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Basic Maintenance: How to Replace Your Spark Plugs, Wires, Cap and Rotors on your Mercedes Benz
 
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Pelican Technical Article:

Basic Maintenance: How to Replace Your Spark Plugs, Wires, Cap and Rotors on your Mercedes Benz

Steve Vernon

Time:

2 hours2 hrs

Tab:

$190

Talent:

**

Tools:

Torx Socket set, Allen keys, Flat Head Screwdriver, Spark Plug Socket, Extension and driver

Applicable Models:

Mercedes-Benz 190E (1984-93)
Mercedes-Benz 300E (1986-92)

Parts Required:

Wires, Plugs Rotor and Distributor cap

Hot Tip:

Work on a cold engine

Performance Gain:

Cleaner running engine

Complementary Modification:

Repaint your valve cover

One basic tune-up procedure for just about any car on the road is the replacement of your spark plugs and spark plug wires. I recommend examining and/or replacing your spark plugs every 30,000 miles, or about once every other year. In reality, you can probably go longer than that, (most manufacturers recommend an interval of 100,000 miles) but, you never really quite know how long the plugs are going to last. A lot of factors can contribute to the plugs wearing out faster than you might expect especially as the car ages. Another part you should check is the distributor cap and rotor. In this article, we will show you how to replace your rotor, distributor cap, seal, wires and plugs.

Begin by prepping the car. The only thing that you really need to do is to make sure that the car is cold. If you try to remove or install spark plugs in a hot car, then you may encounter problems with the spark plugs gumming up or damaging the relatively delicate threads in the aluminum cylinder head. Make sure that the car is cold, or at the bare minimum, only slightly warm to the touch.

If you are only changing the plugs and rotor, it is a good idea to label the wires so you will know which goes on which. Begin by removing the plastic cover that holds the wires along with a vacuum line along the top of the valve cover. It simply pops out using a screwdriver. If your car is older, there is a good chance the plastic is brittle and may crack. The cover on our project car had been taped together in several places.

Once the wires are free from the cover remove them from the plugs. Grab the wires by the boot and turn them slightly and pull straight out. Do not attempt to pull them out by the wires as there is a pretty good chance you will just rip the wire from the boot.

Remove the wire from the coil and feed it back through the intake manifold so it can be removed with the distributor cap.

Remove the three Allen bolts holding the distributor cap and cover to the head. You can now remove the cap, cover and wires as one piece.

Remove the three Torx screws holding the rotor to the cam shaft and replace with a new rotor. There is a guide key that the rotor fits into that lines it up, do not try and force the rotor on any other way than sliding it into the guide key. The rotor comes with new Torx screws. Replace the dust seal on the dust cap while you are there.

At this point you may want to think about refurbishing your valve cover. Pelican Parts has an article on how to do this.

Push the new cover over the new distributor before you install it on to the engine. The new distributor does not come with new Allen bolts so make sure you remove the bolts from the old one before you throw it out. Place the new distributor and cover on the head and tighten.

Remove the old plugs and check for any signs of an unhealthy engine. Burnt, wet or oily plugs are all signs of engine trouble and should not be ignored. Typically, you want to see a slightly tan, burnt appearance. This will indicate that your engine is running normally. A really good idea when working around your plugs is to tape your socket and extension together. There is a small rubber grommet inside the spark plug socket that helps hold the plug in place while in a vertical position, this grommet also has a tendency to separate the socket from the extension when you don't want it to and will leave you fishing out your socket with needle nose pliers. Slide the extension all the way down until you feel the socket firmly grip the spark plug. The spark plugs should be tight in the cylinder head, but not overly difficult to remove with a little force. Install your new plugs and torque according to your engine specs.

I don't recommend using anti-seize compound on your plugs as the theory is that the anti-seize tends to act as an electrical insulator between the plug and the cylinder head. This could have detrimental effect on the firing of the spark due to the loss of a good, consistent ground connection.

With the new plugs installed you will need to run the plug wires, along with the vacuum line back into the plastic cover in the valve cover. I found this to be the most frustrating part of the whole job, as they have a tendency to slip out of place and be a general pain. Just take your time and get it right. Once the wires and cover are snapped in place, attach the boot to the plug by firmly pushing the boot down.

