Mercedes-Benz Forum banner

1 - 17 of 17 Posts

·
Registered
1994 SL500
Joined
·
137 Posts
Discussion Starter #1
An FYI for anyone interested. About 10000 miles ago I had the engine out of my 94 SL500 and went completely through it. This overhaul included all new ignition parts, caps,rotors, wires and plugs. On the advice of someone who supposedly knew I put in the Bosch Platnum+2. (Two ground electrodes with an open end gap). The reasoning given was unshielded spark and all the other irrelevant BS. The first 6 or so thousand miles I was still working and never made short trips. After retirement trips to and from the local market etc became routine. I found that the first trip in the morning, if I did not go far enough to accomplish a full warm up, when I shut it off long enough to go into the store, on restart the engine would miss horribly and I would need to carefully nurse the throttle to even get it to move. After months of checking everything I could think of, even so far as to carry my dvom with me and check temp sender and ambient sender values cold, partial warm up, heat soak, full warm in parking lots and checking everything I could think of in the ignition system I changed the spark plugs to a "standard configuration" plug. As this was an experiment I did not even get platnums but the cheapest thing I could get. PROBLEM SOLVED The car idles and runs better, the fuel economy is noticeably better and most importantly no partial warm up engine miss. I have not fully digested the cause and effect but I would guess it is probable that the gap, approximately .080 on the end gaps which is non adjustable is more than double the factory recommended .035. Whatever the reason I just thought that I would share the experience if anyone else runs into similar problems.
 

·
Registered
1997 SL500, 1948 Rover 75 P3, 1984 Citroen 2CV, 1953 BSA Bantam D1, 1966 Velosolex Moped
Joined
·
1,141 Posts
An FYI for anyone interested. About 10000 miles ago I had the engine out of my 94 SL500 and went completely through it. This overhaul included all new ignition parts, caps,rotors, wires and plugs. On the advice of someone who supposedly knew I put in the Bosch Platnum+2. (Two ground electrodes with an open end gap). The reasoning given was unshielded spark and all the other irrelevant BS. The first 6 or so thousand miles I was still working and never made short trips. After retirement trips to and from the local market etc became routine. I found that the first trip in the morning, if I did not go far enough to accomplish a full warm up, when I shut it off long enough to go into the store, on restart the engine would miss horribly and I would need to carefully nurse the throttle to even get it to move. After months of checking everything I could think of, even so far as to carry my dvom with me and check temp sender and ambient sender values cold, partial warm up, heat soak, full warm in parking lots and checking everything I could think of in the ignition system I changed the spark plugs to a "standard configuration" plug. As this was an experiment I did not even get platnums but the cheapest thing I could get. PROBLEM SOLVED The car idles and runs better, the fuel economy is noticeably better and most importantly no partial warm up engine miss. I have not fully digested the cause and effect but I would guess it is probable that the gap, approximately .080 on the end gaps which is non adjustable is more than double the factory recommended .035. Whatever the reason I just thought that I would share the experience if anyone else runs into similar problems.
Hi grumpy, Just a thought - I understand (but I'm not sure) that the plug leads fitted to our cars have a resistance built in. Could it be that resistance + bigger gap equalled too much for the coils? I'm no auto electrician just thinking simplistically.
Glad you solved the problem anyway :thumbsup:
Steve
 

·
Registered
1994 SL500
Joined
·
137 Posts
Discussion Starter #3
My present line of reasoning is as follows: For whatever reasons mercedes seems to be extremely sensitive to battery voltage. In the morning, particularly if the car has set for a few days the battery voltage is low. Admittedly the alternator should be making up the difference but??? When the car runs for 10 to 15 minutes the engine has started to warm up but is not at operating temperature, in particular the intake manifold is still cold and the intake air is cold pulling from in front of the radiator. You shut it off and the heat in the engine rises to the top, the highest point in the cooling system is the thermostat and that is where the temp sensors are. The temp sensors do change from shut off, going into the store, and heat soak, coming back. My assumption is that the change in the temp sensor readings between shut off and restart is sending false information to the engine management leaning out the fuel mixture. The combination of the leaner fuel mixture, exacerbated by the cold intake air, being harder to ignite and the much wider spark plug gap is in fact placing more demand on the ignition system than it is capable of handling. The secondary resistance in the ign system is built into the connector on the spark plug end of the plug wire. The spark plug wires themselves are wire core and non resistant. Just as an aside I have checked all my spark plug wires from the rotor contact inside the distributor cap to the spark plug connector individually with a dvom and they are all within spec.
 

