W126 not running correctly

[roondog]

hello,
Encountered my first issue since owning my 380SEL, I'm not very well mechanically minded so I can only describe the problem to you peeps and hope someone might be able to tell me what could be up with it.

Its like the engine is running at half capacity.
A noticeable vibration At low revs which wobbles the car.
Great loss of power/ acceleration/ economy

A friend says it could be spark plugs? distributor?

Hopefully getting it looked at next weekend but just thought I'd post it up,
What else am I going to do on a Sunday Afternoon!

 

[merc85]

On two of mine in the past it was the ignition leads were the cables go into the metal heat shields. YOu can cut them back and rejoin for a temp repair, but idealy new leads cap and rotor should sort it.

 

[johnsco]

Plus 1

I strongly recommend buying genuine MB ignition parts.
There are some very poor imitations around ... as I found to my cost with out 380SE.

 

[ianrandom]

The leads cost a fortune from MB, I'd recommend getting the plugs from MB though as they are cheap and the correct type.

 

[grober]

Get yourself down to a local garage with an old fashioned oscilloscope engine analyser and someone who can use it. This will allow you to monitor all the HT firing lines and track down the fault. First port of call on the HT side should be the rotor arm and distibutor cap IMHO followed by the leads. An examination of all the plugs should help identify exactly which ones are not firing.
The other possibility is that the timing chain has jumped a cog or two- It's a single chain and a known weak spot of these engines.

 

[roondog]

Cheers guys, I'll use some of this info when I take it down to the garage on Saturday.
I'll post up what the mechanic finds to be the problem

 

[219]

If it hasn't been replaced recently , or isn't a genuine Bosch item , the distributor cap is the first thing to check .

 

[carat 3.6]

As above, the distributor cap and rotor arm are the first on the list.

 

[johnsco]

I agree.
These are more likely causes of problems and cheaper to replace than HT leads.

 

[roondog]

If it hasn't been replaced recently , or isn't a genuine Bosch item , the distributor cap is the first thing to check .

The garage has gone ahead and ordered new uprated spark plugs (BOSCH)
New ignition leads (BOSCH)
New rotor arm (BOSCH)
and distributor cap- but this part is not made by BOSCH - I'm aware that its better for the car for it to be a Bosch part, how much of a difference will it make?

I'm tempted not to use the distributor cap they have ordered, although I'm finding it difficult to find the BOSCH part in the UK

 

[ray_hennig]

The garage has gone ahead and ordered new uprated spark plugs (BOSCH)
New ignition leads (BOSCH)
New rotor arm (BOSCH)
and distributor cap- but this part is not made by BOSCH - I'm aware that its better for the car for it to be a Bosch part, how much of a difference will it make?

I'm tempted not to use the distributor cap they have ordered, although I'm finding it difficult to find the BOSCH part in the UK

Is the cap made by Beru? If so, it should be OK.

If your bank manager is a good egg, get the cap from MB.

By the way, I don't like the sound of 'uprated' spark plugs. I think for your car (certainly, for mine) you need 'downrated' plugs - the most basic copper cored, non-fancy, non-resistor plugs from Bosch, Beru, NGK. I'm sure someone will come along with the right reference for you. Also, if my experience is anything to go by, do not assume the MB will supply this right ones.

The clue with plugs is the price. If they're cheap, they' may well be right. If they're expensive, they're almost certainly wrong.

RayH

 

[ianrandom]

Yes the spark plugs should be the basic type and most importantly shouldn't be the resistor type.
Because of this the dealer is the best bet for plugs as even the suppliers often have the wrong plugs listed for the W126.

 

[roondog]

Is the cap made by Beru? If so, it should be OK.

If your bank manager is a good egg, get the cap from MB.

By the way, I don't like the sound of 'uprated' spark plugs. I think for your car (certainly, for mine) you need 'downrated' plugs - the most basic copper cored, non-fancy, non-resistor plugs from Bosch, Beru, NGK. I'm sure someone will come along with the right reference for you. Also, if my experience is anything to go by, do not assume the MB will supply this right ones.

The clue with plugs is the price. If they're cheap, they' may well be right. If they're expensive, they're almost certainly wrong.

RayH

Ah right with the plugs I think my use of language was wrong there as I don't know my way around a engine. I've just presumed the new ones are of 'better quality' hence my use of that word.
I do know the replacement plugs are BOSCH and they're £3.50 each, I'm sure the mechanic has ordered the right ones but I'll be sure to check.

Also I'm pretty sure the cap they have ordered is by BERU so I'll go ahead with it and see how it goes.

Thanks mate

 

[stwat]

The correct plugs are around £2.50 each from the dealer. I find it virtually impossible to buy the none resister type plugs from anywhere but MB.

 

[ianrandom]

Ah right with the plugs I think my use of language was wrong there as I don't know my way around a engine. I've just presumed the new ones are of 'better quality' hence my use of that word.
I do know the replacement plugs are BOSCH and they're £3.50 each, I'm sure the mechanic has ordered the right ones but I'll be sure to check.

Also I'm pretty sure the cap they have ordered is by BERU so I'll go ahead with it and see how it goes.

Thanks mate

Bet they have an 'R' in the designation denoting resistor. Normal mistake.

 

[jaymanek]

Set of leads from Magnecor.. Bosch or Beru Cap & Rotor Arm from Euro (or other) and a set of non resistor spark plugs should see that issue fixed.

If its a fuelling issue it may get more complicated.

 

[roondog]

Just Had the new parts fitted-

BERU distributor cap
BOSCH Rotor arm
Ignition leads
BOSCH spark plugs

I'm glad to say the problem has been fixed.,the car to me seems to be running even better than before. Less lumpy, smoother gear changes and improved power from engine. It did cost £160 altogether with labour which Is quite much for a few leads and a bit of plastic.

 

[carat 3.6]

Just Had the new parts fitted-

BERU distributor cap
BOSCH Rotor arm
Ignition leads
BOSCH spark plugs

I'm glad to say the problem has been fixed.,the car to me seems to be running even better than before. Less lumpy, smoother gear changes and improved power from engine. It did cost £160 altogether with labour which Is quite much for a few leads and a bit of plastic.

That's cheap, but glad to hear the car is running well again.

 

[alabbasi]

160GBP is pretty good if it included the plug wires.