Misfire, where to look next...

[MoreMayhem]

I've been trying find the source of a misfire on one cylinder. So far I've found that there is very low, almost undetectable spark on cylinder #5. Car is an 88 325i with a stock M20B25 engine.
Here's what I've done so far to try and figure it out:
Followed Bentley guide for checking the ignition system, including:
Tested coil: resistance checks within spec.
Tested spark plug leads: all about 5400 ohms
Tested leads with a spark tester: all have strong, snapping spark except for #5.
Tested contact points in distributor to where the spark plug and coil plugs connect: all 0 ohms resistance.
Tested rotor contacts: good.
Tested recently replaced CPS: good
Looked at CPS alignment and distance from teeth on harmonic balancer: good
Looked at teeth on harmonic balancer: none missing except for where they are supposed to be missing.
Coolant temp sensor measures within spec.
173 ECU swapped with another ECU.
Replaced spark plugs with new NGK (not that it matters since the fault seems to be before the plugs)
Tried swapping spark plug leads around on the distributor, and it seems that whenever a lead is connected to #5 there is no detectable spark on the tester.
Compression tested. Okay #s
Leakdown tested. 13% was highest, dry.
Smoke tested, repaired leaks and re tested.
Sat in the passenger seat pulling out my hair.

I'm at a loss where to look next and would welcome any suggestions.

[DesertBMW]

incorrect valve lash adjustment. worn out valve stem. cracked intake manifold seal at problem cylinder.

[MoreMayhem]

Valve lash was checked/adjusted three months ago, replaced intake manifold gaskets then too & subsequent smoke test didn't reveal any leaks there. Valve stem seals are suspect, car still has original head and 262000 miles. But I don't understand how any of those things would cause a no or weak spark condition? Does the ECU somehow monitor these things?

[uturn]

I'd say since swapping leads result in the same cylinder not getting spark that it's the distributor cap. The metal cover the distributor cap mounts, the screw on the left tends to strip out the threads and can allow the cap to get out of alignment.

[_JDizzle_]

I had a misfire in my 325e all i did was replace the rotor button and distributer cap and it was gone

[MoreMayhem]

Thanks for the responses. I looked through the maintenance log and the cap and rotor were replaced in Jan 2012, about 30k miles ago. Think they should last longer than that, but have ordered replacements and hop that ends the problem.

[_JDizzle_]

Yeah if theres any cracks or gaps in the distributer it can develop a misfire thats what happened to me

[MoreMayhem]

Thanks for the help guys. New Bosch distributor cap and rotor and it seems to be running great. I had convinced myself it couldn't have been these items as I had replaced both within the last 30 thousand miles. So stoked it's running right & so pissed at myself for not replacing the cap and rotor months ago. Bremi was the previous brand installed, don't know if they generally produce crappy parts, but it seems I at least had one.

[TobyB]

Bosch isn't at all what it used to be...

t

[_JDizzle_]

:)