·
Registered
2005 SLK350, 91 300SL with Pano Top, 04 S500, 2015 Tesla Model S
Joined
·
2,084 Posts
I had same experience last year. Installed recommended Bosch plugs at proper gap and car ran horribly. Then just put in the cheapest Champions and she ran like a champion ever since. Go figure.
 

·
Registered
1994 SL500
Joined
·
137 Posts
Discussion Starter #5
When I went to get new plugs they did not have the original equipment style bosch in stock so I am running on NGK's. As you said running like a champ.
 

·
Registered
'93 SL500 (sold), '88 GMC Sierra 360,000 miles, '86 Yamaha FJ1200 (criminally fast)
Joined
·
770 Posts
When I went to get new plugs they did not have the original equipment style bosch in stock so I am running on NGK's. As you said running like a champ.
Someone told me NGK's are nice plugs, but are designed for smaller engines/ ignition systems. They may fail early.

Someone may correct me, but that's what I heard.

2 types of sparkplugs.......

(1).... mass-produced ( China- bad quality control during production) purchased at places like Pep Boys, etc.

(2)..... Same plug..... Bought at a local indy parts place.... made in smaller batches.

I replaced plugs that were new and they had cracked porcelain. I found this out from a famous engine / car builder.
 

·
Registered
1994 SL500
Joined
·
137 Posts
Discussion Starter #7
NGK's are the ONLY spark plug that would work in my Q45. Bosch, Champion, Nipondenso 12000 miles and the engine would develop a miss. NGK's 70000 miles. The problem was that the recommended NGK for that car listed out for $29.50 EACH at the time. Best deal I ever got on a set was from a friend of a friend at a Bap Geon parts store that sold me a set for $12.00 each. That is still a $107.00 plug change with tax and I screwed them in myself.
 

·
Registered
'93 SL500 (sold), '88 GMC Sierra 360,000 miles, '86 Yamaha FJ1200 (criminally fast)
Joined
·
770 Posts
NGK's are the ONLY spark plug that would work in my Q45. Bosch, Champion, Nipondenso 12000 miles and the engine would develop a miss. NGK's 70000 miles. The problem was that the recommended NGK for that car listed out for $29.50 EACH at the time. Best deal I ever got on a set was from a friend of a friend at a Bap Geon parts store that sold me a set for $12.00 each. That is still a $107.00 plug change with tax and I screwed them in myself.
The price...... OUCH!! Are they certified for aircraft??

( But your Q45....... nice car!!)
 

·
Registered
1994 SL500
Joined
·
137 Posts
Discussion Starter #9
Interesting, that was my initial reaction. 30 bucks a pop and the wheels never leave the ground. All in all it was the best automobile I ever owned. Got rid of it with 200,000 on the clock and in that time outside of normal maintenance I had put in three sets of plugs (not including the cheaper ones I tried) three sets of brake pads two sets of tires one o2 sensor one set of cam cover gaskets a radiator an alternator and a set of drive belts. At 200,000 the only change I detected in the car was that it had long since lost the new car smell. The only reason I got rid of it was it was my wife's car and at that mileage I always worried that it was going to toss something at an inopportune time.
 

·
Registered
2005 ml350 2001 e55 amg
Joined
·
144 Posts
I once had a honda s2000. I remember the factory NGK's for it being well over $20 a piece. Fortunately, I only had to by four though. When you have a 9000 rpm redline though you want to make sure that you get what the manufacturer calls for.
 

