Confusing compression readings! Ideas?
Posted: Sun Apr 22, 2012 7:46 pm
I have a Corsa b, X12XE 1.2 16v, with 230,000 km on the clock (yes, I know....).
I've had it since 120,000 km (one careful owner and service history) and it was in reasonable nick then, and I've looked after it, with regular maintenance and some fairly typical repairs.
Recent problems started a few months ago with the water pump. It went into the garage for a handbrake repair (seizing in the cold Finnish temps) and an oil leak (dipstip holder) repair, and the guy said the noise meant the water pump had gone. I was only 2 years ago I last had it done, but I've done about 70,000 miles in that time, and it was a bit noisy!
Anyhow, then about a week later I noticed the heater not working. I tracked that down to loss of coolant, which I then tracked to a cracked pipe to the radiator. Fixed that and the coolant level. But then the EML came on, and OP-COM threw an EGR fault out. So, stripped and cleaned that, which was caked in carbon, and all was well again. But then EML came on again. Fixed it again.
A day or two later, the car started to run really bad, with obvious compression issues. I thought the coil might be going, so changed that and thought to change the plugs too. In the process, found 2 spark plugs loose in the sockets
So, then it seems to be going okay again. But then EML comes on again. This time I thought, let's put a new EGR valve on. This went okay, though the water temp reported being higher, which I put down to a different resistor, as the OP-COM reported 89 degrees. Now it's burning oil really fast. In three weeks I've had to do three 2 litre top ups. Two litres a week! And it's a little smokey from the exhaust (no big clouds) when I'm reversing or just staring out, but clears with normal running, though I can smell the oil burning.
So I did the breather pipes too, just to be sure, and they were full of oil/water sludge. Camshaft casing seems fine, no sludge on oil filler cap and no oil in water coolant. But still getting compression issues and OP-COM reporting random misfiring, mostly in Cylinders 3 & 4.
So, next was a compression test. And now for the [grim] readings:
Cylinder 1 - Dry: 220, Wet: 222, spark plug: good
Cylinder 2 - Dry: 160, Wet: 175, spark plug: good
Cylinder 3 - Dry: 245, Wet: 260, spark plug: carbon/sometimes oily
Cylinder 4 - Dry: 245, Wet: 250, spark plug: oily
All the plugs have previously been fine on changes twice a year.
Cylinder 1 seems fine. Rings seem okay, and spark is fine. Cylinder 2 is low on compression. This could be damaged rings or just some bore wear or both, but the wet/dry difference is still less than 10%. Does this need looking at?
But then cylinder 3 & 4 have me confused. High compression and oil, with obvious deposits on the piston heads. But high compression? Is the compression forcing oil through the valve guides or stem seals? Should I run hotter plugs? 245 is 11% higher than the 220 in Cylinder 1. Is that okay? I've read that 10 to 15% difference is okay. But then when they run wet, they go to 260, which then means the different to Cylinder 1 becomes 17%. That seems high. And then wet to wet of Cylinder 3 & 4 to Cylinder 2 is a whopping 48% difference. No wonder the engine doesn't seem to be running very smoothly. I'm amazed it's running at all.
So, what to do. Would doing the head gasket and the valve stems and valve rails fix the worst problems for Cylinders 3 & 4, and then it's probably just the piston rings on Cylinder 2, which I could perhaps ignore? If 3 & 4 come down to the level of 1, then that is not so bad if 2 is a bit low. Oil Smoke Stop would probably help with that.
Or do you think Cylinder 2 has a broken valve. Or, is the fact that adjacent Cylinders 3 & 4 showing high compression and oil/carbon mean the head gasket has gone between those two cylinders (wouldn't that bring lower compression?). That doesn't seem to make sense.
I'm confused. Too much variation in all the variables - I cannot make sense of it. Any ideas?
I've had it since 120,000 km (one careful owner and service history) and it was in reasonable nick then, and I've looked after it, with regular maintenance and some fairly typical repairs.
Recent problems started a few months ago with the water pump. It went into the garage for a handbrake repair (seizing in the cold Finnish temps) and an oil leak (dipstip holder) repair, and the guy said the noise meant the water pump had gone. I was only 2 years ago I last had it done, but I've done about 70,000 miles in that time, and it was a bit noisy!
Anyhow, then about a week later I noticed the heater not working. I tracked that down to loss of coolant, which I then tracked to a cracked pipe to the radiator. Fixed that and the coolant level. But then the EML came on, and OP-COM threw an EGR fault out. So, stripped and cleaned that, which was caked in carbon, and all was well again. But then EML came on again. Fixed it again.
A day or two later, the car started to run really bad, with obvious compression issues. I thought the coil might be going, so changed that and thought to change the plugs too. In the process, found 2 spark plugs loose in the sockets
So, then it seems to be going okay again. But then EML comes on again. This time I thought, let's put a new EGR valve on. This went okay, though the water temp reported being higher, which I put down to a different resistor, as the OP-COM reported 89 degrees. Now it's burning oil really fast. In three weeks I've had to do three 2 litre top ups. Two litres a week! And it's a little smokey from the exhaust (no big clouds) when I'm reversing or just staring out, but clears with normal running, though I can smell the oil burning.
So I did the breather pipes too, just to be sure, and they were full of oil/water sludge. Camshaft casing seems fine, no sludge on oil filler cap and no oil in water coolant. But still getting compression issues and OP-COM reporting random misfiring, mostly in Cylinders 3 & 4.
So, next was a compression test. And now for the [grim] readings:
Cylinder 1 - Dry: 220, Wet: 222, spark plug: good
Cylinder 2 - Dry: 160, Wet: 175, spark plug: good
Cylinder 3 - Dry: 245, Wet: 260, spark plug: carbon/sometimes oily
Cylinder 4 - Dry: 245, Wet: 250, spark plug: oily
All the plugs have previously been fine on changes twice a year.
Cylinder 1 seems fine. Rings seem okay, and spark is fine. Cylinder 2 is low on compression. This could be damaged rings or just some bore wear or both, but the wet/dry difference is still less than 10%. Does this need looking at?
But then cylinder 3 & 4 have me confused. High compression and oil, with obvious deposits on the piston heads. But high compression? Is the compression forcing oil through the valve guides or stem seals? Should I run hotter plugs? 245 is 11% higher than the 220 in Cylinder 1. Is that okay? I've read that 10 to 15% difference is okay. But then when they run wet, they go to 260, which then means the different to Cylinder 1 becomes 17%. That seems high. And then wet to wet of Cylinder 3 & 4 to Cylinder 2 is a whopping 48% difference. No wonder the engine doesn't seem to be running very smoothly. I'm amazed it's running at all.
So, what to do. Would doing the head gasket and the valve stems and valve rails fix the worst problems for Cylinders 3 & 4, and then it's probably just the piston rings on Cylinder 2, which I could perhaps ignore? If 3 & 4 come down to the level of 1, then that is not so bad if 2 is a bit low. Oil Smoke Stop would probably help with that.
Or do you think Cylinder 2 has a broken valve. Or, is the fact that adjacent Cylinders 3 & 4 showing high compression and oil/carbon mean the head gasket has gone between those two cylinders (wouldn't that bring lower compression?). That doesn't seem to make sense.
I'm confused. Too much variation in all the variables - I cannot make sense of it. Any ideas?
