very constant and had no rythem to it,
although it was clearly mis-firing.
The vehicle was already mis-firing now, I would have to wait for it to go cold to catch the problem in the act so had a play with the scope to gather some evidence of what I could scope from cold to warm to actually catch what changes as the problem is occuring.
Trouble codes through EOBD (none)
Relative compression, secondary ignition, injectors and Cam and Crank signals with the scope, didn't really show any obvious problems to chase.
After some more tests, I narrowed the suspect cylinder to be cyl 1.
Out with the WPS.....
I stuck the WPS in cyl 1 and noticed straight away that compression was low both Cranking and Running Low enough to disrupt combustion.
I also put the WPS in cylinder 2 for comparisson, which had almost twice the peak compression
I zoomed in on the cyl 1 capture and knew the cylinder was leaking and I suspected that the Inlet valve/s were not sealing 100%
I then left the vehicle overnight to cool ready to set my traps in the morning
The next morning...
I put the WPS in cyl 1 and put another channel on the crank sensor to allow accurate measuring later.
I put lots of time on the screen and also turned up my sample rate so my waveforms would not be distorted.
I started the car and allowed it to idle whilst watching the scope.
I could see the peak compression dropping gradually from just under 100psi almost instantly. Then after about 2mins 20 the peak compression takes a dramatic nose dive until the engine can be heard/seen to be lumpy. The peak compression drops and settles at just under 40psi (this is way too low for any meaningful combustion to take place).
cylinder 1 loosing compression gradually(First 1min 40 after start up)
The end of this capture is 3min 20 of running
I then proceeded to put the WPS into cyl 2 and the peak compression is seen to settle at roughly 114psi and holds steady for over another 4 minutes (even after testing cyl 1 and allowing abit of heat soak in the middle of setting the cyl 2 test up)
This is cyl 2 after roughly 10mins of running
I zoomed in on the cyl 1 compression capture and initially when I first started the vehicle up the cylinder all measured up good.
slowly but surely as the peak compression falls the incylinder waveform starts to show a cylinder that is not sealed.
The Intake valves were still suspect for not sealing efficiently.
I had abit of time to play with this car and have not used the WPS on the Intake manifold before so I thought it was the perfect oppertunity (kind of), it is always better to know what you should expect to see on a known good car.
I put the WPS on fairly central outlet on the manifold,
BLUE = cyl 1 secondary ignition
RED = cyl 1 injector
GREEN = WPS
GOLD = Crank signal
I noticed there was an anomaly on the Cyl 1 intake stroke but wasn't sure what I was looking at.
After doing some research and seeking a little help it became clear what was happening in the intake manifold.
I have tried to label the capture up to best describe what I am trying to say.
Also on the cyl 3 intake stroke, this has the biggest rise in pressure (less vacuum) due to the number 1 cyl being on its compression strokeand loosing some compression into the intake manifold through the leaky Intake valve/s(This is my theory, it sounds plausable but may not be correct)
I have tried to describe it better in the capture
I did not strip and repair this vehicle but the customer has confirmed that the engine shop did some head work (relaying a message from her dad) and now the car drove perfect
I wrote this post because I am addicted to the WPS at the moment and think it could prove to be a very powerful tool in the workshop.
I did not mean for this post to be so long winded.
I must of got carried away, I hope you don't fall asleep before the end LOL
With a Scope, WPS, a little imagination and lots of practice you really can make the invisible... visible
Ps, I nearly forgot, a manual cylinder leak down test proved to be roughly 5% leakage and a manual compression test did not show the fault clearly either????