What spark plug should I buy for a 928 S4?
 

I want to buy a set of OEM-style plugs for my 1988 928 S4, but I am baffled by the large variety of plugs that available for these cars (Bosch offers 8 different models alone)! What particular plug brands and models do you recommend?

There is only one plug to use in your stock S4 WR7DC+ $1.95.

+1 to what Roger says. Bosch would love to sell you something newer and more expensive, but your first trouble visit to a mechanic that knows the 928 and he will pull them out and put in the stock plug to see if that doesn't fix your problem.

just out of curiosity what negative affects occur when running non oe plugs (like lets say a Bosch Platinum unit)?

none, as long as it is the correct heat range.




My name is spelled correctly here>>>>>>>>Russ

If you are really set on using platinum or more plugs, i would recommend NGKs or Densos..I had a bad experience with the Bosch platinums in my 944 (and my son's Hyundai)..in both cases when swapped with NGKs the problems went away.
I've heard others complain as well, so i think it's more than me.

Of course spark plug threads are like motor oil threads..everybody has a favorite!

how about denso iridium spark for my 81 928

The stock plug works very well, and has a long history from many users of working well. Use something else and you get to wonder if any minor or major trouble is related to the non stock plug.

Never heard of any problems with the stock plugs - v - heard plenty of problems with non stock plugs.
This is one area where I stick to the original plug.

+1 on using stock plugs. I too had problems with Bosch Plats with my Mitsu Turbo. NGK all the way if you need to use Plats.

Iridium plugs are best used on boosted cars with water/ methanol injection, provided that ypu keep the gap tight. In this application they can prevent the flame kernel from being blown out, causing misfires.

In general, regular plugs work well in our cars because they have a large electrode of solid metal that gets warm and stays warm. Platinum and other precious metal plugs have a very tiny center electrode that is surrounded by ceramic. Under ordinary running conditions, the ceramic can develop odd fluffy deposits and over time the center electrode can erode way back into the ceramic.

I have run Platinums in Bosch fuel injected cars of our era, and they tend to last no longer than 20 to 25,000 miles. An ordinary plug will run until the gap is so large that the plugs will no longer fire and the distributor cap looks like a science experiment. The platinums will often have wierd deposits, while the most ancient stock plugs will look like textbook pictures of perfect combustion. You could regap them and run them some more, even at 80,000 miles, which I have seen, BTW.

There is enough metal in a standard plug tip that when you really get them hot, they will burn all the deposits away from the tip. Platinum plugs do respond to ''Italian tune ups'' but they still will have a shorter lifespan than you might expect. When I was doing tune ups for a living, I would get poorly running cars from cutomers, and take them out and rev the piss out of them. They would always run fine. I had one customer who would come back every week, until I finally changed out the plugs for stock NDs . Bosch and NDs were the best, and I tended to use Japanese plugs on Japanese and Italian cars, and Bosch plugs on German cars. Stay away from Champions.

BTW, it is true that some cars absolutely would not run on Platinum plugs when they first came out. FI Fords come to mind. Many people continue to run these ''superior'' plugs in applications where they do not work well. Large metal center electrodes work well in our cars, and especially in lower compression, less extreme environments like the OBs. YMMV SmileWavy

Spark plugs
 

I just replaced my old 4 prong platinum plugs with $50 new ones...."could" these plugs cause idle problems??????? the old plugs ran fine........
Tom Taylor

Its a cheap place to start looking.

Great thread.

be gentle with ngk plugs this was very light pressurehttp://forums.pelicanparts.com/uploa...1281909926.jpg
http://forums.pelicanparts.com/uploa...1281909953.jpg

Skeery!

I've had a nice experience with the Bosch Super4's, and I think it's because of the high compression ratio in my engine (10,4:1) and the fact that it runs high octane 99-fuel. The car seems to pick up throttle much easier than before, and there is no black smoke from the exhaust anymore.. (Unburnt fuel).