·
Registered
2007 CLS 550, 1998 Harley Road King, 2011 F-150 EcoBoost, '65 Shelby Cobra
Joined
·
978 Posts
I had trouble getting a smog cert. a month ago. It went through, but just barely. My indy says one reason is the Platinum plugs I am running. He says go back to the stock Bosche and forget about it! That is also the opinion of many on this forum. I know Albert (aam) is a big believer in that.

I am going to take their advice in the near future.
 

·
Greek God of the R129
SL500-500SEL-190E
Joined
·
8,391 Posts
Lol,
One more time, our ignition wires have resistors in them, that's why they are expensive.
Do not put plugs with resistors in, they will not last long.

If you have ign. wires do not use platinum plugs, as simple as that.

Regards,
aam.
 

·
Registered
1994 SL500
Joined
·
137 Posts
Discussion Starter #13
A post script on the plug issue. I bought this SL barely running. Drove it home, still don't know how it made it as it had the original engine wire loom with the insulaion powdered and bare wires everywhere. proceded to overhaul almost everything that would unbolt. Never having driven one of these things I had no idea how it should run. Drove it down to San Diego yesterday, first time it has gone out of town, and was amazed at how it ran. With the plug change it is like a completely different car. I may have to recant on every bad thing I have ever said about it, with the exception of Mercedes INSANE love of allen and torx head cap screws. With out a doubt two of the worst cap screw head designs known to mankind. I was thinking about my old racing days (early and mid 60's) and a guy who's name I can not recall, when you get old your brain leaks. He ran a streamlined Corvette at Bonneville. He always believed that as long as you had the correct heat range a plug was a plug. To prove his point he made a record run with 8 different plugs in a small block chevy. I just don't understand these modern engines sensitivity to spark plugs.
 

·
Greek God of the R129
SL500-500SEL-190E
Joined
·
8,391 Posts
You are correct, you said in the 60's points condenser etc.
Those were the days that you could repair everything with a pair of pliers and a screwdriver. Haha.

Do you also remember the radio static noise from the generator and plugs?
Sometimes an other car on the traffic light, you would pick up also their static.
Was gas about 29 cents a gallon? Lol.

Then the electronics started to come.....
Those old good days are gone my friend. :(

Wtf, is that spark plug looking thing?
A tampon?
An oxygen sensor?
Oups, I forgot there was no tampon or 02 sensor thing then. ;) Hahaha.

Regards,
aam.
 

·
Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
Joined
·
10,196 Posts
I have no problem with the Bosch Platinum +4's. My stock 560SL ran a 15.073 1/4 mile with them and beats the window sticker gas mileage. My 1996 SL600 engine came delivered to me with them and that also ran fine.
 

·
Registered
'93 SL500 (sold), '88 GMC Sierra 360,000 miles, '86 Yamaha FJ1200 (criminally fast)
Joined
·
770 Posts
Many of my racing / engine building friends say pretty much the same thing. OEM, when it comes to stock ignitions. I was going to put headers on my GMC truck, but the cost compared to the difference was a waste of time / money....

I used to street / strip drag race my '70 GTO, back in the late '70's, and won 98% of the time because my set-up was stock but also was proper running condition, verses the other guys screwed around with their cars and couldn't get it right.

Stock plugs...... After market tricks can be just 'tricks'.
 

·
Registered
"NEW OWNER" of a 1991 SL 500 weekend toy. Hope I don't go broke maintaining it!
Joined
·
600 Posts
My present line of reasoning is as follows: For whatever reasons mercedes seems to be extremely sensitive to battery voltage. In the morning, particularly if the car has set for a few days the battery voltage is low. A.
i can verify this is true. Go to Autozone and ask them to check your battery (for free) Mine was 79 percent and all m gremlins disappeared with new battery
 
1 - 17 of 17 Posts
Top