marineboy0

This one has me beat - so much for preventative maintenance!

About 2 months ago I switched all the original spark plugs from the originals after 60k M on a 1999 ML320 to new NGK Iridium plugs. I have owned the SUV since new and know all of its history - since I have done all but the warrantee work on it.

2-3 weeks later the vehicle has started to show a curious problem. When cold the vehicle starts fine. The vehicle runs fine - no performance or missing etc. Idling is fine. When the car is fully warmed up the car restarts okay but just occasionally and particularly when the engine has been left 2-3 hours but is still warm the car will not start. Wait 2 frustrating hours more and the car starts.There is no engine service light. The car on one occasion stalled after being driven 0.5miles at a junction and would not restart for about 25minutes. All other times the problem has been not starting when partially warm.

The issue is not related to flooding - it happens without touching the gas peddle. When it happens I have proven that there is no spark to the HT leads. The battery is good and the car turns over fine. (problem also occurs with a replacement battery). Just to eliminate the spark plugs - I bought another brand or platinum and spent 2 hours just now fitting all twelve of them. But the same problem occured. The car would not start initially - no charge but after 30minutes and trying again - it fires up straight away?

Any ideas?
- is it likely that I distrubed something / some connector
- is the ECU on the way out?
- is it something coincidental like the immolisation on the key?

HELP I"M GOING

MB Fanatic

There is a distributor in your engine that seems like is slowly going bad. The distributor rotor sends the electrical signal to the spark plug to spark, if this doesnt work correctly than your spark plugs wont either. This is going to be a costly repair from the sounds of things.

E55AMG99

Some possibilites involving spark plugs that I've encountered on other engines in my time.

1. The spark plug leads might be damaged at the end where they connect to the plug and can cause intermitent spark. Take them off and test them with an OHM meter.

2. Spark plug gap might be too wide. Most NGK are .041 from the factory and most late MB engines use much smaller gap. Damage to the coil(s) can result from the plug failing to fire. Caution here- some contend that the Iridium plug needs a wider gap compared to Platnium. I have not seen this personally. Check with both MB and NGK.

3. Not spark plug related but has some similar symptoms to a crank position sensor problem.

Good luck.

sosh

There is no distributor as such. Its all electronic. There is no Rotor, points, etc as found in older cars so it is not that

twowheelin

You mentioned that you were not getting a spark so the problem is not the plugs. I would suspect a wire or connector problem on or near the coil packs. I have only glanced briefly at the ignition on my 02 SLK, but it looks like there are multiple coil packs for each cylinder bank. If you're missing spark you may want to check the inputs to the coil packs and confirm that they are getting pulses from the ECU. Please keep us posted on the result...

TresX

I'll bet the farm that you have a faulty Crankshaft position sensor. Do you have any lights that light up on your dash? If it were the spark plugs causing a misfire you would get a CEL. The time that you said the car stalled, were you coasting at a low speed? Anyhow, I guarantee it. The part is $35 online and can be installed in 15 minutes. Good Luck!

x15jq

yeah def crank possition sensor, i had the same sympotoms, probably just a coincidence to your spark plug work. I wouldnt worry about it the part is cheap!

mleskovar

I had one go out as well...intermittent, wouldn't start, wait, keep trying and eventually it starts. Fixed under extended (thankfully) warranty. If you search you'll find this is a common failure part. Is this the same part as a "cranshaft position interlock sensor" for about $65 on the internet? Where is it? How do you check it? Any adjustment required or just replacement? Does cleaning something bring them back to life? I learned the hard way never to put in different/not recommended spark plugs. If you think you'll get more performance from a different plug you're gambling that there's a chance the engine designers after all that work screwed up on the plug. Get real.

E55AMG99

You should make this a public service announcement!

MB-Dude

Agree with most of the above... probably not the spark plugs, per se. However, a spark plug is a spark plug in the combustion chamber. Its only purpose is to provide a gap by which a spark is "jumped" across a gap. The rest is rather obvious. The proper combination of fuel-to-air-to-spark is incredibly crucial in gasoline engines, and today's engine management schemes make the room for error surprisingly small.

What is important relative to spark plugs is (A the depth the plug extends into the chamber and, B) the gap. Both are critical to proper operation. Personally, I use Bosch Platinum +4 spark plugs and have had zero problems. If you are concerned about the spark plugs, you should verify two items:
1. The proper NGK plugs have been installed for your engine
2. The spark gap is set correctly
Both are ridiculously simple to check; the gap, in particular is crucial!

Regardless, never underestimate the importance of preventive maintenance! Marineboy0 - You did the right thing by changing the plugs, but your root problem may not be related to the spark plugs. Today’s engine management is extensively inter-related with computers and sensors.

TresX

MB-Dude...you are spreading false information........

YOU SHOULD NOT USE RESISTOR PLUGS ON MERCEDES!!! The ignition system is very carefully designed for use with non-resistor plugs. Resistor plugs add secondary resistance is excess of design specs and alter the secondary voltage wave form.

Sooner of later you will have problems such as rough idle or high emissions.

The proper plug is Bosch H9DC (NOT the HR9DC resistor type), and these are not commonly available at McParts, but are readily available for two bucks each from Mercedes parts specialists like Fastlane.

Any spark plug with an "R" in the designation is a resistor type and should NOT be used.

The issue is not "platinum" versus conventional copper core plugs. It's resistor versus non-resistor and Bosch Platinums HAVE RESISTORS.

