odd compresion test results

Post by **IaininTenbury** » Wed Aug 05, 2009 12:26 am

Just had a friend contact me with engine problems on a 948cc. All the readings were around 180-190psi which seems rather high for a Minor, and its not running smoothly and very smoky on the exhaust - ie: a visible plume of smoke in the rear view mirror. Its come on very recently, and obviously sounds like a piston ring probelm or valve guide problem, but wouldnt that go hand in hand wiht low compressions on the affected cylinders?

linearaudio · Post by **linearaudio** » Wed Aug 05, 2009 8:08 am

If it's come on suddenly, suggests possibility of a broken/seized ring in one cylinder. Do all the plugs look the same colour?
If they do then more likely to be a failure affecting all cylinders, flooding carb maybe?

Post by **bmcecosse** » Wed Aug 05, 2009 8:16 am

Indeed these are exceptionally high readings for a 948 - unless it has been highly modified! Something wrong with the compression tester - or the readings have been mis-read ? Maybe the readings are 1.8/1.9 Bar - which would be exceptionally poor - I doubt it would run at all, so that's likely not it! Any chance the car has been mis-fuelled with diesel ??

Post by **MarkyB** » Wed Aug 05, 2009 8:19 am

What colour smoke is it making?

Post by **rayofleamington** » Wed Aug 05, 2009 6:03 pm

I was also wondering about the fuel if it came on 'very suddenly'

Compression tester could have been read wrong, or be faulty or indeed the head has been skimmed a lot! The last time I saw 190 was on a Fiat punto engine (with a small headgasket leak)

Post by **PSL184** » Wed Aug 05, 2009 6:16 pm

Is there also a loss of power or is that side of things normal? Diesel would certainly produce smoke - clouds and clouds of the stuff to the point that you would look like a smog machine for miles around (depending on the amount added of course) and if a large amount was added you would get a significant loss of power.....

Post by **bmcecosse** » Wed Aug 05, 2009 7:50 pm

Well - it's said to be 'not running smoothly'!

Post by **PSL184** » Wed Aug 05, 2009 7:52 pm

Not running smoothly does not necesarilly mean down on power though?

Post by **bmcecosse** » Wed Aug 05, 2009 7:56 pm

Weeeeeellllllllllll. Nit picking now !! maybe diesel gives just as much power when diluted with petrol - after all - it does have higher cal value than petrol - which is one reason why it gives better mpg. So - if it CAN be burned in the engine - it may give power - but not smoothly!

Post by **PSL184** » Wed Aug 05, 2009 8:00 pm

No wasn't nit picking Roy - Diluted diesel may well give same or even more efficient burn but neat diesel won't.....

Post by **bmcecosse** » Wed Aug 05, 2009 8:04 pm

I'm jangling your chain!!

Post by **PSL184** » Wed Aug 05, 2009 8:27 pm

Post by **IaininTenbury** » Fri Aug 07, 2009 12:20 am

As far as I know its not got diesel in it, though I'll mention that to the onwer.

(I had diesel in a petrol vehicle once and attended service filling station and a Morris J van. Presumably the attendant thought "van = diesel" and I never noticed. It still ran but really poor - not idleing, and a very serious smokescreen. Sovled by filling with petrol and just running it till it cleared.... I don't think this one is in that league).

Seems to be running with similaror slightly down on power, but blue smoke and not as sweet as it used to be. The compression readings mystify me - hence the posting. I'll probably get to see the car over the weekend so will have a look and a retest then.
The engine is original with about 70k on it.

Post by **IaininTenbury** » Fri Aug 14, 2009 12:43 am

Turned out to be a faulty compression tester which gave the high readings! Actual results were normal, but rather low on number three so its a ring/valve problem to look at...
Ta for the help and advice