Spark plugs & wires - 2001 ml320

[kwiklee]

In my case idling and acceleration was rough plus the CEL light came on and off when it did the CEL code given (i cant remember the exact code) translated to misfiring on cylinder 6 5 and 4. Being as I am the second owner i am not sure if the previous owner changed the plugs and wires so i might as well take the opportunity to change all. Its the tranny fluid change i dread as my truck has 75k on the clock

[43sqd]

Originally Posted by kwiklee

In my case idling and acceleration was rough plus the CEL light came on and off when it did the CEL was on the code given (i cant remember the exact code) translated to misfiring on cylinder 6 5 and 4. Being as I am the second owner i am not sure if the previous owner changed the plugs and wires so i might as well take the opportunity to change all. Its the tranny fluid change i dread as my truck has 75k on the clock

In your first post you said that you had codes P0170 & 0173 and that you installed a delar purchased MAF sensor. After that did you clear the codes and see if the same codes reappeared?

The other questions I have to ask is how did you obtain the original codes in the first place? Did the present misfire codes show up when you originally had the codes read, or are they something new? The biggest mistake you made was not writing down the original codes. It's very odd that cyls. 4,5 & 6 are all misfiring, since they are all on one side, the driver's side. It's hard to believe that all the wires or all the plugs or a combination of both, all decided to fail at the same time.

[kwiklee]

Originally Posted by 43sqd

In your first post you said that you had codes P0170 & 0173 and that you installed a delar purchased MAF sensor. After that did you clear the codes and see if the same codes reappeared?

The other questions I have to ask is how did you obtain the original codes in the first place? Did the present misfire codes show up when you originally had the codes read, or are they something new? The biggest mistake you made was not writing down the original codes. It's very odd that cyls. 4,5 & 6 are all misfiring, since they are all on one side, the driver's side. It's hard to believe that all the wires or all the plugs or a combination of both, all decided to fail at the same time.

True i regret not noting down the codes but that was because the CEL went off but heres the sequence of events.
When the CEL first came on codes PO170 & PO173 came up cleaned MAF but it made no difference so i ordered a new MAF unit from OEMS parts direct and installed it. After a few start cycles the CEL went off buy its self. The truck ran ok for a while but i noticed rough idling when cold and hesitation when accelerating but no CEL came on. It gradually got worse like on long highway runs it would misfire at speeds and then the symptoms will disappear. It got to the point when it would stall in traffic not start for a few minutes then start up with the CEL showing it is at this point i run a scan and get various codes relating to misfire on 4 5 and 6 cylinders plus the PO170 & PO173 but the next day the CEL goes off and the truck runs okayish. I have orderd Bosch plugs and karlyn sparkwire set from autohaus and i will change them when i get back to Nigeria where my truck is.

[kelland]

Originally Posted by kwiklee

True i regret not noting down the codes but that was because the CEL went off but heres the sequence of events.
When the CEL first came on codes PO170 & PO173 came up cleaned MAF but it made no difference so i ordered a new MAF unit from OEMS parts direct and installed it. After a few start cycles the CEL went off buy its self. The truck ran ok for a while but i noticed rough idling when cold and hesitation when accelerating but no CEL came on. It gradually got worse like on long highway runs it would misfire at speeds and then the symptoms will disappear. It got to the point when it would stall in traffic not start for a few minutes then start up with the CEL showing it is at this point i run a scan and get various codes relating to misfire on 4 5 and 6 cylinders plus the PO170 & PO173 but the next day the CEL goes off and the truck runs okayish. I have orderd Bosch plugs and karlyn sparkwire set from autohaus and i will change them when i get back to Nigeria where my truck is.

I had a similar problem when i got my ml430, when i sent it to be lpg converted the fitter said it was mis-firing, he noticed this only on tickover by his well tuned ear, the car had the maf already replaced and wasnt noticeable on acceleration but if you listened carefully you could hear a base/pop noise, we changed all 16 plugs the bosch ones were the only ones with the correct gap this never solved the problem so it went to a mercedes dealer with the full computer system.....not the little laptop programme used by many, the full system does a live run and shows how far out each plug fires out of time, the amount of time was a cats whisker but was noticeable to a professional ear!
the cause was the leads and several were replaced, if i remember the come in 2 parts a short and long one and I was warned if i chose to ignore the problem the coil packs will suffer and the cost will then go up. once the leads were replaced the firing on the live printout was spot on!
When this was diagnosed i did get a price for a full set from a car outlet for £100 but the garage warned me that pattern parts are not of the quality of diameter and/or insulation, also with the manufacturers ones you can buy the leads individually!

[2002ml320]

So I was accelerating onto the highway and I lost a cylinder. I went to the dealer and they diagnosed a misfire. They wanted $1,350 to change the plugs and wires! I was blown away. I found a local place that would do it for $800 but I still thought it was too high.

So I ordered the parts online. I was told that the wires should be Bremi or Beru to ensure factory quality. I found those for $200. Then I was told the factory plug is a Bosch part# FR8DPP33. I also ordered these online for $4.71 each. I wanted to use the Bosch 2's but I was told not to. I am not sure how accurate that is but why take a chance. Could not find or order the plugs from Autozone or Advance Auto they both said they could not get them. So in total it cost me about $260 in parts incl S&H. WHAT A DIFFERENCE.

Here are some pointers as I just finished the project. Took me 2.5 hours.

