andyreed

Fabia 1.4 16V Comfort 42K miles

Hi,

I've just been testing my cylinder pressure as the engine management light came on and the garage said 'piston rings £1000 repair' based solely on the fault codes. Reading some of the other posts there has been some misdiagnosis of this all-encompassing light so here's what I got:

1: 180PSI 12.4bar
2: 195PSI 13.4bar
3: 195PSI 13.4bar
4: 215PSI 14.8bar

The guide that came with my halford's compression tester said a discrepancy of more than a bar indicates a problem so it's not good but I wondered what the pressure should be? Also the guide said to open the throttle when cranking - really? Do I understand this correctly - does this mean foot to the floor?

I just read about pouring oil into the cylinder to clear carbon deposits - should I have a stab at this? Anything else I should try before resigning myself to an expensive bill?

Any thoughts gratefully recieved.

Lummox

They all look fine to me.

But the piston ring issue doesnt lead to a drop in compression, it leads to oil consumption and the contamination of the inlet system.

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Unit 18 Automotive Services
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dave a

most people carry out compression tests completely incorrectly!

was the engine hot when tested?
did you do a wet and dry test on each cylinder?
was the battery voltage stable throughout the test?
did you do it with WOT?
did you disconnect injectors?


A compression test should be carried out on a hot engine, each cylinder should be first tested dry and the result noted. Each cylinder should be tested for at least 10 seconds, to get an accurate result you should connect a booster pack to ensure all cylinders receve the exact same cranking speed.

once a cylinder has been tested dry you should squirt around 10ml of engine oil into the combustion chamber to seal the rings against the bore and so compression isn't lost through the ring gaps. The result should be noted.

The above should be done with all cylinders and then post the results, a large difference between 2 cylinders isnt critical, around 10-15% of a difference is normal on an everyday road engine. If you do have a large difference between a wet and dry test on 1 cylinder that is far more worrying.

A basic compression test doesnt always show a lot, its a crude method tbh. For a much more accurate test get a 'leakdown' test carried out at a good garage, in this test each cylinder is turned to TDC (or as close as necessary to have both inlet and exhaust valve closed) and pressurised with compressed air to about 120psi. The machine measures a percentage of cylinder loss which is a much better factor than using a cranking Psi which is very hit and miss.

A leakdown test will not only tell you there is a leak, it will tell you where it is going, if the coolant begins to bubble its headgasket, exhaust hisses than its exhaust valve, inlet hisses than its inlet valve, hissing from dipstick is a sign of loss past the piston rings (or possible oilway past headgasket)


Hope this helps,

Dave

jim campbell

i had the same problem on a x reg 1.4 16v comfort , ended up being cracked cylinder head , piston rings

Lummox

Agree 100% there.

We are getting a lot of 1.4 16v engines recently that are suffering from poor valve seating. They missfire on a specific cylinder but the compressions usually indicate nothing wrong. Do a leak test however and you can usually hear the air coming back through the inlet manifold.

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Unit 18 Automotive Services
www.unit18.co.uk

andyreed

Excellent, that's really handy thanks. From knowing nothing about this I now feel much better informed. I'll arrange a leak test and for the fun of it I'll have a better go at the compression test I made a pigs ear of today! (for the record: warm engine yes, the rest pretty much no).

So out of interest does anyone know what the cylinder pressure should be for the 1.4 16V Fabia, like when it came out of the factory?

cphaza

not sure what they are supposed to be but i just rebuilt an old vectra engine which blew the head, most i was getting was 140 out of each of them, and that runs smooth so if your minimum is 180, id be quite happy with that. Did anyone have the eml come on with this problem saying lambda sensor?