Another update on the missing 528i

grumpsjr · Post by **grumpsjr** » Sun Mar 22, 2009 10:50 pm

Hi all,

Thought I would give you an update on this continuing saga, as new symptoms have developed.

Pierre and I swapped distributors the other day, which did not solve the issue. This would suggest that I do in fact have a bad AFM. GrigGreg is going to loan me one to see if that helps things - Warner Hall and I did some experimenting with his AFM and this seemed to be at least somehow related to the miss.

That's the background: since replacing the distributor I've driven the car quite a bit, and the miss is getting progressively worse. At first it was just occasionally at idle. Now it's at all RPMs, all throttle positions, mostly when the engine is warm and has been driven for 15 minutes or so.

Interestingly, yesterday, before the miss started getting really bad, the tachometer started fluctuating. Today, the tach bounces all over the place (across 1-2K rpm variance) and is usually coincident with a miss episode.

I'm wondering if I have a bad coil (do they slowly go bad, or die all at once) or bad +/- coil wire given the problems with the tach? The coil ignition wire is new.

Your continued help is greatly appreciated!

1st 5er · Post by **1st 5er** » Tue Mar 24, 2009 8:24 am

Eavesdropping.

Lenny D. · Post by **Lenny D.** » Thu Mar 26, 2009 1:02 pm

Forgot what you have replaced so far, but I've had trouble with an off-idle miss resulting from bad HT wires, particularly the coil lead. A set of new Beru wires lasted only two years before causing me much distress until I replaced them, problem solved. Just checking...

Pete K · Post by **Pete K** » Tue Mar 31, 2009 1:42 am

I'm no expert, but I'm pretty sure you'll always get tacho problems with an electrical miss. I thought mine was a fuel problem but turned out to be the points (obviously not the same problem for you though) and my tacho was dropping to half as only half the plugs were firing.

Cheers

grumpsjr · Post by **grumpsjr** » Tue Mar 31, 2009 9:27 am

Makes sense. About the only three things left to switch are the AFM, the coil, and the wiring harness. EVERYTHING else (plugs, cap, rotor, distributor, ECU, ICM, vacuum lines, vacuum valve to brake booster, plug wires) has been switched. I should have a REALLY nice running car when I get it figured out. Will keep you all posted once I scare up another AFM and a coil.

Thanks for the input!
Brian

On Mon, Mar 30, 2009 at 11:42 PM, Pete K <peter.kilner@flsmidth.com (peter.kilner@flsmidth.com)> wrote:

I'm no expert, but I'm pretty sure you'll always get tacho problems with an electrical miss. I thought mine was a fuel problem but turned out to be the points (obviously not the same problem for you though) and my tacho was dropping to half as only half the plugs were firing.

Cheers

Pete K
'75 520i
'79 323i

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