06 N52, Low compression on cylinder #5

[ceb5]

Have a 06 325i with a N52 engine that is foreign to me. The car would idle great until you tried to drive and then it would go into limp mode. This was 6 months ago when I got this car and remember that It had a code for cylinder 5 and also a 02 sensor code. I had did a compression check a #5 was down about 40lbs. compared to other 5 cylinders. Car was not smoking, running hot or using oil so I figured it had a burnt valve and pulled the head off. First time I had ever seen a head set up like this but with help from All Data finally got it off. To my surprise I don't see anything wrong with valves on cylinder 5. they are opening like they are supposed to and I can spray Carb cleaner into the exh. or intake ports and valves don't leak. Wish I had done a leak-down test on it before pulling it apart but to late now. Just wondering if anyone else has run into this before and could give me a idea of what to look at.

[bms5]

Do a fluid leakage test on the piston rings. It’s not very scientific but should still provide insight into what’s happening. Preferably turn the crankshaft so that #5 piston is 1-2” down from TDC. Pour a small amount of solvent or gasoline onto the top of the piston so that the piston is just covered with fluid. Do the same with #2 cylinder which will be at the same position as #5. Compare how long it takes for the liquid to leak past the rings down into the crankcase. If you have stuck rings, it should leak much quicker on your weak cylinder. If that is the case, use a stronger cleaner to ‘soak’ the rings to try and free them up. Seafoam may be one product to try. I know BG 44K worked really well if you can get some of that.


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[ceb5]

Do a fluid leakage test on the piston rings. It’s not very scientific but should still provide insight into what’s happening. Preferably turn the crankshaft so that #5 piston is 1-2” down from TDC. Pour a small amount of solvent or gasoline onto the top of the piston so that the piston is just covered with fluid. Do the same with #2 cylinder which will be at the same position as #5. Compare how long it takes for the liquid to leak past the rings down into the crankcase. If you have stuck rings, it should leak much quicker on your weak cylinder. If that is the case, use a stronger cleaner to ‘soak’ the rings to try and free them up. Seafoam may be one product to try. I know BG 44K worked really well if you can get some of that.


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Great idea, didn't think about doing that. I was looking at how much trouble it was going to be to get oil pan off so I cold pull #5. Didn't really want to do it, believe the problem is in the head. Will try this when I get back after lunch. Thanks!