Tech Tip No. 16

Ned Ritchie

Originally published in the quattro quarterly

Copyright 1997

Wrong Spark Plugs

Over the years I have traveled to many Quattro Club track event and safety seminars.  Usually at each event the following scenario takes place.

Says the owner of the Quattro, "I just can't believe it. I had a tune up a few days ago to prepare for the event and now the engine runs terrible. I find it hard to start and it misses under load."

I and a few knowledgeable owners will reply,

. . . bet you're using Bosch platinum plugs.

We open the hood and sure enough there are five clean Bosch WR7DP plugs. Usually someone has a set of old plugs that they're carrying around in some tool box. The used but correct plugs are installed and the engine runs perfectly.

The Bosch WR7DP platinum spark plugs just do not work in the turbo application.  I've talked to some Bosch employees, but they've not heard of the problem, but were willing to listen.

What spark plugs should you use? The smart thing is to use what is recommended in your owner's manual.  Audi has done a lot of testing to determine the correct plug, and the Bosch platinum is not one of them.

What do I recommend? On Audi 10-valve turbocharged engines I recommend the following:

Bosch W7DTC

NGK  BP6ET

These are a long life plug with three ground electrodes that enable the plug to last up to three times as long as standard plugs. But, here is a bit of trivia about multiple electrode plugs.  Multiple electrode and platinum plugs of any type to not work with the Jacobs Ignition System.

If your budget can afford it use the better spark plug that is used on the Audi 20-valve turbocharged engines that was not available when the 10-valve engines were made:

Bosch F5DPOR

These plugs have a pair of platinum electrodes that are side gapped, but have a price hovering around $20.00 each!

On my 400+ hp 20-valve turbo engine it was beyond the recommended time to replace these plugs even though the car was running well.  Upon examination the plugs looked as good as the $20.00 plugs I was installing. I put the old plugs into my daughter, Marni's, 4000S quattro as an experiment, and they've been running well for three years.

INTENDED ACCELERATION ^®

© Copyright 1997-2000 by Ned Ritchie