Place the outer dust cover over the distributor and you are all set.

If you are going to be reusing your wires make sure you number them to help when reinstalling.
Figure 1

If you are going to be reusing your wires make sure you number them to help when reinstalling.

Remove the plastic cover that the spark plug wires and a vacuum line sit in.
Figure 2

Remove the plastic cover that the spark plug wires and a vacuum line sit in. You can just gently pry it out with a screw driver (yellow arrows). The plastic gets brittle over the years and don't be surprised to find a previous owner taped it together (red arrows).

Figure 3

Pull the wires off by grabbing them by the boot, slightly twisting and pulling straight out

Figure 4

Remove the wire from the coil (yellow arrows) and thread it back through the intake system to free it up

Remove the three Allen bolts (red arrows) holding the distributor and cover on the head.
Figure 5

Remove the three Allen bolts (red arrows) holding the distributor and cover on the head. Remove from the engine while keeping the bolts for the new distributor.

This image shows how to change the rotor and seal.
Figure 6

This image shows how to change the rotor and seal. Remove the old rotor by undoing the three Torx screws (green arrows) and install the new one in its key way. Remove the old dust seal (red arrow) and install the new one.

Install the new interior cover over the distributor while it is on your bench, and then install it on the head.
Figure 7

Install the new interior cover over the distributor while it is on your bench, and then install it on the head. Transfer the old hardware (three Allen bolts) to the new parts and tighten.

With your socket and extension taped together install the new plugs.
Figure 8

With your socket and extension taped together install the new plugs.

Run the new wires to the appropriate plugs and secure them in the plastic cover in the valve cover.
Figure 9

Run the new wires to the appropriate plugs and secure them in the plastic cover in the valve cover. Install the outer distributor cover and you are done. Note: we refurbished our valve cover, if this interests you there is an article on how to do it.

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Comments and Suggestions:
Tim Comments: Hello, I have a 1986 MB 190E 2.3 and would like to replace the distributor rotor. But I did not see any screws on the rotor. However, I tried to remove the rotor but it is very tight. Is there any special tools to remove the distributor rotor? Thank you so much for your help.
-Tim
October 10, 2015
  Followup from the Pelican Staff: If there is no fastener, it pulls off. It maybe stuck from age.- Nick at Pelican Parts  
Gary Comments: Re the question about access to the bottom bolt on the Distributor: The fan has in irregular gap between the blades, turn the fan so this larger gap lines up with the lower bolt.
September 23, 2015
  Followup from the Pelican Staff: Thanks for the input on this one. We appreciate the help.
- Nick at Pelican Parts
 
scottsbenz Comments: Hey Gang, I want to change the trans fluid in my 1998 W208 CLK320 and am told the oil type is critical. Please may I know correct ATF? Many thanks, Bruce.
July 23, 2015
  Followup from the Pelican Staff: MB Automatic Transmission Fluid (Part Number 001 989 21 03 10)

