'91 300CE spark plug recommendation?
 

M104.980 motor - any quick recommendations? I have read, and read, and read...

Bosch F 9 DCO listed in manual and it has Bosch F8DC4 in it now. I haven't been real pleased with how the car has run since I got it, so I was thinking of trying something else (current plugs need changed).

Some links indicate NGK BP5ES, some NGK BP4ES or BP6ES, and I've run across NGK BCP5ES...

Any suggestions?

ryan

Spark plugs generally don't have *too* much impact on the overall running of cars like they used to. Ignition systems are such high energy that as long as you are running the right heat range specified by the car manuf., thats the best you can do. Its kind of like asking "What brand of oil should I use". The answer is use what you want and change it often. Spark plugs are kind of the same way....

NGK's heat range scale is opposite of Bosch's IIRC, which is why the numbers appear different. That being said, stick with copper core plugs only on these engines. Platinum and Double Platinum plugs sometimes do cause issues on cars older than 1995, and thats what they always try to sell me first.

I accidentally put 70,000 miles on my last set of spark plugs because I thought I had changed them halfway. The were toasted, gap a mile wide, NGKs, and one of them was a completely different NGK model (I think the parts store screwed me) than the others. I replaced them with new Bosch copper cores and the engine ran....exactly the same. :D

I would check the condition of the rotor and cap as far as looking for issues in the ignition system. They are critical to smooth spark in all situations. These cars are higher RPM cruisers so they tend to burn through caps/rotors a little faster than other cars.

If you went to the dealership parts counter they would sell you F8DC4's. F9 DCO must be an superceded part number because none of my parts sites stock them.

Here in the uk the standard recomended plug is NGK BCP5ES. However I use NGK BCPREIX-11, which together with SHELL V-POWER fuel gives a better idle and a slight improvment on engine rpm pickup. (scientivicly tested by my right foot!) :D

Ryan, shortly after I bought our 1991 300CE in 2000 I asked an experienced tech at our local MB dealer what spark plug he recommended for that car. He said that from their Service Department's experience the 104 engines perform best with Bosch F8DC4 spark plugs. So I use them exclusively in our 1991 300CE, 1992 300CE and 1995 E320. All run superbly and I change spark plugs every 30,000 miles. Be sure to gap per the Owner's Manual specification.

Inpsect the condition of the distributor cap and rotor when you change spark plugs. Clean terminals, or replace as required ... likely every 60,000 miles. Recommend carefully inspecting the ignition wires since they can cause running issues also.

I am definitely replacing the wires - will probably buy a set from Kingsborne. I bought wires for my 560SL there - high quality and very pleased with them. Am also replacing the coil...

What's the difference between NGK BP5ES and BCP5ES?

ryan

From what I can figure out the NGK BCP5ES has a 5/8" hex, according to the NGK spec page - not sure what that means about the size of the BP5ES.

I mentioned in my previous post purchasing wires from Kingsborne - these would be around $130. I found these Bosch wires on Amazon for half of that -

http://www.amazon.com/Bosch-09146-Premium-Spark-Plug/dp/B000BYB3E2/ref=au_pf_ss_1?ie=UTF8&Model=300CE|779&n=15684181&s=automotive&Make=Mercedes-Benz|63&Year=1991|1991&carId=032

The specs mention a stainless steel Mag winding....and nothing about a copper core - which I read about numerous times in other threads.

What do you think?

ryan

If your 91 CE uses the 103, then you should not use the F8DC4's because the seating is different. You are building up carbon on exposed threads.

Bosch H9DC0 is the correct plug and can still be obtained at the dealership for a decent price. I paid $4.20/each last week for a set I needed.

Reference article for other recommended plugs:
http://www.w124-zone.com/articles.php?article_id=16

Both of those plugs seat exactly the same. Only difference is the F8's are slightly "colder" plug.


http://www.peachparts.com/shopforum/showthread.php?t=277252

The seating differs as shown here

http://w124-zone.com/wp-content/uplo...0/08/plug2.jpg

ps2cho, a 1991 300CE has the 104 engine with DOHC.

Post 1 in this thread - M104.980 motor...

Can someone offer an opinion on the spark plug wires linked in post #6 above?
Is there that big a difference?

ryan

Ryan, I would buy a Beru ignition wire set. That set will be significantly more expensive than a Bosch set, but it has the 90 degree spark plug connectors like the original ignition wire set resulting in a much neater installation.

Interesting. I'm really confused now! I just replaced my plugs a few months back and swore they were F8DC4. I found my invoice and I did indeed order F8DC4, I ordered based on MY and chassis # as I always do. I ordered extras and found them in my toolbox. Well they actually sent me H9DC0! Which is the "correct" plug based on the picture you provided. Weird.

JohnM., your 1991 300E with a 103 engine calls for a Bosch H9DCO spark plug. Whereas, a 1991 300CE with a 104 engine calls for a Bosch F8DC4 spark plug. At least per the database of the online parts supplier I frequently use.

I like my NGK V power plugs.Next time I will run E3s.