+ First two steps: Make sure engine is COLD!
- Take off engine cover. Just pops off by lifting up from front
- Remove top of air filter box 6 clips on box and 2 clips on hose

+ ML320 is a 6 cylinder but it has TWO PLUGS PER CYLINDER so you need 12 plugs and the ignition wire set comes with 12 wires.

+ Start the with passenger side much easier. Learning curve is fast and once you do 2 plugs and wires it will go faster. You DONT want to learn on the driver's side.

+ Wear gloves or your hands will get cut up. Especially on the drivers side from the heat shield

+ You DO NOT have to take off the coil packs on the passenger side as long as you have an extension long enough to get into the cylinder and clear the coil packs.

+ I found it easier to pull the wires off the coil packs with the coil packs STILL ATTACHED to the engine block. You can get more leverage... use pliers. I actually found this to be the hardest part.

+ Tools needed: Pliers, Spark Plug tool 5/8" w/extension(s) 2.5" & 5", and Torx #T30, some WD-40 or plug grease will help the wires pop on easier. A flashlight will also help but not necc.

+ I found that having different size extensions small 2.5" and medium 5" was very helpful b/c the spaces to get the plugs are different on each cylinder due to hoses and other engine parts.

+ On the drivers side remove coil packs after popping off old wires and then connect all new wires.

+ You really dont need to do one at a time as I have read on other posts. You will notice that each coil pack is labeled A & B for each wire.... AS IS the cylinder. So really as long as you can read A & B you will know where each wire needs to go. I needed a flashlight to actually read the lettering. Without it I could not see A & B.

+ Out of the 12 wires 4 are longer. These are for the two cylinders closest to the windshield. 2 on driver side and 2 on passenger side. The other 8 wires are all the same length.

Good Luck... DIY and save $$$$$ for your toys!!

[kwiklee]

Originally Posted by kelland

I had a similar problem when i got my ml430, when i sent it to be lpg converted the fitter said it was mis-firing, he noticed this only on tickover by his well tuned ear, the car had the maf already replaced and wasnt noticeable on acceleration but if you listened carefully you could hear a base/pop noise, we changed all 16 plugs the bosch ones were the only ones with the correct gap this never solved the problem so it went to a mercedes dealer with the full computer system.....not the little laptop programme used by many, the full system does a live run and shows how far out each plug fires out of time, the amount of time was a cats whisker but was noticeable to a professional ear!
the cause was the leads and several were replaced, if i remember the come in 2 parts a short and long one and I was warned if i chose to ignore the problem the coil packs will suffer and the cost will then go up. once the leads were replaced the firing on the live printout was spot on!
When this was diagnosed i did get a price for a full set from a car outlet for £100 but the garage warned me that pattern parts are not of the quality of diameter and/or insulation, also with the manufacturers ones you can buy the leads individually!

I got quoted £381 for the set of plugs and ignition wires from a main dealer but forum members have recommended autohaus. The price came to $307 about £150 including UPS delivery to the UK for the 12 bosch plugs and 12Karlyn spark plug leads. Autohaus take paypal payments which is handy.

[ml28]

Thanks again Benzworld - you saved my behind again! I was having rough idle problems (truck felt find at part to full throttle) and read that it could be anything from spark plugs to EGR valves to clogged catalytic converters to coil packs. I started with spark plugs (which didn't look really bad @ 75K miles), the MAF sensor was not dirty as others had observed, then I added some fuel system cleaner - still no improvement. I did more research and came accross this post. I ordered the spark plug wires from Autohaus AZ - 16 wires for $183. The hardest part was pulling the wires off the coil packs - they were on really tight. After I put the wires in and verified routing, I started up the truck and was pleasantly surprised - rough idle gone. I can't thank you all enough - I need to get a smog check this month to renew my registration. It would surely have failed the way it was running. I was considering taking the truck to the stealership if the wires didn't fix the problem.

[kwiklee]

Originally Posted by ml28

Thanks again Benzworld - you saved my behind again! I was having rough idle problems (truck felt find at part to full throttle) and read that it could be anything from spark plugs to EGR valves to clogged catalytic converters to coil packs. I started with spark plugs (which didn't look really bad @ 75K miles), the MAF sensor was not dirty as others had observed, then I added some fuel system cleaner - still no improvement. I did more research and came accross this post. I ordered the spark plug wires from Autohaus AZ - 16 wires for $183. The hardest part was pulling the wires off the coil packs - they were on really tight. After I put the wires in and verified routing, I started up the truck and was pleasantly surprised - rough idle gone. I can't thank you all enough - I need to get a smog check this month to renew my registration. It would surely have failed the way it was running. I was considering taking the truck to the stealership if the wires didn't fix the problem.

i bought these pliers from Ebay in preparation for changing my plugs and wires
to tackle those stubborn boot plug wires, i have a 17mm open wrench what other tools would i need to make it easier?

Update:

just got my bosch plugs and wires from autohaus

[43sqd]

Originally Posted by kwiklee

i bought these pliers from Ebay in preparation for changing my plugs and wires
to tackle those stubborn boot plug wires, i have a 17mm open wrench what other tools would i need to make it easier?

Update:

just got my bosch plugs and wires from autohaus

Get yourself a tube of dielectric grease, and with a Q-tip coat the inside of each end of every wire. Only use a small amount just to make it look wet. This will prevent the rubber from sticking to the porcelain on the plug and will aid removal in the future.

[killsoft]

Originally Posted by azinn

This place ships worldwide and has what your looking for -
Autohaus AZ Shipping Options and Charges

That's where I got mine. Great company.