To be sure, Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
 
Pieter Comments: Ps. I forgot to tell you this is a 1998cc engine.
June 22, 2015
  Followup from the Pelican Staff: OK, got it. - Nick at Pelican Parts  
Pieter Comments: My 190E Build for Japanese market has a different distributor more towards the left of the engine, held by 1 one stardrive bolt. First question is this metric or imperial sized? I attempted to use a stardrive T40, but it is too loose and the next size T45 is much too big.
Second question: if it is meant to be a T40 Stardrive how do we actually remove this bolt. We are sure this T40 will slip thus causing damage to the inside part of the bolt.
June 22, 2015
  Followup from the Pelican Staff: being it is not a US vehicle, I don't think i have seen this. Can you share a photo? I may be able to help if I see it. - Nick at Pelican Parts  
scottsbenz Comments: Nick I would value your suggestions on why the car stumbles during acceleration. All vital signs like compression etc etc are excellent on the 2.3 motor, it will start, idle and cruise, but on acceleration seems to starve for fuel, dies on hills, and I dare not overtake other cars. Things like the fuel pressure regulator and the EHA unit have been suggested, since catalytic converter has been cleared, new fuel pump filter fitted, and fuel pressure from the pump checked and found OK. Any ideas please?
November 25, 2014
  Followup from the Pelican Staff: All can't be that well if it runs that way. if the exhaust is clear and backpressure has been confirmed to be normal, you have to look at how the engine is breathing. If there is good spark and fuel pressure and volume, there may be a restriction in air delivery. Inspect the air intake pipe and load sensor operation.- Nick at Pelican Parts  
scottsbenz Comments: Nick I also quizzed my long-time and excellent MB spares man in Adelaide, who advised their listings for the plugs are Bosch H8DC and they are gapped at .8mm.
November 24, 2014
  Followup from the Pelican Staff: Cool. thanks again. - Nick at Pelican Parts  
scottsbenz Comments: Hello again Nick. FYI and for other owners of 190E-2.3 cars, NGK advise that the listed plug Iridium BPR6EFIX.10has a fixed plug gap of .10mm hence the .10 suffix which should not be changed since it may damage the iridium surface. Again thank you for your help. Regards, Bruce.
November 23, 2014
  Followup from the Pelican Staff: Awesome. I am glad you found and it appreciate you sharing your findings with me. - Nick at Pelican Parts  
scottsbenz Comments: Thanks for your reply Nick.
November 23, 2014
  Followup from the Pelican Staff: No problem.

I had a thought. Go to the NGK plug site, and see what plug type, part number and gap they list. They may have it. - Nick at Pelican Parts
 
scottsbenz Comments: Hi Pelican guys, Just bought a 190E-2.3 in Australia, but handbook does not tell spark plug gap or ignition timing setting. Can you help please? Regards and thanks, Bruce.
November 22, 2014
  Followup from the Pelican Staff: Sorry, I don't have that info. - Nick at Pelican Parts  
seab Comments: thank you every much you guys just saved me monees
October 23, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
rick Comments: How do you get the coil cover off to change the coil wire ... don't want to break it ... won't budge.

I can't seem to get at the allen socket on bottom of cap also .. not enough clearance with the fan
September 4, 2014
  Followup from the Pelican Staff: There should be a retaining tab at each side of the cap.- Nick at Pelican Parts  
mike Comments: Do you have to change the rotor and distributor cap or can you just change the spark plugs?
July 21, 2014
  Followup from the Pelican Staff: You can do just the plugs. I would inspect the cap and rotor to see if it is worn. - Nick at Pelican Parts  
Sylvie Comments: Finally answered my own question, posting here for future reference:
A TX-30 Hex bit on a 3/8 x 1/4 socket - for length. Not easy.
June 28, 2014
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
 
Sylvie Comments: How on earth do you unscrew that bottom bolt on the distributor cover? I can't seem to get to it at all.
June 28, 2014
  Followup from the Pelican Staff: With an Allen wrench or long Allen bit on a 1/4 inch ratchet. - Nick at Pelican Parts  
JamesA Comments: Thanks for the very informative article. When I look at the parts ordering page, however, it's also showing an "ignition cable," which isn't mentioned in this article - although you do show another "wire" going to the "coil/intake system." Is this the ignition cable?

Thanks for your help!
May 9, 2014
  Followup from the Pelican Staff: I believe so. Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
 
Jim Comments: Hi Guys, I have a Mercedes '89 W124 300E and I am a little confused not unusual sais my wife.
I can see my distributor cap and my leads plugged in and the 3 hex screws. My confusion is that all the caps I see advertised are orange as are my niples sticking out and the leads pluged in. My question is the black cover with the 3 hex screws and orange points sticking out only a cover with the orange distrubuter cap inside or is this the whole unit in one with the nibs without another distributor cap inside? Please help Thank you
April 12, 2014
  Followup from the Pelican Staff: It can be just a black cover, or integrated into the cap. The part you order should come correct for your vehicle. - Nick at Pelican Parts  
mikepoulin Comments: how to remove the cap over the ignition coil terminal?
August 10, 2013
  Followup from the Pelican Staff: You can use a straight blade screwdriver to pry open the cover for the ignition coil - Kerry at Pelican Parts  

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