2002 R53 with about 220K miles. Driving to work yesterday cruising at 70mph and sudden power loss with SES and ASC lights. Limped home on 3 cylinders and parked it. Pulled fault codes and only P0303 showed. Pulled plug wire off No. 3 and started it. No change, so clearly No. 3 is the problem (right?). Removed #3 plug and it was wet with fuel. Checked resistance of plug wire. I think it's good as it was similar to others. Tried new plug, no change. Attached a cheapo spark tester to plug wire and ran engine. Plenty of sparking going on. Pulled plug again and stuck my wifi borescope down the cylinder and could make out the top of the piston but not much else. Appears to be fuel pooled on low side of cylinder. So...it seems I have spark, fuel and hopefully compression (need gage and will compression test tomorrow). What else should I check? Should I replace wires and coil pack just to be sure? They are original! After market coil packs are as low as $20, but anything to watch out for? I've read about sensors being bad, but why would it just be cyl 3? Thanks!

 

Before you buy a compression tester, do a simple dollar bill test. If fails (flutters), most likely a burnt valve.

 

Thanks, I'll give that a shot, but the problem occurred instantaneously, so I question whether a burnt valve would do that. I suppose if it cracked or a piece broke off, it would be sudden.

 

I too vote for likely burnt valve, or broken valve spring. Compression test should reveal something.

 

Don't buy any parts without first doing a diagnostic, even if they're cheap, you may still be spending money you don't need to spend.

Compression & leak down test is where to start then work from there.

 

Thanks. Will do. I'm getting the extension tube today that I need to get down in the plug well with my compression tester. Fingers crossed that it's not major.

 

150 psi in Cyl #1 and 0 psi in #3. Ruh Roh.

 

Like I posted in another thread about low compression...

Now a leak down test can help pinpoint the source of the low compression.

With #3 cylinder pressurized leaking air noise from the intake is a bad intake valve, from the exhaust a bad exhaust valve. From the #2 or #4 cylinder spark plug holes a bad head gasket. From the oil fill opening in the valve cover bad rings/piston.

'course, almost certainly the head's going to have to come off or maybe even the engine needs to come out and be disassembled. At 220K miles you might want to address some other things at the same time you are addresseing the low compression issue.

 

Already got the head off. One of the exhaust valves has a 1/4" X 1/8" chunk missing. Everything seems to look OK, except for some pitting/spalling on the cam lobes. If I replace the cam, will I need to have the cam towers machined to fit, or is just an R&R?