Bosch wires new in 2006 bad at 20k on '89 525.

[Tiger]

Check the resistance of each spark plug wire. Then check the rating of resistance on the plug end to see if it match. They are usually 1000 ohm.. and you can go up to 1300 ohm before there is really some misfiring.

Your plugs condition concerns me. Cross reference those plug conditions to plug chart.

[Gene in NC]

Below is old post. Adding it now because review of service history uncovered short service life on wires.

Recently, a reputable parts guy claimed that Bosch wires now crap. Uncertain if true.

On the other hand our other '89 525 has over 80 k on second Bosch set and I used the original 80k set of wires from that car to debug the problem with the 20k wire set car.

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m20 severe stumble @ low power when hot.
'89 525 5s 184k has m20 w severe intermittent but very frequent stumble, and effect of low power when hot, especially under load. Starts and idles fine, even when hot. Before hot it runs fine. Test from home with cold engine ran strong and smoothly. 1.2 mi to freeway, 2 mi at up to 70mph OK. 1 mi on freeway return OK. City street at 35 mph stumbles so bad was happy to get home.

Problem first started 135 mi from home while on loan to my son. He reported problem, but then reported OK when switched to Shell 93. Met him !/2 way home to swap cars. Surprized to find condition as below.

Stumble feels like cross firing in the distributor. Sharp break like ignition but engine acts like it is being "stopped" by cross fire with back and forth load on the driveline. Snatches drive line back and forth. Worse than just flicking ignition on and off. 5th speed impossible. 4th making progress at 70 on I 40 W but more and more rougn as we head west from the coast toward Raleigh, encountering more grades as we complete the 360 ft elevation change from sea level . By I 95 can't keep up with slowest traffic. Talked to indy who thought that even if cross firing another 30 mi wouldn't hurt anything.

Took off with condition worsening, tow seemed only way to get home. Max speed 45/50 and concerned about accident in 80 mph traffic.

Then what appeared in the rear view mirror but something that was almost as slow, one of those GM RVs, based on the Toronado, towing a Honda. Caught his draft on a down hill and drafted that sucker the last 25 freeway miles. A little dicy keeping up a couple of times, but MacGuyver would have been proud.

Dropped off the draft with 7 mi of city streets to go. Problem went away unitil the last mi when grades become more frequent and longer.

So what have I done?

Tested as above.

Pulled plugs (11k m on W8LCR) and they are a mess. No two have same appearance. Common condition is insulator clean on one side with heavy deposits on the other. #1 & 2 are sooty, while # 3-6 look a little wet. Oil or fuel? Can't tell but 24 hours out of engine appearance unchanged.

Five plugs have some of the deposit (about 25%) broken off down to bare insulator. Break goes from tip of insulator up in a roughly "v" shape. Son put about 5k on the car over the winter and has been known to use the cheapest gas that the car can possibly run on.

Compression unchanged.

Aha, must be a bad dist cap. Nope, dist cap looks new. Must have been replaced just before I bot the car about 11k m and 12 mos ago.

Any ideas? Would like to drive it to Vintage at the Vineyard 5/27. Oh man, would I like to have a digicam to post photos of the plugs.

[winfred]

yea new bosch is semi crap, funny thing the factory solid core wires go for like 200k miles if kept free of oil and other harmful elements