mj1pate

Folks; My 86.5 928 has suddenly developed symptoms like "running on 4 cylinders". The fuel system is new , stem to stern, except injectors (which were rebuilt 5 years ago). The ignition system is new as of 8 years ago, 40k miles. I'd like to try "suspect good" used coil wires if some one has two to loan or sell, before I buy a new wire set. Anyone have a pair that I could buy/borrow?

Speedtoys

Where are we?

James Bailey

You changed the ignition secondary stages/igniters at that time on the bulkhead in front of the radiator ?

mj1pate

Speed toys; "we" are in central Maryland :-)
James: no, the igniters (power amps?) have not been replaced. The coils, wires, rotors, caps were replaced.

If someone has a couple suspect good coil wires to loan/sell, I would appreciate it.
Just to note: the maf was calibrated 4 or 5 years ago. Should also note that in the middle of of a recent rough running period away from home, the engine "magically" changed to running perfectly, long enough to get me home. Then, upon restarting several days later, same rough running and Exhaust smoke. Haven't disconnected the maf to see if any change, but I wanted to eliminate single bank issue first and need to decide how to sequence the rest of trouble shooting. Hate to see this old girl go down. It really does run well for the most part.

SeanR

If the front ignition amps have not been changed then go ahead and do so, they do and will fail. You can test your coil wires with an ohm meter to see if they are busted.

mj1pate

Yes that makes sense. I've ordered the amps and will replace them. After 29 years, a refresh seems in order. I'll ohm the cool wires as well.

davek9

Before "shotgunning" this, why don't you use a Timing Light to see which Coil Bank is not working, if that indeed is the issue?

Those parts are like 80 buck's "each" !!

mj1pate

Yep. Still have a timing light! I'll verify each plug circuit is getting spark. I ordered the Huco Amps vs Bosche, about that price for their complete pair. The Bosche are even more expensive than $80 apiece. I suspect Bosche may be better, but the Audi forums reviews indicate some years and 40k miles are anticipatable with Huco. Their consensus was however: maybe should Keep an extra on hand.

M. Requin

Just went through this, but happened to have a new set of Beru's ready to install. First check with timing light on coil wires indicated both banks firing, checking individual wires found two distributor cap plug wire connections corroded, i.e. no spark. Replaced wires, no further issues (still have to install the rest of the set). Massive amount of humidity lately in our part of the world has caused marginal connections to fail, I suspect. I'll mail up two suspect coil to dist wires if you still need them.

mj1pate

Thanks Requin... I'll do some measurements first.

On which note: I know I'm missing this in the tech notes and shop manual: what are the resistance ranges for the spark plug and coil wires?

dr bob

The coil wires themselves are metal cored and have very low resistance. The ignition wires themselves have very low resistance, but have resistors in the plug connectors.

There are several ways to check for spark energy, the least invasive and probably safest is the clamp-on timing light method. Even a cheap one will do the job.

If you've been messing with high-side ignition pieces, it's worthwhile doing at least a visual inspection of the caps and rotors. Look for cracks of course, but also for any evidence of arcing inside the cap. Telltales include blackened and/or eroded contacts. The high-voltage arcing generates a metal 'plasma' that can coat the inside of the cap de a path to ground for the spark energy. Humidity contributes. If no arcing, wipe the insides carefully and replace. Otherwise replace with new.

Arcing and connector failure at coil wires is usually pretty obvious when you pull the wire ends out. The same arcing, sometimes a blue/white powdery deposit if water was involved. The coil wires themselves seldom fail unless there's heat from a poor connection and associated arcing. Note that the coil wire connections and the plug leads where they connect to the caps are perhaps the only legitimate use for "dielectric grease" on the cars. Use it to waterproof the connections inside the boots after cleaning and drying everything.