Take a look at the service CDs. They have several examples of both normal and anamolous of secondary wave form traces and show at least one with excess secondary resistance. It may not result in any noticeable difference when the plugs are new, but as they age - wear and build up deposits, the number of misfires will increase resulting in more idle roughness and higher emissions than if the proper non-resistor plugs are used.

Bosch H9DCs (for M103 engines) cost about two bucks each and have a normal service life of 30K miles. The H9DC0 has a "heavy duty" electrode. They were OE, but they are more expensive, and the standard electrode H9DC work just as well over the 30K service interval.

Spending more money to by the WRONG plug is just plain foolish!

E55AMG99

A spark plug is a spark plug ??? Bull*****! If so, why did you pop the extra bux for the fancy pants Bosch Platinum +4? Not taking your own Internet advice?

mleskovar

What about heat range? Another variable that is very dangerous to change unless you know what you're doing (or even have a need to). Gap isn't as critical as you think as long as it's within the allowable range...otherwise you'd be constantly pulling and regaping them as they wear. Platinum are desireable because they have a broader heat range. Resistor vs. non resistor is VERY important as noted by TresX. Bottom line, they say "recommended" for a reason.

MB-Dude

All valid points by TresX, E55AMG99, and mleskovar, and I respect their views. However, I had occasion to try different plugs and other items in (thus far) a vain attempt to solve a computer emission problem. You can read about that problem in this same forum, under a thread about Resetting ECU’s.

During some initial work on that problem and long distance driving (San Jose to San Diego), I had an opportunity to run used MB plugs, new MB plugs (both same part number MB 003-159-81-03) and the Bosch Platinum +4. Whether you accept it or not is your affair, but the data indicated better overall performance (including gas mileage) with the Bosch plugs. Emissions were on par, perhaps slightly better with the Bosch, but they were so close, I count them as equal. I’m not saying the Bosch plugs are a “wonder plug” – quite the contrary. It is simply an alternative that provides measurable improvement.

As for comments like “a spark plug is a spark in the chamber”, I apologize if the comment was taken out of context. The point I was trying to make was that a spark plug provides the mechanism by which a spark is introduced to the chamber. It is part of a complex arrangement, but by no means is the most important. The air-fuel ratio and precise timing of the spark are more critical to complete ignition. The spark plug is important, but not as much as the other items. An engine will run – albeit poorly – with an incorrect spark plug. But it will rarely fire consistently if timing and air-fuel ratio are out of fairly narrow bounds.

Regarding the resistor vs. non-resistor, I admit that’s an interesting point of view, and one that I will research further. TresX suggests rough idle and/or high emissions as a result of the resistor-style plug. As noted above, the current engine situation is quite satisfactory. The engine at idle, either cold or “at temp”, is rather smooth (engine has 96K miles on it). I will try putting the new set of MB plugs in to see if there is a change in idle performance. Using a laptop that I have, I can connect to the engine management and monitor the data objectively. With this I can get engine idle results. Emissions, at least thus far, have been very good; very clean engine. Regardless, I am interested in researching the resistor vs. non-resistor theory a bit more.

The question of heat range brought forward by mleskovar is also important. But that is where the depth or height of the ceramic insulator comes into play. The shape of the ceramic insulator within the combustion chamber is important and all spark plugs must have a shape as designated by the engine designer. Plug runs too cold and it will foul prematurely; run too hot and the electrodes will not stand up in the long-haul. Yes, heat range is important and ANY change in plug type/manufacturer should be a careful comparison of the physical characteristics of the replacement plug.

Why do I spend a few extra bucks for “fancy pants” Bosch plugs? Simply to experiment and try something new. By changing things in a controlled manner, we can learn from new experiences. Currently, I am running Bosch plugs in my SL600; standard MB plugs in my wife’s SL500. I’m not completely convinced Bosch is hands-down better… that’s why I started the related thread on an open discussion on spark plugs. Perhaps I should read what lurks in there before sending this thread response. Hope the above calms everyone down.

E55AMG99

Hey Dude,
Sorry to jump on your back. Your coments were s little too general for some of us.

MB-Dude

No offense taken E55AMG99. The beauty of forums like this is everyobne has an opinion, and everyone has a different point of view. Through exchange of ideas and thought, we all gain -- even if some of us (like me) are not as clear up front. Sorry to all if my original thoughts sent shivers and pains in your private parts. It certainly wasn't my intent!

Back to marineboy0, who asked the original question... any update? Whatever you do or how ever your MB gets fixed, don't ever give up on good ol' preventive maintenance.

marineboy0

I got the Crank position sensor and a torx socket , installed the new sensor. Problem apparently gone. The vehicle is transformed from being a liability to running as normal. Million thanks to all who shared their experience.

Just an extra comment on the sparkplug discussion - although this may not apply to MB engineering, many other cars have been shown on dynometers to benefit from replacement HT leads and iridium plugs, which are claimed to reduce ignition limitations at higher rpm. Not that an ML320 SUV is often reved above 4000rpm.

On the ML320 '99 63k, which we have had from new, up until the CPS went south, the iginition has run perfectly. But on the other hand, the air flow meter, bearing on the support shaft, door locks, fuel pump, sun roof, seat heaters,....etc all did not

Anyway - I still like the car much more than most others I have had and it keeps things interesting.

Anyway - once again - Thanks for the advice

MB-Dude

Glad to read about the happy ending relative to your ML. Hope the experience has reinstated your belief in preventive maintenance!

TresX

I'm glad things worked out for you. I told you the CPS was the culprit!

mleskovar

Where is the CPS and what is involved in changing it? Does anyone know how they "go bad" or what's the proper diagnostic check at the part level? A picture would be great.