W202 C240 (1997) spark plug change

[kth286]

phil

you need to have the correct plugs for your engine as some plugs are resistor plugs and some are non resistor plugs in other engines.

It will spoil the workings of the ECU if the wrong plug is installed.

My plugs for example are the non resistor at about £2 each from the dealer.

A lot of people have put fancy and expensive mutiple electrode plugs in this 6 cylinder 104 engine to find it just does not work properly.

On the question of leads, there are just 3 on my 6 clinder engine and they are the original ones at 169,000 miles, no problem.

They are straightforward wired leads and juat need a wipe over.

 

[television]

I have sent you the fitting instructions

 

[philharve]

The correct spark plugs

phil

you need to have the correct plugs for your engine as some plugs are resistor plugs and some are non resistor plugs in other engines.

It will spoil the workings of the ECU if the wrong plug is installed.

My plugs for example are the non resistor at about £2 each from the dealer.

A lot of people have put fancy and expensive mutiple electrode plugs in this 6 cylinder 104 engine to find it just does not work properly.

On the question of leads, there are just 3 on my 6 clinder engine and they are the original ones at 169,000 miles, no problem.

They are straightforward wired leads and juat need a wipe over.

Hi kth286

Yes, I am aware that there are differences in spark plug performance and fitting the wrong one could have an adverse effect upon performance. I let myself be guided by the Halfords list of 'equivalent spark plugs' when making my purchase. Your comments make me wonder if I made a wise decision.

The Bosch plugs were about GBP2.50 each, the NGKs about GBP4.00 each.

So, there are HT leads in some engine designs! You mention you have 3 in your 6 cylinder. Does this mean you have 3 coil packs and your ignition is based upon the 'wasted spark' principle: it fires on the exhaust stroke?

REGARDS

Phil

 

[philharve]

Wasted sparks anyone?

I have sent you the fitting instructions

Hi Malcolm

Yes, I received the diagrams for a 6 cylinder rather than a 4 but I'm sure the principles are the same. I don't foresee any problems. I note the torque tightening recommendation and the special tools which don't look that special.

The plug arrangement and their location puts me in mind of my old Triumph Dolomite Sprint which had one change of HT leads in 18 years. The plug 'wells' also had to be cleared out with compressed air or tissue paper as they were prone to filling with engine oil. The wells had to have tubular inserts which if they weren't oil tight lead to oil leaking into the wells. Fun times!

I also see what 'kth286' meant by 3 coil packs for his 6 cylinder. I was under the impression I had a coil pack per cylinder which probably means - I need to check - relies upon firing once and not twice per cycle.

REGARDS

Phil

 

[television]

The paper I sent covers all engines,,details at the top

 

[philharve]

6 or 4 cylinder the principle is the same

The paper I sent covers all engines,,details at the top

Hi Malcolm

I was referring to the illustration which was of a 6, but I take your point.

REGARDS

Phil

 

[television]

Hi Malcolm

I was referring to the illustration which was of a 6, but I take your point.

REGARDS

Phil

Thats OK it will not take as long then

 

[bigasotonuk]

Hi Phil,
The 230K engine to remove the plugs you have to remove the large centre cover on the rocker cover this then exposes he the spark plugs, 2 of which have the coil packs directly on top of them, the coil packs attach to the spark plug via a plug cap under the coil pack, each coil pack then has a HT lead to one of the other plugs, when I replaced mine I fitted new leads and 2 new caps, as I had a misfire, the cause was traced to one of the coil packs plug cap, even if you don,t replace the leads do yourself a favour and replace these caps.
A cautionary note though this may not effect your car because of age it still maybe worth noting, MB's did have a notorious reputation of wiring loom damage due to heat in this area (wiring to coil packs) causing ECU failures etc. resulting in replacing ECU and fitting new engine harness, this was more commonly seen in the Inline 6 cylinder motors it has been known to effect the 4 cylinder from posts I have read on other forums. The harnesses that were effected were modified by utilising better quality of cable, but from experience all cable will be effected by the extreme heat generated from this area, I noticed my loom on my car the insulation had gone very hard and cable not as flexible as it should be so try not to unecessarily handle and bend the LT cables feeding the coils, for fear of possible damage.
Very easy to do Phil should easily do it half hour or so.

