89 325i Problem...

I thought I had ruled out everything except the coil but here's where I stand now.
The engine idles alright but breaks up at random intervals during
revs. I put a timing light on the coil wire and the miss shows up there so I know I have a spark issue. Not sure if cap and rotor could affect it there though. Could this possibly be a computer issue or is it as simple as cap and rotor? Any way to tell without dumping in parts?
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These engines really don't like a worn cap and rotor. They'll run with an almost non-existant rotor, but not well.
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if the cap/rotor is more than 10 years old, i say change it anyway...
problem might also be a failing coil... I would expect the "computer" to fail consistently rather than intermittently.
could you borrow a coil and test it?
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On Wed, 11 Jan 2006 02:41:40 GMT, snipped-for-privacy@earth.net (keith) wrote:

Looks like I'll be doing the cap and rotor and hoping for the best..

I would expect the same but who knows for sure.

I switched coils with my son's 67 325is and the problem persisted. The question comes in the fact that I get an intermittent spark directly off of the coil. If I got a consistent spark at the coil and the engine still misfired it would be much easier to figure out. I guess I'll change the cap and rotor and see if it makes a difference. They're definitely older than 4 years old but I don't know how much older...
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- snip

what about the TDC pickup? not sure what engine/computer you have, but have a look at what is "triggering" the coil to spark.... could you use a 5v led and resistor to see the low tension impulse?
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On Wed, 11 Jan 2006 17:24:01 GMT, snipped-for-privacy@earth.net (keith) wrote:

Already ruled out the sensor. That was actually one of my earlier suspicions though. Pulled the cap today and the rotor fell out in little pieces... How the hell was it still running??? The entire end of the rotor (about 1/2") was missing completely. Someone said in an earlier message that they'd still run with the rotor tore up but damn...
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Well, replaced the cap along with the rotor and car seems to run perfectly once again. Haven't been out for a drive yet but doesn't exhibit any of the symptoms it did before. The cap was pretty well mangled inside from the pieces of the rotor bouncing around but I'd have replaced it anyway just to know it was good. Still can't believe the car actually ran with that much of the rotor gone and the cap in that condition. Any other car I've ever owned would have refused to run long before it got to this point...
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That's exactly how I found the worn out distributor bushings in my 318i. I took it in to the dealer because I couldn't figure out why it was missing; he put a new cap and rotor on it and called it good; and the same day after it warmed up real good the distributor shaft whirled in the housing and snapped of the new rotor. Apparently the old one had gradually worn itself a groove in the cap but the new one got caught on the connectors and broke off.
wrote:

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Don't forget the plug leads too.'Carbon string' types can go high resistance with age and cause misfiring. And/or the insulation break down.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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You might want to check for excessive play in the distributor shaft. I had this problem on my high mileage 318i and had a devil of a time diagnosing it. The engine would stumble at high rpms but only after being thoroughly warmed up. Then after the oil had thinned out a bit the distributor shaft would whirl in its housing causing intermitent spark. Back in the days of points and condensers we would find this problem because it would lead to very erratic spark timing that would show up when we did a tune up, but now that we never have to do that job the problem goes undetected.

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