Vauxhall Corsa B - Low Compression + Running Terrible

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Fri 20 Jul 2012 15:37
Vauxhall Corsa B - Low Compression + Running Terrible - gAnDo

Hi all I hope somebody can give me some advice.

My Corsa has been running terribly recently. No power when accelerating, EML coming on and car juddering when going 25mph+, trouble starting, starting then stalling, lurching forward and slowing down when accelerating. It hasnt been fun.

I have a code reader and always get the following code: 00044 - Lean Exhaust

I have tried the following with no success:

  • Replaced coolant temp sensor.
  • Replaced lambda sensor.
  • Cleaned throttle position sensor.
  • Cleaned throttle body.
  • Checked throttle position sensor using Opcom and all seems well there
  • Last summer I serviced it... fuel, oil, air filters, spark plugs, new oil & brake pads
  • Changed HT leads

So I ran an compression test the other day and got the following results in bar:

  • 1 -> 5.9
  • 2 -> 6.1
  • 3 -> 6.2
  • 4 -> 6.0

According to the manual the compression ratio is 10.0:1 so seemigly you multiply by 1.38 to get your ideal compression ratio which would be 13.8? Way lower than mine. I also tried adding a spoonful of oil into each cylinder and testing and all jumped up by roughly 0.8 bar.

I have a coil pack coming hopefully today but more likely monday now which I will try and fit but unsure of what to check next.

Does anybody have any idea what it could be?

Thanks.

Edited by gAnDo on 20/07/2012 at 15:38

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Fri 20 Jul 2012 21:33
Vauxhall Corsa B - Low Compression + Running Terrible - unthrottled

A compression ratio of 10:1 does not mean that the maximum presure should be 10 bar on a compression test. It means that the intake air has been compressed to 1:10 of its original volume. Under ideal conditions the pressure recorded would be Compression ratio^1.4. ie 25 bar. The actual compression ratio is less than the static compression ratio. Blowby past the rings will also reduce this number.

The numbers are consistent but far too low. You should be looking at 12-13 bar-twice what you're getting. Did you remember to depress the accelerator while cranking?!

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Sat 21 Jul 2012 02:10
Vauxhall Corsa B - Low Compression + Running Terrible - gAnDo

Hi thanks for getting back to me.

Yes, I follwed the Haynes manual exactly. Car at running temp, DIS module plug disconnected, fuel pump relay disconnected,and throttle fully depressed while turning the engine over.

I must admit my tester was a cheap one off eBay though but you would think it would be too far off.

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Sat 21 Jul 2012 14:06
Vauxhall Corsa B - Low Compression + Running Terrible - unthrottled

I've got much biiger numbers than that even when I've been lazy and not bothered to disconnect injectors.

Maybe there is not a tight seal between the compression tester and the head? In any case, I don't think the root of your problem lies in poor compression. I'd forget about that and move on.

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Sat 21 Jul 2012 14:39
Vauxhall Corsa B - Low Compression + Running Terrible - gAnDo

Ok mate thanks for your input. At least thats one thing to take off the list.

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Fri 27 Jul 2012 01:55
Vauxhall Corsa B - Low Compression + Running Terrible - 1litregolfeater

You did right suspecting the lambda sensor, they can fail every 60,000 or so, but your opcom could have told you if it actually had failed. You must have a leak in one of the exhaust manifold gaskets, or much more likely, a leak in the connection to the EGR valve, or an EGR valve which is permanently stuck, partially open.

I'd have expected more codes, but I would suggest the next step is to take off the EGR valve, examine it and carefully clean it.

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Mon 20 Aug 2012 11:27
Vauxhall Corsa B - Low Compression + Running Terrible - gAnDo

Hi thanks for the reply.

In order to test the EGR I had blanked it off entirely with no change.

Finally bit the bullet and took it to a friends garage. He did the compression test again and all were at 14 he said so I guess my tester is useless!

He then cleaned out the injector which has made it run much better but still not right, so have a replacement throttle body coming which should hopefully solve the problem.

Will post back when it arrives and Ive fitted it.

Edited by gAnDo on 20/08/2012 at 11:27

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Fri 7 Sep 2012 21:48
Vauxhall Corsa B - Low Compression + Running Terrible - gAnDo

New throttle body fixed the problem :D

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