Misfiring and loss of power

[jamsh]

My 1988 300Ce is misfiring on acceleration and has a very erratic tickover, needing a gear change into neutral and left foot on the brake, swiftly followed by the right foot on the accelerator increasing the revs to 12/1400, to prevent stalling.
The initial diagnoses from my garage was that I needed a plug change as at least three of them were 'arcing'. The bil for this diagnosis and the plugs was £130. I drove off thinking that that was that, but after parking up and not using the car for a few days, the same behaviour occurred again 5 days later. Very difficult to drive!
Back to the garage and the diagnosis this time is that the HT leads and the Distributor Cap need replacing at a total cost of £311. I am assured that this will solve the problem.
Any comments would be appreciated.

 

[television]

One thing is for sure, that is that sparking plugs do not arc.
Lead and rotor caps do.

Best thing is to run the engine in the dark and you will see where it is arcing except under the rotor cap.

You could spray some PTFE into the cap and wipe some onto the leads and see how it goes

 

[television]

For the first time I see tha MB now supply caps made by Doduco and are a recomemded replacement for the Bosch

 

[mikevernon]

My 1988 300Ce is misfiring on acceleration and has a very erratic tickover, needing a gear change into neutral and left foot on the brake, swiftly followed by the right foot on the accelerator increasing the revs to 12/1400, to prevent stalling.
The initial diagnoses from my garage was that I needed a plug change as at least three of them were 'arcing'. The bil for this diagnosis and the plugs was £130. I drove off thinking that that was that, but after parking up and not using the car for a few days, the same behaviour occurred again 5 days later. Very difficult to drive!
Back to the garage and the diagnosis this time is that the HT leads and the Distributor Cap need replacing at a total cost of £311. I am assured that this will solve the problem.
Any comments would be appreciated.

Good Grief! You are being severely ripped off so take it somewhere else!
£130 to change the plugs!!!!!
It does sound like the problem is likely to be HT leads, and the arcing they mentioned was probably arcing between the plug cap and earth. A spray of WD40 usually stops it, but replacing the HT leads is a better solution. If the distributor cap shows signs of tracking change that also. Absolute maximum cost of the two items is £100 (GSF or similar), so your garage is trying to charge you over £200 for literally 5 minutes' work. Incredible!

 

[grober]

The spark plug leads with the built in supressors are sometimes very difficult to remove. Merc actually make a modified pliers tool to remove them. The temptation is to pull on the lead wires themselves which will very rapidly render them useless. I WOULD AGREE ABOUT THE CHARGES--- ABSOLUTE RIP OFF altho it does depend on how long they spent on "diagnosis" The plugs are cheap to buy and easy to get at. The proper MB plug leads are expensive but not that bad. If its not the distributor or leads I am afraid to say it may be the EZL ignition module mounted on the wing. These are getting very difficult to repair since any replacements are getting rare. Breakers yards are often the best source. Is the car driving OK now?

 

[fredfloggle]

One thing is for sure, that is that sparking plugs do not arc.
Lead and rotor caps do.

Best thing is to run the engine in the dark and you will see where it is arcing except under the rotor cap.

You could spray some PTFE into the cap and wipe some onto the leads and see how it goes

When plug ceramics become crazed after extensive usage , they also can begin to "track"

 

[BlackC55]

Check the wiring loom. They tend to break up.

 

[television]

When plug ceramics become crazed after extensive usage , they also can begin to "track"

Ceramic will not arc if it is not crazed and as for me I have not seen a crazed sparking plug as of yet, there again if one was crazed then one would replace it

 

[fredfloggle]

Ceramic will not arc if it is not crazed and as for me I have not seen a crazed sparking plug as of yet, there again if one was crazed then one would replace it

"When plug ceramics become crazed after extensive usage "

I have seen it, that's why I mentioned it.

And having worked in a factory that made the things and seen the test rigs, I thought it worthwhile to mention.

As you say , open the bonnet at night will give a clue.

 

[jamsh]

I priced the HT leads and Distributor Cap from MB and they quoted me £170 for the leads and £78 for the cap. They recommended a new rotor arm as well at £33. So, it is going to be an expensive repair. The guy at MB told me that cheap leads and Distributor caps are more trouble than they are worth. The HT leads and Cap on my car are not MB, so I am going to go ahead with it.

 

[grober]

I would check out prices at your local Bosch dealer first. They would be probably cheaper and since the Mercedes parts in question are made by Bosch in the first place what's to lose? Don't be tempted by E bay parts unless you are very sure of their origin- lots of cheap Chinese knock offs--other members on here may have recommendations tho.

 

[television]

See if you can get the Doduco cap its better than the Bosch, but the Bosch will be much cheaper from a Bosch service center

 

[mikevernon]

Jamsh. If you really want to pay £281 to Mercedes for HT leads, cap and rotor arm then go ahead, but your garage will certainly not be buying the parts from them. You can buy parts of similar quality with the same guarantee for a small fraction of that price from GSF or similar suppliers.
Take a look at their website for prices www.gsfcarparts.com .

I have no connection with GSF by the way, but I find them an excellent firm to deal with. They have a fast delivery service to the trade and on the very rare occasions that I've returned anything they have replaced items without question or fuss. I recently returned a battery just days before the expiry of a 2 year warranty and they replaced it with a new one.