relative compression help

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paullap
OneWave
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relative compression help

Post by paullap »

Hi, I am trying to do a relative compression test on a Vauxhaull Corsa D 2006 1.4 XEP petrol.

I get a very good relative compression waveform , I can see 2 low cylinders, But I cant get a ignition sync . So I can identify what cylinders are low.

I have disconnected the injectors to stop it starting

It has 6 wires and all 4 coils in one pack, I can get a signal running but not cranking,
I have tried using a amp clamp to get a coil ramp, \I have tried using a capacitive ignition pickup on a king lead.

I have put the amp clamp on all wires on the coil pack and still nothing when cranking.

Am I doing something wrong ?, Or how do I get a sync when just cranking.


Paul

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PicoKev
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Re: relative compression help

Post by PicoKev »

Paul,

Although the injectors are disconnected the PCM will still be actuating them, so just pick up a signal from number one injector as you would normally do as your sync. You can also substitute a bulb in place of the injector and use your amp clamp as well.

Kev.

paullap
OneWave
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Re: relative compression help

Post by paullap »

Hi Kev, That is a good shout, I will try that and see how it goes, Do you think a Noid light would draw enough current to get what I need?. I will come back and let you know how it goes.

Many Thanks


Paul

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PicoKev
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Re: relative compression help

Post by PicoKev »

That will be a no on the noid light!

Measure your injector resistance and explore your bulb rack for the nearest match you have. :D

Kev.

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TwoWaves
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Re: relative compression help

Post by Technician »

Can you not doing something like this;
Attachments
Capture of relative compression testing.PNG

liviu2004
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Re: relative compression help

Post by liviu2004 »

Get a spark plug out, then repeat relative compression. 1-4-3-2. Easy as daylight.

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Re: relative compression help

Post by Technician »

If that is what I think you mean, then surely an engine with one cylinder down completely on compression will raise the cranking speed and lower the current demand, which would also mean that he would have four separate traces to study?

I'd of thought it much easier and more accurate to look up on the wiring diagram which trigger wire is cylinder 1, and then put the amps clamp round the battery lead and crank away. Surely it can't get much simpler than that can it?

paullap
OneWave
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Re: relative compression help

Post by paullap »

Hi Everyone, Thank you all for the suggestions, I am very new to the Pico and I am trying to learn the quickest and easiest way to do things,So on this car I started with the relative compression , so I know that I have 2 cylinders with a compression problem, ( which ones?) , I have done 2 things now, I have done a in cylinder compression test on cylinder 1 using the WS500 PressureTransducer and back probed the cam shaft sensor and a relative compression waveform, so I now know where on the intake cam the ignition fires on number one cylinder at T.D.C This is ( for the future). I did this test with the fuel injectors disconnected, I then re connected the fuel injectors and pulled the fuel pump relay and then put a amp clamp around the the injector wire. and got the injection current waveform, This then got me confused (That is not difficult) , the injection process was happening after T.D.C., I thought how could that be, And a very good friend explained to me that it injects in to the inlet manifold on the exhaust stroke ready for when the inlet valve opens. That is as far as I have got so far, Next is to see if I can find out where it is losing compression. Crankcase/ Valves, Head gasket. It is 2 minutes with a cylinder leak-down test on this car, but I want to see it on the pico , You all probably think I am sad,

If I can find out how to post my wave forms on this forum I would love to post them, You can all have a good laugh.

Thanks for helping

Paul

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