 

[philharve]

Coil packs

Hi Phil,
The 230K engine to remove the plugs you have to remove the large centre cover on the rocker cover this then exposes he the spark plugs, 2 of which have the coil packs directly on top of them, the coil packs attach to the spark plug via a plug cap under the coil pack, each coil pack then has a HT lead to one of the other plugs, when I replaced mine I fitted new leads and 2 new caps, as I had a misfire, the cause was traced to one of the coil packs plug cap, even if you don,t replace the leads do yourself a favour and replace these caps.
A cautionary note though this may not effect your car because of age it still maybe worth noting, MB's did have a notorious reputation of wiring loom damage due to heat in this area (wiring to coil packs) causing ECU failures etc. resulting in replacing ECU and fitting new engine harness, this was more commonly seen in the Inline 6 cylinder motors it has been known to effect the 4 cylinder from posts I have read on other forums. The harnesses that were effected were modified by utilising better quality of cable, but from experience all cable will be effected by the extreme heat generated from this area, I noticed my loom on my car the insulation had gone very hard and cable not as flexible as it should be so try not to unecessarily handle and bend the LT cables feeding the coils, for fear of possible damage.
Very easy to do Phil should easily do it half hour or so.

Hi Andy

This is certainly news to me ... the fact that I have only 2 coil packs rather the one per cylinder. I have noted your comments about replacement of the coil packs and HT leads if they should fail. Fortunately, mine are working perfectly [at the moment].

I did wonder about the 'heat issue'. It must get terribly hot beneath the large central cover and I'm surprised the coil packs are in such close proximity to the head. I have seen wiring that has been subjected to great heat and as you say the insulation goes hard then cracks. Attempting to bend wires in this condition usually results in fragments of the insulation flaking off thereby necessitating replacement. It sounds expensive. I'm sure if my indie had any concerns in this area he would have warned me.

My last but one car, a Dolomite Sprint, had deep wells in the cylinder head into which the spark plugs were screwed. I should have thought the depth of a well was at least 5". I have a reputation for being a bit of a tool collector and I've been thinking about buying a cylinder compression tester. I may not use it much myself but I do loan my tools out to friends who are keen to do their own servicing & maintenance, an enthusiasm I'm gradually losing as I get older. If I were to buy a compression tester, what length of extension tube would I need to fit in the well before fitting the gauge? Draper sell a 200mm (M10) tube. Is that overlong? I would, of course, buy a range of adapters for the more common spark plug sizes. Ebay has some good offers of this type of kit.

REGARDS

Phil

 

[groo-bee]

Hi,
I bet the spark plugs were missed, as it can be very expensive getting them done at MB, try this link below, its a "HOW TO" on changing the plugs on a V6 M112 engine, some very good pics, and descroption of the job.
http://cryptiksouls.co.uk/mercedes/plugs/index.html

Hey,

could You please re-share this link - it is no longer valid, but i need to change my sparks and cables immediatly. many thanks.

 

[AnthonyUK]

Hey,

could You please re-share this link - it is no longer valid, but i need to change my sparks and cables immediatly. many thanks.

It’s a 12 year old post so don’t expect an answer
Might be worth in this instance to open a new thread but great that you checked existing ones first.

 

[mioba]

Hey,

could You please re-share this link - it is no longer valid, but i need to change my sparks and cables immediatly. many thanks.

Plenty of info with a simple google,

Don’t skimp on plugs - Bosch OE all the way.

 

[groo-bee]

Plenty of info with a simple google,

Don’t skimp on plugs - Bosch OE all the way.

You sure ?

 

[LostKiwi]

You sure ?

Yes. Or NGK.

 

[groo-bee]

Yes. Or NGK.

NGK PFR5R-11 - this is specified for my engine, and i've already got it. But i would like to get to know how to do it step by step you could say.
That's what i'm asking for - cannot find any service manual for w202, as i had for my W124

Model 124 Maintenance Manual Index

 

[LostKiwi]

NGK PFR5R-11 - this is specified for my engine, and i've already got it. But i would like to get to know how to do it step by step you could say.
That's what i'm asking for - cannot find any service manual for w202, as i had for my W124

Model 124 Maintenance Manual Index

Really? You want a manual on how to change spark plugs????

 

[AnthonyUK]

You ideally want something to safely remove the plug caps (17mm angled spanner for me) and a thin-walled flexi-head socket for the plugs (14mm I think).
I changed mine recently without issue but it is time consuming. Allow at least a couple of hours.