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Discussion Starter · #1 ·
So I use this thread for all things X5 that I need help with and it hasn't failed me yet so here we go.

I have a 2005 X5 3.0i with 138,000 miles. Recently, the engine overheated and led to a full head replacement. After ordering a used head on Ebay, I had is cleaned up and everything was good to go. I have an ASE certification and felt confident installing the head so I went for it. After the install and reassembly I fired up the engine and have worked through some small problems i.e. exhaust leak/vacuum leak/sensor not plugged in (I know right). However, there is a problem hanging out in the form of a cylinder 4 misfire.

The engine starts and runs like a champ for about 30-40 seconds. I've even made it around the block (about 1/4 mi.) with no issues. However, after a bit the engine goes rough and cylinder 4 misses. I've changed the spark plugs/coils, followed by checking for injection issues (cleaning - replacement) with no improvement. I've performed a smoke test with no leaks found and have reached a breaking point. My inclination is that there may be a valve issue I didn't notice before installing the new head, but can't reconcile that idea with the engine running like a champ until it starts missing. I would think a valve issue would be immediately apparent but I may be wrong.

Adding to the enigma is the fact that if I shut the engine off while it's missing and restart, it runs like a champ again. There is no SEL popping on for anything other than the usual 304 code. Any ideas?
 

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Discussion Starter · #3 ·
I performed a very rudimentary test. Fluid in the intake/exhaust and check for leaks after a few hours sitting. No leaks or issues there.

I presume it could be a sticky valve in there, though I am trying to mentally prepare myself for removing the head to check if that is the case. I can perform a compression test since it hasn't been done since install to check for issues. I guess I'm still wondering, if there is a compression issue, should that be evident once the engine starts? Would it take 45 seconds for the engine to notice the issues and have a misfire?

Update: I restarted the engine after being off for only 1-2 seconds and the issue went away only to return exactly 1 minute later.
 

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I performed a very rudimentary test. Fluid in the intake/exhaust and check for leaks after a few hours sitting. No leaks or issues there.

I presume it could be a sticky valve in there, though I am trying to mentally prepare myself for removing the head to check if that is the case. I can perform a compression test since it hasn't been done since install to check for issues. I guess I'm still wondering, if there is a compression issue, should that be evident once the engine starts? Would it take 45 seconds for the engine to notice the issues and have a misfire?

Update: I restarted the engine after being off for only 1-2 seconds and the issue went away only to return exactly 1 minute later.
Out of curiosity, have you tried moving the coil from 4 to some other cylinder and vice versa? See if the misfire travels? Wouldn't be the first time a "new" coil wasn't.
 

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Discussion Starter · #5 ·
Yes. The first step was swapping the coils between cylinders. The misfire did not travel. Update: the complete dissassembly was performed with no leaking valves or sticking valves found. After reassembly, the same thing happened again. Cylinder 4 is the culprit again. My next step is to check/clean the injector on that cylinder. I'm trying to isolate any issue that would only affect one cylinder. Things I ruled out are O2 sensor, Vacuum leak, Timing issues, and CVV since these would all cause issues in all cylinders not just cylinder 4. Please correct me if I am wrong.
 

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You took the whole cylinder head off and apart and reassembled it, but still no compression test ? BTW if the DME detects a weak cylinder it will often cut off the fuel to that cylinder entirely.
 

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Discussion Starter · #7 ·
SOLVED: Yes I am embarrassed to say but the mistake was a surgeons worst nightmare. One of the washers from the head bolts was loose in the head. It was found.....you guessed it.....lodged into the spring of cylinder 4. Removed, rebuilt, and running. Thanks for the help and great advice folks. I appreciate you all.
 
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