Jumped timing chain ID with a scope

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Jumped timing chain ID with a scope

Postby ScannerDanner » Fri Feb 24, 2012 12:59 pm

Ok guys here is the set up. IT is a 2006 Chevy Malibu with a 2.2 Ecotec engine. These engines are notorious for jumped timing chains. It has all of the symptoms, a rattling noise in the chain area, P0300 misfire code, rough unstable idle with 12 inches of vacuum.
I want to verify a jumped chain without removing the valve cover and of course I want to use my pico to do it. Some background on this engine. It is a waste spark ignition system. The ICM controls the 2 coils based on inputs from the PCM. It has a crank sensor that reads a reluctor directly off of the crankshaft. The cam sensor is "synthesized" meaning the cam signal is generated by the ICM based on firing KV of the #1 cylinder. So there is no cam sensor.
So I cannot do the conventional cam/crank relationship waveform. It would be of no value in this situation. What I am thinking I would like to do is to use a pressure transducer in one of the spark plug holes and sync it with an ignition firing event (either a coil current ramp or PCM to ICM base circuit control signal).
I am not sure this test will reveal the issue either? I believe the peak of compression on the transducer will not be shifted in relation to the ignition firing event on this engine no matter how far the chain is off. I think maybe the only thing I would see is a low compression peak, although I have seen engines with a chain a few teeth off that read good static compression. I think I am rambling now, sorry. I know I can do conventional compression testing, but that is not the point here.
How about comparing vacuum to compression pressures on the scope? I'm looking for some ideas and I am weak on the transducer testing side of a scope. I have a PV350 pressure transducer. Any suggestions? What other tests can I do to identify this jumped chain using the scope?
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Re: Jumped timing chain ID with a scope

Postby Darren Cotton » Fri Feb 24, 2012 2:24 pm

The best way is to do a running compression test with your transducer... Then post the capture and we can have a look.

I take it this Ignition system is a Compression Sense Ignition (CSI) I have had a fair bit of dealing with two of these of late..

If you picked up the Cam out signals and crank you should get something like this

Zafira 22SE  Runing Comp.jpg



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Re: Jumped timing chain ID with a scope

Postby ScannerDanner » Fri Feb 24, 2012 2:37 pm

Darren
Would you like me to set up this waveform at idle or during a snap?
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Re: Jumped timing chain ID with a scope

Postby Robski » Fri Feb 24, 2012 2:41 pm

I remember the first one Darren :shock:

Just out of interest Paul is there much pressure coming from the tail pipe ?

Not my strong point are pressure transducers as i don't have one yet, but with an overlay tool & time markers you can time your valve opening events & this should tell a story.
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Re: Jumped timing chain ID with a scope

Postby Darren Cotton » Fri Feb 24, 2012 3:03 pm

ScannerDanner wrote:Darren
Would you like me to set up this waveform at idle or during a snap?



Why not do both just in case you have have excessive back pressure, this will show up, as this was the fault with my one which was storing P0300,

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Re: Jumped timing chain ID with a scope

Postby ScannerDanner » Fri Feb 24, 2012 4:02 pm

Here are some waveforms, let me know what you think. I believe that transducer testing (exhaust/intake compared to compression) is the only way to ID this chain problem on this engine.
Ignition timing and cam signal (synthesized) will not change with a jumped chain on this motor, I am convinced of that. Let me know if you think I am wrong and why? Thank you
Attachments
f.psdata
2000 RPM steady
(2.5 MiB) Downloaded 272 times
e.psdata
Snap Throttle
(7.37 MiB) Downloaded 232 times
d.psdata
Idle
(7.64 MiB) Downloaded 239 times
c.psdata
Cranking
(4.5 MiB) Downloaded 233 times
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Re: Jumped timing chain ID with a scope

Postby ScannerDanner » Fri Feb 24, 2012 4:03 pm

Ok, those files didn't show up like I expected. How do I fix that?
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Re: Jumped timing chain ID with a scope

Postby Darren Cotton » Fri Feb 24, 2012 5:12 pm

Something not right with your set up forget the crank and cam for now just do running comp at idle

change the scaling and time base. Do it on a 20ms or 50 ms and use a trigger, thats all we will need for now..

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Re: Jumped timing chain ID with a scope

Postby ScannerDanner » Fri Feb 24, 2012 6:25 pm

These are taken during idle using the KPA scale on the PV-350 (1mv=1KPA I think)
Attachments
p.psdata
(2.11 MiB) Downloaded 241 times
o.psdata
(1.75 MiB) Downloaded 240 times
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Re: Jumped timing chain ID with a scope

Postby Richard Boyd » Fri Feb 24, 2012 11:49 pm

Hi Paul,

It appears as though this engine does have a timing issue. With this transducer on this particular engine, the actual valve events can be a bit hard to distinguish - the easiest event to measure is Exhaust Valve Opening - or EVO. I don't have my information systems readily in front of me, but a quick Google search led me to this document with the camshaft specifications for the 2.2 Ecotec: http://dspace.mit.edu/bitstream/handle/ ... sequence=1. The EVO timing on this vehicle should be in the neighborhood of 49° BBDC. To calculate this on this engine first measure the total time of the engine revolution (refer to Figure 1).
image1.jpg
Engine Revolution


This engine event took 134.0 mS or is running at 892.9 RPM. It order to calculate cam timing lets zoom in on the EVO event. (refer to Figure 2).
image2.jpg
EVO Event


Here we can see that EVO took place approximately at 29.13mS after TDC or 23.48° BBDC. Obviously this is significantly off from the spec of 49° BBDC. Judging by the noise in the timing chain cover I would throw out a guess that the timing chain is loose and it jumped a tooth.

Then again it is Friday and my math might be WAY off. Thanks Paul and have a great day!

Regards,

Richard Boyd
Crag Technologies, Inc
http://www.pc-oscilloscopes.com
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